Abstract:For landfill stability design,the 2-dimensional method is convenient and simple,but it does not consider the effects of the landfill's geometry that may contribute to an instability failure.In this study,for the first time,a 3D seismic stability analysis method for landfills under earthquake loading is proposed.This was achieved by dividing the landfill into two zones called the maximum horizontal and maximum vertical lengths along the liner itself and analyzing the overall slip failure along the liner system.The method is based on the assumptions as follows:(1)the entire landfill slip is along the liner system,(2)because of the restrictions of surrounding bedrock,the entrance of the landfill is considered to be the main slip direction,thus assuming that the angle between axis and the shear stress at the bottom of the landfill is fixed,(3)the friction between the lateral zone interfaces is ignored (4)pressure applied at the base is concentrated at the center of the bottom surface.Through the 3D stability analysis method,considering the effects of horizontal and vertical seismic coefficients,a factor of safety (F_s)is established.Based on this method,the relationships among the height to width ratio,shear strength of the liner system,horizontal seismic coefficient,vertical seismic coefficient,and F_s are studied and discussed.The height to width ratio and horizontal seismic coefficient are shown to have an important effect on F_s.In addition,when the horizontal seismic coefficient is fixed,F_s decreases with an increasing height to width ratio.With a height to width ratio between 1 and 10,F_s decreases faster.However,when the ratio is greater than 10,the rate of the decrease of F_s becomes smaller.When the ratio is greater than 1 000,the curve is nearly linear,and F_s can be considered unchanged.Although the height to width ratio is an important factor affecting the stability of the landfill,this effect is reduced when the horizontal seismic coefficient become large.Thus,during landfill stability analysis,the selection of an appropriate analysis method according to the specific geological environment is important.In addition,the horizontal seismic coefficient is an important factor that affects the stability of the landfill.When the height to width ratio is fixed,F_s of the landfill decreases continuously as the horizontal seismic coefficient gradually increases from 0 to 0.3.Compared with the horizontal seismic coefficient,the effect of the vertical seismic coefficient is small and can be neglected for stability analysis.By comparing the results from 2D and 3D seismic stability analyses,the 2D method is found to greatly underestimate the stability of the landfill,whereas the 3D method is found to be more realistic.The 2D method will accurately reflect the stability of the landfill only in the case of a large height to width ratio.The 3D seismic stability analysis method established in this study is a valuable tool for landfill design.

Abstract:Because of their light weight,high strength,and good seismic performance,steel structures are widely used in construction.At present,the research on the seismic performance and safety assessment of steel structures receives widespread attention at home and abroad;most of this research focuses on assessing the seismic performance of steel structures based on the performance design method,with little research on earthquake damage.Under such circumstances,the author firstly analyzed the main design parameters,such as web height,web thickness,flange width,and flange thickness,which affect the component damage evolution rule,and the author found that the most sensitive design parameters are web height and flange width,which provided a theoretical basis for the establishment of the storey damage model.Then,according to the analysis results,we obtained the damage value relationship between the frame beam,frame column,and storey damage evolution and analyzed the effect of sensitive factors on storey damage evolution,such as the stiffness ratio of column to beam,the height-width ratio of the structure,the axial-compression ratio of the frame column,and the steel corrosion rate.Finally,in order to study the influence of storey damage location and degree to the seismic damage of the steel frame structure,the author revealed the influence of storey damage on structural damage by analyzing the effect of single-storey steel frame structure damage on structural dynamic characteristics under El Centro seismic wave excitation.Inputting multiple seismic waves,the author got the relation between the damage value of structural integrity and the velocity-to-acceleration ratio of the seismic wave peak and ultimately established the damage evolution model of steel frame structures. The multi-level damage evolution model of "component-storey-structure" can provide the theoretical foundation and basic data support for establishing the storey damage model of steel frame structures under seismic excitation.

Abstract:The Finite Element method was used to analyze the dynamic response of pile groups in the ground subjected to the liquefaction-induced lateral flow of soils.The u-p Finite Element formulation was used to depict the coupling effect of water and sand soil particles in the Finite Element analysis.A 3D numerical model was developed to analyze the effect of a 2×2 pile group subjected to liquefaction-induced lateral spreading. In this model,sand was simulated using a pressure-independent multi-yield surface plastic model.Clay material served as a nonlinear hysteretic material with a multi-surface kinematic plasticity model,and the pile group maintained its linear behavior in the process of calculation.The clay layer and saturated sand layer were meshed in a 20-node brick element and separately in a 20-8 node element.The boundary of the numerical model was considered as the shear beam boundary,which simulated the shear effect of the soil layer during the earthquake.Finally,the Rayleigh damping method was used to model the damping of the system.The dynamic response of each pile in pile group was compared,and it showed that the bending moment and displacement time history of piles at different depths developed in the same way,and the time of maximum bending moment and displacement of the pile appears to lag behind the time of peak acceleration of the input seismic wave.The maximum bending moment and displacement of the leading pile were larger than the those of the back piles.By comparing the maximum bending moment and displacement,it can also be concluded that,as depth increases,the maximum bending moment first increases and then decreases.The bending moment of the pile at the 2.5 m depth was greater than those at other depths. In terms of displacement,as depth increased,the maximum pile displacement decreased,and the maximum displacement of the pile head was greater than other observed points on the pile.This demonstrated the different behaviors of the pile bending moment response.In order to consider the effect of pile spacing on the pile group effect,several Finite Element models were developed for different pile spacing.This modeling concluded that the maximum bending moment appeared to occur in the boundary of different soil layers.As pile spacing increased,the maximum bending moment and pile head displacement in the group increased.In the pile group with pile spacing equal to 7D (diameter),the maximum bending moment of the each pile was very close.The difference was about 3% when pile spacing was equal to 5D,and the difference was about 4%,when pile spacing was equal to 3D.The maximum bending moment of the first pile group was 10% larger than the bending moment of the second pile group.In the last part of the study,the cause of the pile group effect was analyzed and a basic understanding of the seismic design requirements for this type of pile group was obtained.

Abstract:Overhead high-voltage electric-transmission lines play an important role in the operation of a reliable electrical power system.Damage to these lines can cause great economic loss and bring inconvenience to human life.A substantial number of transmission lines have been damaged by catastrophic earthquakes around the world.The transmission tower tilt or collapse,conductor breakage,foundation subsidence,and insulator destruction were the major types of failure.It is necessary to study not only the seismic response of transmission lines in the elastic and plastic phases but also their collapse process.Progressive collapse analysis is a well-understood physical occurrence in which the loss of local load-bearing capacity propagates through a system,precipitating complete collapse or a major portion of it.The vulnerable points,collapse mode,and capacity of the structure can be evaluated by it,and these data can be used for the design of new towers or for evaluating existing towers.Many scholars have studied the nonlinear responses of single transmission towers or tower-line coupled systems.Numerical simulation of progressive collapse is a challenging task,which includes material and geometric nonlinearity,contact and collision between elements,and losing the load-bearing capacity of elements.Nowadays,there are mainly four numerical analytical methods used for the collapse analysis:the discrete-element method (DEM),combined finite-discrete element method,applied-element method (AEM),and finite-element method (FEM).The FEM,based on continuum mechanics,is the most widely used method in structural engineering.For linear elastic problems,the method has proved to be advantageous.Furthermore,the method is very effective for solving nonlinear problems by using reasonable constitutive relationships.The method can be used in the solution of large-scale and complex industrial problems,while other methods are extremely difficult to use.During the collapse process under an earthquake,some elements lose load-bearing capacity,which is a problem for the FEM.Commonly,the method of removing these elements is used,which is called the birth-death element method.The conductors and ground wires can be simplified as concentrated masses for the seismic analysis of transmission tower-line coupled systems.In this paper,this method is used.With the simplified model,by using the finite-element program ABAQUS,the progressive collapse analysis of a transmission tower under an earthquake is conducted.The results show that the vulnerable points and progressive collapse process obtained are in good accord with the results obtained by using the tower-line coupled system with three towers and four span lines.Therefore,the simplified model can be used in the seismic analysis of transmission tower-line coupled systems.

Abstract:Cast-in-place piles are generally chosen as the foundation for high-speed railway bridges to control settlement.One of the working conditions for the pile foundation design is seismic action.A three dimensional coupled nonlinear bridge-pier-pile-foundation numerical model was established using the typical earthquake record as the input excitation.The combined effects between superstructure and foundation,dynamic soil-structure interaction,material nonlinearity,side skin friction between pile and soil layers,and pile base resistance were taken into account in a dynamic finite element analyses that considered three-dimensional seismic actions.Parameter sensitivity analyses of the compression modulus of the major soil layer in addition to the elastic modulus of the pile material,pile diameter,and pile length were performed.Results showed that the design of the pile foundation can effectively control the deformation of a bridge under earthquake conditions.Side skin friction differed during earthquakes and cannot be neglected.The suitability of pile dynamic behaviors modeled by beam element is open to discussion.The dynamic response of a bridge was influenced mainly by pile length and the compression modulus of the major soil layer and,secondly,by the elastic modulus of the pile material.Pile diameter had no prominent impact on the dynamic response of the bridge.

Abstract:Prestressed anchor sheet pile wall is a light-weight retaining structure.As a new style of retaining structure,the stressed form of a prestressed anchor sheet pile is similar to a beam-style structure.This is deemed to be more reasonable than the stressed form of a cantilever that is usually used for stabilizing piles.In addition,because of advanced deformation compatibility and better seismic performance,the prestressed anchor sheet pile is widely used in landslide treatment.An investigation of seismic hazards in the Wenchuan earthquake suggests that a stabilizing pile has many advantages in terms of landslide treatment.Because this structure plays an important role in landslide treatment,many researchers have performed analysis on static design and loading characteristics;however,there is limited research on the seismic design theory of prestressed anchor sheet pile walls.The FLAC3D model was used to study the seismic response of this structure,including the distribution of seismic earth pressure along the pile,deflection of the pile,and dynamic characteristics of cable stress in the anchor. In addition,the analyses of multiple cases were completed using various parameters of ground motion;thus,the influence of the parameters on the dynamic interaction law of pile-soil-anchor was systematically derived.Through FLAC3D and a contrasting calculation,some conclusions are obtained.First,the anchor cable plays a limited role in the displacement of a pile wall structure,and an increase in soil pressure appears near the anchor cable. Because plastic deformation occurs in the soil on the surface of foundation before piling,paying attention to the embedded soil before piling is important as it has an active effect on the structural seismic performance.Second,the axial force is the largest in the free section of the anchor cable,and the value is an equivalent distribution.In the inner anchorage section,with an increase in anchorage depth,the axial force decreases.Shear stress increases sharply near the end of the inner anchorage section.The shear stress and anchorage depth curves are similar to a date pit,and with the increase of anchorage depth,the curve becomes gradually smoother.Moreover,the influence of ground motion characteristics on the seismic effect needs to be considered.Under ground motion,the seismic response order is consistent with the acceleration response spectrum near its natural period.The above research provides a basis for further details of prestressed anchor cable sheet pile walls in future.In addition,the results of this study strengthen the understanding of seismic performance and provide a reliable basis for further research.

