Abstract:A full-size nonlinear numerical model for a track-subgrade-foundation coupled system was established in this paper. In the model, the nonlinear stress-strain relationship for soil material, influence of static stress state after subgrade construction on subsequent dynamic computation, and dynamic interaction between reinforced concrete base and upper layer of formation were considered, the construction process of a track-subgrade system was simulated. Results show that a more reasonable spatial vibration response of rails can be obtained by using a solid element to simulate the rail than using beam element. Vertical dynamic displacements at the bottom of each layer of subgrade simultaneously vary with time and space. In transverse direction of the subgrade, the maximum vertical dynamic displacement at different moments within the width range of track slab is about 0.04 mm, and can be regarded as uniformly distributed. Distributions of vertical dynamic displacement along the depth at different times are similar, and the maximum value is about 0.8 mm according to the exponential function attenuation, less than the standard of 3.5 mm allowed in Chinese high-speed railway. In the longitudinal direction of the railway, the locations of peak value of vertical dynamic displacement correspond to the spatial location of applied moving loads. Distribution patterns of vertical dynamic displacement at the same depth are similar at different times. Overlap effects induced by adjacent loads corresponding to the front and rear wheelset on the same bogie are noticeable above the bottom of the lower layer of formation.

Abstract:To analyze the deformation of concrete-filled steel tubular piers of bicycle bridges under different impact forces in Xiamen City, Fujian Province, 20 impact loads corresponding to different impact velocities of 40, 60, 80, 100, and 120 kN/h, from cars, light vehicles, medium vehicles, and heavy vehicles were calculated based on AASHTO code design formulas in America. A three-dimensional model of a bicycle viaduct is established using SAP2000 finite-element software. The results show that the pier is still in an elastic state when it is subjected to the impact load of a car and light truck. Under the impact of a medium-size truck with velocity ≥ 100 km/h or that of a heavy truck with velocity=100 km/h, the pier enters the plastic state and the maximum plastic rotation angle is 0.28E-3 rad and 0.64E-3 rad, respectively, but the overall plastic deformation is within the controllable range. When a heavy truck impacts with 120 km/h, the pier will enter the plastic stage in a large range, and this will probably directly affect the normal service function of the bridge.

Abstract:As a lifeline project in transportation systems, the seismic performance of bridges is particularly important. Seismic isolation technology is mainly used to reduce structural seismic damages through seismic isolation devices, and it has become an important measure to improve the seismic capacity of bridges in strong earthquake areas. To promote the further development of seismic isolation technology in the field of bridge engineering in China, first, the design methods of seismic isolation bridges are summarized; the seismic response and damage of seismic isolation bridges are generalized; and the studies on the nonlinear dynamic performance, seismic isolation effect, seismic random response, vulnerability, and performance optimization methods of bridges with different seismic isolation devices are examined. Second, the application and research progress of seismic isolation technology in skewed bridges, curved bridges, and railway bridges are outlined. According to the relevant research results of the seismic performance of bridges, the application and development prospects of the new post-earthquake resilience design concept in the field of bridge engineering are introduced. Finally, the experimental research on the seismic isolation bridge is summarized, and the shortages and development tendencies of existing seismically isolated bridges are pointed out.

Abstract:To study the influence of the beam between pylons on the static and dynamic characteristics of cable-stayed bridges without backstays, taking a bridge without backstays as an example, four finite element models are set up to analyze the static and dynamic structural characteristics and seismic response of solid beams, big hollow beams, small hollow beams, and the structure without beams with the three-dimensional static and dynamic finite element method. The static calculation results show that in the four schemes, the cable tension of structure with solid beam under the most unfavorable load reaches the safety factor critical value. Moreover, the deflection of the main beam and the longitudinal deformation of the main tower decrease as the weight of the pylon beam increases. The shrinkage creep deformation value of the pylon without beams under long-term load deviates from the main span. The dynamic calculation results show that for the second scheme, the axial force and transverse bending moment value of the tower bottom are the largest. The transverse shear force is the largest for the fourth scheme, and the stiffness of the structure without beams is small, which makes the pylon prone to transverse instability. Considering the static and dynamic analysis results, construction convenience, and the maintenance of structures, it is suggested that the solid beam tower be used in the structure.

