• Volume 36,Issue 4,2014 Table of Contents
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    • Interfacial Wavelet Superposition Method for Out-of-PlaneWave Motion of a Free Field in a Layered Half Space

      2014, 36(4):765-772.

      Abstract (1415) HTML (0) PDF 482.55 K (1595) Comment (0) Favorites

      Abstract:The wave motion of a free field for general engineering can be simplified as a 1-D wave motion of an elastic layered half-space model,approximate solutions of which can be obtained by numerical methods.For such problems,the seismic waves are assumed to be vertical body waves propagating in the vertical direction, and site strata are regarded as nearly horizontal stratified structures.Even though there are many types of algorithms for seismic response analysis,all algorithms can be broadly classified into two main types.The first are numerical methods in the time domain,and the second are numerical methods in the frequency domain.However,numerical methods in the time domain,such as the finite difference method,finite element method,and boundary element method,are currently used.When these methods are used to calculate the free wave field in a layered half space,it is necessary to first discretize the computational region.The definite-solution problem of the continuous wave field is transformed to the problem of numerical computation of the discrete element nodes by methods of mathematical physics.The numerical formulas are usually expressed as a group of equations or explicit iteration schemes step-by-step in the time direction. However,the precision of approximate solutions computed by these numerical methods is affected by many factors,such as the mathematical algorithm,model range,mesh size,time step,and boundary condition.Inputting improper parameters will cause instability of the numerical algorithms,even causing no results to be obtained after a large amount of computation. Considering the generalized reflection transmission coefficient matrix method for synthetic seismograms,a new method is proposed,hich provides improvements for numerical methods in the time domain for solving problems of 1-D wave motion in an elastic layered half-space.When the method is used to compute a wave field in a layered half space,the element nodes are set at the wave impedance interfaces,which are called interfacial nodes.According to the wave motion principle of superposition,the wave field values between layers can be computed from the interface nodes,in which none of the nodes are set.Interfacial node values are made in accordance with the refracting and reflecting regulations at wave impedance interfaces and traveling time of waves between wave impedance interfaces,the expressions of which can be written as a group of time delay equations.Interfacial node values can be obtained after solving time delay equations.The wave field values in a layered half space can be obtained from one of the interface nodes at the free surface.Considering Huygens principle, the motion at interfacial nodes can be regarded as secondary sources or wavelet sources,when seismic waves pass through impedance interfaces.Therefore,the motion at interfacial nodes is called an interfacial wavelet,and the above method for determining the free wave field in a layered half space is called the interfacial wavelet method.The interfacial wavelet method is suitable for 1-D wave motion problems corresponding to the wave field of horizontal layered media caused by normal incidence.Two numerical results demonstrate that the proposed method has high accuracy and fast computing speed. In theory,the method can also be used to solve 2-D wave motion problems corresponding to the wave field of a horizontal layered media at oblique incidence.

    • Vortex-induced Vibrations of a Free-span Submarine Pipeline underAsymmetric Pipe-soil Boundary Conditions

      2014, 36(4):773-777,789.

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      Abstract:The submarine pipeline from offshore petroleum fields must frequently pass over uneven seafloor areas.In such cases,the pipeline may have free spans when crossing depressions.If dynamic loads occur,the free span may oscillate,and time-varying stresses may create unacceptable fatigue damage.A major source for dynamic stresses in free-span pipelines is vortex-induced vibration (VIV)caused by steady current.This effect is dominant on deep water pipelines because wave-induced velocities and accelerations decay with increasing water depth.Vortex-induced vibrations in a free-span pipeline are a highly complex phenomenon in which the fluid-pipeline-soil coupling should be considered.One challenge for free-span analysis relates to accurate prediction of VIV and design of a pipeline system to mitigate its effects.In this paper,VIV of a free-span pipeline under asymmetric boundary conditions is analyzed.The submarine pipeline was modeled by using an Euler-Bernoulli beam.The two ends were restrained by an extension spring and a twist spring.The wake flow was described by Van der pol equation,and a wake oscillator model was introduced.The model parameters were estimated according to experimental data.The coupling equations were decoupled by the modal principle,and the numerical results were obtained by Runge-Kutta method.It was concluded that stricter asymmetric boundary conditions relate to more difficulty in the high mode and higher response frequency,which had little effect on the response amplitude.

    • Shaking-table Tests on Response Characteristics of Seismic Peak Acceleration of Subgrade

      2014, 36(4):778-783.

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      Abstract:Many slopes of subgrades fail during earthquakes.Therefore,it is necessary to evaluate the stability of slopes under seismic loading in the design of the subgrade.The pseudo-static method is one of the most frequently used methods in seismic stability analysis of slopes and is the specified method in the “Specifications of Seismic Designs for Highway Engineering.” One of the key factors in this method is the effect of amplification of the peak acceleration of a seismic load.To study this effect,a large-scale shaking-table model was developed with a subgrade model at a scale of 1:20.A series of tests was performed with various inputs of seismic wave type,amplitude,and frequency.Seismic wave type included one type of artificial-seismic wave (sinusoidal wave)and two types of observed seismic waves (EL Centro and Wenchuan seismic waves).The amplitude and the frequency of each wave were determined by the scales of model similarity.In these tests,accelerometers were set at various locations in the subgrade model.Accelerations of the model under seismic loading were then measured in both vertical and horizontal directions.Amplification coefficients were calculated by dividing these accelerations by the measured acceleration at the surface of shaking-table.Test results show that horizontal seismic waves are greatly amplified by the subgrade;amplification of vertical seismic waves was not noticeable.Maximum amplification coefficients of 2.45 and 1.3 were located at the surface of the slope for both vertical and horizontal waves,respectively.The amplification coefficient of the horizontal seismic wave varied along the height of the subgrade and was divided into three stages of height increase such as increasing,decreasing,and later increasing again.The maximum amplification coefficient was reached at the highest point of the pavement,and it varied along the pavement.The amplification coefficients were greater at the surface of the slope than those inside for both horizontal and vertical seismic waves.For horizontal waves,the amplifications differed significantly under seismic waves with different frequencies,wave type,and amplitude.The amplification coefficient increased with an increase in frequency in the test.For the three types of input waves,the amplification coefficient was maximum under EL Centro seismic waves and minimum under sinusoidal waves.Moreover,the amplification coefficient decreased with an increase in amplitude.These results show that the amplification varies under different seismic loads and should be evaluated according to actual situations.Further,these results are helpful for determining seismic load in the seismic stability design of subgrades.

    • Numerical Simulation of Blasting Dynamic Response ofSmall Spacing Tunnel Expansion

      2014, 36(4):784-789.

      Abstract (1334) HTML (0) PDF 543.80 K (1404) Comment (0) Favorites

      Abstract:With the rapid economic development in China,an increasing number of highway tunnels require reconstruction and expansion because the road traffic volume is increasing exponentially.The original Damaoshan highway tunnel is a separated four-lane expressway located between Fuzhou city and Xiamen city,Fujian province,southeastern China.The expansion scheme of this tunnel includes new construction of a four-lane tunnel between the original two tunnels and expansion of the right hand original tunnel into a four-lane structure.Thus,the expanded Damaoshan highway tunnel will comprise a series of closely spaced tunnels.The newly constructed four-lane tunnel,22 m long and 255 m2 wide,will be merely 5.89 m from the original tunnel. Moreover,the structure safety of the nearby original tunnel must be ensured to maintain effective traffic flow during the explosions for the construction of the new tunnel.Thus,the blasting vibration must be strictly controlled.In this study,semi-empirical theory and direct initiation method are used to determine blasting loads in numerical simulation of blasting dynamic response.With the project background of the first application of the Damaoshan highway four-lane tunnel expansion,a numerical analysis model is established using LS-DYNA3D software from the direct initiation of explosives to simulate blasting effects on an adjacent operation tunnel. The numerical analysis model is based on a multi-material unit and fluid-structure interaction technique to simulate the explosive detonation and the dynamic response of the nearby structure,respectively.The element type is SOLID164,and the non-reflected boundary condition is used.Influences of the rock calculation range,mesh size,material hardening condition,and failure strain on the numerical simulation are analyzed.The rock failure strain value in this study is obtained by comparing the explosive cavity radius between the numerical simulation and experience formula.The simulation results show that the blasting effects for the ideal elastic-plastic material model are larger than that for the hardening elastic-plastic model.The maximum relative error of vibration speed is approximately 20%.Moreover,the numerical results of vibration velocity generally comply with the Sadaovsk formula fitted by on-site measured data.Therefore,the results of this study are useful for tunnel constructions and similar projects.

    • Research on Earthquake-induced Geological Disasters in the Karst Area in Guangxi and Methods for Engineering site Preparation

      2014, 36(4):790-796.

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      Abstract:Earthquakes have caused severe geological disasters in Guangxi,where Karst is widely developed.In this study, the distribution of Karst in Guanxi and the cause of certain earthquake-induced geological disasters in the Karst areas were analyzed.This paper introduces methods for engineering-site preparation in Karst areas.The present state of engineering-site preparation for Karst areas is reviewed and future research directions for engineering-site preparation for Karst areas are presented.

    • Scaled Model Test Study of the Dynamic Behavior of an Offshore Wind Turbine Support Structure

      2014, 36(4):797-803.

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      Abstract:Offshore wind is a safe,clean, and stable source of renewable energy,which is a strategic option for overcoming the problems of energy shortage and environment contamination. Because of their high,slender,and flexible nature,accompanied with mass and stiffness distribution,offshore wind turbines are dynamically sensitive structures in which their dynamic behavior is strongly affected by environmental loading and the stiffness of their foundations.The first natural frequencies of these structures are very close to the forcing frequencies imposed by the environment and the onboard machinery.Changes in the foundation stiffness under cyclic loading will ultimately result in changes to the natural frequency of the structure.However,little is known about the long-term dynamic behavior of the entire offshore wind turbine structure.Therefore,the design of foundations and prediction of long term performance remain challenging.In the design work of offshore wind turbines,the soft-stiff type is usually chosen under general circumstances in which the natural frequency is between 1P and 3P bands.This study establishes a simplified wind turbine model based on the dynamic model test platform at the University of Surrey.The model system includes a foundation,tower,and top mass.On the basis of the novel cyclic loading provide system,four groups of tests were conducted to study the long-term dynamic behavior of a wind turbine model supported on a pile foundation.This investigation focused on changes of the model turbine’s first natural frequency and studied the influence from the amplitude of cyclic loading.For the observed tests results,detailed analysis was performed on the basis of soil behavior and its migration pattern.The test results and a series of similitude relationships reveal the dynamic behavior of an wind turbine structure. Moreover,suggestions for foundation and structure selection for a prototype wind turbine are given.

    • Suitability Analysis of Pile column Pier Foundation Using Low Strain Method and In Situ Experiments

      2014, 36(4):804-812.

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      Abstract:The propagation of stress waves in a pile-column system was analyzed using the elasticity theory and was verified by in situ experimentation.This study first analyses the propagation of a semi-spherical stress wave after transient shock in a column-pile system according to the Saint-Venant principle.The results indicate that the stress wave caused by shock on top of the bent cap or on a combined section of pile and column can still satisfy the plane section.A method is introduced to verify this assumption in which shock is applied to a certain point in a pile-column system,and the peak time of the stress wave is collected in the same section by conducting a multi-channel equipment.If the difference of each peak time is less than a certain value,it can be concluded that the wave propagation is unanimous and satisfies the plane section.Two groups of in situ tests were performed on a pile-column system in which shock was applied to the top of the bent cap and to a combined section of pile and column.Stress waves were collected on the section at the top of the column,the combined section of pile and column,and the pile section under the tie beam.When shock was applied to the top of the bent cap,the wave velocity value was in a common range,and the stress waves reached the outer edge of the pile section synchronously.It was considered that the stress wave reached the center of the same section at the same time by calculating the difference in peak time of the stress wave at the outer edge and at center of the section.Thus,it was concluded that the plane section can be applied in such a mode.However,this conclusion is not completely valid when the stress wave in the pile is caused by shock on the combined section of the pile.In the pile section near the tie beam,the value of the peak time of the stress wave in each channel varied;therefore,the stress wave did not reach the center of the section at the same time.However,in the pile section slightly far from the shock point,the value of the peak time of the stress wave in each channel was reached at nearly the same time.The propagation of stress waves were transform to uniformity,thus for the mode of shock on the combined section,the plane section can be applied to the surface at a distance from the shock point.

    • Influence of Near-surface Velocity Structure on Site Characteristics of Strong Ground Motion

      2014, 36(4):813-819.