Abstract:The scattering problem of elastic waves is of great engineering significance,especially in earthquake engineering.Frequently,the response of the scatterer is needed to evaluate the safety of structures during earthquakes.The ground motion can be used as dynamic input for the finite-element method calculation,which is a way to realize the non-uniform input.This article puts forward the wave function combination method for a three-dimensional (3D)problem to solve the irregular valley scattering problem. The application of the earthquake input to the dynamic finite-element calculation for a high-face rockfill dam can meet the requirement for non-uniform input and,at the same time,avoid the problem of the reflection of the outward wave by the artificial boundary.The theoretical derivation of the wave function combination method for the 3D problem and the validation of the program are introduced,as are the basic steps needed to apply this method to the earthquake input.

Abstract:Foundations in saturated sand have the potential to liquefy under the effects of earthquakes,and foundation failure caused by liquefaction can lead to a serious damage of underground structures.Considering Opensees as the computing platform,a dynamic numerical simulation was performed to calculate the seismic response of a box tunnel with mid-columns in saturated sand when seismic waves of different amplitudes were input.Acceleration responses and the spectral properties of ground and structure,as well as the permanent deformation of the ground,aftershock displacement of the tunnel,and internal force distribution of the tunnel,were studied.The results show that the additional internal seismic forces in a box tunnel in saturated sand are controlled by the relative displacement of the surrounding soil.The permanent displacement of the tunnel such as side shift and floating probably appear after the main shock;in addition,remnant internal forces also probably occur.

Abstract:The pumped-storage power station is widely used and can change the excess electric power at low grid load into high-value power during the peak period.Limited by the topography and geological conditions,the main dam of the reservoir of many pumped-storage power stations has to be built on reservoir bottom backfill.The existence of the reservoir bottom backfill in the concrete-faced rockfill dam will affect the modulus decay,damping ratio,and natural cycle of the dam,and is one of the important factors affecting the dynamic response of concrete-faced rockfill dams.In order to further study the influence of deep reservoir bottom backfill on the dynamic response of concrete-faced rockfill dams,by using a three-dimensional finite-element method and equivalent linear model based on a pumped-storage power station under construction,the seismic response of the upstream concrete-faced rockfill dam,including dam acceleration,dynamic response of the concrete panel,displacement of joints,and dynamic strain of the geomembranes,are studied and evaluated systematically.The results show that,because the existence of the reservoir bottom backfill material makes the dam body prolong the natural period of vibration,a high-order natural vibration period can easily coincide with the seismic predominant period and the high-mode vibration can be amplified,resulting in an acceleration distribution that is different from the standard distribution and an acceleration amplification that is weakened significantly.Surrounding areas of the concrete panel were in tension,most of the regional was pressed,the net tensile stress of the concrete in the panel was within the bearing capacity of the concrete,and the concrete panel is safe,but it is still necessary to take reasonable measures in corresponding parts in order to avoid the hazard due to potential cracks.Vertical joints were open around slabs and closed on the river valley.Vertical joints present a peripheral open-middle-close trend,and the results closer to the condition of no reservoir bottom backfill show that the effect of the joint deformation is small when built on either rock or rockfill.The dynamic strain of the geomembrane along and vertical to the river was less than the yield strain;the maximum strain appears on the boundary of the materials due to the obvious difference in material properties between the main rockfill zone and reservoir bottom backfill zone.We recommend that the replacement method used in an appropriate zone between the main rockfill zone and concrete plate can improve the dam safety of penetration.This paper can provide a reference for similar projects.

Abstract:Rail transportation such as high-speed railways,metros,and skytrains develop fast and go deep into the densely populated inner cities,where its vibration impact on the environment cannot be ignored.Open trenches,gravel-filled trenches,and piles in a row are three common vibration-isolation measures.We established a model test,which uses the acceleration as the evaluation index of vibration,and studied the vibration-isolation effects of open trenches,gravel-filled trenches,and piles in a row.Test conditions among each group of tests are the same except for the isolation measure.Each isolation measure's isolation effect can be analyzed by contrasting the results between this isolation measure and the test group without an isolation measure;the effects of different isolation measures can be analyzed by contrasting the results between test groups without different isolation measures,so the effects of different vibration-isolation measures can be objectively evaluated.

Abstract:The earth-rockfill dam is the most common and economical type of dam because of its convenient construction method and ease of material supply.Many high earth-rockfill dams have been or are planned to be constructed in the west of China,an area with intense seismic activity.Some of them are sited on a deep overburden layer that has an important influence on the dynamic response of dams.In this study,we consider a domestic core wall rock fill dam still under construction as a 3D FE numerical example.The area where the dam is located has an overburden layer hundreds of meters thick,and its tectonic stability is poor.The 3D mesh used in FE calculation has been simplified appropriately.To determine the initial stress field required for the dynamic calculation,the Biot's consolidation theory was adopted to simulate the sediments of the overburden layer and the dam filling and water storage processes of the reservoir.In addition,the Duncan-Chang E-ν model was used to complete the static calculation.The equivalent linear method was used to conduct dynamic analysis;this method,proposed by Shen Z J,considers the increase and change in pore water pressure during vibration.Scholars have always considered soil as the undrained boundary in former studies.This can result in an excessive accumulation of residual pore water pressure,which does not conform to the actual situation. In this study,the residual volumetric strain obtained by the empirical formula is divided into two parts:the excess pore water pressure and residual deformation.The results show this method to be rational and useful.On the basis of the equivalent linear method,one earthquake is divided into many time intervals;a total stress method is used in the analysis of every interval,and the time difference is completed according to the Wilson-θ method.Subsequently,we calculate the increase of the residual deformation and pore water pressure of each element in every time interval and transform it into initial stress or initial strain.The static analysis is continued,and changes of the node displacement,effective stress,and element strain were obtained.The residual deformation and pore pressure are completed by the empirical formula.Every time interval is calculated in the same manner,and then,the stress and strain,residual deformation,and pore pressure can be properly derived.Residual displacement,acceleration amplification,and residual pore pressure are analyzed according to the FE results.The numerical results show good agreement with the common properties. Therefore,this adopted method is capable of investigating the dynamic response of core wall rockfill dam on deep overburden layer under strong earthquake loading.The treatment of the residual pore water pressure accumulation in the soil may have a certain reference significance for analyzing such problems.

Abstract:Based on one industrial underground pipeline,with soil-pipe interaction and traveling wave effect taken into consideration,a finite element model was built to study the dynamic response of pipelines under uniform and non-uniform excitation,and the influence of some relative factors was analyzed.The results are:the peak value of the displacement response curve under non-uniform excitation,as well as shape,differs from that under uniform excitation.Horizontal displacement under non-uniform excitation is apparently greater than that under uniform excitation,while vertical displacement under non-uniform excitation is slightly greater than that under uniform excitation.The stress response of one monitor point differs from that of other points on the same section under both uniform and non-uniform excitation,and the stress response under non-uniform excitation is more intense compared to that under uniform excitation.Displacement and stress of a pipeline in the subsurface is usually influenced by the change in soil properties and pipe trend and bucking under seismic excitation.

Abstract:Underground pipelines are the big arteries of present-day industry,agriculture,and city life.It is important to ensure the safety of pipelines in operation,especially under seismic loading.For underground pipelines,seismic damages can be classified as either wave-propagation damage or permanent ground-displacement damage.There have been some events where pipe damage has been due only to wave propagation.More typically,pipeline damage is due to a combination of hazards.However,the damage from large ground displacements typically occurs in isolated areas of ground failure and tends to be greater,whereas wave propagation tends to cause less damage.Large liquefaction-induced displacement (lateral displacement and settlement) is a potential source of major damage to underground pipelines during earthquakes.Therefore,soil liquefaction does major damage to underground pipelines during earthquakes.In order to analyze the damage to underground pipelines under a slope due to sand liquefaction,a three-dimensional nonlinear analysis was carried out to study the pipe characteristics damaged by liquefaction-induced large displacements using the FLAC finite-difference method and to analyze the displacement characteristics of the slope due to sand liquefaction and the pore water pressure buildup.A numerical model was established,which is similar to the real engineering project dimensions.The model consists of the saturated sand and dry sand layers,as well as the pipeline buried under the slope.The saturated sand on the foundation was modeled using a Mohr-Coulomb soil model coupled with a Finn model,which is the pore water pressure generation model.The dry sand of the slope was also modeled as a Mohr-Coulomb model without the pore water pressure generation model.The soil-pipe interaction was simulated by a bilinear elastic model,in which the elastic modulus before liquefaction is 103 times that after liquefaction.The base boundary was a rigid boundary.The calculation process is divided into two stages of static and dynamic analysis.In the initial static analysis,in order to compute the gravity stresses,the base boundary was fixed both horizontally and vertically,and the side boundaries were only fixed horizontally.In the dynamic analysis,free-field boundaries were used,and the sine waves were applied to the base boundary.After computing the static stress conditions,a time history dynamic analysis was carried out for sine wave velocities with different frequencies and amplitudes.It was shown that the occurrence of sand liquefaction and large displacement was caused by large sine waves.The displacement of the slope increased with time,which was different in the various parts of the slope.The displacement below the toe of the slope was bigger than that below the crest of the slope,and the sand above the slope had a trend of slipping into the foot of the foundation.The displacement of the pipe increased linearly in the first stage,and then increased nonlinearly with the increase in damage.The liquefaction-induced large displacement does damage to the buried pipe;the displacement of the pipe increases with an increase in the amplitude and frequency of applied sine waves.It is possible to use the nonlinear method to simulate the soil-structure interaction.It is necessary to find a simplified analysis method for predicting pipe damage.

Abstract:Vibration from blasting for construction of a water conveyance tunnel at the Baifeng Reservoir main dam has potential effects on dam safety.In order to ensure the safety of the dam during blasting for the main dam water conveyance tunnel,blasting vibration must be monitored.By analyzing particle vibrating velocity,the effects of blasting vibration on the dam were monitored.Vibrations during four blasting events were monitored.Correlative data was collected using a TC-4850 vibrometer and a 3-component TYTEST velocity sensor.The response and characteristics of vibration from construction blasting were analyzed based on the data from three directions at each measuring point.Measurements included vibration history,peak,and frequency spectrum analysis.Results of the peak analysis showed that the maximum vibration velocity at each measuring point was less than 1.0 cm/s.This satisfied the design requirements for the control of blasting vibration velocity.The maximum vertical and horizontal displacements at each measuring point were within 0.013 mm.The maximum vertical and horizontal accelerations at each measuring point were within 2.559 m/s².Results of the frequency spectrum analysis showed that the vertical and horizontal vibration frequency corresponding to maximum peaks on the Fourier spectrum were in the range of 14.71~34.0 Hz.This range of frequency response was outside the natural response frequency of dam structure,which did not experience the effects of resonance.Compared with the particle vibration velocity of the dam's foundation,the particle vibration velocity at the top of the dam structure was amplified.Therefore,the particle vibration velocity at the dam foundation was less than that at the top of the dam,and consequently,under the threshold at which security controls at the dam's foundation would be triggered.All of the analyses demonstrated that blasting vibration associated with construction of the conveyance tunnel had no significant effects on dam safety and stability.