Abstract:To strengthen the bottom two stories of a multistory masonry frame structure, it is necessary to study its seismic deformation performance. Taking a masonry building with a bottom two-story frame and an upper four-story frame as the object, a finite element calculation model was constructed with finite element software STRAND7. Considering the horizontal and vertical loads, the seismic deformation performance of the two-story frame at the bottom of the multistory masonry building was analyzed. Simulation results showed that the vibration mode of the building structure was significantly affected by the lateral floor stiffness. The changes of the first mode frequency in the X direction and second mode frequency in the Y direction were the fastest, and the bending frequency in the floor plane changed the slowest. The whole structure showed a linear shear deformation in the X direction and a flexure-shear deformation in the Y direction, due to the filled wall in the Y direction assuming the function of seismic wall. Deformation of the bottom two-story frame was small; under the influence of a 7-degree earthquake, deformation of the second story of the bottom two-story structure was more serious than that of the first story, and the two-story frame structure at the bottom of the multistory masonry house was in an elastic working state.

Abstract:The current method of evaluating the flexural strengthening performance of reinforced concrete beams does not consider the difference in the disaster resistance of different buildings; thus, the bearing capacity parameters obtained are not objective enough, and as a result, the evaluation results are different from the actual test results and the evaluation accuracy is low. Considering the above, a method based on damage-reduction mode is proposed for evaluating the flexural strengthening performance of reinforced concrete beams. The initial tensile strain at the bottom of the beam, the ultimate bending capacity of the normal section of the beam, and the load deflection of the normal section of the reinforced concrete beam are calculated, and the flexural strengthening of the reinforced concrete beam is simulated based on the damage-reduction mode. Then the parameters of the bearing capacity of reinforced concrete beams after flexural strengthening are obtained and inputted to general program ANSYS; then, the flexural strengthening performance of reinforced concrete beams is evaluated using the program. The simulation results show that the flexural strengthening performance of reinforced concrete beams with damage-reduction elements is significantly improved. Moreover, the evaluation results of this method are basically consistent with the actual evaluation results from experiment, and the evaluation accuracy is high.

Abstract:In view of the low fitting degree between actual and predicted values in the current methods of predicting the post-earthquake survival probability of reinforced concrete frame structures, a prediction method based on the finite element is proposed. Numerical analysis of the constitutive model of reinforced concrete frame materials was carried out using the correlation value of the concrete constitutive model and numerical calculation of the reinforcement constitutive model. The finite element simulation of reinforced concrete was realized by combining building and construction drawings. Maximum vertical load of the finite element model of the reinforced concrete frame was taken as the vertical ultimate bearing capacity of the whole structure. The random Pushdown method and the random vertical IDA methods were then introduced to obtain the survival probability of a reinforced concrete frame after an earthquake. Experiments showed that it is feasible to apply the finite element to prediction of the survival probability of reinforced concrete frame structures after an earthquake. The fitting degree between the predicted value and the actual value is higher than in the current method. Performance of the proposed method was perfect, providing a basis for further development of this field.

Abstract:Seismic shear force response of super high-rise structures, calculated by the mode-superposition response spectrum method, cannot meet the requirements of the minimum shear force coefficient in code. Therefore, the concept and adjustment method of minimum shear force coefficient were sketched in this paper. Two models with different shear force coefficients were then adopted to analyze their differences in structural elasticity and elasto-plastic seismic response, and discuss the influence of shear coefficient on the seismic response of super-tall buildings. Finally, the minimum shear force coefficient of the two models was adjusted to satisfy code requirements through strength and stiffness adjustment methods; rationality of the structural response induced by different methods was then analyzed. Results demonstrated that, compared with the structure without a specified minimum shear force coefficient, the elastic base shear force of the structure with a specified minimum shear force coefficient was larger, and story drift ratio and elasto-plastic displacement responses were smaller, i.e., the safety of the structures was enhanced. The elastic overturning moment demand and elasto-plastic base shear values of the two models, adjusted by the stiffness adjustment method, were greater than those adjusted by the strength adjustment method. Using the two methods, the maximum vertex displacement and story drift ratio were similar, although there was an abnormal situation wherein the story drift ratio changed with stiffness. In terms of meeting seismic requirements, stress condition of the components was superior and the component cross-section more reasonable and economical by using the strength adjustment method.

