Abstract:Currently, research on the prediction of earthquake damage to urban buildings is mainly concentrated on aboveground structures. With the development of underground space and the increasing number of underground structures, prediction of earthquake damage to underground structures is attracting increasing attention. This paper systematically introduces the form and mechanism of earthquake damage to underground structures. Then, we summarize the seismic prediction methods typically used for underground structures based on a review of recent research on the prediction of earthquake damage to underground structures. These methods include the investigation and statistical analysis of earthquake damage, numerical simulation, the shaking table test, and probability analysis. An analysis of the typical applications of these methods and their advantages and disadvantages is presented. This paper can provide support and serve as a reference for future research on the prediction of earthquake damage to underground structures.

Abstract:Time-delay compensation is an important problem in the real-time hybrid seismic testing of buildings. In this paper, research on time-delay compensation methods are summarized and these methods are divided into time-based displacement prediction, displacement prediction based on the feedback force, methods based on loading system model inversion, methods based on control theory, and comprehensive compensation methods based on concept integration. All of these methods are introduced and described.

Abstract:To study the characteristics of the probability-density evolution of the nonlinear responses of base-isolated structures under different design parameters, we used a two-particle model to simulate a base-isolated structure. We then used the Bouc-Wen model and the Bouc-Wen model of stiffness degradation to describe the nonlinear characteristics of the isolation layer and the superstructure, respectively. Based on the probability-density-evolution theory, we analyzed the nonlinear random seismic responses of base-isolated structures. Using a random-ground-motion model to generate artificial ground motion, we propose basic steps for analyzing the probability-density evolution of the nonlinear random seismic response of base-isolated structures. By changing the design parameters of the base-isolated structure and considering the randomness of the excitation, we investigated the probability-density-evolution law of its nonlinear random seismic response. The results show that displacements of base-isolated structures can be controlled if the damping ratio, period ratio, and ratio of yield to weight are in a reasonable range.

Abstract:In this study, we used a displacement-based seismic design method to test the seismic performance of a new type of unbonded prestressed prefabricated concrete beam-column frame joint and to investigate the overall seismic design of an unbonded prestressed prefabricated reinforced-concrete-frame structure with new beam-column joints. First, we used sap2000 finite element software to design a prestressed three-dimensional structure and establish a corresponding finite element model. In addition, we established a model of the beam restoring force of the beam-column joint to determine its constitutive relation to the self-defined plastic hinge. We then performed a pushover analysis to characterize the seismic performance of the structure and compared it with the corresponding performance level requirements under different target displacements. Based on the results of the elastic-plastic pushover analysis of the structure with uniform load in the Y direction, we analyze and discuss the story drift ratio and failure mechanism of the structure. The results show that according to a design featuring "good function," "life safety," and "prevention of collapse," the expected results are achieved and the story drift ratio and weak-story performance can meet the corresponding code requirements. Three seismic waves are selected to analyze the elastic-plastic dynamic time history of the structure, the results of which indicate that the structure fabricated using the new beam-column joint can meet the relevant requirements regarding seismic performance in the displacement-based seismic design.

Abstract:In this study, we analyzed the performance-based fragility of a typical 20-story reinforced-concrete frame-shear wall structure. First, the appropriate ground motion records were obtained and the amplitude was adjusted in step lengths of 0.2g. We then established 300 structure-ground motion sample spaces and determined the structural damage indexes and performance parameters. The incremental dynamic analysis method was used to calculate the structural seismic response. To study the uncertainty of the structural response, as the ground motion parameter, we used the acceleration response spectrum of the fundamental period and then analyzed the relationship between the structural seismic demand and the ground motion. On this basis, we established the fragility curve of the structure based on the acceleration response spectrum for the analysis and evaluation of its structural fragility. The results showed that with increases in the ground motion intensity, the IDA curve changes from a monotonic increase to a non-monotonic increase. The IDA curves (16%, 50%, and 84%) can be used to accurately measure the performance of the structure. The frame-shear structure was found to perform well under earthquake. With increases in the seismic intensity, the growth rate of the exceedance probability differs.