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      Abstract:Strong ground motion can cause significant changes in unconsolidated layers;therefore,the influence of near surface velocity structure on the characteristics of strong ground motion should be clarified.A combination of S-wave seismic exploration and microtremor testing is conducted near two seismic stations in which a series of aftershock records was recorded during the Wenchuan earthquake sequence.At the MXT station,both field tests and seismic records show a prominent resonance of 5 Hz caused by a high impedance contrast at the boundary between silty soil and a pebble bed.This boundary occurs at a depth range from 10 m to 11 m and is imaged as a strong reflection with a two-way time approximately 0.1 s.Borehole data from this site verifies that the velocity increases from approximately 200 m/s to 400 m/s at a depth of 10 m depth.However,the 20 m depth boundary shows a contrast between a pebble bed and slate and is imaged as a very slight reflection with less significance in the seismic spectrum.This phenomenon may have occurred because an excessively high amplitude at 0.1 s covered the reflection of the deeper boundary.At the WUD station,the SH-wave reflection profiles with two-way travel times of approximately 0.22 s and 0.50 s mark the boundaries of silty soil,roundstone,and sandstone.The reflectors respectively caused 2.3 Hz and 1.45 Hz resonances observed in the records of earthquakes and microtremors.Two or more boundaries of impedance contrast could have caused different actions with various focal mechanisms at the WUD station.The results of this study are summarized as follows:(1)A comparison of the test results and the strong ground motion characteristics revealed that the depth of the strong impedance boundary and the average shear wave velocity are the main factors in controlling the dominant frequency at the site;stronger impedance is predominant in transforming the characteristics of the seismic spectrum.(2)Whether microtremors or earthquakes,site spectrum characteristics are always influenced by the surface velocity structure.In particular,the corresponding frequency range of the highest amplitude or amplification is near the dominant frequency.Therefore,the spectral shape of the surface should be affected by the velocity structure of unconsolidated layers.(3)When the microtremor records are controlled by a surface wave,the effect of the shallow impedance boundary may stronger than deep boundary.Moreover,earthquakes can make the main frequency of the seismic response lower than that by microtremors because of the deeper impedance boundary and the nonlinear nature of soil layer.Furthermore,the characteristics of the seismic spectrum also show diversity due to the focal mechanism and the propagation path.

    • Analysis of Modification Technique for ReducingLoess Liquefaction Potential

      2014, 36(4):820-823.

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      Abstract:Loess in China are mainly distributed in the terraces of the Yellow River,including in the Gansu, Ningxia,Inner Mongolia,and Shanxi provinces, covering an area of 6.4×106 km2 that accounts for about 6.6% of China's territory. The loess in western Gansu belongs to the class of unsaturated loess with a wide distribution range. Formed near the sand source, the eolian loess mainly includes sand loess, low-viscosity loess, and clay loess.Low-viscosity loess in Gansu has large thickness, with development pores and aerial weak cementation, which under dynamic loading is likely to produce large settlement deformation. It also has strong water-collapse characteristics and a tendency toward liquefaction. Such material brings arduous engineering challenges and foundation treatment construction problems. Low-viscosity loess in general has weak alkaline and poor cementation strength, with large deformation under a force dynamic. Because underground water easily uplifts after loading, liquefaction is a serious problem. Acid modified and chemically modified technology can effectively improve the loess seismic subsidence problem. The principle of acid-modified loess chemical modification is using phosphoric acid and a weak acid as a loess acidification treatment, considering that the loess formed in a dry climate gives priority to calcium carbonate. Then, other salts (Boric salt) are added to form the cementation bonds such as boron bridge bonding and hydrogen bonding. Filling material (calcium salt) is added to adjust the ratio of particle size to reduce the liquefaction potential. The acid modified method reduces the low-cohesion loess' ability to liquefy. The liquefaction test showed that under 50~65 kPa dynamic stress, the modified loess had a very slow rise in pore water pressure , a very small deformation, and almost no stress reduction. Under a dynamic stress of 65 kPa, its liquefied deformation was no more than 0.2%, corresponding to resistance to an IX-level earthquake. The following ratio was confirmed: 10%~30% calcium, 6%~13% boron material with 3% phosphoric acid. If a higher level of anti-seismic resistance is required, add 8%~13% of boron material. The acid-modified method creates no chemical toxicity, and the price of the raw boron material is lower than that of the lime cement. Therefore, this method has some economic and social benefits. 

    • Triaxial Tests on Dynamic Deformation and Strength Characteristics of Fine-grained Soil in Super-deep Overburden Layer

      2014, 36(4):824-831.

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      Abstract:The dynamic deformation and strength characteristics of fine grained soil in the super-deep overburden layer is the focus of engineers because soil buried deeply underground cannot be bulldozed easily.In this study,a series of dynamic triaxial tests is performed in silty sands buried deeply in the super-deep overburden layer foundation of an earth-rock fill dam,and the dynamic deformation and strength characteristics of soil in an earthquake zone are analyzed.The results show a strong linear relationship between the maximum dynamic shear modulus of testing soils and the mean effective stress of soils in the dual-logarithm coordinates system.The decay (increasing)curves of soil dynamic shear modulus (damping ratio)in various confined pressure conditions can be unified by the model of soil reference shear strain, and the decay (increasing)curves of soil in an arbitrary stress condition can be obtained through the extension of decay(increasing)curves of soil in testing stress conditions.The dynamic strength characteristics of testing soils is influenced by the density of soil and the testing stress condition;significant differences in the characteristic parameters of soil dynamic strength testing with various failure criteria are shown when the soil is the condition of unequal stress consolidation.

    • Statistical Analysis of Dynamic Nonlinear Parameters of TypicalSoils in Wuhan Area

      2014, 36(4):832-837.

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      Abstract:In recent years,seismic safety evaluation has been conducted at many engineering sites in the Wuhan area in which the dynamic nonlinear parameters of various soils were obtained.These data show diversification of soil patterns and a reasonable layout of space.According to factors such as the soil's nature,geological formation,and physical and mechanical properties,the strata are classified roughly as silty clay,clay,silt,silty sand,silty and fine sand,fine sand,and coarse sand.Among these categories,750 groups of silty clay are identified in addition to 244 groups of clay,63 groups of silt,69 groups of silty sand,93 groups of silty and fine sand,153 groups of fine sand,and 31 groups of coarse sand.Considering the influence of depth,or confining pressure,these groups are further divided.For silty clay,373 groups are classified at 0~10 m,272 at 10~20 m,79 at 20~30 m,and 26 at 30~50 m. For clay,132 groups are classified at 0~10 m,96 at 10~20 m,and 16 at 20~30 m.For silt,23 groups are classified at 0~10 m,29 at 10~20 m,and 11 at 20~40 m.For silty sand,34 groups are classified at 0~20 m and 35 at 20~50 m.For silty and fine sand,22 groups are classified at 10~20 m,64 at 20~40 m,and 7 at 40~60 m.For fine sand,39 groups are classified at 0~20 m,97 at 20~40 m,and 17 at 40~60 m.For coarse sand (medium sand and coarse sand),13 groups are classified at 15~30 m and 18 at 30~50 m.The dynamic nonlinear parameters of soil samples were tested using a free vibration column apparatus.The dynamic nonlinear parameters of 1403 groups of soil samples from the seismic evaluation reports of the Wuhan area were used to obtain the statistical mean values for the dynamic shear modulus ratios and the damping ratios of seven types of soil with varying depths under eight typical strains.To analyze the rationality of the statistical mean values,two typical engineering sites are chosen in which seismic response analysis is conducted.On the basis of the results,the influences of actual test values and the statistical mean standard values of code DB001-94 on ground motion parameters are compared and analyzed.In addition,the rationality of statistical mean values is demonstrated.Compared with the results of the code,the seismic response analysis results of the statistical mean values are closer to the results obtained using actual test values. Under the conditions of moderate and strong earthquakes,certain differences are noted between the results of the code and the actual test values.These differences cannot be ignored;the statistical mean values are believable and reasonable.These values can be used as references in the case of insufficient soil dynamic parameters at the Wuhan sites.However,the statistical values differ significantly when using different dynamic parameters at the same site.Therefore,for seismic safety analysis of major projects,soil sampling,and dynamic parameter testing must be conducted in accordance with the requirements of relevant codes.

    • Blasting Shock Absorbing Cushion for Improving Slope Stability of Open Pit

      2014, 36(4):838-842,849.

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      Abstract:This paper introduces a type of blast control device that has a simple structure and is easily used in open pits.The stability of a high rock slope is an important technical problem in engineering infrastructure.Excavation by blasting produces a shock effect that directly affects the stability of high rock slope projects.By using the proposed method,large amounts of cracking on the rock slope and progressive damage to surrounding rock masses can be avoided.In addition,it provides a cushion and absorbs a large amount of heavy detonation shock from blasting to prevent instability in the rock slope.This method was first used in the Xujiagou iron open pit in Panzhihua,Sichuan,where it was shown to effectively cushion the heavy detonation shock from explosions,thus avoiding damage to the step surface slope of the rock and its accumulated damages.Moreover,the rock slope stability was improved,the stability of the rock step slope was increased at least 2° after deep hole blasting,and the half-hole ratio was 95%.Furthermore,this method can be used in tunnel and underground engineering.When this blasting technique is used in rock slope excavation with blasting,less material is needed and less damage is produced,which leads to better contour quality,larger profits,and a greater benefit for the blasting perimeter.

    • Research on Seismic Response of Underground Structures in Saturated Foundation

      2014, 36(4):843-849.

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      Abstract:The main achievements of 10 years of research on the seismic response of underground structures in a saturated foundation are presented in this paper.Systematic clarification and investigation are conducted on the dynamic basic formulations and wave propagation characteristics of saturated soils.In the dynamic analysis of saturated soils,the interaction between the soil skeleton and pore water consists of two parts:seepage force and inertial coupling force.It is also revealed that due to the existence of the inertial coupling force,the speeds of two dilatational waves are not equal to those in single-phased solid skeleton and pore water even if the permeability approaches infinity.Moreover,several transmitting boundaries for dynamic analysis of saturated porous media are developed,including the viscous-spring transmitting boundaries derived from both the u-p formulation and u-U formulation in addition to the high-order time-domain transmitting boundary derived from the cylindrical elastic wave radiation problem based on the u-p formulation.Despite the zero permeability assumption made in the derivation of the undrained boundary,results show that it can provide sufficiently accurate results for earthquake engineering problems.The drained boundary performs well for all permeabilities.In addition,four dynamic centrifuge tests at 1:50 scale are performed to study the earthquake response of a subway tunnel in liquefiable soils.The response characteristics of the subway tunnel in horizontal or oblique liquefiable soils including floatation,lateral displacement of the tunnel,and internal force increments in tunnel segments due to earthquake-induced liquefaction are investigated in addition to the effectiveness of cut-off walls in resisting tunnel flotation.Further,finite element simulation is conducted to analyze the earthquake response of underground structures in saturated soils.We adopt the finite element program DIANA SWANDYNE II,which is a two dimensional(2D),effective stress-based program compiled from the fully coupled u-p formulation.The liquefiable sandy soil is modeled by using the generalized plasticity constitutive model Pastor-Zienkiewicz III,which is capable of simulating cyclic liquefaction,contraction of loose sand,and dilatation of dense sand.The contact characteristics between soil and the structure are also considered.Finally,the mechanism of underground structure flotation in liquefiable soils during earthquakes is studied.Due to the smaller apparent density of the tunnel structure compared with the saturated liquefiable sand,the soils at both sides beneath the tunnel structure tend to intrude into the space underneath the tunnel structure,leading to the structure flotation.The mechanisms of various remedial treatment methods for liquefiable soils such as increasing the tunnel buried depth,retrofitting the soil under the tunnel structure,and setting cut-off walls are studied by finite element simulation.The effectiveness of these methods is evaluated,and references for parameter design are proposed.These new achievements,which allow insight into the mechanism of the seismic response of underground structures in saturated foundations,are obtained from theoretical research on the wave propagation characteristics and are based on model tests,numerical simulations,and mechanism analysis.The study outcome will be beneficial for further research on the improvement of seismic design methods and seismic safety measures for underground structures in saturated foundations.

    • Numerical Simulation of Permanent Deformation of Embankment Induced by Train Load in Permafrost Regions Along the Qinghai-Tibet Railway

      2014, 36(4):850-856.

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      Abstract:With the completion of the Qinghai-Tibet Railway (QTR),several types of damage induced by traffic loads have occurred in the permafrost embankment;therefore,the safe operation demand and speed increasing scheme of the railway will be severely affected.Permafrost is an important engineering characteristic of the QTR and is the main reason for the settlement deformation of the embankment.The embankment deformation induced by trains includes elastic and plastic deformation.Although the residual plastic deformation will ultimately become accumulative permanent deformation with an increase in load number,plastic deformation might be only a small proportion of the total deformation in the embankment induced by a single train load.Uneven deformation in an embankment is caused by excessive post-construction settling and creates a severe negative influence on the service period of a train and on the safety and comfort of its passengers.Therefore,the accumulated settlement of embankment under the traffic load is an important influence factor of embankment stability.Making an accurate estimate of permanent embankment deformation is of great significance for guaranteeing the stability of trains and the design of railway embankments.In this study,a Duo test section is analyzed,and on the basis of dynamic tri-axial tests with samples taken from the QTR,an empirical accumulative plastic strain model is created in frozen and molten states.The CREEP subroutine is used to provide a theoretical foundation for calculation of permanent deformation of the QTR embankment.The results indicate that when the depth is 2.5 m or less,the accumulative permanent deformation of the embankment increases with an increase in train speed.However, when the depth is 8.2 m,the accumulative permanent deformation decreases as the train speed increases.The cumulative plastic strain increases gradually and maintains a constant level with an increase in depth to the top of the embankment under traffic loading and increases to maximum at the embankment center.Moreover,permanent deformation increases with an increase in train speed.Further,the maximum deformation of the embankment increases from 8.9 mm to 47 mm when the axle load increases from 8 t to 25 t.Because axle load has a significant influence on embankment deformation,controlling the axle load of a train may be effective in slowing the uneven deformation of the embankment.Permanent deformation increases with an increase in train axle load,and the influence of the train axle load is reduced with an increase in depth.In addition,long-term settlement in the embankment center increases with an increase in the equivalent vibration.Permanent deformation increases from 31.8 mm to 35.8 mm,or 13%,when the equivalent vibration of the train is 50 000 times and 100 000 times.After that,however,accumulative permanent deformation increased by 5.9%,3.7%,and 2.5% for each respective 50 000 times increase in vibration.The accumulation of permanent deformation of the embankment increases rapidly in the early train run and then gradually slows.Therefore,protection and repair of the embankment should be conducted early.Finally,the freeze thaw condition has a significant effect on the accumulated permanent deformation of the embankment.The cumulative plastic deformation on the embankment surface decreases with an increase in frozen depth and increases with an increase in thawed depth.The work provides experimental data for further research on the dynamic characteristics of frozen soil.