Abstract:Research into numerical simulation methods of the seismic performance of steel grid structures based on a Revit platform design building model has important applicative value for improving the seismic performance and safety of steel grid structures. Based on the location of elevation and axle net, this method designs the steel grid structure components, then determines the general framework of the building model of an actual steel grid structure through the Revit software platform. It realizes the constraint between the members and the beams of the building model through binding restraint, and the constraint between concrete and steel section through contact restraint. It adopts the displacement-controlled loading method to carry out the axial and reciprocating loads on the pole top of the building model and along the beam and axis directions, and uses TurnTool virtual simulation software to simulate the seismic behavior of the steel grid structure. Results of an application of this method showed that the change of load and displacement of the steel grid structure under low cyclic reciprocating load was relatively stable. In the plastic stage, under low cyclic reciprocating load, the longitudinal tie bar of the structure had a restraining effect on the concrete. The smaller the spacing was between members, the better was the ductility of the structure. The longitudinal tie bar improved the force behavior of the sample steel grid structure. The seismic simulation results of the designed model were highly accurate.

Abstract:To investigate the effect of damage accumulation on the seismic behavior of steel-reinforced high-strength concrete (SRHSC) frame joints under earthquake, five groups of SRHSC frame joints under low cyclic loading tests were studied, and the damage accumulation process and its effects on the stiffness and strength of the frame joints were analyzed. This study begins with the modeling of material damage. First, the unilateral effect of the concrete under a cyclic load is considered by introducing the stiffness influence coefficient, and then the Faria-Oliver constitutive model is improved to establish a material damage cumulative constitutive model adapted to the steel-reinforced concrete structure. Based on the material damage constitutive model, a refined numerical analysis model was established for seismic SRHSC frame joints using ANSYS. Compared with the hysteretic curves of SRHSC frame joints under low cyclic loading, the results show that the cumulative damage model can reflect the damage characteristics of SRHSC frame joints under seismic loading. The influences of the parameters of axial compression ratio, stirrup ratio, and steel ratio on the seismic behavior of SRHSC frame joints were further analyzed. The research results can provide theoretical and technical references for the study of the cumulative damage of similar SRHSC frame joints under earthquake.

Abstract:To study the seismic resistance of the concrete structure of multi-story hollow block houses, seismic tests were carried out on the concrete structure of a model six-story hollow block house, scaled 1:5. Model parameters were selected according to actual prototype parameters and requirements of the similarity theory, and horizontal and vertical loads were applied by an electro-hydraulic servo loading device and hydraulic jack. A dynamic characteristic test, seismic response analysis, structural maximum seismic response, and displacement response analysis were carried out. Results showed that, with increasing degree of damage, the natural frequency of the model structure increased while damping ratio decreased. Seismic effect on the multi-story hollow block building model with core column was strong. Under strong earthquakes, dynamic characteristics of the structure changed greatly, and the failure layer displayed the maximum response of the building structure. When the acceleration was 125 cm/s, the maximum displacement of the structure was 2.73 mm, lower than the standard value, indicating that the model structure had certain ductility.

Abstract:In this paper, the shear pin and shock absorber of a double-spherical surface seismic isolation bearing with the same spherical directions were examined. Both influencing factors and rules of shear pin and shock absorber mechanical parameters of the bearing were studied. Using the response spectrum analysis method, effect on the shearing force of the shear pin is discussed by varying pier height and site category. In addition, the influence of geometric parameters on the mechanical properties of the shock absorber are discussed by FEM analysis. Stress and strain distribution of the shock absorber subjected to yield load and ultimate load were also analyzed. Results showed that the shearing force of the shear pin was greatly influenced by pier height and site category. Mechanical properties of the shock absorber were mainly controlled by three geometric parameters, d₀, L₁, and L. The influence law of geometric parameters on the mechanical properties of the shock absorber described in this paper can provide a reference for the preliminary setting of the mechanical parameters of the shock absorber.

Abstract:The dynamic characteristics of a twin-tower asymmetric single-side mixed girder cable-stayed bridge with a main span of 820 meters were analyzed. First, we calculated the seismic response of the bridge under multi-point excitation with the relative motion method to analyze the influence of a traveling wave effect on the dynamic response of some key points, i.e., the tower top, main girder, and the tower bottom. At the same time, we compared and analyzed the dynamic responses under different incident angles. Results showed that, compared with the results of uniform excitation analysis, under multi-point excitation, the internal force of the main tower was smaller, but that of the main girder was larger. Earthquake excitation with different incident angles also had a great influence on the internal force of the cable-stayed bridge, which made the internal force increase (or decrease) up to 20%. Therefore, in the design of this type of asymmetrical hybrid beam cable-stayed bridge, the influences of non-uniform excitation and input direction of ground motions should be considered.