Abstract:With an actual skewed continuous rigid-frame highway bridge in the western US chosen as the research object, this paper investigated the impact of differences in the vulnerability of unequal height piers and the skew angle on the seismic fragility of piers. The model sample database was generated using 100 ground motions inputted in the longitudinal direction of the bridge considering the uncertainties of structural parameters and ground motion. Then, with peak ground acceleration taken as the intensity measure, the seismic responses of each pier were obtained via nonlinear time history analysis using OpenSees. The curvature ductility ratio of piers was defined to measure the damage state of the bridge. After the pier damage indexes were derived, seismic fragility curves of piers were obtained with reliability theory, and the damage modes and characteristics of piers were judged. On this basis, fragility analysis was performed by changing the skew angle, and the impact of this change on the seismic fragility of piers was obtained. This study found that the damage probability of the shortest pier was greater than that of the other piers, and the top and the bottom of piers first entered the plastic stage. The seismic responses of bridge were influenced significantly by skew angle, and the damage sequence of each pier was related to the characteristics of the bridge structure. The fragility of two-side pier columns at the same bent pier was opposite the variation trend of the skew angle; serious damage corresponded to an obvious trend. The skewed rigid-frame bridge with unequal height was weak in the shortest pier. Moreover, as the skew angle increases, the damage of the short pier at an obtuse angle should be given more attention and enhanced design criteria should be developed, especially for the seismic design of skewed rigid-frame bridges.

Abstract:Given that the vulnerability evaluation of bridges is indispensable for traffic hazard assessment, it is of practical significance to study the seismic vulnerability of bridges. Aiming to improve the accuracy of the current seismic vulnerability analysis methods of bridges, this study proposes a seismic vulnerability assessment model of reinforced concrete bridges based on fuzzy evaluation. The uncertain parameters in the bridge evaluation process are analyzed from the aspects of the bridge structure level, material level, and boundary layer. Based on the analysis results, considering that bridge loss is a relatively fuzzy concept, the fuzzy evaluation method in fuzzy mathematics is introduced to evaluate the seismic vulnerability of bridges. The damage analysis of bridge supports under displacement, the damage analysis of piers under energy, and the overall damage analysis of bridge structures under a certain period are combined. Then a multi-level fuzzy vulnerability assessment model is constructed. The experimental results show that in the longitudinal direction, only slight damage occurs, and the probability of slight damage in this direction is small. In the transverse direction, the probability of slight damage is higher, and moderate damage may even occur. Under earthquake action, the bridge damage is mainly slight failure and moderate failure, and the probability of serious damage is very small.

Abstract:In this paper, we use two-dimensional numerical analysis to study the importance of establishing a reasonable damping matrix in the seismic response analysis of high-gravity dams in the time domain. First, we selected four high-gravity dams of different heights as examples and determined their seismic responses under horizontal excitation by three seismic waves using six different damping matrices. Then, the reasonability of the different damping matrices was assessed by comparing their solutions in the frequency domain. The results indicate that the seismic response in the time domain of a gravity dam with a height greater than 250 m is a dynamic analysis problem of a long-period system, and attention should be paid to the approach used to model the damping matrix. In this case, we suggest using a Rayleigh damping matrix with two frequency parameters rather than a mass-proportional damping matrix or a stiffness-proportional damping matrix with one frequency parameter. To accurately analyze the seismic responses of a dam, both the fundamental frequency of the dam and the frequency characteristics of the input seismic wave should be considered.

Abstract:The use of different Rayleigh damping coefficients in the seismic response analyses of large quayside container cranes will generate very different results. By taking into account factors such as the boundary constraints of the container cranes, with reference to the method commonly used in engineering for calculating Rayleigh damping coefficients, we improve the method for calculating the damping coefficient and the frequency selection method for container crane structures based on a comparative analysis of similar model-test data and simulation results. Using the simulation method and shaking table tests, we compare and analyze the dynamic responses of the container crane structure under different Rayleigh damping coefficients. The results show that the influence of the methods used to calculate the Rayleigh damping coefficient and to select the frequency on the seismic response of the container crane structure increases with increases in the strength of the earthquake. When the peak acceleration is 0.4g or 0.62g, the average error between the simulation result and the test value obtained by the existing damping-coefficient calculation method exceeds 20%, whereas the error between them is within 10% when using the improved damping-coefficient calculation method.

Abstract:This study explored the damage sequence of key components (pylon, support, foundation, and pier) of long-span three-pylon cable-stayed bridges with super-high piers in mountainous areas under earthquake action. The under-construction Pingtang major bridge in Guizhou province was taken as the case study. First, the spatial finite element model was established based on OPEENSEES software. Then, the seismic vulnerability model of cable-stayed bridges was established based on the probability theory. Finally, incremental dynamic analysis was carried out with concrete strain and relative displacement of support as vulnerability indicators. The vulnerability curves of components were obtained, and the failure order of components of this type of bridge was analyzed. The results showed that transverse earthquakes will cause more damage to the cable-stayed bridge than longitudinal earthquakes; the middle tower bearing and the side tower foundation in the bridge structure are most vulnerable to damage under longitudinal earthquakes; and the side tower bearing and the transition pier foundation in the bridge structure are most vulnerable to damage under transverse earthquakes.