    • Three-dimensional Numerical Simulation for Vehicle Dynamic Load and Dynamic Response of Ballastless Track Subgrade

      2014, 36(4):857-867.

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      Abstract:With the development of high-speed railways,ballastless tracks are widely applied,and the dynamic characteristics of the subgrade form the basis for design,construction,and maintenance of the ballastless track/subgrade system.In a sense,the distribution rule of dynamic response under the action of train loads and the influence of subgrade parameters lags far behind the construction of high speed railways in engineering because it is highly complicated.The dynamic system, which includes rail,track,and roadbed,is so complex that it cannot be solved by available theory.In this paper,the numerical simulation method is introduced to describe the dynamic action of a roadbed bearing high speed rail loads.A three-dimensional(3D)finite element model of the track-subgrade system is established with the aid of ANSYS for dynamic response of ballastless track subgrades bearing vehicle dynamic loads and load input behavior.Moreover,by using the choice method and basis of unit type,a constitutive model of subgrade and material parameters is established.According to the distribution mode and behaviors of vehicle dynamic load and load input characteristics,a two-car,eight-wheelset vehicle model was introduced to obtain contact pressure time-history curves of fastening when two bogies pass between neighboring cars through Fourier transform.In addition,the rationality and applicability of the model are verified according to the data obtained from in situ testing.Vertical dynamic stress,dynamic displacement,and dynamic acceleration are calculated for a CRTS II type slab ballastless track and a double-block ballastless track when a passing train has a speed of 300 km/h and an axle load of 170 kN.Furthermore,the relationship between the response laws and the rail-subgrade construction are analyzed.Interrelated analyses reveal that vertical dynamic stress,dynamic displacement,and dynamic acceleration decay with an increase in roadbed depth.Dynamic acceleration decay deceleration was the fastest.In addition,the type of track influenced the dynamic response only at the top of the roadbed.

    • Influence of Different Damping Matrices on Seismic Response in Deep Soil Sites

      2014, 36(4):868-873.

      Abstract (3344) HTML (0) PDF 411.56 K (1996) Comment (0) Favorites

      Abstract:Seismic response analysis of soil plays a major role in the seismic safety assessment of engineering sites;it reflects the influence of the characteristics of engineering sites on the input ground motion parameters of a structure.Seismic analysis can either be performed in the time or frequency domains.The dynamic analysis of soil is based on the principle of soil dynamics and the viscous damping model,and the Rayleigh proportional damping matrix is built on the assumption that the vibration modes are orthogonal about the damping matrix;therefore,two structural vibration modes can be chosen to obtain the proportion coefficient of the damping matrix.The selection of viable damping models is important for seismic response analysis of deep soil layers in the time domain,and in this paper,the influence is discussed using six different damping matrices formed by the hysteretic damping ratio and modal damping ratio. The paper first introduces two damping matrices based on the hysteretic damping ratio and Rayleigh damping,which is based on the viscous damping ratio.Then,six different damping matrices are constructed for the seismic response analysis of a deep soil site: the first and second frequencies,the first frequency and the frequency closest to the predominant frequency of the seismic wave,the first frequency and third frequencies,a common model based on the first frequency used in soil dynamics,and other forms,such as equivalent damping matrices based on the first frequency and the translation frequency.The damping frequency can be considered as independent in the frequency domain and an accurate solution can be obtained.The time domain solution is obtained using ANSYS,which uses a one dimensional soil column for the simulation.Using a deep soil site as an example,the influence of the different damping matrices on the seismic response is analyzed under an input of synthetic bedrock seismic waves and a natural seismic wave,the Shanghai Sheshan bedrock seismic wave,recorded in the Wenchuan earthquake.The seismic response results at different depths of the soil are compared with the frequency domain solution. The results show that the influence of the damping matrix is greater on the accelerations than on the displacements. The peak ground acceleration is most overvalued by 47.28%,and most undervalued by 32.53% compared to the frequency domain solution.The cause for the different influences of these damping matrices is investigated.The chosen wave spectrum characteristics are different,and the degree of influence of a damping matrix also varies depending on the input wave spectrum characteristics.The spectrum characteristics of a seismic wave should be considered during the selection of a damping matrix.The frequency information of actual bedrock seismic records are generally abundant and due to the frequency correlation of the selected damping in the time domain,using only one frequency is often not sufficient to reasonably reflect the characteristics of a seismic wave.Therefore,both the spectrum of a seismic wave and the actual soil condition at the site should be considered to determine an appropriate damping matrix to obtain more accurate and reasonable results.

    • The Influence of Slope Angle on the Elevation AmplificationEffect of Rock Slope Acceleration

      2014, 36(4):874-880.

      Abstract (1330) HTML (0) PDF 1.59 M (1495) Comment (0) Favorites

      Abstract:A large-scale shaking table model test of a slope with a scale of 1:10 was introduced.The model slope was composed of soil with a height of 1.8 m,length of 4.4 m,and width of 4.4 m and included four slope angles of 30°,45°,50°,and 60°.The materials of the model test were blanc fixe,river sand,gypsum,clay,and water in various ratios.A series of tests was performed with various input seismic wave types,amplitudes,and frequencies.On the basis of field investigation results,shaking table test results,and theoretical analysis results,the influence of slope angle on the elevation amplification effect of rock slope acceleration was discussed.The results indicate that the amplifications of peak accelerations gradually increased with increases in slope angles.In addition,two inflection points were noted at slope angles of 45° and 50°,respectively,which suggests landslide hazards mainly occur on slopes with angles greater than 45°.Moreover,the amplification along the slope strike direction was essentially consistent,and the step was smooth.

    • Influence of Pore Water Pressure on Dynamic Response of High speed Rail Subgrade

      2014, 36(4):881-886,891.

      Abstract (1247) HTML (0) PDF 1.68 M (1125) Comment (0) Favorites

      Abstract:Ground vibration in a saturated subgrade caused by a high-speed train differs from that by a low-speed train. However,few studies focus on the influence of pore water pressure on ground vibration even though the key reason for the difference in ground vibration between saturated and elastic subgrades is a function of pore water pressure.Therefore,it is necessary to analyze the characteristics of the alteration of pore water pressure under various train speeds and to discuss the influence of pore water pressure on ground vibration.The 2.5-D finite element method (FEM)is used to analyze the influence of pore water pressure on the ground vibration of saturated subgrade.On the basis of the Biot theory,the governing equations of saturated porous media are established and transformed into frequency-wave number domains by double Fourier transform.The track and embankment are modeled by Euler beam.The saturated subgrade is modeled by 2.5-D FEM,and the train loading in the model is also transformed into frequency-wave number domains.The viscous damping absorbing boundary is used to reduce the influence of the finite element (FE)boundary.The 2.5-D FE model is validated by field vibration test results of the Sweden X2000 high-speed train.The results of the 2.5-D FE model match the field test results both in vibration interval and displacement amplitude.Therefore,this 2.5-D FE subgrade model is reliable for studying ground vibration in saturated subgrade.The paper discusses the influence of train speed,porosity,and coefficient of permeability of the saturated subgrade on ground vibration.The results show that when the train speed is low,the vertical vibration amplitude of the saturated ground is smaller than that of the elastic ground due to the influence of pore water pressure. However,when the train speed is high,the pore water pressure rises sharply and notably affects the ground vibration.The train loadings share the soil skeleton and the excess pore water pressure,which leads to the decrease of stress in the soil caused by the train loadings and the decreasing in vibration amplitude.When the train speed is larger than the Rayleigh wave velocity of the soil,or close to the shear wave velocity,there are several critical velocities.When the train speed is larger than the first velocity,a second velocity occurs that may lead to the increase in ground vibration amplitude.Thus,when the train speed is 252 km/h,the vibration amplitude increases and approaches that of the elastic model.The increase in train speed increases the high-frequency vibration in the subgrade,which leads to a sharp rise in excess pore water pressure owing to relatively slow pore water pressure dissipation.When as the train speed is very high,the changing of stress in the subgrade is assumed mainly by the excess pore water pressure,and the soil skeleton is less affected.As a result,the excess pore water pressure causes a small alteration of the amplitude of ground vibration when the train speed changes to high speed.The influence of porosity and permeability coefficient of the saturated subgrade on the pore water pressure is notable when the train speed is high.The results show that when the train speed is high,the pore water pressure of the saturated subgrade increases as the porosity decreases.As the permeability of the saturated subgrade increases,the pore water pressure within a 0.5 m depth increases,and deeper pore water pressure decreases.Therefore,to control ground vibration in the saturated subgrade,compact material with high permeability is suggested for subgrade material.

    • Characteristics and Stability Analysis of Shuiyanzhai Landslide in Tianshui City

      2014, 36(4):887-891.

      Abstract (1277) HTML (0) PDF 980.86 K (1082) Comment (0) Favorites

      Abstract:On the basis of the geologic investigation and field survey,this paper studied the main characteristics of the 2013 Shuiyanzhai landslide;analyzed the influence of terrain conditions,formation lithology,geologic structure,earthquake,rainfall,and human activities on the landslide;and calculated the dynamic landslide stability of the analyzed formation under the simulated action of static forces and different earthquake intensities using GeoStudio software and a variety of stability evaluation methods.The results showed that the landslide originated in a giant loess of mudstone tractive type.Landslide material and landslide mass have significant regionalization in the plane and stratification in profile.Stratum lithology and tectonic movement are the main internal causes,whereas rainfall and earthquake are important external causes.The landslide area is currently in a steady state,but the stability can be reduced and even reactivated by environmental change in the future.The landslide is in a limited equilibrium state under a Ⅶ degree seismic action.Failures occurred in the region when horizontal peak ground accelerations (PGA)reached greater than 0.15 g.

    • Research on Reinforcement Mechanism of Silt Embankment Using Geotextile Discrete Material Pile

      2014, 36(4):892-897,918.

      Abstract (1278) HTML (0) PDF 1.35 M (1014) Comment (0) Favorites

      Abstract:Sixu expressway is located in the Huaibei Plain,which is covered by silt or silty sand.However,because this type of soil is prone to liquefaction under seismic loading,liquefaction resistance measures should be considered when engineering projects are planned for this region.The liquefaction resistance of a geotextile discrete material pile and the bearing capacity of a composite foundation are examined in this study.In addition,the reinforcement mechanism of the geotextile discrete material pile with a silt subgrade is determined.The pore water pressure dissipation,bearing capacity of the composite foundation,pile-soil stress ratio,and pile body stress were researched by using the finite difference method and field testing,which is beneficial for obtaining the reinforcement mechanism of the composite foundation.Moreover,this paper presents design proposals of a geotextile discrete material pile.The results indicate that under seismic loading,a geotextile discrete material pile can effectively drain and successfully achieve anti-liquefaction.The excess pore pressure ratio increases with distance from the pile axis,and the silt becomes more inclined to liquefaction.An engineering example is used with numerical calculation to determine that effective pile spacing is 2 m,or approximately 3.3 times the pile diameter.Further,in the silt foundation,the bearing capacity of the single geotextile discrete material pile is 50% larger than that of gravel pile under the same conditions,and the composite foundation bearing capacity of the geotextile discrete material pile is 25% more than that of gravel pile.In static load testing of the composite foundation,soil pressure boxes are respectively buried at the top of the pile,at the bearing plate,and at the contact surface of the pile and soil to determine the bearing capacity of the pile and soil under the action of static load.In the two types of composite foundations,the pile-soil stress ratio increases with an increase in the upper load.This change in the geotextile discrete material pile is more prominent because geotextiles have additional lateral restraint effects on pile bodies.When the composite foundation is under a large load,the deformation of the pile is less than that of the soil;thus,a change occurs in the pile-soil stress ratio.Moreover,geotextiles have obvious reinforcement effects for the gravel pile,although damage is possible when excessive tension is placed on the ring.When the soil cannot provide adequate lateral pressure,lateral displacement of pile body is easily produced,and damage by ballooning can occur. The pile body stress test shows that maximum stress appears at four times the pile diameter range,which proves that the design of geotextile discrete material pile based on ballooning damage is reasonable.Hence in order to avoid damage on the top of the pile,it is necessary to reasonably select the geotextile material in consideration of the pile bearing conditions or to assume reinforcement measure in the area of pile body stress concentration.

    • Study on Vertical Dynamic Response Characteristics and Damage Identification of Existing Bridge Pile

      2014, 36(4):898-904.