Abstract:On June 17, 2019, an M_S6.0 earthquake occurred in Changning County, Yibin City, Sichuan Province (28.34°N, 104.90°E), China, followed by aftershocks.Seismic observation data from the regional seismic network were used to calculate the focal mechanism solutions of 14 M_S>3.0 earthquakes in the range of 28°-29°N, 104°-105°E, based on the CAP method.Combined with data from 27 focal mechanism solutions of the study area from previous research results, the stress field of the study area was inverted using MSATSI software.After gridding the study area as 0.1°×0.1°, the distribution of 25 stress fields was obtained.Most of the stress fields were stable.The fault type of the mainshock was mainly a thrust earthquake according to the stress grid where the mainshock was located.Results of this paper can provide a reliable reference for seismogenic mechanisms, active structure, and the determination of seismic tendencies in the Changning area of Sichuan Province.

Abstract:The existence of outgoing long-wave radiation anomalies before great earthquakes has been confirmed many times. To further analyze abnormal changes in long-wave radiation before strong earthquakes, determination indeces of long-wave radiation anomalies were extracted. Based on outgoing long-wave radiation (OLR) data from geostationary satellite data, the wavelet transform and power spectrum estimation were applied to analyze the OLR anomalies from several strong earthquakes in Mainland China. Results indicated that the anomalous amplitude of OLR increased to different degrees within three months of six strong earthquakes. Results were consistent with those of previous earthquake cases. Anomalies in the epicenter and surrounding area presented the normal process of "start, enhance, maximum, weaken, and disappear." When the anomaly reached its maximum value, areas with anomalies >1×standard deviation of the annual average value reached tens of thousands to hundreds of thousands km². Amplitudes of relative power spectra were >10×standard deviation. In addition, amplitudes of relative power spectra in the epicenter and vicinity were >1×standard deviation from the annual average value in a period of 40~75 days. The anomalies characteristic of these strong earthquakes were indicative of short-term predictions.

Abstract:Water tube tiltmeters can clearly record information from long-period solid earth tides. However, because its natural period is long, it cannot respond to short-period tilt deformation, leading to the missing of short-term anomalous information. In this paper, the natural period of the instrument was reduced and the observation frequency band was expanded through mechanical structure optimization. Through use of sensors with higher precision and amplifier circuit, the signal-to-noise ratio of the instrument was improved, and normal observation of solid earth tide was ensured. By chitinous contrast observation, the difference in observation data after expansion of the frequency band was analyzed.

Abstract:In this paper, the Yellow River terraces T₀, T₁, T₂, T₃, and T₄ in Lanzhou basin, which are related to the distribution of construction projects, were divided on the basis of existing data, and 201 models of soil layers for seismic response were established. Surface ground motion parameters of the deposit terrace in Lanzhou basin, with 10% probability of exceedance in 50 years, were obtained. The correlation between the deposit terraces and the seismic ground motion parameters, such as peak acceleration A_m and the characteristic period T_g of acceleration response spectrum, were analyzed. Results showed that the overburden thickness of terrace from T₀ to T₂ was positively correlated with the peak acceleration A_m with 10% probability of exceedance in 50 years. The overburden thickness of T₃ terrace and above had a significant decreasing effect on the increase of A_m. T_g value increased with increasing overburden thickness of the terrace from T₀ to T₃, but no longer increased synchronously when the overburden thickness increased to a certain extent, indicating that the influence of overburden thickness of the terrace on T_g was limited. There was no relationship between elevation of terraces and surface ground motion parameters with 10% probability of exceedance in 50 years.