Abstract:Xi'an metro line 2 runs under the Bell Tower in Xi'an.In order to reduce the effect of the vibration on the Bell Tower caused by the long-term operation of the metro, a steel-spring floating slab track bed is adopted.Mainly based on the measured data,which monitors the influence of the Bell Tower's vibration under the operation of subway line 2,this paper compares and analyzes the measured values of vibration on the steel-spring floating slab track bed and usual track bed.The differences in the damping effect between the spring floating slab track bed and the usual track bed is worked out to evaluate the vibration-damping effect of the steel-spring floating slab track bed in the subway.

Abstract:Using the piezoelectric effect of piezoelectric ceramics,this article developed a new piezoelectric friction damper based on semi-active control theory,and described its structure and working principle.The ABAQUS finite-element model of the new piezoelectric friction damper was established.By the model,the damper hysteresis curve was obtained under different conditions,and a hysteretic damper performance test was conducted.Simultaneously,the finite-element calculations and experimental values of the damper were compared.By comparing the hysteresis curves of the finite-element simulation and the hysteretic damper performance test,the following conclusions could be obtained. The hysteresis curve of the damper which installs one piezoelectric ceramic actuator was full,and the friction energy performance of the new piezoelectric friction damper was good;the hysteresis curve of the damper which installs two piezoelectric ceramic actuators was fuller than installing one piezoelectric ceramic actuator,thus by installing two piezoelectric ceramic actuators,the friction damper could obtain better friction energy performance;the cause of the deviation between the theoretical and experimental values was that the driver displacement of the piezoelectric ceramic actuator was small and was affected by many manufacturing factors;so the actual output of the damper was small.Then;a model of a new piezoelectric friction damper installed on a power transmission tower was established by ANSYS;and the acceleration response of the layers of the power transmission tower model was computed by MATLAB.The friction energy performance of the new piezoelectric friction damper in the actual structure could be verified.The following conclusions could be obtained through the finite-element simulation:the effect of the damping control of the new piezoelectric friction damper installed on a power transmission tower was good,and the new piezoelectric friction damper had good practicability.This article can provide a theoretical basis for the engineering applications of the damper.

Abstract:The impact of the liquefaction of tailings on a seepage field and the pore pressure distribution in a tailings dam are studied in this paper.A program named SAFTD is created based on the theory of seepage for porous media considering the characteristics of seepage in a tailings dam.SAFTD could predict the final phreatic surface by adjusting the mesh grids near the phreatic surface on the assumption of the initial phreatic surface,and a classic example is given to validate the reliability of this program.Then,SAFTD is used to simulate the seepage field and pore pressure change of the typical upstream tailings dam prior to and after the liquefaction.The numerical results indicate that the center section of the phreatic surface raises remarkably after liquefaction,but changes little near infiltration points and frozen points.The pore pressure in the tailings dam increases by 18%~280% approximately,and the lower right of the initial starter dam has the largest pore pressure increment.The simulation result is consistent with the analytical result of Mochikoshi's #2 tailings dam discussed by Ishihara.

Abstract:Using a GDS dynamic triaxial system,undrained dynamic triaxial tests on saturated sandy gravel were performed,the liquefaction characteristics of the saturated sandy gravel were analyzed,and the effects of gravel content on the dynamic liquefaction strength and dynamic pore pressure were analyzed.Results show that gravel content has a large influence on the liquefaction strength of saturated sandy gravel,monotonically increasing with increasing gravel content.The dynamic pore water pressure increases with the increase of cyclic times.When the consolidation ratio is the same,the dynamic pore water pressure ratio increases with increasing dynamic stress amplitudes under the same cycle ratio.The failure time of vibration affects the development pattern of pore water pressure significantly.The dynamic pore water pressure develops in the hyperbolic-type with lower failure time of vibration and can be expressed by the arcsine function for greater failure time of vibration.The dynamic pore water pressure increases with increasing gravel content.Effect of gravel content on the liquefaction characteristics of saturated sandy gravel can be explained from the microstructure features of the sandy gravel and can be analyzed through the inter-particle state parameters.

Abstract:Abutments occupy an important position in a bridge system.The stability of a bridge station directly affects the seismic performance of a bridge.Vast amounts of seismic damage and bridge failure caused by abutment damage have occurred.This damage is often accompanied by large ground deformation induced by soil liquefaction.To study the landslide mechanism of abutment in liquefied sites,the fully coupled effective stress analysis method was used to simulate the characteristics of liquefied sand under a seismic load with a Paster-Zienkiewicz-modified Mark-III model.The effects of beam weight and liquefied layer position on abutment displacement were studied.The compaction effects on sandy soil liquefaction were also analyzed.Numerical simulation produced results consistent with those of the shaking table test suggests the ramming processing alone does not reduce the risk of sand liquefaction.

Abstract:Re-liquefaction induced by aftershocks causes serious hazards on soil structures after the end of the main shock. In this study,the influences of aftershocks on an artificial island are discussed based on the FE-FD coupling finite element analysis method at different scales of aftershocks and interval time between the main shock and aftershock.The results indicate that with dissipation of excess pore-water pressure after the main shock,liquefied areas in the sand layer of the artificial island gradually decrease;however,the liquefied areas expand rapidly when an aftershock occurs,and can possibly be larger than the liquefied areas induced by the main shock;the extent of damage to the artificial island is much worse when an aftershock occurs than when it does not.The increasing of the interval time between the main shock and aftershock results in the drainage consolidation during this time significantly improving the ability of the artificial island to re-liquefy;thus,full-scale re-liquefaction in the artificial island is difficult when the excess pore-water pressure entirely dissipates.Settlement and horizontal displacement of the artificial island increases with increase of the peak acceleration of the aftershock and the liquefaction point-in-time of the sand layer occurs a few seconds early.After the main shock,with drainage by consolidation in the soil,settlement of the artificial island continues to increase,and is even larger than the settlement induced by the main shock,but the horizontal displacement barely changes.Before the aftershock,if the sand layer of the artificial island is still liquefiable,the sand layer may play a role in seismic insulation and reduce the hazards caused by the aftershock to the artificial island.Therefore,it is necessary to consider multiple seismic fortifications during a period of time for offshore structures,especially for artificial islands.

Abstract:The all-covered type of sheet-pile wharf is a new type of sheet-pile structure,and research into its seismic performance is important for its design and construction.In this study, based on the FEM-FDM soil coupling calculation platform,the cyclic elastic-plastic constitutive model is introduced.The FORTRAN dynamic programming software is used for saturated sandy soil liquefaction numerical analysis.This software can effectively simulate saturated sand under earthquake dynamic nonlinear and large deformation and can also simulate sand liquefaction flow at the barrier of the pile and the front wall.The results are:under the action of earthquakes,the excess pore water pressures of liquefiable soils increase and there is large deformation due to horizontal flow;the horizontal damage to the front wall is greater than the vertical damage.The maximum shear wall is located in the seabed and before the wall at the junction.The barrier pile is the location of the maximum shear displacement parallel to the bottom of the front wall. The rod tension in the back increases gradually,while that in front reduces gradually.Through the analysis of sheet-pile wharf disasters caused by seismic liquefaction,the results of this study provide a reference for seismic and liquefaction resistance design.

Abstract:Submarine landslides,a natural hazard,not only destroy subsea infrastructure but also trigger life-threatening tsunamis.Because of its destructive potential,many scholars are studying the failure mechanism of seabed slopes.There are many factors that induce submarine landslides,e.g.,earthquakes,volcanic eruptions,gas hydrate dissociation, and so on.However,the instability of the seafloor in shallow waters may be induced by waves.This study treats the stability of a submarine slope as a plane strain problem and adopts an elasto-plastic constitutive model obeying the Mohr-Coulomb yield criterion.To analyze seafloor stability under wave loading,a large-scale elasto-plastic finite element program called ABAQUS combined with a strength reduction method is adopted.Based on linear wave theory,wave-induced pressure is implemented by developing a loading module in this program.Pressures are applied on the slope surface as pseudo-static loads at a particular time during the wave period. In addition,a typical example is presented,and a factor of safety (FS) and corresponding critical sliding surface (CSS) for the submarine slope under wave loading are obtained using the improved finite element program.A previously programmed analytical code based on an upper-bound approach of limit analysis is also employed to validate the numerical solutions.Based on this,a series of comparative analyses is performed.The effect of wave parameters such as wave length,wave height,and water depth on slope stability and the positions of the CSS are discussed by comparison with the results from the FEM and upper-bound approach.Some preliminary understanding of the instability mechanism of submarine slopes subjected to wave loading is achieved.The results show that the finite element result is close to the limit analysis result.The factor of safety oscillates with time under static water conditions and decreases gradually with increasing wave length and wave height.In addition,the FS of the submarine slope approach the hydrostatic FS as the water depth increases.This means that when the depth of water reaches a certain value,waves have no effect on the submarine slope.By analyzing the impact of the wave parameters on the CSS,increasing water depth is found to have no influence on the position of sliding surface,but the potential sliding surface position at different times changed significantly.

Abstract:A 1:30 scale model of an anti-inclined rock slope interlayered with silt was constructed,and a large-scale shaking-table test was performed to study the dynamic responses (acceleration and displacement) when the moisture content of silt layers change.The results are as follows:the horizontal amplification coefficients on the slope face after the silt layers became saturated were less than those before saturation;the coefficients increased with slope height in a nonlinear fashion;the coefficients on the slope face were larger than those in the slope body;before saturation,the displacement of the slope face increased in a nonlinear fashion with an increase in height;the displacement of the upper slope face (relative height between 0.6 and 0.9) was larger than those in other sections;after saturation,the displacement first increased and then decreased with increasing height,maximum displacement occurred near the top of the slope;and the slope displayed a bulging shape.Before saturation,slope failure occurs when the amplitude of the seismic wave is 0.3 g.After saturation,when the amplitude is no less than 0.4 g,first,slope failure occurs at the shoulder,then the slope slides and shears out from the upper levels,and simultaneously,longitudinal cracks appear and intersect with the horizontal fractures.The top of slope is left shattered.