      Abstract (1636) HTML (0) PDF 2.29 M (1275) Comment (0) Favorites

      Abstract:Integrity detection of the pile foundations of existing structures is a difficult problem worldwide.Integrity testing of newly constructed pile foundations includes detection methods such as mining with the observation method,drilling core method,low-strain test method,and ultrasonic method. However,for damage detection of pile foundations in service,the existence of platforms and bridge structures above pile foundations makes the observation method difficult because the mining depth of the soil around the pile is very limited.Drilling core methods cannot be achieved because drill core must be drilled from the pile top.For ultrasonic detection,there is no channel available for installing ultrasonic transducers.For the low-strain test method,velocity sensors cannot be placed at the top of the pile;therefore,vertical vibration cannot be recorded.In this paper,vertical impact load is applied on the upper cap surface above the detected pile.According to the vertical velocity response of the cap surface and pile head,we analyze the integrity of the bridge pile foundation in-service.Bridge pier-cap-pile-soil explicit dynamic finite element models are based on ANSYS LS DYNA.In the finite element models,impact load is applied on the cap surface,and the vertical velocity responses of the complete pile and the cracked pile are both recorded.Two types of pier-cap-pile-soil numerical models are used in this study with six and eight piles,respectively.The results show that when the impact load is applied at the cap surface on top of the pile to be detected,the stress wave goes through the cap and propagates downward along the pile.Similar to the principle of sonic echo in pile integrity testing,the stress wave reflects at the pile bottom or fracture surface where impedance changes significantly.From the vertical velocity response curve of the pile head,the reflected stress wave from the pile bottom or the fracture surface can be identified to determine whether the pile is complete or cracked.This paper also presents the vertical velocity response of the cap surface;the response curve is more complicated than the pile head because of multiple reflections of stress wave at the pile-cap interface.Therefore,accurate evaluation of the reflected wave is difficult.Loading the vertical impact at the pile head produces a simpler waveform of vertical velocity response of the pile head than that when using the cap surface.The reflected wave response of the pile head is more obvious,and it is easy to judge the pile bottom or the fracture surface by the reflected wave.Moreover,the waveform of vertical velocity response of the pile head can be used to accurately evaluate the pile integrity.However,arrangement of velocity sensors at the pile head is difficult;that at the cap surface is more practical.The waveform of vertical velocity response of the cap surface is very sensitive to the positions of velocity sensors and changes often.Thus,when recording the vertical velocity response of the cap surface,there is a strong need for a plural arrangement of velocity sensors to measure the response waveform.Such an arrangement is also important for filtering and analysis aided by signal processing technology.

    • Study on Liquefaction Estimation Method Based on State Parametersof CPTU in Situ Measurement

      2014, 36(4):905-910.

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      Abstract:The in situ performance of sandy soil and the volume change characteristics of the evaluation index (state parameter) have always been difficult to effectively determine, although these parameters are very important.Using the state parameter (Ψ) to explain the pore pressure static cone penetration test is an emerging trend.Considering that the soil state parameter is related to the volume change of the evaluation index,the sand dilatancy trend and liquefaction resistance in a sandy soil site were increased with an increase in confining pressure.Therefore,it is viable that the state parameter can be used in the soil liquefaction discrimination. In this paper,the Suqian Xinyi expressway project is taken as the background,and a relevance model is established among the status parameters of cone penetration test with pore pressure measurement (CPTU), cycle resistance ratio (CRR), and standard penetration number (N).In addition, two types of new methods for estimating sandy soil liquefaction by state parameters are established.

    • Stochastic Seismic Responses of a Large-spanMulti-tower Cable-stayed Bridge

      2014, 36(4):911-918.

      Abstract (1316) HTML (0) PDF 1.72 M (1100) Comment (0) Favorites

      Abstract:This paper establishes a structural model of the Jiashao river spanning bridge using the ANSYS finite element software,in which the tower and the beam are simulated by beam44.In addition,link8 is used to simulate the cables in the model.Through the solving of the dynamic equation,the results of the model show the dynamic response of the Jiashao bridge.This paper analyzes these responses to study the principles of structural dynamic response of a large-span multi-tower cable-stayed bridge under a stochastic seismic effect.The results show that,on the whole,the displacement of a beam at each span under three-dimensional uniform excitation has the same response.The horizontal and vertical RMS response of a beam’s displacement gradually increases from the base of a tower toward the center of the beam,but the value in each span varies to certain extent.The longitudinal bending moment of the tower,where the height is lower than the place of constraint of the tower-girder,increases linearly with reduction in the height of the tower,but the bending moment of the remainder of the tower decreases with increase in the height of the tower.With respect to the different longitudinal constraints of the tower-girder in the models,the displacement of the main beam in the middle span and the internal forces in the base of the towers show clear differences among the models.Analysis shows that the internal forces in the base of the towers are deeply affected by the constraint conditions of the tower-girder,and that there is interaction between the constraint conditions of the tower girder and the internal forces in the base of the towers.When each tower is under a longitudinal constraint,the RMS of the vertical displacement of a beam reaches its maximum value.The displacement is intermediate when each tower has vertical dampers (parts of towers have vertical constraints)and the minimum values of displacement are obtained when each tower has only vertical dampers.If a longitudinal tower-girder constraint is set in a tower,the internal forces in the bases of the towers are significantly enhanced as compared to when dampers are used.In addition,in this study,the traveling wave effect on the dynamic response of a large-span multi-tower cable-stayed bridge was analyzed.The results show that the RMS-value curves of the longitudinal displacement of a beam are similar under different seismic wave velocities.The minimum value is obtained at the location where the longitudinal tower-girder constraint is set,and the displacement gradually increases toward the center span.When the seismic wave velocity is in a lower range of values,the relationship between the velocity and the longitudinal displacement of the main beam is not very obvious, but when the velocity is in a larger range of values,the longitudinal displacement of the main beam increases with increase in velocity.Furthermore,the RMS values of the base of a tower’s moment and shear show the same variation as the displacement of a beam under different velocities.In general,this study indicates that the traveling wave effect has the greatest impact on the response,and that there is a certain relationship between structural response and a traveling wave.

    • Analysis of Seepage Field of Underwater Tunnels in a Semi infiniteAquifer under Wave Action

      2014, 36(4):919-923,945.

      Abstract (1420) HTML (0) PDF 1.41 M (1144) Comment (0) Favorites

      Abstract:The existing seepage field calculation model of underwater tunnels generally ignores the influence of waves.On the basis of the theory of linear wave-induced pressure in soil,Laplace transformation was used to obtain the lining pressure and inflow.The results indicate that when the wave steepness exceeds 0.09,the lining bears more than that when pressure is applied by still water.The lining pressure and inflow increase as the soil permeability coefficient decreases.When the lining permeability coefficient kL=1×10-7 m/s both the lining inflow caused by waves and still water decrease.Moreover,the lining seepage field is influenced both when the water period ranges is 5~10 s and the depth d

    • Dynamic Stability Analysis of Slopes Reinforced by Anchor Anti slide Pile

      2014, 36(4):924-930.

      Abstract (1209) HTML (0) PDF 2.32 M (1109) Comment (0) Favorites

      Abstract:The seismic performance of anchor anti-slide pile is strong, however, dynamic research data on this topic are scarce.The pseudo-static method,time-travel analysis method,and strength reduction dynamic analysis method were adopted to study the dynamic stability of this support form through an actual project conducted at a railway station in Dali.This study describes the entire application process and reveals the differences in these methods.In addition,the dynamic stability of this slope and the seismic performance were studied to ensure the safety of this slope.These research results can provide a reference for similar projects.

    • Analysis Method of Site Seismic Stability Based on ArcGIS

      2014, 36(4):931-938.

      Abstract (1658) HTML (0) PDF 5.63 M (1223) Comment (0) Favorites

      Abstract:China is a country with active earthquakes.Due to its dense population,the work of protecting against and mitigating earthquake disasters should be performed,which will directly affect the economic development and social stability of the country.Thus,various effective measures must be applied to minimize the damages of earthquake disasters.Developments in soil dynamics and earthquake engineering are examples of advanced science and technology methods used in earthquake resistance and defense.Site seismic stability is a topic of great concern in geotechnical engineering and engineering seismic areas and has important significance for disaster prevention and mitigation.In modern society,information technology has developed rapidly.The development of 3 s technology,Geographic Information System (GIS),Global Positioning System (GPS),and remote sensing (RS),provides a new driving force in digital way for soil dynamics and earthquake engineering through acquisition,processing,and application to the Earth and to spatial data of humanistic factors.Geotechnical earthquake engineering problems were studied,and regional site seismic stability and degrees of liquefaction evaluation technology have been developed on the basis on the advanced technology of the ArcGIS platform.For example,the geotechnical earthquake zoning system in Tangshan and its southern region has been initially shaped on the basis of ArcGIS,which has provided a foundation for further research and engineering applications.The China Academy of Building Research has released a report titled “The research of geology of earthquake engineering in intense seismic area of Tangshan,” which systematically analyzed and summarized geological concerns in various sites and foundations including seismic faults,earthquake liquefaction,ground motion,seismic damage analysis,and geological mapping of earthquake engineering in 1976.The formation mechanism and distribution characteristics of various seismic effects have been detailed,analyzed,and studied.This content-rich and impeccable composite report is significant for guiding the study of earthquake disaster.In addition,many research achievements have been converted to paper maps including 24 photographs.However,the visibility and operability are unsatisfactory because the comprehensive understanding of the layer properties is insufficient.Moreover,the report does not effectively address geometry such as points,lines,and polygons.In this paper,the shortcomings of the aforementioned report are summed up and corrected,and a technical method for site seismic stability evaluation based on ArcGIS is presented. ArcGIS and AHP are combined to analyze the main factors affecting the stability of seismic ground,and a zoning map for site seismic stability is created.All dispersive basic data of each factor is digitized and visualized to establish an interactive relationship between the spatial graph database and the attribution database.AHP is the basis of the data operation,which is used to determine the weight of the distribution properties of various areas in each interior factor and between factors to determine the stability of the seismic ground and to conduct quantitative analysis for overlay analysis in ArcGIS.In this study,the southern region of Tangshan is used.Special consideration is made,and the zoning map of site seismic stability is used to confirm the feasibility of this method.The results of each method have been compared with an aerial map obtained three days after the Tangshan earthquake.The results indicate that the distribution for the grade of site seismic stability roughly corresponds to the aerial map,which illustrates that the method proposed in this paper is applicable to analysis of site seismic stability.

    • Dynamic Stability Analysis of Railway Embankment Engineering in Permafrost Regions of the Qinghai-Tibet Plateau

      2014, 36(4):939-945.

      Abstract (1477) HTML (0) PDF 3.22 M (1261) Comment (0) Favorites

      Abstract:Analyzing the dynamic transfer mechanism of the plain-fill railway embankment under locomotive loading in a scientific and reasonable manner is of primary importance for stability prediction of the embankment,especially in the permafrost regions.It also provides a valuable reference for the construction of significant water conservancy projects,such as large dams and reservoirs,in the permafrost regions of the Qinghai-Tibet plateau. Based on the strong motion observation tests at the Beilu River segment in the permafrost region,the nonlinear dynamic finite element method was applied to the numerical calculation of the plain-fill and block-stone embankments to analyze the influence of the block-stone layer.The results show that vibration transmission can be controlled through the block-stone layer,which can decrease the effect of vibration on the stability of the embankment.Meanwhile,the vibration settlement from train-induced vibrations mainly occurs in the roadbed;the maximum displacement of the block-stone embankment can reach up to 0.9 mm,which is less than the displacement of the plain-fill embankment.The maximum principal stress of the block-stone embankment is greater than the plain fill embankment,however,the amplitude and the range of maximum shear strain is smaller.

    • Influence of Piling on Damping Coefficients of Soil Surrounding Piles

      2014, 36(4):946-951.

      Abstract (3349) HTML (0) PDF 566.75 K (2500) Comment (0) Favorites

      Abstract:The accuracy of drivability analysis for piles with large diameters is very important for pile driving safely.The prediction of soil resistance to driving (SRD) is the focus of this analysis.Numerous models have been developed to predict soil resistance.With many outstanding advantages,the technology of high-strain testing is the basis for a new advanced method for pile-driving analysis.The Case Pile Wave Analysis Program (CAPWAP) method is generally used to analyze dynamic tests data to obtain the SRD.CAPWAP is based on one-dimensional wave theory,which is widely used in pile foundation monitoring and bearing capacity evaluation in ocean engineering.Using CAPWAP to analyze the data from dynamic testing,the SRD can be determined during the entire pile installation procedure.When using CAPWAP,soil factors and pile parameters such as damping,quake force,and wave velocity should be determined.Among the parameters,the soil damping coefficient of friction Js and top of pile Jt,have the greatest influence on pile bearing capacity.Soil damping coefficients are the most important parameters of soil dynamics.Various models have proposed distinct Js and Jt,and each soil type has a specific damping value.For example,the Smith model proposed values of 0.16 and 0.48 for Js and Jt,respectively,and the Case model recommended Js values of 0.15 for cohesive soil and 0.65 for cohesionless soil;Jt was 0.5 regardless of soil type.Many models widely use the value of 2.54 mm for quakes.Although many scholars give different experience values,the Case damping coefficients are widely adopted in most cases. Engineering applications reveal that various soil parameter values strongly influence the SRD;therefore,the study of soil parameter values is meaningful.To obtain more accurate damping parameters and to improve the reliability of CAPWAP,this study examines the results of pile dynamic testing of an engineering application in the East China Sea.During pile installation,the pile is struck up to 1868 times to penetrate the design depth,with each blow containing a set of corresponding force and velocity curve.In this study,we analyze approximately 200 curves by CAPWAP to obtain a set of soil parameters for each layer.To obtain the changes in Js and Jt with depth,numerous data are analyzed.First,a study is conducted to determine Js and Jt with various penetration depths.The results show that the soil damping coefficients increasingly decay rather than remain constant during piling and change with penetration depth.Therefore,when using CAPWAP to predict the soil resistance to driving,using a constant for Js or Jt during the entire pile installation is not reasonable and will result in error.To further study the changes in soil damping coefficients during pile installation,the relationship of soil damping coefficients with blows is examined.It is determined that the change trend of blows is in contrast to that of the damping coefficient.Finally,this study analyzes the change trend of soil damping coefficients with depth.During the piling procedure,the factor value is shown to steadily decrease in a manner similar to a linear gradient.