Abstract:The Ninghe-Changli fault, with a length of about 170 km, is the demarcation between the Yanshan uplift, the Shanhaiguan uplift, and the Huanghua depression. This paper reprocessed and analyzed the data of four shallow seismic survey lines broken in the past. Shallow tectonic and activity characteristics of the Ninghe-Changli fault were then obtained. To obtain a high-quality seismic exploration time profile, the Vista seismic processing software system was applied, and the true amplitude recovery of the data and surface consistency amplitude compensation method were used. To make clear the activity age of the fault, through the intermediate data during the process, a seismic survey depth profile was obtained. The data of the depth profile were then compared with the stratigraphic sequence data near the survey line to obtain the buried depth of the upper breakpoint and the latest age of fault activity. The shallow seismic exploration profile revealed that the shallow part of the Ninghe-Changli fault consists of a main fault and a secondary fault; the shallow depth of the breakpoint on the Ninghe-Changli fault is 40~100 m. Fault activities showed a segmental character:the activity age of the northern part of the fault is early late Pleistocene, and that of the southern part is middle late Pleistocene. The fracture with the NE-trending is a positive fault, and the fracture with the NW-trending is a strike-slip fault.

Abstract:Drift correction is important since gravity residuals, aside from interference due to instrument and power failure and natural and human factors, are strongly influenced by long-term drift. In this study, continuously observed gravity data from a recent five-year period at Gaotai seismic station were analyzed. Nonlinear drift characteristics of the spring gravimeter, and the rationality of corresponding drift correction using the multinomial polynomial fitting method, are discussed. Results of the relaxation analysis and the mobile gravity observation showed that the linear and nonlinear drift characteristics of the PET gravimeter at Gaotai seismic station were clear. This seriously influenced the extraction of other weak gravity signals. Nonlinear drift correction was carried out under the double constraints of relaxation analysis and mobile gravity observation. The obtained residual gravity was more accurate and reliable. This study can provide a more accurate reference for future earthquake prediction.

Abstract:Using the inversion of gravity anomaly to test three-dimensional seismic wave velocity structures has some drawbacks, e.g., the solution is not unique and the reliability is not high. The surface wave inversion is fully fused to the gravity anomaly inversion equation, which reduces the non-uniqueness of the traditional inversion method and improves its reliability. Taking the Sichuan-Yunnan area as an example, the 3-D seismic velocity structure was analyzed using the fused gravity anomaly inversion method. Through conversion of velocity and density, the corresponding gravity anomaly data was obtained. Because surface wave frequency data were sensitive mainly to seismic shear wave velocity, gravity anomaly data and initial shear wave velocity were connected. According to the relationship between seismic wave velocity and rock density, an inversion equation of the gravity anomaly was obtained to analyze the velocity structure. Active blocks of the Sichuan-Yunnan area, in the range of 21.6°-34.2° N, 97.1°-105.9° E, were selected for experimental data. Through experimental analysis, it was found that the residual values of gravity anomaly data and surface wave frequency data were 6.24 mGal and 0.027 km/s, respectively, and the fitting effect was good. Through analysis of shear wave velocities at different depths in this area, it was found that at the 24-km depth, there are relatively low-velocity layers in the upper crust, and low-velocity layers in the middle and lower crusts at depths of 44 km. Resolution of this method for analyzing the structural solution of three-dimensional seismic wave velocity in the Sichuan-Yunnan region was high.

Abstract:Cross-fault deformation monitoring is an observational technique for the vertical and horizontal monitoring of faults. In this paper, we analyzed rock soil classification of monitoring indicator sites on cross-fault deformation, the classification of surface rock soil, influencing factors on the stability of monitoring indicators, and examples of monitoring indicator sites. Results showed that rock soil classification of monitoring indicator sites needs improvement. Rock soil at monitoring indicator sites was reclassified, and a naming method for monitoring indicators was provided, with the aim of promoting the further development of cross-fault deformation monitoring.

Abstract:To avoid the use of too many field control points in the spatial scale measurement and analysis of active faults using high-altitude remote sensing images, and to reduce the complexity of the measurement process and improve measurement accuracy, a spatial location method using remote sensing images from aerial triangulation is proposed. By accurately expressing the mathematical relationship between the three-dimensional space coordinates of the ground point and the corresponding image point in a planar coordinate system, control points with high overlap rates (high probability) in the active fault area were selected, and other control points were ignored to reduce the demand of field control points. Ground coordinates of control points and coordinates of image points were taken as known values, and orientation parameters, which accurately expressed the geometric rotation relationship of the object side of the satellite images, were taken as the unknown values. According to the error equation of the rational polynomial coefficient model, ground coordinates of the active fault area were determined by taking the least square as the criterion. The main active fracture interpretation marks of the remote sensing images in the positioning area included linear marks, vertical dislocation marks, and horizontal dislocation marks. Activity degree of active faults was divided into three grades:strong, medium, and weak. Experimental results showed that the spatial scale measured by this method was accurate, and interpretation and characterization of the fault morphologies were consistent with the actual scenario.