Abstract:The failure modes of rock slopes can be classified into five types:plane,wedge,circular,toppling,and buckling failures.These failure modes mainly depend on the lithological characteristics of the rock,properties of the discontinuities,and degree of weathering.Generally,rock slope stability analysis under the plane failure mode mainly focuses on the sliding stability of a potential sliding mass subjected to gravity,hydrostatic stress in the slope,and seismic loads.However,there exists the possibility of overturning failure around the toe of slopes because of the fact that all loadings do not act through the centroid of the sliding mass.This failure mode is completely different from common topping failure,which involves the rotation of columns or blocks of rock about the fixed base,mainly occurring in anti-dipping layered rock mass slopes with steep dipping discontinuities.Thus,the existing methods for the stability assessment of the five common failure modes are no longer applicable,and a new method to determine the overturning failure is required.Note that although this overturning failure mode has not been observed and recorded,it is not impossible under extreme rainfall conditions coupled with the strong ground motion in Southwest China.Aiming to resolve this issue,this study presents an analytical approach for the stability analysis of overturning rock slopes.Considering the combined loadings mentioned above,the generalized analytical formula for the anti-overturning stability factor is derived based on the moment equilibrium theory.Based on the definition of the safety factor against overturning for earth-retaining structures,an anti-overturning stability factor is defined as the ratio of the resultant resistant moments to resultant driving moments.A comparative analysis by the variation of parameters was implemented,and the effects of the hydrostatic stress and seismic load on the anti-overturning stability factor of rock slopes are discussed.For a steep rock slope with a tension crack,the stability factor against overturning decreases rapidly from the infinitely great value for a dry slope to a finite value for a saturated slope.For the saturated rock slope,the safety factor against overturning changes significantly with the changes in the water pressure distribution.In addition,the vertical upward seismic force and horizontal seismic force on the slope face weaken the stability against overturning.It can be concluded that the hydrostatic stress in the tension crack plays a vital role in inducing the overturning failure and that the seismic load is secondary and can increase or decrease the possibility of overturning to a certain extent. On the basis of this,a series of preliminary charts for rock slope stability against overturning is produced and can be used to assess the seismic stability against overturning for saturated rock slopes.This series is produced by considering the different combinations of parameters such as the horizontal and vertical seismic coefficients,distribution modes of water pressure in the tension crack,and relative depth of tension cracks to the height of the slope.

Abstract:Levee engineering is mostly built in densely-populated area,so the crash will always cause serious consequences especially for the levee filled by sandy soil which may develop into liquefaction under the action of earthquake.Therefore, the usage of reasonable methods of liquefaction on the levee to determine the dynamic stability under earthquake action is very necessary. This paper, in view of a practical levee engineering, conducted dynamic characteristic research on five kinds of materials to be used, basing on the research results of soil material dynamic characteristic test, and estimated liquefaction possibility of the levee by using the nonlinear shear wedge method which can consider the interaction between the levee and the foundation. Research shows that: the nonlinear shear wedge method can consider the interaction between the levee and the foundation, and is simple and practical; soil relative density, void ratio, particle size and particle distribution characteristics have a great influence on its ability to resist seismic liquefaction; in a set operation under the condition of 8 degree earthquake, only the silty loam levee will not lead to the occurrence of liquefaction, the other four materials exist the possibility of liquefaction, in conclusion, it is appropriate to select the silty loam to build the levee.

Abstract:In evaluating the damage caused by earthquakes,attention has been paid in the past to ground liquefaction and displacement during or immediately after the earthquakes.For this reason,only the analysis of liquefaction in sandy ground during earthquakes is performed in most dynamic analyses.However,the damage to complex ground that contains sand,silt,or clay layers and long-term settlement over several weeks or years after the earthquake cannot be ignored mainly because of the long time required for the dissipation of excess pore water pressure (EPWP) and the recovery of the ground rigidity.In this study,a multi-story car park with a steel frame is designed and constructed according to Japanese Architectural Building Standards.This study will investigate the seismic performance of the building during and after a great earthquake that is predicted to hit the central part of Japan in the near future.Special attention is paid to the differential settlement caused by liquefaction and long-term settlement after the earthquake.The analysis is performed using a 2D soil-water coupled dynamic/static finite element analysis program DBLEAVES,considering ground-foundation-superstructure as one whole system.The program can analyze not only the static and dynamic behavior of natural complex ground but also solve soil-structure interaction problems.The applicability and accuracy of the program have been verified by many investigations.A rotational kinematic hardening elasto-plastic model called the cyclic mobility (CM) model is adopted in this analysis to describe the nonlinear behavior of cohesionless soils under both dynamic and static loadings,particularly the cyclic mobility of sand during liquefaction.With the CM model and an effective-stress-based FEM code,the mechanical behavior of soil,change of EPWP,and consolidation can be defined.The input earthquake wave is an approximation of three synchronized seismic waves whose main shock lasts about 150 s with a maximum acceleration of 182 gal.Before the dynamic analysis,a static analysis considering the ground-structure as one whole system is performed to determine the initial effective stress of the ground.In the dynamic analysis,an equal displacement boundary condition,sometimes called a periodic boundary condition,is used for two side boundaries to manage the energy-loss problem.In this study,a comparison of long-pile and short-pile foundations is presented.As mentioned above,the ground behavior is described by the CM model;in addition,the long piles and super structure are modeled as beam elements,and the short piles are modeled as elastic solid elements.The analysis shows that liquefaction occurred mainly in loose and medium dense sand layers.The long-pile foundation has a better capacity for resisting differential settlement,whereas the short-pile foundation (improved ground) has a better capacity for resisting ground liquefaction.In all cases,most of the differential settlement occurs during earthquake motion,while the post-liquefaction settlement is relatively uniform despite its large amplitude.Therefore,serious consideration should be given not only to the liquefaction behavior of the ground during earthquake motion but also to the long-term settlement after the earthquake.

Abstract:Fixed offshore platforms and jack-up drilling platforms can be constructed at the same time because of the development of new jack-up vessels and construction techniques.Unfortunately,a side effect may occur on the pile foundations of the fixed platform when the spudcan penetrates nearby.It is very difficult to simulate the whole dynamic process by a finite-element method.This paper primarily solves the formula of the squeezing soil effect using ball cavity expansion theory.On the basis of the analytical solution,a new pseudo-static method is proposed,which can approximately take the dynamic effect into account.It is analyzed for the bearing capacity,mises stress,and maximum horizontal displacement of pile foundations at different spudcan penetration depths based on an actual project.The simulation results are contrasted with the simple static simulation method.The comparison shows that the bearing capacity is 6%~8% lower than the static simulation result,the Mises stress is 30%~80% higher,and the maximum horizontal displacement is two times larger.

Abstract:Permafrost is distributed widely in our country.Although pile foundation is the main foundation form for large bridges in frozen zones,few studies have been conducted regarding the dynamic characteristics of pile foundation construction in permafrost.An improved nonlinear analytical model for frozen soil-pile dynamic interaction was developed on the basis of model test results of the dynamic characteristics of pile foundations in various subzero temperature soils under lateral dynamic loads and an analytical model of pile-soil-structure interaction with the dynamic beam on nonlinear Winkler foundation model. This improved analytical model simulates the nonlinear lateral pressure effect of the frozen soil around the pile with an improved bidirectional compression-only multi-yield spring. Vertical friction effects between the frozen soil and pile, extrusion and separation effects of frozen soil under pile tips, and damping effects of the far-field soil on the dynamic characteristics of pile foundations are also considered in this analytical model. The parameters of the bidirectional tensionless multi-section yield spring are determined by the nonlinear p-y relationship of frozen soil. The p-y relationship whose parameters were based on the results of the indoor frozen soil compression test was simulated by the combination of a cubic function and a constant function. Displacement-force response of the pile head and pile shaft responses to bending moments at different depths under dynamic forces were very similar to the model test results. Results indicate that the improved analytical model is potentially helpful during the analysis of frozen soil-pile dynamic interactions.

Abstract:The CEL method,which is widely used in the research on spudcan penetration,is a new simulation method.However,there are many questions which have not been answered,especially about the effect of penetration velocity and the mass scaling method.This paper firstly simulates two models with no piles which have different penetration speeds.Then,two models with square piles are also simulated with different penetration speeds.Additionally,the mass scaling method is verified.The simulation results show that the penetration speed has little effect on the soil resistance and more effect on the soil failure mode and shear stress.When the model has a pile,the horizontal displacement is relatively unaffected by the penetration speed,and the Mises stress of the pile increases with the penetration speed.The mass scaling factor also has little effect on the horizontal displacement of the pile.The Mises stress has an irregular relation to the mass scaling factor.Therefore,caution should be carefully taken when the mass scaling method is used.

Abstract:The vacuum preloading technique has often been applied to underwater soft-ground improvements in intertidal zones.However,in those construction activities,the varying water pressure load has not been considered,and the vacuum load was just taken as the vacuum pressure below the membrane.This treatment was obviously conservative.This research aims to analyze the effect of variant water pressure on the soil ground improvement through practice,and proposes a determination method for the vacuum load for the vacuum preloading technique in intertidal zones.The preloading may be taken as the sum of the vacuum load and the average water pressure above the membrane,and the latter should be calculated through the intertidal water level during the construction period and the ground elevation.This method for load determination may serve as a valuable reference for engineering design.

Abstract:An investigation of the dynamic response of saturated soil plays an important role in classical application fields such as soil mechanics,hydrology,ocean engineering and so on.Furthermore,it is essential to the development of emerging sciences and technologies,such as the mechanical characteristic of skin and soft tissue in biology.Therefore,it is important to provide appropriate theoretical analyses and numerical simulation methods.In addition,the transient response of saturated soil is also essential to the understanding of deformation and the pore water pressures generated by ground motion.This response is a key factor in the dynamic analysis of building foundations,offshore structures,and wave propagation in geological medium during blasts or earthquakes.Saturated soil is one that exhibits a solid faction and a porous space filled with a viscous fluid on a microscopic scale.Two approaches are possible for addressing the description of such a soil.The first approach is at the microscopic scale.Here,the "solid elastic" and "viscous fluid" phases each constitute distinct geometric domains.A geometric point is found at a given instant in one of these two clearly identifiable phases.The second approach considers the problem from the macroscopic level.The elementary volume is considered to be the superposition of two material particles with different kinematics occupying the same geometric points at the same instant.Thus,the saturated soil is considered as a two-phase continuum;the skeleton particle is constituted by the solid matrix and connected porous space,and the fluid particle is formed from the fluid saturating this connected porous space.There are many theories describing the characteristics of saturated soils,e.g.,Biot Theory,porous media theory,hybrid mixture theory,and so on.Most of the transient response studies for saturated soils are solved by numerical methods such as the finite element method (FEM)and finite difference method (FDM).Compared to the FDM,the most attractive feature of the FEM is its ability to handle nonlinear material and complicated geometries (and boundaries)with relative ease.In this investigation,based on Biot Theory,a mathematical model of a two-dimensional saturated elastic soil is established,and a time-domain FEM for analyzing the transient dynamic response of saturated soil under cyclic loading is presented.To verify the efficiency and accuracy of the proposed method,a one-dimensional saturated soil column subject to two different surface loadings was simulated.The first numerical example models the transient response of the saturated soil column due to sine wave loading.The second case is for the dynamic response of the soil column subject to step loading.For both numerical examples,the solid displacement history and pore pressure history are presented and compared with analytical solutions.Good agreement between the computed results and analytical solutions show the efficiency and accuracy of the proposed method.