    • Comparative Test Study on Dynamic Characteristics of Undisturbed and Remolded Marine Silt

      2014, 36(4):952-957.

      Abstract (1542) HTML (0) PDF 508.16 K (1349) Comment (0) Favorites

      Abstract:The behaviors of dynamic strength,dynamic shear modulus,and damping ratio of undisturbed and remolded marine silt by dynamic triaxial and resonant column tests are analyzed.The test results show that under the same conditions,the dynamic shear modulus and reference shear strain of undisturbed silt are greater than those in the remolded soil,although the damping ratios are closer in value.In addition,the normalized G/Gmax-γ/γr and λ-γ/γr can weaken the influence caused by disturbance of the remolded silt. Moreover,the stress ratio of liquefaction and dynamic strength of undisturbed marine silt are smaller than remolded soil in the same conditions.Along with the increase in consolidation ratio,the difference in dynamic strength of undisturbed and remolded silt decreases under the same equivalent vibration cycle times.Further,the pore water pressure of remolded silt increases sharply,and the pore water pressure of remolded soil tends to be stable when the samples are about to be damaged.

    • ]Influence of Embankment on Liquefaction Properties of Foundation Soil

      2014, 36(4):958-962.

      Abstract (1174) HTML (0) PDF 522.58 K (1024) Comment (0) Favorites

      Abstract:The liquefaction resistances of foundation soil subjected to embankment loading and those without loading are compared and discussed by using the WWCC program developed independently by the Geotechnical Research Institute of Hohai University.Three different seismic waves and various heights of embankments are used to conduct dynamic finite element analysis of an embankment constructed in Guangdong, China.China has incurred multiple earthquakes;approximately one third of the total earthquakes in the country had magnitudes greater than 7.Earthquakes cause severe losses because many highways are located in earthquake prone areas.Such damage has attracted an increasing amount of attention from highway engineering academics because seismic loading causes liquefaction of ground soil.Foundation soil liquefaction occurs when pore water continuously accumulates and is influenced by the effect of embankment loading on foundation soil.The embankment loading causes a rapid increase in the pressure of pore water,and the shear strength approaches to zero,which leads to losses in sand bearing capacity and formation of the flow state.The main earthquake damage to roads located in liquefaction areas is large structure displacement.Damages to expressways caused by foundation liquefaction vary and include sinking, cracking,movement,breakage,and embankment collapse. At the present,many studies on foundation soil liquefaction focus mostly on natural foundation.A book titled “Specification of Earthquake Resistant Design for Highway Engineering” presents various liquefied standards.However,the criteria mentioned in this book are applicable only to the exploration stage;few studies have reported the effect of overlying buildings on the liquefaction properties of subgrade soils.Therefore,this paper studies the liquefaction resistance of subgrade soils in the highway engineering on the basis of previous research.When the natural foundation is subjected to additional embankment loading,the distribution of stress and pore water pressure in the foundation soils is changed.The effect of embankment loading on the foundation soil is so obvious that it is necessary to pay close attention on the research.In this study,three different seismic waves are used to conduct dynamic finite element analysis of an embankment.The results show that embankment loading significantly enhances the liquefaction resistance of subgrade soils,which means that the embankment loading has a positive effect on the liquefaction resistance of an expressway.The liquefaction resistance increases when the depth of the foundation soil increases;the highest increase was 38%.Moreover,a parameter study is conducted to further analyze the effect of embankment height on the liquefaction properties of subgrade soils.The results show that a higher embankment relates to higher liquefaction resistance.The influence of various heights is more obvious in deeper layers of foundation soil;that on shallow layers can be ignored. Based on the research of liquefaction properties of foundation soil subjected to embankment loading,it can be concluded that the liquefaction resistance of highways is markedly safer with an embankment load.

    • Correction of Unsymmetrical Exponential DynamicConstitutive Model of Soil

      2014, 36(4):963-967.

      Abstract (1342) HTML (0) PDF 550.18 K (1069) Comment (0) Favorites

      Abstract:The unsymmetrical exponential (UE)dynamic constitutive model is used to describe the soil characteristics under dynamic loading.This model has the advantages of describing asymmetric cyclic loading,low memorization,explicit physical meanings of the model parameters,and simple expressions. However,the UE model is asymmetric and is unable to appropriately fit the distribution of soil damping ratio variation with changing strain when it is used to describe the soil hysteresis loop under constant amplitude cyclic loading.By introducing two transient variable parameters in the skeleton curve of the UE model and using Massing’s method of doubling the stress and strain variables to structure the hysteretic curve,the correction model can accurately determine the shear modulus and damping ratio under different strains.The shear modulus and damping ratio were then used determine the expression of the transient parameter, and they were substituted in the hysteretic curve equation. Finally,the hysteretic curve expression and the actual skeleton curve were obtained.The results show that the correction model can overcome the limitations of the UE model and is in good agreement with the actual data.

    • Stability Analysis of a Typical Loess Slope Supported by Block Stone Retaining Wall in Tianshui

      2014, 36(4):968-974.

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      Abstract:In this study,field and laboratory tests are used to obtain the soil conditions and mechanical properties of a 013 loess slope in Tianshui.This study introduces a hierarchical support scheme using a block stone retaining wall,and the stability of the slope is verified on the basis of the strength reduction method.Moreover,the safety factor and the equivalent plastic strain law of this slope is determined before and after application of the support using ABAQUS software in which the yield criteria of the corner point circumcircle of the Drucker-Prager (D-P) criterion is adopted.The horizontal displacement law of the slope before and after the support is also obtained using ABAQUS.The results show that using the finite element strength reduction method, the safety factor of the slope without support is 0.59;in ciontrast,the safety factor of the slope in block stone retaining wall is 1.41.Therefore,the stability state of the slope is reached. Moreover,on the basis of the finite element strength reduction method,the equivalent plastic strain zone of the slope without the stone retaining wall is located at the foot of the slope,and the failure form of the slope is local soil failure with a maximum plastic strain of 0.023.Therefore,no sliding surface is present in the slope.By comparison, an equivalent plastic strain zone occurred under the slope supported by the rock block,and the failure form of the slope is also local soil failure. In addition,the maximum plastic strain is 0.02.With further reduction of the soil strength,the upper soft soil will develop a sliding surface through the slope in the stone retaining wall.At the same time,the stone retaining wall will decrease the horizontal displacement of the soil,which can prevent the total displacement from sliding to a free surface.

    • Influence of High-rise Building Foundation Depth on the Stability of the Composite Foundation

      2014, 36(4):975-979.

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      Abstract:With the rapid development of high-rise buildings,the stability and safety of high-rise building foundations is becoming increasingly important.The depth of a foundation is one of the most important factors affecting the stability and safety of buildings.At times,construction codes cannot be met by projects because of factors such as condition of the site and demand for land.Since the depth of a foundation can impact its stability,we used a high-rise building as an example to determine the strength parameters of the composite foundation soil and the stability of the foundation was checked under the condition of the worst buried depth by calculating the bearing capacity,safety parameter of resistance to slip and overturning,and the stability on the whole.Our results show that a reduced depth of foundation can lead to a stable foundation under better engineering geology conditions.These results can be referenced by similar projects.

    • Several Dynamic Spatially Mobilized Planes of Sandy Soil and Researchon Strength Criterion Adaptability

      2014, 36(4):980-986.

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      Abstract:In practical geotechnical engineering,widely used strength criteria include the Mohr-Coulomb,Drucker-Prager,and Matsuoka-Nakai criteria.These guidelines define the laws that should be obeyed by the stress on a certain spatially mobilized plane when geotechnical materials are damaged.These planes have different characteristics.The spatially mobilized plane of the Mohr-Coulomb criterion is orthogonal with large and small principal stress planes,and the angle between the major principal stress planes is 45°+φ/2.It is assumed that the ratio between the shear stress and the normal stress on the plane is constant;then,the Mohr-Coulomb criterion can be obtained.The Drucker-Prager criterion describes the law that should be obeyed by the principal stress on an octahedral plane when geotechnical material is damaged.That is,the ratio between shear stress and normal stress on an octahedral plane is constant when the geotechnical material is damaged.The plane with the same normal stress is orthogonal with the tendency of geometric space,and the angle between the axes is the same.If a corner of the orthogonal hexahedral principal stress unit is located in the origin of the axes of a three-dimensional geometric space,then a 45°angle is present between the sliding surfaces in the space of three orthogonal planes intersecting the line with the axis.Based on the Mohr-Coulomb criterion,the Matsuoka-Nakai criterion presents a spatially mobilized plane (SMP)with non-fixed normal stress.The SMP is changed with the changes in principal stress.The intersection between the unit of main stress in the spatially mobilized plane and the axis of three-dimensional geometric space is respectively√(σ1 ),k√(σ2) and k√(σ3),if the intersection is respectively k(√(σ1))n、k(√(σ2))n and k(√(σ2))n.Then,the spatially mobilized plane can be expanded to different dynamic spatially mobilized planes and different spatially mobilized plane strength criteria.On the basis of true triaxial tests on sand and the traditional principle of the spatially mobilized space,a variety of dynamic spatially mobilized spaces and appropriate strength criteria have been introduced.In this paper,the first-power dynamic spatially mobilized plane(σ),the quadratic-power dynamic spatially mobilized plane (√σ ),and the third power dynamic spatially mobilized plane (?σ) are proposed.The essence of the quadratic dynamic spatially mobilized plane(√σ)is same as the Matsuoka-Nakai criterion based on the SMP.If the ratio of the shear stress and normal stress on the surface of the dynamic spatially mobilized plane is equal to constant and has the same shear strength criterion as the axisymmetric triaxial compression failure of the Mohr-Coulomb criterion,the criterion of dynamic spatially mobilized plane can be obtained.On the basis of the true triaxial test data of sand,comparative analysis of the theoretical strength and the traditional strength as well as the newly established strength criterion and the actual strength of true triaxial test data is conducted. Through the analysis and comparison,the quantitative strength error of each criterion is determined.Comparative analysis shows that for the sand under complex stress conditions,each criterion can reflect certain regularity.However,certain errors are present,and the constant term changes with complex stress conditions.The (?σ) dynamic spatially mobilized space strength criterion showed the best consistency.

    • Test and Study on Strength Weakening Behavior of Soil around a Pile under Cyclic Loading

      2014, 36(4):987-990.

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      Abstract:Liquefaction does not occur in a soft foundation under the action of wave cyclic loading;however,increases in period,amplitude and stress decrease the effective strength of soil.As a result,soil foundations lose bearing capacity.In addition to vertical load,a wharf structure also bears loads of waves,ice,and ship impact.Because these loads are generally cyclic,the soil around a pile will experience a fatigue effect.As a result of cyclic loading,the soil will incur structural damage and weakening.In this study,we use indoor dynamic triaxial testing to simulate the combined stress of cycle wave loading and vertical loading,and we apply these loads to the soil of Tianjin port to study the relationship among soil strength,combined stress,and soil depth.The laws of soil under combined stress loads at various depths are then obtained by the dynamic tri-axial test research.Moreover,a simple formula to determine soil strength weakening is presented to provide scientific data for further evaluation of the soil strength weakening in engineering applications.

    • Seismic Analysis of Large scale Aqueduct Structures Based onthe Probability Density Evolution Method

      2014, 36(4):991-996.

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      Abstract:Using the orthogonal expansion method of random processes,the non-stationary seismic acceleration process is represented as a linear combination of the standard orthogonal basis functions and the standard orthogonal random variables.Then,using the random function,these standard orthogonal random variables in the orthogonal expansion are expressed as an orthogonal function form of the basic random variable.Therefore,this method can use a basic random variable to express the original earthquake ground processes.The orthogonal expansion-random function approach was used to generate 126 representative earthquake samples,and each representative sample was assigned a given probability.The 126 representative earthquake samples were combined with the probability density evolution method of stochastic dynamical systems and random seismic responses of large-scale aqueduct structures was investigated. In this study,four cases were considered;aqueduct without water,aqueduct with water in the central trough, aqueduct with water in a two-side trough,and aqueduct with water in three troughs,and probability information of seismic responses for these cases were obtained. Moreover,using the proposed method,the seismic reliability of the aqueduct structures was efficiently calculated.This method provides a new and effective means for precise seismic analysis of large-scale aqueduct structures.