Abstract:On August 9, 2017, an M_S6.6 earthquake occurred in Jinghe County, Xinjiang, China, and its epicenter was at 44.27°N, 82.89°E. Based on the broadband waveform recorded by the Xinjiang Seismic Network, we used the cut-and-paste method to invert the focal mechanism solutions of the main shock and 14 M_S ≥ 3 aftershocks. Additionally, the stress field in the source area was inverted using MSATSI software. According to the focal mechanism solutions and surrounding geological data, we infer that the seismogenic fault is the eastern segment of the Kusongmuqike piedmont fault, and we identified nodal plane I with a strike of 89°, dip of 43°, and rake of 91ås seismogenic fault plane of the main shock. Of the 14 aftershocks, 11 were the thrust type, one was a normal faulting type, and two were the strike-slip type. The P axis is concentrated in the near N-S direction and has a small inclination angle, whereas the inclination angle of the T axis is large. This indicates that the stress field of the source region is characterized by a nearly N-S horizontal compression. The focal depths of the M_S6.6 earthquake sequence ranged from 12 to 21 km, but were concentrated in the range of 15-20 km; thus, they were slightly shallower than the focal depth (21 km) of the main shock. The inversion result of the stress field in the source area accords with the statistical results of the focal mechanism parameters; thus, both indicate that the source area is mainly controlled by the horizontal stress field in the near N-S direction.

Abstract:Ideal reference sites of the generalized inversion technique (GIT) are not always available. To overcome this limitation, in this article, average site amplification factor, calculated by the quarter wave-length method, and the high-frequency attenuation parameter, obtained from the spectral decay method, were adopted as the empirical reference site (ERS) of the GIT. Rationality of ERS-GIT was verified, through comparison with other methods, based on 615 groups of strong ground motion records of 95 aftershocks of the 2008 Wenchuan M8.0 earthquake, recorded by 28 strong motion stations during May and August 2008. Reasons for the differences among the various methods are discussed. Results showed that the average stress drop, as calculated by the ERS-GIT, classical GIT method, and nonparametric GIT method was 1.15 MPa, 0.78 MPa, and 0.52 MPa, respectively. Quality factors obtained from the results of the ERS-GIT and classical GIT methods were Q(f)=75.02f^1.27 and Q(f)=65.56f^1.22, respectively. Taking the predominant frequency of the site as a boundary, the local site responses calculated by the ERS-GIT coincided with those of the H/V spectral ratio method and classical GIT method at long period and high frequency, respectively.

Abstract:A three-dimensional finite-element model of a pipeline crossing a fault, the pressurized fluid, and the surrounding soil was established using the finite-element software ABAQUS. Pipelines in different faults (strike-slip fault, normal fault, and reverse fault) were simulated under static load and seismic load, and the conditions as regards whether the pipelines were filled with pressurized fluid were compared and analyzed. The deformation behaviors of pipelines with and without pressurized fluid under static load and seismic load were obtained. By comparing the behaviors, the influences of the mass and pressure of the fluid on the pipelines under static load and seismic load were obtained. The results show that the fluid in pipelines improves the deformation resistance of the pipeline under static load; thus, the pipelines are safer; however, under seismic load, the fluid triggers the deformation resistance of the pipeline, and thus, the pipelines are less safe.

Abstract:The large-scale shaking table model test is an important means to study the dynamic response and failure mode of slopes; selection of similar materials is the key to the success of the test. Two types of representative slopes in the loess region were taken as research objects, based on laboratory soil dynamics tests conducted on undisturbed soils of loess landslides. Different mixture ratio methods of similar materials with six different similar ratios are proposed. Parameters of similar materials under the condition of two similar ratios were analyzed by quantitative outline. According to the constraint of similar criteria, an evaluation system for material similarity of soil slopes in large-scale shaking table tests is proposed and then optimized by fuzzy mathematical theory.