Abstract:Conversion methods from seismic loads to uniform-amplitude loads are basic research topics in geotechnical earthquake engineering.Through a series of dynamic triaxial tests,the feature of soil deformation under irregular seismic wave loading and the relationships of soil deformation under irregular seismic wave loading and fixed-number wave loading are analyzed.The ratio of residual strain under a constant-amplitude sinusoid wave with 20 cycles and an amplitude of 0.65 times the seismic wave peak value to residual strain under seismic loading is defined as the strain ratio C,and the relationship between the strain ratio C and sand density is investigated.The results show that soil deformation development under irregular seismic loading obviously differs from that under sinusoidal loading,and the strain time history is mainly controlled by the performance of ground motion,rather than seismic loading amplitude and soil type.Under impact loading,the peak value (instead of other pulses) plays a significant role in control.Under a vibrating wave,besides the peak value,some other pulses with similar amplitudes and peak values have influences on the soil deformation.The strain ratio C will decrease with the increase of the relative density of the sand.When uniform sinusoidal loading,with 20 cycles and an amplitude of 0.65 times the seismic wave peak value,is employed instead of irregular seismic loading to modify residual deformation of soils under real seismic loading,the strain ratio C will decrease with the increase in the relative density of the sand.Meanwhile,the strain ratio C of impact-type loads is much larger than that of vibrating loads.

Abstract:Residual deformation behaviors of deposits under cyclic loading at different stress levels and cyclic loading amplitudes are studied by a large-scale dynamic triaxial test.The residual deformation of the deposits under different initial conditions is also discussed.Residual strains under cyclic loading are found to show a linear relationship with lg(1+N) when N is less than 30.Shen's empirical equation is suitable for calculating the residual strain of deposits under cyclic loading.The initial conditions have a significant effect on the residual strain of deposits.Residual shear strain is the largest under undrained conditions,medium under drained conditions,and smallest under air dried drainage conditions.When the residual deformation of the deposit under cyclic loading is calculated using Shen 's equation,the equation's parameters should match the actual engineering conditions.

Abstract:In order to study the dynamic properties of red clay under cyclic loading conditions,a series of cyclic triaxial tests are carried out on undisturbed red clay obtained from Shanglin county,Guangxi.The impacts of water content,confining pressure,and consolidation stress ratio on the dynamic properties of red clay such as the dynamic stress-strain relationship,dynamic elastic modulus,and damping ratio are analyzed.It is indicated from the test results that the stress-strain curve of red clay from Guangxi is close to a hypobolic style;due to the effects of the initial shear stress,a higher dynamic stress is needed to obtain the same strain under anisotropic consolidation as under isotropic consolidation;the dynamic modulus decreases as the dynamic strain increases;the decrease in amplitude decreases with the increase of the dynamic strain;and the initial stress state has the most significant impact on the dynamic elastic modulus.The damping ratio is affected by the consolidation stress ratio,confining pressure,and water content of red clay from Guangxi,and it increases as the dynamic strain increases,with its value distributed between 0.1 and 0.2.The damping ratio data has a high discreteness.Based on the hyperbolic model by Konder,test data are fitted,and relevant parameters are obtained.This research could be a reference for further design of dynamic properties and numerical calculation,and it also provides relevant parameters.

Abstract:With the rapid development of the automotive industry in China,"black pollution" caused by scrap tires has become increasingly significant.A reinforcing earth structure using scrap tire columns (STC) is presented in the current research.Horizontal cyclic shear tests and vertical excitation tests were conducted to validate the effectiveness of scrap tire columns reinforced sand (STCRS) on horizontal and vertical damping.The results of the horizontal shear tests show that when the maximum shear strain is 1%,the equivalent damping ratio of STCRS increased by about 10% more than the sand itself,and the shear modulus decreased by 20%~25%,improving the horizontal damping performance.In the vertical vibration tests,the acceleration attenuation showed characteristics of fast speed and large amplitude,indicating that STCRS had a significant damping effect compared to unreinforced sand.STC reinforced sand as a material for seismic isolation is feasible,and is also a new use for scrap tire resources.

Abstract:The silt under a retaining wall foundation in the Hangu area of Tianjin was studied in this paper.Specifically,a consolidated undrained dynamic triaxial shear test on the silt of different particles is described,and the conclusion is that the dynamic strength of silt was impacted by the particles.The test used isotropic consolidation,and the ambient pressure is equal to 100 kPa.After consolidation,we applied an axial dynamic load in the undrained condition.The test waveform is a sine wave,and the vibration frequency is equal to 1.0 Hz.The sample used a periodic shear axial strain of 5% as the failure criterion.The test instrument is a DDS-70-type dynamic three-axle instrument.Silt samples were compacted in three layers in the cylindrical specimen.The sample water content is equal to 20%,and the dry density is 1.60 g/cm³.The diameter of the sample is 39.1 mm,and the height is 80 mm.We prepared soil samples with different clay contents.The soil's dynamic strength refers to,under the static stress conditions,the cycle load necessary to make the soil sample achieve certain failure criteria.We have drawn the following conclusions.Under the same test conditions,silt particles had a great influence on the dynamic strength.When the dynamic load is equal to 100 N,and the No.1 silt clay content is 20.3%,the vibration frequency reached 42,far less than that for the No.2 and No.3 silty soils.The clay contents of silts Nos.2 and 3 are 13.2% and 7.2%,respectively.With the increase in dynamic load,the No.3 silt vibration frequency is 2.2 times that of No. 1.A higher clay content means that the proportion of fine particles is greater,the coarse particle content is lower,and the plasticity is greater.That is,it is closer to clay.Friction of fine particles was significantly less than that of coarse particles.Therefore,the coarse silt's dynamic strength is relatively large.Pore water pressure generated under a vibrating load is an important factor affecting the soil strength and deformation.Pore water pressure is the key to the analysis of dynamic strength by effective stress.From the test results,for the three kinds of silt in the shearing process, the pore water pressures grow but do not reach the value of 100 kPa of the applied confining pressure.The pore water pressure is stable between 75 and 85 kPa.The more fine the particles,the lower the dynamic strength contained by the silt.The cyclic shear stress ratio (CSR) of silt with 7.2% of viscosity particles was about two times that of silt with 20.3% of viscosity particles.The dynamic strength of silt could be fitted by the CSR and power function relation created by the failure time of the vibration.In the shearing process,the pore water pressure of silt did not reach the numerical result of the ambient pressure,and eventually stabilized at 75~85% of the ambient pressure.Additionally,from this trial it could also be concluded that the growth pattern of pore water pressure could not be fitted by the unified Seed model,and the growth of pore pressure was influenced by many factors.

Abstract:

Abstract:When an earthquake occurs,seismic waves propagating from the earthquake source to the ground include transverse waves (S-waves) and longitudinal waves (P-waves).Transverse waves produce dynamic shear loads whereas longitudinal waves produces dynamic tension and compression loads.Consequently,under the effects of these two dynamic loads,horizontal shear vibration and vertical tension and compression vibration occur simultaneously in loess.By simultaneously applying axial and radial dynamic loads on a triaxial specimen and using stress on the surface of the specimen at an angle of 45°,the effects of seismic tension and compression and shear dynamic loads are simulated and the characteristics of the dynamic shear modulus and dynamic strain of loess are analyzed under bidirectional cyclic load coupling.The test results indicate that phase difference has certain effects on the dynamic shear modulus of loess. With φ=180° as the turning point,the dynamic shear modulus of loess decreases first and then increases with increase in the phase difference, and when the phase difference is 180°,the loess dynamic shear modulus decreases to its lowest level.Analysis of the initial dynamic shear modulus of loess under the bidirectional cyclic loads shows that with increase in the phase difference, the initial dynamic shear modulus of loess follows the same development law as that of the dynamic shear modulus.When the phase difference is in the range of 0° to 90°,the initial dynamic shear modulus of loess decreases quickly,but when it is in the range of 90° to 180°,the decline velocity slows down. Correspondingly,the initial dynamic shear modulus increases slowly when the phase difference is in the range of 180° to 270°;however,the increase in the velocity of the initial dynamic shear modulus becomes higher when the phase difference is in the range of 270° to 360°.When the value of the confining pressure is 200 kPa and the radial vibration amplitude is 20 kPa,the initial dynamic shear modulus of loess under the phase difference of 180° accounts for only 10.77% of that under the phase difference of 0°,which is a decrease of approximately 90%,and the decline ratio shows an increasing trend with increase in the radial vibration amplitude.This indicates that the phase difference has significant effects on the initial dynamic shear modulus of loess,especially when the loess is exposed to bidirectional cyclic loads,with a phase difference of 180° between the axial and radial loads,the loess initial dynamic shear modulus drops dramatically and the ability of loess to resist the shear deformation becomes very weak or even lost.When the phase difference is less than 180°,its increase tends to accelerate the development of the loess' dynamic shear strain,and when the phase difference is greater than 180°,the development of the loess' dynamic shear strain reduces with its increase.The test results show that the load combination with a radial vibration amplitude of 60 kPa and phase difference of 180° has the most unfavorable effects on the deformation development of loess,and the dynamic shear strain of loess rises almost linearly with the increase of cycles under this combination.As a result,the destruction of loess occurs in a few cycles.Therefore,high radial vibration amplitudes should be avoided when the phase difference between the axial and radial dynamic load is 180° in practical projects.By calculating transformation,the manner in which the changes in the dynamic tension and compression and shear loads affect the development of the dynamic shear strain of loess is analyzed.The results show that the dynamic tension and compression load quickens the increase of the dynamic shear strain of loess,and when the dynamic tension and compression and shear loads change synchronically,the change of the dynamic shear load has more prominent impacts on the development of the dynamic shear strain of loess.