    • Analysis of Designed Velocity Response Spectra Subjected to Near-fault Ground Motion

      2014, 36(4):997-1002, 1013.

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      Abstract:In recent years,several disastrous near fault earthquakes,such as the Wenchuan earthquake in China,the Chi Chi earthquake in Taiwan,the Kobe earthquake in Japan,and the Northridge earthquake in the United States,have occurred.A large amount of near-fault pulse-type earthquake data from all these earthquakes has been recorded,and has attracted close scrutiny and extensive research.This seismic record contains obvious long period velocity pulses.Near-fault ground motions not only cause serious damage to buildings,but also cause slope instability and damage to infrastructure,These disasters have a serious impact on the economic infrastructure and safety of people.Therefore,understanding the response of structures to near-fault ground motions is necessary.This allows for more reliable and efficient seismic design.Different ground motion records contain different types of information such as peak acceleration,peak velocity,peak displacement,and duration of ground motions.Near-fault ground motions have prominent features and destructive force and their velocity response spectra are significantly different from the velocity response spectra of far-fault ground motions.This study used 30 near-fault earthquake records from the Pacific Earthquake Engineering Research Center’s strong motion database;the records contain magnitude,fault mechanism,soil layer shear wave velocity,and fault distance information.First,a motion equation for a single degree-of-freedom system was established.Then,a state-space method and MATLAB was used to change the motion equation to a state equation.Next the equation was solved to obtain the velocity response of a single degree-of-freedom system and based on the velocity response,the velocity response spectra of the single degree-of-freedom system was obtained.Because the velocity response is related to the acceleration response and the displacement response,the velocity response of structures are analyzed in the present study.The features of the velocity response spectra were obtained by normalizing and averaging,and then the 30 near-fault earthquake records selected from the PEER strong motion database were divided into different groups based on the period corresponding to the peak velocity.A velocity design spectra was established using a piecewise linear fitting method.The reasonableness of the velocity design spectra was verified by comparing the velocity design spectra and the velocity average spectra of different groups.The results show that the velocity response spectra of near-fault ground motions consist of four stages:ascent segment,peak segment,depression segment,and horizontal segment.The damping ratio of the structure has no influence on the spectral shape of the velocity response spectra,but the damping ratio of the structure can affect the spectra peak of the velocity response spectra.When the damping ratio of the structure is different,the maximum relative error of the velocity response spectra peak is 16.68% after pairwise comparison.

    • Textual Evidence for the Existence of the Houfeng Seismograph Based on the Two Capitals System in Ancient China

      2014, 36(4):1003-1007.

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      Abstract:The actual existence of Zhangheng's seismograph is still controversial in science and historical circles, in great part because of contradictions within historical records. According to the History of the Later Han Dynasty: Biography of Zhang Heng, in the first year of Yang Jia (132 AD), Zhangheng made the seismograph and died in the fourth year of Yonghe (139 AD). During this time, there was only one earthquake that occurred in Longxi, Gansu Province, according to the History of the Later Han Dynasty, which occurred in the third year of Yonghe (138 AD). It is generally considered that this event must be the one the seismograph so famously recorded.The paradox lies in an inconsistency between historical records of the 138 AD Longxi earthquake. An accounting of property damage at the capital appears in the History of the Later Han Dynasty: WuXing Zhi, which means at the time of the Longxi earthquake, a destructive earthquake also struck the capital. However, according to the History of the Later Han Dynasty: Biography of Zhang Heng, when the Longxi earthquake occurred, no earthquake was felt at the capital.Therefore, in 138 AD, when the Houfeng seismograph recorded the earthquake, people in the capital should have strongly felt it. It would not be surprising that the seismograph could record the earthquake if people could feel it. Because of the conflict between the historical accounts, and because the seismograph was lost soon after its invention; many people believe that the seismograph did not really exist.This paper proposes another interpretation of the seemingly contradictory records. There were two capitals during the Eastern Han Dynasty: Chang'an and Luoyang. We know that the seismograph was tested in Luoyang. We propose that the capital that suffered earthquake damage was Chang'an, which would solve the paradox and serve as a powerful proof that the seismograph existed at that time.

    • Study on the Gravity Variation in Hexi Area and the MenyuanMS5.1 Earthquake

      2014, 36(4):1008-1013.

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      Abstract:To study the relationship between gravity field variation and earthquakes, this study analyzes the relationship between gravity field variation in the Hexi area and the MS5.1 earthquake area near Menyuan in 2013 on the basis of gravity field variations obtained through mobile gravity observation in the Hexi area from May 2010 to October 2013. On the basis of gravity change in the Hexi area during the study period,the accumulated gravity change in a longer period is applied using the line from Minle to Tianzhu in the northern Qilian Mountain as a borderline of positive and negative gravity.The gravity change is positive in the Hexi Corridor north of the borderline and negative in the Qilian Mountain area south of the line. In the north and south region of the borderline,the accumulated gravity variation changes sharply from positive to negative.Moreover,a high gradient belt of gravity change located on the North Qilian Mountain Fault is formed between Tianzhu and Minle,and the accumulated gravity positive change is up to 70 × 10-8 ms-2 in the northern region.The accumulated gravity change forms two negative extreme value zones in E’bao and Tianzhu,where the minimum is -70 × 10-8 ms-2,and a negative depression zone is formed between Tianzhu and E’bao,where the 2012 MS4.9 and 2013 MS5.1 earthquakes near Menyuan occurred.The results shows that the gravity field variation is larger near the active faults in the Hexi area,including the Qilianshan North Rim Fault located between E’bao,Menyuan,and Gulang,and the Changma-Menyuan and Zhuanglang River faults. Moreover,a high gradient belt of gravity variation in these regions is consistent with these faults.The Menyuan MS5.1 earthquake occurred between E’bao and Menyuan near the high gradient zone of gravity variation.The gravity variation shows the local gravity anomaly characteristics caused by fault tectonic activity.

    • Focal Mechanism Solutions and Seismogenic Structure of theBadong MS5.1 Earthquake of 2013 Using the CAP Method

      2014, 36(4):1014-1018.

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      Abstract:Using the records of nine stations in the Hubei and Chongqing Regional Seismic Network,we obtained the focal mechanisms of the Badong MS 5.1 earthquake in 2013 using the “Cut and Paste” (CAP)method. Our results show that the best double couple solution of the MS5.1 event is 166°,79°,and -22° for strike,dip,and rake angles respectively;the strike,dip,and rake angles of the other nodal plane are 298°,68°,and -168°,respectively,and the optimum focus depth is 5.5 km.The results show that the earthquakes mechanism was a thrust along strike slip faults,with the principal stress P axis mainly in the EW direction and the lord tension T shaft mainly in the NS direction.The focal mechanisms of the biggest aftershocks are mostly normal dip slips,and the aftershock sequence mainly propagated along the EW direction, with a few propagating along the NS direction. Therefore,we infer that the seismogenic structure of the MS5.1 earthquake and aftershocks was the EW strike portion of the Daqiao fault.

    • Variations in Apparent Stress Prior to and after theTangshan MS4.8 Earthquake

      2014, 36(4):1019-1025.

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      Abstract:On May 28,2012,an earthquake of MS4.8 occurred in Tangshan,and was followed by earthquakes of MS4.0 and MS3.5 in Baodi.Data from this series of earthquakes (Tangshan MS4.8,and the Baodi MS4.0 and MS3.5 earthquake series,from January 2011 to June 2013),recorded by the Digital Seismic Network in Tianjin,were used to calculate the apparent stress in this region.First,the multi window FFT was used to obtain the observed spectrum,and then after extracting the instrument response it was corrected for geometry spreading and attenuation.For geometry spreading correction,Gail’s three section geometry spreading model was used.The frequency-dependent Q value was used for inelastic attenuation correction.A genetic algorithm was applied to determine the pair of fC and Ω0 of Brune’s ω2 model,which yields the least deviation between the theoretical ω2 model and the corrected spectral.The seismic moment (M0) was calculated from Ω0,and ES was obtained by integrating the corrected spectral with limited bandwidth compensation.Apparent stress was calculated from M0 and ES.Furthermore,the time distribution of apparent stress and the average value of apparent stress are presented.The results are as follows:First,a high apparent stress appeared before the MS4.8 earthquake and its peak value appeared at the mainshock;then,the apparent stress decreased after the MS4.8 earthquake.The size of the apparent stress accurately reflects the state of the stress field in the hypocenter region.Therefore,it can be used as the basis for determining the seismic trend.Second,the apparent stress before and after the MS4.8 earthquake is generally positively correlated.The apparent stress increases with magnitude,but,on the whole,the apparent stress value is greater before the MS4.8 earthquake than after.

    • Application of the Multi-parameter Method to the Shanxi Seismic Belt Based on Earthquake Corresponding Relevancy Spectrum

      2014, 36(4):1026-1032.

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      Abstract:Using the method of multi-parametric moving maximum probability based on earthquake corresponding relevancy spectrum,we quantitatively identify and analyze the temporal-spatial evolution characteristics of multi-parametric precursory anomalies occurring before moderate-strong earthquakes in the Shanxi rift zone and adjacent regions,and discuss the development of these earthquake precursory anomalies.We established a database of earthquake corresponding relevancy spectrum with spatio-temporal attributes after performing retrospective research of earthquakes,and developed extrapolative prediction ability.This study presents a new method for the prediction of moderate-strong earthquakes in the Shanxi rift zone and adjacent regions.Since the time-interval in this study is 12 months,we performed temporal scanning of the multi-parameter earthquake corresponding relevancy spectrum in the northern,central,and southern districts of the Shanxi seismic belt.The target earthquake magnitudes in the northern,central,and southern districts of the Shanxi seismic belt were ML≥ 5.0,ML≥ 4.5 and ML≥ 4.5,respectively.The selected parameters for the northern district were b value,earthquake absence and frequency,and that for the central and southern districts were η value,b value,and earthquake absence and frequency.The retrospective research period was from 1970 to 2009,and the extrapolative prediction period was from 2010 to September,2013.The results show that during the retrospective research period of 1970 to 2009, seven of the nine major changes in the multi-parametric moving maximum probabilities occurred before the occurrence of the target earthquakes and there were two false predictions in the northern district.There were nine and five major changes in the multi-parametric moving maximum probabilities in the middle and southern districts,respectively,before the target earthquakes.During the extrapolative prediction period,the major change in the multi parametric moving maximum probability of the northern district corresponds to two ML5.0 earthquakes in 2010.There are no obvious anomalies in the central district and ML≥ 4.5 earthquakes do not actually occur in this district. A major change in the multi-parametric moving maximum probability in the southern district appears from March,2010 to May,2013,with the possible occurrence of a ML≥ 4.5 earthquake.The study area is the Shanxi rift zone and the adjacent region(33°~42° N,106°~117° E) and the target earthquake magnitude for the study area is ML ≥ 5.0.The retrospective research period is from 1970 to 2009,and the extrapolative prediction period is from 2010 to September,2013.As the studied time interval is 12 months and the window and step length are 2° × 2° and 0.2°,respectively,we selected b value,and earthquake absence and frequency to perform spatial scanning of the multi-parameter earthquake corresponding relevancy spectrum in the study area.The spatial result shows the presence of large anomalies before the occurrence of the target earthquakes in both the retrospective research period and the extrapolative prediction period,and the high anomaly areas gradually reduce and disappear after the earthquakes.The main anomaly characteristics are as follows.There are large anomalies near the epicentral area about one year before the occurrence of moderate-strong earthquakes.The high anomaly areas gradually enlarge and intensify,following which,earthquakes occur.About 1~2 years after the moderate strong earthquakes,the anomalies dissipate,decrease,or disappear.If high anomaly areas continue to be present,they may be the reflection of subsequent moderate strong earthquakes.

    • Analysis of Spatiotemporal Characteristics of Wave Velocity Ratio in Three Seismically Active Blocks of East China

      2014, 36(4):1033-1038.

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      Abstract:Zhang Guomin et al.(2005) presented the Chinese active block division research results, analyzing the regional characteristics of East China seismic geology and seismic activity on three plots.(Comparing seismic wave velocity space and time,we can see that each earthquake block’s seismic wave velocity curve changes with time differences.In the eastern part of Shandong Province and in the Yellow Sea seismic block,recent seismic velocity shows low-value anomalies,but the abnormal amplitude is relatively small,and therefore the possibility of moderately strong earthquakes occurring in the short term is small.East China seismic wave velocity distribution in space is connected to low-value anomalies;in nearly three years of seismic wave velocity spatial distribution, East China Earthquake low velocity ratio anomalies were mainly concentrated in southern Shandong Province.Analyzing this together with the Anqing MS4.8 and Gaoyou MS4.9 earthquake characteristics,a high-value area before an earthquake will show a significantly large scope of discrete convergence phenomena.The East China area,which spans the three tectonic units North China,Southern China, and Yellow Sea,has a complex geologic structure.The regional deep fault has an obvious effect on the regional tectonic movement and strong earthquake activity and distribution.The Tancheng-Lujiang (Tan-Lu) fault zone, a great fault across the East China area,spawned the Jiangxi region’s 2005 Jiujiang-Ruichang MS5.7 earthquake,as well as the Dingyuan MS4.2,Anqing MS4.8,Ruichang-Yangxin MS4.9,and Gaoyou MS4.6 earthquakes.In this fault belt, the intensity and frequency of moderate seismic activity is significantly increased.Studying the East China region,especially the ratio of wave velocity features near the area of the Tan-Lu fault zone,can give a scientific basis for the seismic trend in the region,enhance the use value of seismic station information,and realize the organic combination of earthquake monitoring and prediction.This study uses the China Earthquake Networks Center earthquake catalog data for the East China area (27°~38° latitude,111°~125° longitude) to calculate that,for a Richter magnitude where ML≥1,there were 2 815 events from January 2008 to September 2013,with a seismic wave velocity ratio of 1 834.According to the East China region’s boundary and tectonic characteristics,the study area is divided into the North China,Southern China,and the Eastern Yellow Sea blocks (Figure 1) to study and analyze the data. As Figure 1 shows,the distribution of earthquakes is relatively uniform,and the area of earthquake monitoring station density is high,so that the spatial and temporal characteristics of wave velocity ratio representing the region calculate the wave velocity ratio very well.