Abstract:Based on the effective stress principle of saturated soil, the dynamic interaction model of saturated soil-underground utility tunnel (UUT) system was established by considering the soil as a solid-liquid two-phase medium. During modeling, the Duncan-Chang nonlinear constitutive model was adopted under static condition of geostress balance, and the Davidenkov nonlinear viscoelastic model was adopted under dynamic condition of seismic wave action. Then the dynamic artificial boundary conditions considering the viscoelasticity of saturated soil were used, and the ground motions were transferred to the dynamic loads applied on the nodes of the artificial boundary. The seismic responses of UUT were investigated under different soil materials, different rigidity of the structure, and the soil-structure interaction. The results show the following:(1) The deformation of the structure reaches the maximum when the predominant periods of the site and the earthquake wave are similar; (2) the thinner the UUT wall, the larger the depth, and the greater the structure size; moreover, the larger the structure stiffness, the greater the structure deformation; (3) the deformation of the structure will be enlarged if the state nonlinearity of the interface between soil and structure is neglected.

Abstract:In this study, 123 effective drilling holes in Urumqi, Xinjiang, were selected from 841 drilling holes obtained during 2004-2015. The boreholes were below 30 m and recorded well. Through the calculation of equivalent shear wave velocities at depths of 5-30 m, the regression equation coefficients were separately obtained by linear fitting, square fitting, and cubic fitting. By comparison, it was found that the fitting error of the three equations decreased with the increase of depth, and the error of the cubic term was always less than those of the linear equation and the square equation at the same depth. Therefore, in this paper, the cubic equation is suggested as an empirical formula to estimate the v_S values of boreholes in Urumqi area. By comparing the results with the results of Boore, it is shown that the equivalent shear wave velocity v_S(d) and v_S30 at different depths have regional differences. The research results in this paper can provide references for solving the v_S30 of boreholes with depths less than 30 m in Urumqi, Xinjiang. Finally, the applicability of the three fitting formulas to Karamay is tested using borehole data in Karamay from 2004 to 2015. It is found that the closer the depth is to 30 m, the smaller the error. Moreover, the linear model and the square model are relatively reliable, with an average error close to 0, and the boreholes at depths greater than 10 m are overestimated. The cubic model features a relatively large error and its results are almost underestimated at all depths.

Abstract:In this work, an overall finite element model, considering the nonlinear dynamic interaction of soil-pile-evaluated station structure systems, was established with the software ABAQUS. The transverse seismic performance of an elevated metro station was systematically analyzed, considering the spectral characteristics of input ground motions. Horizontal deformation and the acceleration response of the structure, and the dynamic internal force response at the column bottom were obtained and analyzed. The results showed that the dynamic response of the superstructure of the elevated station was stronger than that of the understructure, especially the maximum shear force and bending moment at the column bottom. Meanwhile, earthquake waves with obvious near-field pulse-like characteristics should more easily enhance the seismic response of the elevated structure.

Abstract:Soft soils have characteristics of high sensitivity and low strength and are easily subject to seismic subsidence during earthquakes. In this study, the nonlinear dynamic finite element analysis of the seismic subsidence response of soft soil site was performed based on the OpenSees numerical simulation method. The results show that the peak acceleration of ground motion has a significant effect on the uneven seismic subsidence of foundation soil. As the peak acceleration of ground motion increases, the amount of seismic subsidence, the impact depth of seismic subsidence, and the damage to the horizontal surface also increase. The characteristics of the ground motion spectrum have an important impact on the soft soil earthquake subsidence. If the predominant frequency of ground motion is similar to the natural frequency of the site, the larger the amplitude, the more serious the seismic subsidence is. Simultaneous input of horizontal and vertical ground motions can better reflect the vibration and seismic subsidence response of the soil. The results have a certain guiding significance for exploring the mechanism of seismic subsidence of soft soils.

Abstract:In this paper, the effects of suction and net confining pressure on the strength deformation of unsaturated loess were studied. The main test methods included the conventional triaxial test and triaxial test under constant suction for saturated undisturbed loess and unsaturated undisturbed loess, respectively. Additionally, the soil-water characteristic curve models were used to analyze the drainage law at the shear stage. The results showed that the volumetric deformation during the consolidation and shear stages for undisturbed soil increases with increasing net confining pressure under constant suction; however, it decreases with increasing suction under constant net confining pressure. The CSL line of saturated soil in the p-q plane gradually exceeds that of the unsaturated soil under low suction because with the increase in p value, the void ratio of saturated soil becomes smaller compared with that of unsaturated soil and the contribution of smaller void ratio to shear strength is gradually greater than that of unsaturated soil. The parameter models proposed by Huang et al. and Hu et al. were obtained and used to predict the moisture content during the shear stage. The influence of shear rate on the change of moisture content is apparent; therefore, the two models are suitable for the condition with a slow shear rate and full drainage. The parameters of the model proposed by Fang et al. were different with different shear rates.