Abstract:Based on field investigations and previous research results,this study analyzes the tectonic background,seismic activity,and hydrogeology condition of the Sanjiangkou reservoir area.The Yushan fault is the main fault located in the southeast margin of the Sanjiangkou reservoir area.The other major fault is termed the Mawu fault,which is exposed in the west margin of the Sanjiangkou reservoir area.The active age of the Yushan fault is mid-Pleistocene and the Mawu fault is pre-Quaternary.The level of historic and current seismicity is low in the reservoir area.Employing structural analogy and probabilistic statistic methods,the probability of the induced earthquake in the Sanjiangkou reservoir area is discussed.These results are used to compare the Sanjiangkou reservoir with other reservoirs that have experienced earthquakes.The structural analogy method analysis showed that the possibility of tectonic-type reservoir-induced earthquakes is small following impoundment.However,there is the possibility of a karst subsidence-type reservoir-induced earthquake.This event could occur because of the existence of a large amount of thick layers of limestone in the reservoir area that could foster karst development.The loading and infiltration effects of water may easily cause rock collapse and crack propagation in the karst cave.This would induce a karst subsidence-type reservoir-induced earthquake.Considering the conditions of the Sanjiangkou reservoir area eight induced earthquake factors were selected to conduct the probabilistic prediction of the earthquake magnitude.These factors were reservoir water depth,lithology,regional state of stress,fault activity,degree of karst development,fault permeable depth,communication with the reservoir water,and seismic activity background.Based on the geological conditions and induced earthquake environment of the Sanjiangkou reservoir area,the reservoir area was divided into three segments: the head (Xintanzi-Shiliwan),middle (Shiliwan-Niubizi),and end (Niubizi-Xiamakou) regions.Using the MATLAB software programming,the probability of five earthquake magnitude was calculated for the three segments.The larger earthquake magnitude grading range was selected that corresponded to the relative probability value.The grading range was considered as the possible earthquake magnitude.The probabilistic statistic method analysis showed that the reservoir's head region (Xintanzi-Shiliwan) had a small possibility of an induced earthquake with a possibility of earthquake occurrence of 0.02. The reservoir's middle region (Shiliwan-Niubizi),where the karst development is unlikely,had a possibility of induced earthquake of 0.96.The end region (Niubizi-Xiamakou) may induce microseismic activity with the possibility of induced M_L (M < 3.0) of 0.10.

Abstract:Ningxia and its neighboring area are located in two blocks of the northeastern margin of the Qingzang-Tibet plateau:the Erdos block and the Alashan block.The geological structure in this area of the plateau is known to be unstable.Over recorded time,many large or great earthquakes have occurred in this area.Based on previous research results,we employed two different earthquake location methods,i.e.,double-difference and genetic algorithm,to recompute the location of small earthquakes that were recorded by the Ningxia Regional Earthquake Monitoring Network from 1991 to May 2014.This process consisted of first employing the theoretical travel time method to delete or modify the seismic events whose arrival time error exceeded 10 s.Next,we selected seismic events that contained S and P waves recorded by at least three stations.In addition,Pg,Sg,Pn,and Sn seismic phases are included in each earthquake event.The velocity model was obtained from four seismic sounding profiles that crossed the research area.In addition,a horizontally layered velocity model was used.The double-difference method results showed that the seismic source depth was not so different from that obtained using the genetic algorithm method.But only a few earthquake events (approximately 25% of the total 4 688 seismic events) can meet the relocation requirement in the double-difference method.Therefore,the genetic algorithm method can be used to recalculate and reanalyze the depth characteristics of small earthquakes and their relation to the deep fault in the research area.Relocation results showed that the seismic zone distribution by depth is more apparent.Statistical analysis,taking the relocation calculation into account,showed that more earthquakes happened from 5 to 30 km.The average depth was 18 km.The space distribution of small earthquakes in this area was obtained.To facilitate the analysis of the relationship between the occurrence of earthquakes and faults in this region,we divided the geographic research region into four districts on the basis of their tectonic characteristics and concentration region of small earthquakes.These districts were named A,B,C,and D. In each district,the seismic profile perpendicular to fault was obtained.In district A,the results showed that the seismic depth was mainly distributed from 5 to 25 km.The earthquake distribution width was 50 to 60 km.In district A,earthquakes occurred primarily in the upper and middle crust or in the top of the lower crust.It was postulated that fractures parted only the upper or middle crust while not the Moho.In district B,the small earthquake distribution was primarily in the north-south direction.In this district,the earthquakes were primarily distributed from 5 to 35 km.The width of the epicenter was approximately 50 km.The dip of the seismic zone was from SE or NE,with an angle of approximately 50°.The fault fracture was primarily in the middle or lower crust.In district C,small earthquakes occurred along fault F₁₀ and F₁₁.The epicenter width was approximately 70 km.The seismic source was mainly ≤22 km.The dip of the seismic zone was to the NE,and the dip angle was approximately 40°.The fault fracture was confined to the middle crust.In district D,the depth range of the seismic source was primarily from 0 to 25 km.The dip of the seismic zone was to the NEE,and the dip angle was approximately 50°.But the dip of the Haiyuan fault was to the SW,which is different from the results reported in previous studies.The geologic structure and the fault activity of this district are more complex.These results imply that the fracture depth of fault F₉ and F₁₄ is deep to at least the middle crust. The genetic algorithm calculation results revealed that the depth distribution of a large number of reported earthquakes is denser and that the epicenter of the seismic distribution is along the faults that resulted in the great earthquakes.The depths of the deep faults extended to the middle or lower crust.

Abstract:At present, Chinese seismic design codes for engineering projects classify site conditions primarily by their equivalent shear wave velocity at a depth of 20 m below the surface, which is referred to as V_S20. However, the parameter widely used abroad in seismic design codes is the equivalent shear wave velocity at a depth of 30 m below the surface, V_S30. This non-standardized parameter has led to inaccurate site condition descriptions when foreign models for earthquake engineering or seismic resistance are applied to Chinese engineering projects. Several methods have been used in an attempt to estimate V_S30 from site profiles with 20 m-deep boreholes for strong motion stations located in the Sichuan and Gansu Provinces. These estimation methods include: extrapolation (constant and gradient), Geomatrix site classification correlation via shear-wave velocity, and remote sensing (terrain and topography). In this study, gradient extrapolation was the preferred estimation method for sites with shear-wave velocity profile data. When combined with Geomatrix site classification, the average V_S30 for each site was derived from 147 estimated V_S30. Thus, gradient extrapolation followed by Geomatrix site classification can be used to assign a V_S30 to a site without 30 m-deep borehole data, unifying global engineering design codes.

Abstract:This study describes the use of finite element analysis to study the seismic response of a typical karst site compared with that of other sites.The results showed that compared with other non-karst sites,karst field soil has a stronger amplification effect on the seismic wave,and the ground motion frequency is higher.When there are holes in the karst site,the seismic peak ground acceleration is larger than that of a non-holed karst foundation.These results provide a reference for the ground motion parameters determined at a karst site.

Abstract:Temperature is an important factor that influences the physical and mechanical properties of rocks. Many scholars have studied various types of rock crushing, but few have examined the characteristics of crushed limestone previously exposed to different temperatures. This study involved a heating limestone specimen, 50 mm in diameter and 100 mm in height, in a high temperature furnace heating cylinder before performing a uniaxial crushing experiment. Various phenomena were observed including axial splitting and bursting strength at low temperature. However, the strength of fracturing and splitting at high temperature decreased significantly as cleavage was simultaneously reduced. Sample pieces were completely reassembled and similarly sized fragments grouped together. Fractal mathematical theory applied to the analysis of rock fragments indicated that limestone block distribution is a fractal. Therefore, the fractal dimension D was considered an appropriate statistic to represent the characteristics of limestone crushed after exposure to high temperatures. The fractal dimension D has a negative correlation with temperature where it decreases with increasing temperature. The experimental data was represented in the rectangular coordinate system by plotting temperature on the X axis and fractal dimension on the Y axis in a scatter plot. Linear regression used for curve fitting the data resulted in y=0.001 9+2.506 2x and a very large correlation coefficient. The observed influence of temperature on limestone mechanical properties mainly involved mineral physical properties and changes in microstructure. Mineral composition and crystal lattice structure may change when a rock is exposed to different temperatures. Fragment comparison with scanning electron microscope (SEM) revealed that limestone subjected to high temperature had different microstructural characteristics than untreated limestone. Room temperature limestone had a smooth surface. Limestone subjected to high temperatures had an uneven surface and partially broken cement.The rock surface appeared to contain long, wide fissures across grains, rough mineral grain surfaces, and increased detrital material. These characteristics reduced the mechanical properties and caused the change in fractal dimension. This internal mechanism in the limestone explains why fractal dimension decreases with increased temperature. In addition, limestone samples were gray-black at room temperature and light gray when heated to high temperatures. High-temperature exposure caused calcium carbonate formation and magnesium carbonate oxidation that led to the observed color change.

Abstract:The M4.6 earthquake in Laizhou,Shandong,occurred on November 23,2013,and it was the largest earthquake recorded since 1970.This event was also notable as the most potent earthquake in the interior regions since the M5.2 earthquake of Cangshan 18 years earlier.The Shandong Digital Earthquake Network Center has recorded 86 aftershocks until March 02,2014,including 18 earthquakes of more than M_L2.0.The earthquake occurred between the Jingzhi and Yishu faults (along NE direction) with the Liucun-Laizhou,Zuocun-Xiankuan,Matou-Dagu faults around the epicenter.The focal mechanism describes the nature and source of the rupture process,and is an important foundation for understanding the stress state of the source region,earthquake faults,and analyzing the causes of the seismic event.Therefore,the determination of the earthquake focal mechanisms is of great significance in the understanding of the mechanical process of earthquakes,for seismic interpretation,and for the understanding of the post-earthquake seismogenic stress distribution mechanism.Thus the causative structure of the Laizhou earthquake sequence is discussed on the basis of relocating the Laizhou earthquake sequence using the double-difference method and analyzing the focal mechanism of the stronger earthquake using the "cut and paste"(CAP) method.Eighty-six earthquakes were relocated using the double-difference method,and 75 basic earthquake parameters were obtained. The precise epicenter was located along the direction of Zuocun-Xiankuan fault,which is consistent with the location,strike,and dip of the Zuocun-Xiankuan fault.The depth of the entire earthquake sequence was found from 4 to 9 km,and the advantages of depth was at 5~7 km.The result showed that the main earthquake rupture occurred in the upper crust.The analysis of the vertical profile by precise positioning showed that the focal depth from SE to NW gradually becomes deeper,and the dip direction is in the NW direction,which are consistent with location,strike,and dip of the Zuocun-Xiankuang fault.The focal mechanism of the 4.6 earthquake was inverted using the CAP method.Thus,the synthetic seismograms fit well with the observed seismograms,and the inversion result is verified.The focal mechanism showed that the moment magnitude of the M4.6 earthquake was M_W = 4.5,one nodal plane had a strike of 193°,a rake of 144°,and a dip of 69°,and another nodal plane had a strike of 298°,a rake of 25°,and a dip of 57°.The first nodal plane appeared to have occurred close to the Zuocun-Xiankuang fault.Combining the precise relocation results,profile depth distribution,focal mechanism of the M4.6 earthquake,and intensity distribution by macroscopic investigation using the relationship of Zuocun-Xiankuang fault occurrence,it was concluded that the Zuocun-Xiankuang fault may be the seismogenic fault of Laizhou earthquake sequence.