    • Influence of Topography on Ground Motion

      2014, 36(4):1039-1046.

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      Abstract:The influence of topography on ground motion intensity parameters,response spectrum,and peak ground acceleration (PGA)were studied.This study used measured data of the Wenchuan earthquake from large-scale shaking table tests and the monitoring stations in the Xishan Park,Zigong,Sichuan province,China.The results show that the peak ground acceleration at 6# and 7#,which are at higher altitudes,are larger than those at the other stations;the peak ground acceleration at 1#,which is at the lowest altitude,is the smallest of all the monitoring stations.This demonstrates that local outstanding landscapes can amplify seismic waves.Comparing the correlation coefficient of the fitting functions of the peak intensity parameters shows that the sequence of correlation between the amplification coefficient and the fitted curve is PGD > SMV > PGA > PGV > EDA > SMA.With respect to the 10 types of comprehensive intensity parameters,the sequence is V_RMS > SED> Ia > ASI > Ic> HI > VSI > CAV > A_RMS > D_RMS.This study's results show that the curves between the amplification coefficient and height of the 16 intensity parameters are highly correlated.In the EW direction,the height does not affect PGD,SMA,VSI,and HI,whileV_RMS decreases slightly at the center of the slope;the other intensity parameters increase with an increase in height.In the EW direction,the height has no influence on PGD,V_RMS,SMA,SED,A_RMS,VSI,and HI,but the other parameters increase with an increase in height.In the UD direction,the height has no influence on SMV,PGD,V_RMS,SMV,ASI,VSI,and HI,whileA_RMS decreases at the center of the slope;the other intensity parameters increase with an increase in height.With an increase in the relative height,the amplification coefficients in the three directions show a noticeable increase.The maximum among the PGA amplification coefficients in the EW direction is 1.768 (recorded at the 6# monitoring station);the maximum value in the NS direction is 1.717 (recorded at the 7# monitoring station);the maximum value in the UD direction is 1.341(recorded at the 6# monitoring station).It is evident that the maximum values of the PGA amplification coefficient are similar in the horizontal directions,and that the values in the horizontal directions are larger than those in the vertical direction.Ignoring the effect of local topography,the amplitude of the response spectrum increases with an increase in height for a short period,decreases in height for the section with period T ≤ 1 s,and the T > 1 s period is not affected by the height.In the horizontal direction,the response in the short section,whose periodT ≤ 1 s,is highly affected by height,and the response in the long section,whose period T > 1 s is negligible.In the vertical direction,the amplification effect of height on the response spectrum decreases with an increase in the period.However,when the period is larger than T > 1 s,the effect of height on the response spectrum can be ignored.The ground motion is amplified by the local foveate topography,and the height also affects the ground motion.However,the influence of the local topography is larger than the height.This study increases our understanding of the effect of topography on ground motion.

    • Crustal S-wave Velocity Structure and Radial Anisotropy in Xinjiang Region

      2014, 36(4):1047-1058.

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      Abstract:Northwest China is an ideal site for studying the effects of mountain basin coupling due to its complex topography and tectonic structure.In this study,we construct crustal shear wave velocity structure and radial anisotropy in the crust and uppermost mantle in the Xinjiang region by ambient noise seismic tomography.The data include 9 months (2009 January to 2009 September)of three component continuous data recorded at 74 seismic stations of the China Provincial Digital Seismic Networks and regional Kyrgyzstan and Kazakhstan Networks.Empirical Rayleigh and Love wave Green’s functions are obtained from interstation cross correlations.Group velocity and phase velocity dispersion curves between 8 s and 50 s periods are measured for each interstation path by applying the time frequency analysis method with phase matched processing.The group velocity and phase velocity maps show clear lateral variations that correlate well with major geological structures and tectonic units in the study regions. At short periods(<20 s), the basins show low group velocity and phase velocity,and the eastern part of Tarim Basin displays relatively lower velocities than the western part.A small patch of high velocity is observed in the northwest part of Tarim Basin,indicating that the structure beneath Tarim Basin is not horizontally homogeneous.The orogenic belt shows high velocity.As the period increases,the imprint of the sedimentary layers diminish. At long periods (>30 s),surface wave velocities are strongly influenced by crust thickness and shear velocities in the lower crust and uppermost mantle.High velocity is observed beneath the basins.In contrast,the Tianshan orogenic belt stands out as a low velocity region.SV and SH wave velocity structures of the crust and upper mantle are inverted from Rayleigh and Love wave dispersion maps.Because of thick sedimentation in the basins,S wave velocities of the Tarim and Junggar basins are relatively low at shallow depth,whereas S wave velocities of the mountain area are high due to the widely appearance of magmatic rocks.In the middle and lower crust,the basins show clear features with high velocities,whereas the Tianshan orogenic belt shows those with low velocity.In addition,we compute the radial anisotropy by measuring the differences between SH wave and SV wave velocity.The Tianshan orogenic belt shows negative radial anisotropy,which reflects dominant vertical movement of the deep crustal materials during the process of crustal shortening and thickening beneath this belt.Western Tianshan displays stronger anisotropy than eastern Tianshan,which may be related to different blocking effects due to the Tarim Block.Positive radial anisotropy is a major characteristic of the Tarim Basin in the upper crust,and the velocity of the SH wave of horizontal polarization is faster than the SV wave of vertical polarization mainly due to the effects of the sedimentary layer.In the stable block,the radial anisotropy represents fossil anisotropy left in the latest large scale tectonic movement.Because movement in the entire Tarim block resulted in mineral crystal arrangement dominated in the horizontal direction,the middle crust of the Tarim Basin shows positive radial anisotropy.

    • Application of Satellite Thermal Infrared and MicrowaveRemote Sensing Data to Earthquake Prediction

      2014, 36(4):1059-1063.

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      Abstract:Using four typical earthquakes as examples,the temperature-time sequences of each earthquake’s epifocal area is scanned in small windows using microwave remote sensing and thermal infrared remote sensing,and then surface temperature anomalies before the occurrence of these earthquakes are analyzed.The results show that,although the surface temperatures inverted from satellite thermal infrared and microwave remote sensing has similar change patterns,the former is more obvious.The increase in temperature is not continuous and negative anomalies are also present before the earthquakes.There is a direct correlation between the spatial distribution of the temperature anomalies and faults.The temperature anomaly sections are not large-scale and there were no obvious migrations of the sections.The results of this study are useful for reference in future studies.

    • Preliminary Inspection of Seismic Zoning Maps in China

      2014, 36(4):1064-1070.

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      Abstract:Four seismic zoning maps of China respectively published in 1957,1977,1990,and 2001 are inspected in this study.The isoseismals of shallow earthquakes of M≥ 5 occurring in the mainland of China after the maps were published are overlaid on the maps by means of Geographic Information System (GIS).The total areas with observed intensity of at least 1° larger than the corresponding intensity on the maps are summed.The percentages of areas with positive intensity difference against the entire mainland of China are calculated by the GIS function of special manipulation and analysis.The reliability of each map is tested according to its hazard definition.A key point for improving zoning methods is suggested by recognizing regions with the potential for large earthquakes ofM ≥ 7 on the basis of statistics of deaths,injuries,and losses by earthquakes during the four time periods.

    • Preliminary Analysis of Strong Ground Motion Records of the Menyuan MS5.1 Earthquake

      2014, 36(4):1071-1075.

      Abstract (1406) HTML (0) PDF 971.75 K (992) Comment (0) Favorites

      Abstract:The Northwestern Strong Motion Network Center is the strong-motion network data collection center for five provinces (Shaanxi,Gansu,Ningxia,Qinghai,Xinjiang)of northwestern China,and is responsible for the release of regional destructive-earthquake ground-motion information.An MS5.1 earthquake occurred at the junction of Sunan county,Zhangye city,Gansu province and Menyuan county,Qinghai province on September 20,2013,and the mainshock records of this earthquake obtained from 43 strong motion stations of the Northwestern Strong Motion Network are presented in the paper.The 43 strong motion stations are installed in Gansu,Qinghai province,and include two types of strong-motion seismographs:the MR2002 and ETNA.126 peak ground accelerations recorded by strong motion stations had been calculated after the zero baseline was corrected.The 63MEY strong motion station was closest to the epicenter,at a distance of 37.1 km,with a peak ground acceleration of 40.9 gal (EW),29.1 gal (NS),and 17.5 gal (UD).The farthest station from the epicenter was 63TGM,at a distance of 220 km,with a peak ground acceleration of 1.5 gal (EW),1.5 gal (NS),and 0.9 gal (UD).The effects of anisotropic media and site conditions may have resulted in unequal peak ground acceleration values for different locations with the same epicentral distance.The result is similar to the actual survey results after the earthquake,and therefore,the rapid reporting of intensity is very useful for earthquake emergency rescues.The acceleration records of these 43 stations substantially enhance the digital recording of the near-field strong-motion observations in the loess areas,and also provide fundamental data on seismic fortification,site effects,and intensity attenuation.

    • Inversion of the Focal Mechanisms of the 2014 M4.2 and M4.0 Earthquakes in Rushan,Shandong Using the CAP Method

      2014, 36(4):1076-1080.

      Abstract (1540) HTML (0) PDF 1.32 M (1417) Comment (0) Favorites

      Abstract:There have been many intensive small earthquakes since the M3.8 earthquake occurred in Rushan,Shandong on October 1,2013. Two earthquakes(M4.2 and M4.0)occurred separately on January 7 and April 4,2014.There have never been so many earthquakes in Rushan.A focal mechanism describes the nature and source rupture process and is an important foundation to understand the stress state of the source region,earthquake faults, and for analyzing the causes of a seismic event.Therefore,seismic interpretation and post earthquake seismogenic stress distribution mechanisms play very important roles in determining earthquake focal mechanisms.In this study,using waveforms from the Shandong Seismological Network and comparing the synthetic and the observed seismograms,the focal mechanism of the Rushan M4.2 and M4.0 earthquakes in 2014 are inverted using the CAP(Cut and paste)method.The results show that the two earthquakes get their best focal mechanism at 6 km depth,and that the parameters of the nodal planes are similar,belonging to the strike-slip type.At a depth of 6 km,the correlation coefficients of 40 phases of the M4.2 earthquake greater than 0.7 that were recorded by eight stations are 37,which accounts for 93%.The correlation coefficients greater than 0.9 are 28,accounting for about 70%. Similarly,at a depth of 6 km,the correlation coefficients of 40 phases of the M4.0 earthquake that were recorded by the eight stations are all greater than 0.7 and the correlation coefficients greater than 0.9 are 31,accounting for about 78%.Therefore,the synthetic seismograms of the two earthquakes fit the observed seismograms well demonstrating that the inversion results are credible. The focal mechanism shows that the moment magnitude of the M4.2 earthquake was MW =4.3;one nodal plane has a strike of 290°,rake of 84°,and dip of 22° and the other nodal plane has a strike of 189°,rake of 68°,and dip of 174°. The moment magnitude of the M4.0 earthquake is MW=4.2,one nodal plane has a strike of 289°,rake of 90°,and dip of 27° and the other nodal plane has a strike of 199°,rake of 63°,and a dip of 180°,The hypocentral distance was calculated by the mobile seismic station near the epicenter.The results show that the focal depth is slightly less than 7 km,which is consistent with the inversion results of the CAP method,and therefore,the main rupture of the earthquake was in the upper crust.The parameters of the Rushan fault nearest to the epicenter (strike of 10° normal fault)are not consistent with the focal mechanisms of the two earthquakes,which show that the Rushan fault is not the seismic fault and that the seismic faults may be concealed faults.

    • Location of the Gaoyou-Baoying M4.9 Earthquake Using Apparent Emergence Angle and Seismic Arrival Times

      2014, 36(4):1081-1086.