Abstract:To build a liquefaction-induced lateral spread estimation model, the multivariate adaptive regression spline (MARS) method, which can better deal with multidimensional parameters, is used in this paper. Through verification, we found the accuracy and reliability of the model bears examination. In this paper, (1) in the process of localization, PGA was selected as the seismic parameter to replace M and R in present models, and the calculation accuracy was not affected; (2) in modeling with MARS method, the impacts of various parameters were studied, and the main influencing factors under the two conditions of free face and mild slope were screened; (3) two estimation models were built under the two conditions, then tested by the F and t testing method using the liquefaction-induced lateral spread data from Christchurch earthquakes during 2010-2011. The rationality and reliability of the method were proved. Results of this paper can satisfy the demands of disaster prevention and reduction engineering of geotechnical earthquake engineering, and can also provide a theoretical basis for the disaster zoning of liquefaction-induced lateral spread.

Abstract:Landscape is key to protecting the ecological environment. Considering the destructive influence of earthquakes on landscape pattern, it is of great significance to simulate changes in landscape pattern after earthquake action to determine the vulnerability of landscape design. This paper presents research on the change in landscape pattern before and after an earthquake. Studying the Dujiangyan area of Sichuan Province, China, based on remote sensing image, ArcGIS software, and Fragstats landscape calculation software, and indexing landscape unit characteristics and landscape pattern, we analyzed the changes in landscape pattern before and after earthquakes in this area from 2007 to 2008. The study can provide a reference for post-earthquake reconstruction and future landscape regulation in the Dujiangyan area.

Abstract:Earthquakes are one of the most serious of all natural disasters. If a landscape belt is destroyed by an earthquake, regular building structures in the landscape belt will be also changed. Degree-of-damage evaluation of landscape belts is key to urban earthquake avoidance and disaster reduction, so it is of great significance to study degrees-of-damage to regular buildings in the landscape belt. In this paper, a method based in dimensional analysis of earthquake disaster images is used to evaluate the damage degree of landscape belts. According to the earthquake disaster image quality of regular buildings, fragmentation degree was categorized based on the change characteristics of the image dimensions. Optimal threshold was then calculated according to the crushing probability, and the fractional-dimension method was used to extract image dimension features. On this basis, the spatial autocorrelation degree of damaged regular buildings was transformed into a normal distribution curve. A model was then constructed to evaluate the degree-of-damage of the buildings. This case study proved that the method of landscape zone damage degree evaluation, based on dimensional analysis of earthquake disaster images, can be applied to real-life cases.

Abstract:The ecological environment in an earthquake disaster area is complicated, and area restoration is easily affected by related information. Therefore, the ecological environmental restoration process is complex, and the repair effect is not ideal. In this paper, a three-dimensional model for post-earthquake regional ecological environmental restoration based on laser scanning was designed. Raw data of the tailed position of the natural landscape and facility were acquired through three-dimensional laser scanning. The plane characteristic image segmentation method was used to geometrically correct the original data. Whole data correction and matching was then completed. The normal vector was then used to minimize the modified ecological environment data, and splicing and matching information was obtained. According to the matching information, the re-sampling was carried out to construct the three-dimensional grid model and obtain the overall data from the ecological environment after a regional earthquake disaster. Based on the model, the physical area of the terrain brush was constructed to repair the damaged terrain environment after the earthquake disaster. The method was then applied to the restoration of the ecological environment after the earthquake in a certain disaster area. Results proved that the method has use value.

Abstract:To identify deformation and damage to buildings after an earthquake, a remote sensing image recognition and analysis method for deformation detection of earthquake-damaged buildings is proposed. Remote sensing images of earthquake disaster areas were collected by UAV, and the problem of building structure deformation detection was transformed into a problem of coordinate measurement between components. Sample vector points in the collected remote sensing images were extracted and divided into different kinds of regions. On this basis, the images were clustered and segmented to obtain the characteristics of different types of building structures in post-earthquake images, thus identifying the earthquake disaster situation of different sample vector points. Through the experimental analysis, it was found that the proposed image recognition and analysis method can identify the damaged buildings to a certain extent, although further research is needed to improve recognition accuracy.