Abstract:Using the finite difference method,the two-dimensional elastic wave equation is processed to obtain the finite difference equation.Then,the differential elastic wave equation format is combined with the absorbing boundary and the discrete form of the free boundary.The elastic wave equation finite difference equation is formed to solve the problem.Using the finite difference equation,the displacement on different nodes can be obtained at different times for the rectangle-shaped depression of a semi-infinite inhomogeneous medium.Using the finite difference equation of the two-dimensional elastic wave equation combined with the scientific computation software,MATLAB,and the post-processor software,DIFEM ISOLINE PLOTER,the displacement isoline of the rectangle-shaped depression of the semi-infinite inhomogeneous medium in the x direction can be obtained for different times.The effect of the inhomogeneous media,absorbing boundary,and the rectangle-shaped depression on the wave characteristics is analyzed numerically.

Abstract:Theoretical solutions of the Rayleigh wave in half-space saturated porous media were derived under two different potential functions corresponding to a case with two kinds of compressional waves and amplitude ratio coefficient and a case with a compressional wave (P₁ or P₂ wave) without considering the amplitude ratio coefficient,respectively.The theoretical analysis shows that the derivation of the solution of the Rayleigh waves for the case with two kinds of compressional waves and amplitude ratio coefficient is more rigorous,which is consistent with the fact that there exist two kinds of compressional waves in saturated porous media.Through numerical calculation,we compared the propagation velocities and attenuations of the Rayleigh wave in three different cases,namely,the case with two kinds of compressional waves and amplitude ratio coefficient,the case with P₁ wave without the amplitude ratio coefficient,and the case with P₂ wave without the amplitude ratio coefficient.The numerical calculation shows that there exists distinctive differences among the results obtained in the three cases above.We recommend that the potential functions that consider the two kinds of compressional waves and the amplitude ratio coefficient be applied when studying Rayleigh waves in half-space saturated porous media.

Abstract:Earthquake ground motions can significantly affect buildings when they are amplified in surface soil layers.Therefore,in order to estimate the behavior of buildings during severe earthquakes,it is essential to evaluate those characteristics of amplification.Although investigations have been carried out,many problems remain unsolved with regard to those characteristics.Ground response analysis typically involves predictions of surface ground motions,developing a spectrum of design responses,determining dynamic stress and strain,and evaluating the potential for liquefaction.Methods used to calculate the ground response are commonly divided into linear,nonlinear,and equivalent linear concepts.The linear analysis assumes that the shear modulus as constant.However,soils often exhibit nonlinear behavior,even at low levels of strain.The nonlinear method is time consuming.The equivalent linear method,represented by the SHAKE model,is one of the most frequently used methods for analysis of ground responses to earthquakes.This method is used primarily for approximations because it uses effective strain to define the material property for analysis.However,the equivalent linear method remains the most popular method of seismic response analysis.It has been 20 years since the safety evaluation program LSSRLI-1 was developed and was used for seismic response analysis.At the time,LSSRLI-1 represented the most advanced method and contributed greatly to earthquake preparedness and disaster reduction for China.However,some deficiencies in the model were identified.Based on its focus in the frequency domain with a harmonic wave incident,the exact linear solution was deduced in the time domain,and compiled into a program in the Matlab environment.For the study,eight sites with medium-hard soils were chosen.Seismic responses were calculated using three different methods:the LSSRLI-1,exact solution,and SHAKE2000.The results show that the ground response spectrums and distribution of soil shear strain,calculated using the exact solution and SHAKE2000 methods,are in agreement with each other.The ground response spectrums,calculated using LSSRLI-1,were consistent with the other two methods.However,in some cases,the distribution of soil shear strain,calculated using LSSRLI-1,showed a relatively large deviation from the SHAKE2000 and exact solution methods.The extent of these differences may significantly affect the estimates of ground motion,and cannot be ignored.

Abstract:The seismic fortification levels of electrical equipment have received more and more attention since the Wenchuan earthquake.The current seismic requirement level of electrical equipment in China is lower than that of other international standards,such as IEEE 693,IEC 62271,and JEAG 5003.In China,the seismic level of electrical equipment is decided by combining several conditions of fortification intensity,site condition,and classification of design earthquake,which makes it difficult to determine the seismic level of electrical equipment quickly and conveniently.By comparing domestic and foreign codes about the seismic fortification level of electrical equipment,the advantages of grading fortifications are summarized.Consequently,grading the fortifications for electrical equipment in China was proposed.In order to obtain the principles of this grading,the seismic reliability of electrical equipment was calculated.Design earthquake accelerations exceeding a failure probability of 2% in 50 years,which were higher than the normal value and obtained by survey,were used as calculation parameters.Two typical pillars of electrical equipment were chosen as calculation modals,and the seismic reliability of electrical equipment in ordinary porcelain and high-strength porcelain was calculated using the FOSM method.The use of design earthquake accelerations exceeding a failure probability of 2% in 50 years will meet the seismic target of not collapsing with strong earthquakes,which will further ensure the seismic safety of electrical equipment.The seismic reliability of high-strength porcelain equipment was obviously higher than that of ordinary porcelain equipment.It is an effective method to improve equipment seismic capacity through replacing ordinary porcelain by high-strength porcelain.The reliability results were used as indexes to determine the low,medium,and high levels.Specifically,peak accelerations of 0.1 g and below were considered to be at a low assessment level,and the peak acceleration was taken to be 0.1 g. Values of 0.1~0.4 g corresponded to the medium assessment level,and the peak acceleration was taken to be 0.4 g.Values above 0.4 g comprise the high assessment level,and the peak acceleration was taken to be 0.6 g. By comparing the peak acceleration with those of IEEE and IEC standards,it is found that the proposed seismic fortification for electrical equipment is more reasonable.The acceleration value of each seismic level is slightly lower than the values given by IEEE and IEC.

Abstract:Bridges are usually lifeline engineering-in-traffic projects, and their seismic performance is very important. As an important bridge construction component, piers are vulnerable to damage under strong ground motion. In this paper, in accord with the typical pier structure form of bridge piers in mountainous areas, a nonlinear numerical analysis model is constructed based on a fiber model. The seismic response of different piers under El-Centro is performed using modal pushover analysis (MPA). By comparison with the nonlinear time history analysis method, the applicability of the MPA method for the seismic analysis of different piers is investigated. The results show that the MPA method is not suitable for higher piers where the contribution of higher modes in seismic response is significant. With the implementation of the Western Development Program in recent years, a lot of highways and railways have been planned and built in western China. For bridges with high piers in mountainous areas, a nonlinear numerical analysis model is constructed based on a fiber model. The finite-element analysis is simulated with the code OpenSees, which was developed by Pacific Earthquake Engineering Research (PEER). The Mander model is used to imitate the constitutive model of concrete, and the Giuffré-Menegotto-Pinto model is used to imitate the constitutive model of reinforcement. The incremental dynamic analysis is used to research distribution features of pier section curvature under strong earthquake motions. As a result of the effects of higher modal contributions, the seismic response and seismic performance of bridges with high piers are complicated. The forming and development of a plastic range in the upper position of a pier, the damage process, and the failure mechanism of high piers under different earthquake motions are studied. The base section curvature of high piers and its top displacement are not simultaneous; it is inappropriate for pier top displacement to be used as the performance index. By taking pier section curvature as the performance index, seismic performance characteristics of bridges with high piers in the plastic stage are discussed; the complexity of the seismic performance of bridges with high piers because of the contribution from higher modes is revealed further. The spectral characteristics of ground motion have a great influence on the seismic performance of bridges with high piers. This paper studies six earthquake waves from the PEER database that are class II sites. Because of space constraints, this study involves only the seismic performance of bridges with high piers under transversal earthquake action. After a careful analysis, it is discovered that one pier base section curvature is greater than any other piers when all the piers are plastic; the location of the most dangerous pier depends on the magnitude of the contributions from higher modes. Unlike bridges with low piers, sometimes the damage of higher piers could be more serious than that of lower piers for bridges with high piers. The envelopes of section curvature above the pier base plastic region do not have a linear trend; the occurrence of plastic hinges at the middle and upper parts of piers is attributed to the contribution of higher modal shape. Additionally, the extent and the size of this plastic region are affected by the spectral characteristics of the ground motion. Because of the contribution from higher modes, the bridge with high piers is not safe when designed according to the existing specifications.

Abstract:In this paper,the core idea behind seismic performance-based design is first introduced.Based on a seismic damage survey of retaining walls,the research necessities of seismic performance-based design for gravity retaining walls in high seismic intensity areas are explained. For establishing a framework for seismic performance-based design methods,key technical problems of current specifications and seismic performance-based design methods are summarized.According to large-scale shaking table tests of retaining walls,conclusions about which displacement index can be used as a measure of the seismic performance of retaining walls are presented,along with the criteria and flows of seismic performance-based design methods.Through comparisons between seismic performance-based design methods and specifications of retaining wall examples,the advantages of seismic performance-based design methods are demonstrated.Finally,engineering application suggestions for seismic performance-based design of gravity retaining walls in high seismic intensity areas are proposed.

Abstract:This study employed the convolutional differentiator seismic simulation method constructed using Forsyte polynomials to simulate the seismic wave propagation in a complex heterogeneous media and compared the simulation results to those obtained from the pseudo-spectral method.By comparing the computational time of the pseudo-spectral and convolutional differentiator methods,it was found that the computing time of the convolutional differentiator method is always less than that of pseudo-spectral method when the same computing environment is employed.Consequently,the convolutional differentiator seismic simulation method has an advantage in this regard.By comparing the snapshots obtained using the above mentioned methods,it was found that the dispersion of the snapshots by the convolutional differentiator is similar to that obtained by the pseudo-spectral method,which constituted another advantage for the convolutional differentiator method for seismic wave numerical simulation.Overall,the convolutional differentiator method is a viable alternative for seismic wave propagation simulation.

Abstract:The efficient frequency-wave number code could synthesize high-frequency (10 Hz) regional seismograms (up to a distance of more than 1 000 km) in a medium consisting of a large number of crustal layers,and investigate the effects of regional wave guides on Lg-waves.Lg-waves contain source information and the effect of the near-source structure.The scattering of explosion-generated Rg into S appears to be the primary contributor to the low-frequency Lg from nuclear explosive devices.For three typical crustal models,the synthetic seismograms calculated for EXP and Spall sources show that the generation mechanism of Lg-waves can be explained by a compensated linear-vector dipole source.If the velocity structure is well known,then the Lg-waveform can be synthesized,so we can compare the theoretical Lg-wave's spectrum with the observation's spectrum,and the results can not only be used to estimate the depth of the underground explosion equipment but also a discriminant. A deep understanding of the mechanism of the generation of Lg-waves can help us to create a new discriminant.