      Abstract (1230) HTML (0) PDF 1.59 M (1313) Comment (0) Favorites

      Abstract:An M4.9 earthquake occurred in Gaoyou-Baoying,Jiangsu on July 20,2012.Numerous aftershocks followed the main shock.According to the China Earthquake Networks Center,there were 84 aftershocks with a magnitude of 1.0 and above until July 30,2012;there were 59 aftershocks with a magnitude of 1.0~1.9,20 with a magnitude of 2.0~2.9,4 with a magnitude of 3.0~3.9,and one with a magnitude of 4.0~4.9.In this study,84 aftershocks from July 20 to July 30,2012 were precisely located using the Multiparameter Seismic Location method.The apparent emergence angles and arrival times were extracted according to the wave data with SEED format.The objective function in the Multiparameter Seismic Location method using apparent emergence angles and arrival time was determined.The Monte Carlo method was used to realize its optimization.The apparent emergence angle has a very strong sensitivity to depth.The results of the Multiparameter Seismic Location method are accurate with respect to latitude and longitude,and in particular,enhance the depth resolution effectively.This study used the Multiparameter Seismic Location method to determine the location of the aftershocks of the M4.9 earthquake at the border area between Gaoyou and Baoying.The apparent emergence angles and arrival times were extracted according to the wave data.The results of the Multiparameter Seismic Location method show that the earthquake sequence was densely distributed along the Yangchacang-Sangshutou fault zone,in a spatial belt with a NNE direction.The average depth of the earthquake sequence is 12.21 km,distributed in a range of 5~20 km (up crust),but the dominant distribution is at 12~15 km.The depth of the M4.9 earthquake was at 9.3 km.The depth distribution is more at the strike slip region,where there is a small amount of thrust coming from the detachment plane (belt)at a depth of 12~15 km.The aftershocks are densely distributed at the fault ramp,which is the region of stress accumulation;the main shock occurred at this location.The high speed structure of the lower crust provides a relaxed boundary condition for transversal motion.The depth is concentrated at the brittle ductile transition zone,which is the speed boundary between the high- and low-values,at a depth of approximately 20 km.The different thickness of the lower crust caused the great changes in the earth’s crust.Subei thickness thinning may have contributed to the deep dynamic environment.The results of the Multiparameter Seismic Location method show that the earthquake sequence is densely distributed along the Yangchacang-Sangshutou fault zone.

    • Location Differences between Intermediate and Deep Focus Earthquakes in Taiwan Using Different Location Methods in Java Open System

      2014, 36(4):1087-1092.

      Abstract (1717) HTML (0) PDF 342.40 K (1365) Comment (0) Favorites

      Abstract:The Fujian network monitors earthquakes in the Taiwan region.The seismic stations are distributed beside the epicenter and there is a small opening angle between the seismic stations used for locating and the epicenter.Therefore,the locating methods for intermediate and deep earthquakes,which can be used to obtain better seismic parameters,will directly affect the earthquake rapid reports.This paper uses common methods to locate earthquakes by MSDP,an interaction analysis software package in JOPENS (Java Open System).The results are then compared with the data from Taiwan’s official website to obtain the appropriate location methods for rapid earthquake reporting.The depth of the epicenter to the source is referred to as focal depth and is divided into three categories:less than 70 km (shallow earthquakes),between 70 km and 300 km (intermediate earthquakes),and greater than 300 km (deep earthquakes).The focal depth is an important parameter for seismic studies,seismic tectonics,seismic risk assessment,and seismic event identification.Focal depth’s accuracy affects our understanding of the focal process,fault tectonics, and stress field.Because tectonic plates push into each other,the activities of intermediate and deep earthquakes reflect the driving forces of the plates.The region offshore to northeast Taiwan is one of the active earthquake regions because it is located where the Eurasian and Pacific plates meet.Intermediate and deep earthquakes have different seismic phases than shallow earthquakes.Therefore,developing a fast and accurate location method for intermediate and deep earthquakes is of great significance to rapid earthquake reporting.

    • Application of Shape Acceleration Array in Dynamic Test

      2014, 36(4):1093-1097.

      Abstract (2002) HTML (0) PDF 1.46 M (2418) Comment (0) Favorites

      Abstract:Shape Acceleration Array (SAA) is a sensor based on the microelectromechanical systems (MEMS) testing principle used to test acceleration and displacement with high accuracy,reusability,and automatic real-time acquisition.The instrument device can meet the deformation testing requirements of static geotechnical engineering such as sliding slope,tunnel,embankment settlement,and deflection and deformation monitoring of bridges and is also used for testing of dynamic acceleration,displacement,and temperature.This study is the first domestically to use SAA in a large-scale shaking table test.Moreover,acceleration,displacement,and other dynamic responses of pile,rigid composite foundation,and soil are studied relative to ground motion.The results show that the acceleration dynamic coefficient increases in sand and decreases in soft soil.As the input seismic peak increases,the peak acceleration dynamic coefficient of measuring points at various depths is reduced,which indicates that in the cumulative effect of the earthquake,the ability of the soil to pass seismic waves is weakened.

    • The Application of HKUST Volumetric Change Measuring Method in Dynamic Triaxial Test

      2014, 36(4):1098-1101.

      Abstract (1377) HTML (0) PDF 2.06 M (1634) Comment (0) Favorites

      Abstract:Dynamic triaxial testing is an important method used to obtain the dynamic shear strength,modulus,and damping ratio of soil.However,it is often difficult to accurately measure volume change of a soil specimen in a triaxial test.This paper summarizes several commonly used methods of volumetric change measurement and analysis in dynamic tests in addition to their advantages and disadvantages.Combined with unique features of Geotechnical Digital Systems (GDS)dynamic triaxial test equipment,a novel method of using the total volume measuring wall device of Hong Kong University of Science and Technology (HKUST)is presented.In this novel method,inner cells are used to measure the volumetric change in a soil specimen during a dynamic test by improving the sample base.The accuracy and applicability of this new method are verified and illustrated by conducting tests on clay samples.The test results reveal that this novel method is feasible in dynamic triaxial testing.This method is not applicable for the pull test,and the influence of vibration on total volume measurement requires further research.

    • Comparative Study on Electronic and Automatic Compensated Levels Using DINI11 and NI002 as Examples

      2014, 36(4):1102-1106.

      Abstract (1102) HTML (0) PDF 456.49 K (1548) Comment (0) Favorites

      Abstract:Leveling is the most common method for determining elevation in conventional geodesy and engineering construction surveys.A level is an instrument that provides a level sight and gives level readings for leveling.In this study,we compare electronic and automatic compensated levels,levels that are commonly used currently.Using DINI11 and NI002 as examples,we analyzed the development status,instrument structure,operating principle,influence factors,and anti-jamming capabilities with the observation results,which indicate that the electronic level (DINI11)shows relatively advanced performance and strong anti-jamming capability compared to the automatic compensated level (NI002);however,its measurement precision is lower than that of the NI002 level,and is possibly associated with the magnification of the instrument.In addition,we also discuss the rationality behind replacing an optical instrument with an electronic instrument for precise leveling.Evidence indicates that the DINI11 electronic level can replace the Ni002 automatic compensated level in most seismic stations,especially within stadia of 50 m.The DINI11 electronic level can reach one or second order leveling accuracy,and we believe it can replace the NI002 automatic compensated level for regional leveling.

    • Study on Data Processing Techniques of Borehole Radar

      2014, 36(4):1107-1112.

      Abstract (1101) HTML (0) PDF 3.54 M (1263) Comment (0) Favorites

      Abstract:Borehole radar has been applied to test exiting bridge pile foundations in order to improve the interpretation accuracy of borehole radar detection results.The principles of various data processing methods are introduced in this paper.The radar profile effect is compared through example analysis before and after treatment,and the process of data processing is summarized.The appropriate processing parameter is then selected by comparison.Therefore,a reference for borehole radar data processing for detection of exiting bridge piles is provided.

    • Actual Analysis of Bearing Capacity of Piles with Super large Diameter and Deep Penetration Based on Statnamic Method

      2014, 36(4):1113-1117.

      Abstract (1335) HTML (0) PDF 2.57 M (1897) Comment (0) Favorites

      Abstract:Piles with super-large diameters and deep penetration are widely used in ocean and bridge engineering;however,traditional capacity test methods used for such piles have limitations.Focusing on the imperfections of normal static load and Osterberg cell (O-cell) methods,the statnamic testing method is investigated on the basis of the Second Penang Bridge project in Malaysia.The capacities of piles with super-large diameters and deep penetration in sandy strata are studied.Compared with the results of the O-cell method used on the same pile,the applicability of statnamic testing for super-large diameter,deep penetration piles is analyzed.Results indicate that the equivalent static capacities resulting from the Unloading Point Method (UPM) and the Segmental Unloading Point Method (SUPM) are 30% larger than the results when using the O-cell method.Because of the influences of dynamic soil resistance and pore pressure,the side friction of statnamic testing is also larger than that when using the O-cell method.Therefore,the statnamic method still requires modification.

    • Study on the Monitoring Capability of the Seismic Network at the Dagangshan Hydropower Station

      2014, 36(4):1118-1121.

      Abstract (1188) HTML (0) PDF 1.14 M (1021) Comment (0) Favorites

      Abstract:Located at the northern section of the NS-trending seismic tectonic zone at the border between Sichuan and Yunnan,the reservoir of the Dagangshan hydropower station is at the intersection of three seismic belts,Xianshuihe,Longmenshan,and Anninghe,which present a complex geological environment.The earthquake seismic network at the Dagangshan hydropower station is a dedicated small diameter minor earthquake monitoring network for hydropower station projects and consists of eight stationary monitoring sites located across the Luding county of Ganzi and the Shimian county of Yaan,Sichuan province.The monitoring sites are located at both sides of the Dadu river,around the dam,at the main reservoir area,and at the fault zones,in accordance with the identified key fault zones to monitor reservoir induced earthquakes,increase the precision of locating seismic events,and decrease the lower limit of seismic magnitudes detectable in the area.The theoretical minimum monitoring capability of the designed seismic network in the focused monitoring area is ML0.5.Based on the velocity records,the displacements recorded by the W-A short period seismometer are emulated,and then the max.P-P and the corresponding period on the displacement waveform emulated are substituted into the formula for near earthquake magnitude to calculate the earthquake magnitude.For validation of the background noise of earth motion,the PSD per hour at each station and the RMS values in the range of 1~20 Hz are calculated based on the noise data randomly selected from the background noise of earth motion recorded in a 48-hr interval at the Dagangshan earthquake monitoring network and the mean RMS value is taken as the average background noise of earth motion.Taking the ratio of the maximum magnitude of the S wave to the background noise as the minimum lower limit for seismic velocity detection by the system,the calibration function value R(Δ) is calculated using the earthquake magnitude formula.The minimum earthquake magnitude recordable at each site for various epicentral distances is determined based on the R (Δ). For validation using the b-value curve fitting,the data for the earthquakes,recorded in the monitoring area for which the seismic sources have been determined,and the Gutenberg Richter law are used,and the monitoring capability of the earthquake seismic network is validated using the deviation from the linear relationship between lgN(M)and M.A b-value curve is plotted on the basis of 585 located earthquakes in the range of ML = 0.0~4.0 recorded from Mar to Sep,2013 in the specified area.When the magnitude is below a certain value,the actual number of earthquakes recorded significantly deviates from the reference line,i.e,the total number of earthquakes recorded is less than the number indicated by the fitting curve,implying that the system doesn’t record all the minor earthquakes that have a magnitude below that value,and the deviation value is established as the lower limit of the magnitude detectable by the monitoring system.The statistical analysis of the seismic data recorded indicates that when ML< 0.5,the recorded value is significantly below the fitting line.Therefore,the lower limit of detection at the earthquake seismic network at the Dagangshan hydropower station is ML=0.5.The theoretical monitoring capability of the earthquake seismic network at the Dagangshan hydropower station is calculated based on the near earthquake magnitude formula and the Gutenberg-Richter law.The calculations show that the theoretical monitoring capability in the focused monitoring areas is in compliance with the ML0.5 requirements.The practical minimum magnitudes of completeness at ML0.5 are validated by the actual record,which fulfills the design objectives of the reservoir induced earthquake seismic network at the Dagangshan hydropower station.

    • 3D Dynamic Demonstration of Earthquake Source Using Keyhole Markup Language

      2014, 36(4):1122-1125.

      Abstract (1308) HTML (0) PDF 3.53 M (1225) Comment (0) Favorites

      Abstract:KML(Keyhole Markup Language)is a file format used by Google Earth to express geotag.Google Earth is a powerful 3D virtual software and is widely used in the geosciences.In this study,writing in KML,we achieve a 3D dynamic demonstration of earthquakes occurring since the Wenchuan earthquake on the Longmenshan fault zone.Dragging on the time axis not only shows the three-dimensional spatial distribution of earthquakes,but also provides useful information on the full range of the observed seismic activity and seismic migration.

    • Space time Symmetry of MS≥5.1 Earthquake Disasters inQilian Liupan Mountain Seismic Belts

      2014, 36(4):1126-1130.

      Abstract (1509) HTML (0) PDF 484.91 K (1629) Comment (0) Favorites

      Abstract:Disaster trend evaluation is an important method for improving the accuracy of earthquake forecasting. On the basis of seismic data (MS≥5.1 earthquakes)of Qilian and Liupan mountains obtained since 1954,the symmetry and tendency of earthquake disasters are analyzed in this study and are evaluated by using the methods of commensurability information extraction,butterfly structure diagram,and commensurability degree structure.In addition,the space-time symmetry and trends of earthquakes in the Qilian-Liupan mountain seismic belts are analyzed.The results show strong earthquake signals in 2015 and 2016 and the possibility of greater magnitude earthquakes.Spatial symmetry is used to predict that the next earthquake may occur in the region of 36°~39° N,95°~101° E.This study can be used to enrich the study of the major disaster tendency evaluation.

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