Abstract:There are vast territorial and crisscrossing rivers in China.During thousands of years,the Chinese people have built hundreds of thousands of bridges.With diverse structures composed of various materials,these bridges,which are treasures of Chinese architecture,represent,to some extent,the history of Chinese culture.These ancient bridges,though witnessing extreme weather,have been,and are being,damaged due to construction limitations,long time of loading,and the continuous dynamics of erosion and other natural and human factors.Given this situation,it is critical to protect these ancient bridges with detection technology that does not damage the bridges.For the protection of ancient bridge structures,high precision detection technology that does not damage the detected targets has been an important research topic.To identify damages to ancient bridges with arch-bridge structures,the Shanghai Yingxiang Bridge in the Qingpu District is analyzed in this study.The structural features are analyzed and the deformed part of the structure is determined with the help of a total station device to evaluate the deformation and stress states of the bridge.Furthermore,with the application of micro-motion testing technology,the dynamic characteristic parameter of the structural damage,which includes the intrinsic frequency and vibration mode,is determined.After the analysis of the mode distribution of existing bridges and the observation of mutation of the vibration mode,quantitative evaluation of the structural damage is performed by comparing the deformation features of the structure after locating where the structural damage has occurred.Based on the experimental analysis of this study and considering the structural characteristics and the present situation of the damage,the observation point is set.The location and form of the damage is qualitatively delimited and the three modal distributions of the Yingxiang Bridge are obtained using microtremors.Comparing the three natural frequencies of the numerical results with the microtremor measurements,the significant weaknesses in the whole structure are determined.There is some damage to the Yingxiang Bridge.According to the measurement results,the bridge pier D is damaged most seriously.This indicates that the concrete curing of the middle bridge pier caused the imbalance of stiffness.The Yingxiang Bridge needs reinforcement by concrete,with large amounts in the middle pier of the bridge,to ensure sufficient stiffness to load bearing.In conclusion,microtremor measurements are useful in the detection of damage to ancient arch-bridges.

Abstract:A three dimensional finite model of an X-section cast-in-place concrete pile-soil system is established to simulate wave propagation in a low strain integrity X-section cast-in-place concrete pile (XCC pile).Velocity responses in the time domain at the top of the intact and defective piles are obtained.The velocity response characteristics of the intact pile are analyzed in addition to the velocity response curves of the defective piles.The results reveal that the velocity response at the top of the XCC pile during low strain integrity testing shows serious 3D effects,resulting in the peak value of the incident wave close to the pile center being largest,and the arrival time of the peak value of the incident wave close to the pile center being earliest.The farther a point is from the pile center,the more hysteretic is the peak of the arriving incident wave.The peak value of the incident waves first increases and then reduces from the pile center to the pile boundary.The incident and reflected waves at different points along the ring direction at the top of the intact pile are very similar,but the disturbing waves of different points are not the same.The arrival time of the incident waves in the pile with variable modulus are the same as those in the intact pile,but the arrival time of the peak of the reflection wave at the bottom of the pile with variable modulus is later than that in the intact pile,and the peak value is smaller.The first defective reflected waves at different points along ring direction at the top of the defective XCC pile shows little differences,but the second one shows larger differences.

Abstract:An analysis of the loss of seismic observation equipment in the Jiangsu Province of China since 2009 has revealed three primary reasons for equipment loss related to lightning strikes: (1) Unprotected digital seismic stations. (2) Data line interference from lightning, which is caused by excessive distances between sensors and data collectors. (3) The non-normalized installation of station lines. A summary of basic, yet comprehensive,lightning protection measures, combined with an analysis of actual event occurrences in the Jiangsu Province of China, are presented. These protective measures include: the reformation of the power grid, lightning protection for the distribution systems, lightning protection for signal and communications equipment, and the normalization of wiring plans. If seismic observation equipment and lightning protection equipment are to be connected in series, the background seismic noise and the calibration parameters must be checked. When selecting data for the calculation of background seismic noise, the following two points should be taken into consideration: (1) The data should be chosen from 00:00 to 01:00 every day, when the influence of human activity is minimized. (2) The data must contain no seismic event; otherwise, data should be chosen from the next hourly interval. Liyang Station is presented as a case study of the implementation of lightning protection system for a seismic station. Data from one month prior to the installation of the lightning protection system, one month during the operation of the lightning protection system, and one month during the following thunderstorm season are presented. This case study includes the calculation of the background seismic noise and the calibration parameters before and after the lightning protection system installation, and determines the actual influence of the lightning protection system on the quality of collected seismic data. An innovative installation scheme for decoupling devices, a first for the protection of seismic systems from lightning, is discussed.

Abstract:Crustal deformation observation stations built near the surface cannot avoid distractions that include information from the Earth's interior and exterior.Identifying earthquake precursors and other distraction factors is currently difficult.The regression method is a mathematical model for quantitatively deducting distraction factors.However,a mathematical model cannot describe the change in tendency during different stages when building a regression model.Subsection regression was used to divide data into sections to assist in the use of a mathematical model to conduct regression analysis.The dividing point of the regression model was the turning point for the change in tendency of deformation data.The selection of this dividing point can influence model quality.This study used ground tilt observation data from horizontal pendulums at the Jinghe and Korla stations as the dependent variable and meteorological factors as the independent variable.The tendency change of deformation data was divided into several parts and correlation coefficients were calculated.Scatter diagrams were created to test the results with the model.The results indicated that air and ground temperature were the main distractions for the fixed-point deformation of the horizontal pendulums at the Jinghe and Korla stations.The relationship between meteorological factors and deformation data strengthened existing knowledge regarding deformation observations.The linear correlation of meteorological factors and deformation data was strengthened after deducting the change in tendency.Therefore,the change in tendency may have been caused by regional stress changes according to the study on deformation data from the Sichuan-Yunnan rhombic block and the anomalies observed before the Xinyuan,Hejing earthquake of M_S6.6 in Xinjiang by Sun Yi and Wang Zai-hua.Subsection regression may be the most efficient method to reduce data processing difficulty because it improves performance of the regression method.

Abstract:The conventional transition zone in three-dimensional (3D) operational design is made by splitting the operational area into two parts (land and ocean) in accordance with the basic parameters of the contract after scouting the practical water depth,obstacles,and terrain.Then the acquisition can be made according to two kinds of geometry.of course,the kinds of sources are different due to water depth and land terrains;there are different guns,explosives,and vibroseis.During the period of design,the design of offset points is finished by using professional software,such as green mountain or KLseis.When acquisition is completed, the offset point's optimization is made.There are three problems in the actual operation.Firstly,the progress of the project is limited to permit progress,and permits are very difficult to get in some places,which affect the production schedule.Secondly,the design period is longer due to the conventional design methods.Thirdly,for the complex region,the late offset point optimization makes it very difficult to meet the requirements of the original design,which results in void or invalid shots and affects the economic benefits.Because of these problems,it is urgent to find a method to make design flexible and fast.This design can reduce the design period,improve the design efficiency,and meet the requirement of uniform fold to the maximum extent in the process of optimization design.It is even more important in complex transition zone 3D seismic exploration projects.Our operational designs include ocean geometry,land geometry,sub-swath,and offset point designs.It is vital for the optimization of the operation design method to improve the seismic data acquisition efficiency,ensure the data quality,reduce duplication of shooting,and realize a seamless connection of the data.This requires that the technician designs special micro-geometry and optimizes shot layout in view of project characteristics to meet the needs of maximum uniform fold.This paper presents an automatic optimization design method,that is to say,using a program to optimize reduces the manual errors,makes the acquisition results realize design requirements,and then improves the efficiency.This paper provides a detailed example and gives the detailed flows of design and offset point optimization.Application of automatic optimization design in complex 3D transition zone projects has the following advantages:(1) Flexible application of micro-design or sub-swath design can deal with the relationship between the production schedules and operational efficiency very well.(2)Application of offset point optimization design can effectively reduce void shots,invalid shots,and duplicated shots,which will effectively decrease production costs,shorten the design period,and improve production efficiency.(3)According to the principle of the offset point optimization design,combined with information about the water depth and other obstacles,land and ocean acquisition geometries can be divided,the excitation region can also be easily achieved,and the excitation sources include vibroseis,explosives,and different kinds of air guns.(4)The coordinates of obstacles which the survey department provides can be directly used to offset optimization design,which significantly simplifies the computation steps and saves design time.(5)Automatic optimization design and its flow that the paper gives provide a basis for complex transition zone operations.

Abstract:The Guohe River fault originates from Bozhou,Anhui Province,passing through Guoyang to Mengcheng.According to regional geological inspection,this fault has an exclusive anomaly in gravity and magnetic aspect.In the light of being a hidden fault and thick upper crust,there are few investigations about it,and they tend to be more concerned about gravity and magnetic observations,remote sensing,and historical documents.Therefore,deep geophysical inspection is increasingly important to figure out its characteristics.In order to determine the horizontal location and feature of the Guohe River fault,both the gravity profile and IP sounding method are implemented in the research area's geophysical prospecting.The gravity profile is mainly based on the gravity anomaly,generally caused by density differences,which often indicates the existence of faults. It is easily operated,highly efficient,and low cost.In this paper,57 gravity points have been observed to detect the potential gravity anomaly in a relatively bigger area to narrow down the inspected region for the IP sounding method.During research,the gravity profile had a length of 4 500 m,in a northeast direction,crossing over Guohe River to the north,about 13 km away from Mengcheng county.Results show that gravity profile value has a very obvious decline between the 54^th and 55^th observing points with an amplitude of 1.0 × 10⁵ m·s²,which could be possibly due to the surface elevation difference of 3 m.In any case,the values of the gravity profile increase from southwest to northeast,in the same direction of the Guohe River fault.Aside from the non-background gravity anomaly,there possibly exists a geological anomaly 500 m underground which has density differences that result in the gravity anomaly,located between the 49^th and 53^rd observing points,which could be the result of Guohe River fault.on the basis of this conclusion,the IP sounding method,which is based on the resistivity and polarizability change of the rock underground,is applied in this gravity-anomaly area.During the research,the symmetry quadrupole vertical sounding method is utilized,beginning at the 42^nd gravity observing point and continuing for 1 600 m and 14 acquisition points.When it comes to data processing,the apparent resisitivity and apparent polarizability are considered to be the main parameters for this method.As for the apparent resistivity profile,there lies a tiny contour lift,about 300~500 m deep.This potentially indicates that the Guohe River fault lies at this location.Similarly,at about the same position underground,the contour shows a relatively high anomaly with apparent polarizability over 1.5%,which normally is the effect of a fault or faults or geological structures that contain water.Furthermore,it appears that the potential hidden fault is a normal fault,which lies almost vertically underground.Overall,both the gravity profile and the induced polarized method clearly detect the geophysical anomaly very close to where the fault lies.These two methods verify each other,both having anomalies that agree with the geophysical characteristics of the Guohe River fault.As a conclusion,joint exploration using both the gravity profile and IP sounding method is an effective approach for inspecting faults to detect the plane position and approximate cover depth underground.