Abstract:To study the earthquake damage evolution rule of the beam-column joint in traditional-style buildings with viscous damper under dynamic cyclic loading, a dynamic loading test was carried out on six specimens. A damage model of displacement type, energy type, and displacement-energy type was used to evaluate the damage process. The results showed that the seismic behavior of the joints in traditional-style buildings with viscous damper is superior to that in buildings without viscous damper. The bearing capacity, ductility performance, and dissipation energy capacity of specimens with viscous damper are superior to those of buildings without viscous damper. The damage curves of the Park-Ang model and the Banon model can describe the earthquake damage evolution rule of the beam-column joint in traditional-style buildings. The type of viscous damper will affect the damage evolution and development of traditional-style buildings to a certain extent. Although the ductility of specimens with large design damping force is improved, the cumulative damage is also large under loading.

Abstract:A finite element model of the spring vibration-isolated foundation for a turbo-generator was established by using SeismoStruct for time history analysis. The frequency, vibration mode, seismic responses, inter-story deformation, and spring deformation of the foundation were analyzed. Results show that the natural frequencies of the spring vibration-isolated foundation are lower than those of common ones and the vertical frequencies are far from the working disturbance frequency of the units. The spring vibration-isolated device can reduce the acceleration response of the bedplate under an earthquake and redistribute the horizontal earthquake action according to the stiffness, thus ensuring the maximum seismic capacity of the column. A numerical simulation shows that the foundation design meets the standard of the Code for Seismic Design of Buildings in China and achieves the goal of spring vibration isolation. Overall, the foundation design is reasonable, safe, and reliable.

Abstract:The rhythm of multiplied nine days in different years is a method for predicting the occurrence of imminent earthquakes before they strike. It has the characteristic of counting to day clearly. In this paper, this method is used to discuss the occurrence date of the 1920 M_S8.5 Haiyuan earthquake. The results of this study can be used as a reference to predict the date of large earthquakes in Gansu and Ningxia areas from short impending time scale.

Abstract:This paper studied the inhomogeneity of crustal medium in Jiangsu-Shandong segment of the Tanlu fault zone from large- and small-scale aspects. Using seismic data, the inhomogeneity of velocity structure, unit virtual wave, and Poisson ratio of crustal media were studied. The length of seismic source of the Tancheng M8.5 earthquake that occurred in 1668 was calculated, and the source region boundary along the Tanlu fault zone was determined. The locking section, accumulation unit, and adjustment unit of seismic stress were determined according to seismogenic tectonics and seismicity. Through analysis of the crustal media of the Tancheng M8.5 earthquake and various inhomogeneity parameters, we inferred that the possible region of future large earthquake is the NNE direction region with the range of 33°-34.5°N, 118°-118.8°E, and the highest magnitude can reach M8.

Abstract:The BeiDou navigation satellite system was developed by China and operates independently with full intellectual property rights. With respect to position and communication, it is especially suitable for earthquake emergency environments in which communication is interrupted after a large earthquake. In this study, we constructed an earthquake emergency command system using BeiDou satellite communication technology and geographic information technology. Based on the BeiDou satellite position, the locations of rescue workers at a disaster site can be tracked. BeiDou short message technology is used to ensure emergency communication in blind areas. The platform for data collection, analysis, and comprehensive presentation uses serial communication, multi-threading, an SHH2 framework, Web GIS, and other technologies. Lastly, we constructed a BeiDou emergency command system whose functions include location monitoring, disaster reporting, statistical display, command, and dispatching. The results of this study further improve the ability of the emergency command to acquire information regarding major earthquake disasters.

Abstract:This paper studies the influence of earthquake on the coordinate stability of seven base stations in a short time by collecting the observation data from base stations for BeiDou ground-based augmentation system near the epicenter of the Changning M6.0 earthquake in Yibin County, Sichuan Province, on June 17, 2019. It is found through data comparison that the influence of Yibin earthquake on the coordinate of the base station is closely related to the relative orientation of the base station and the focal fault zone. The coseismic changes of the baseline between base stations indicate the obvious influence of the Changning M6.0 earthquake on the stability of base stations in a short time. The necessity of building the base station stability monitoring system of BeiDou ground-based augmentation frame network is further demonstrated.

Abstract:The Suqian segment of the Tanlu fault has been a focus area of Jiangsu earthquake for many years. Multiphase active fault detection and engineering seismic safety evaluation have been carried out in this area. In addition, many earthquake monitoring methods have been established, such as seismometry, deformation, electromagnetic, and fluid, among others. It is of great significance to study the relationship between active fault movement and earthquake occurrence using gas geochemical method. The two main faults (F_5-1 and F_5-2) composing the fault F₅ in Suqian section of the Tanlu fault are inclined to each other and developed nearly vertically. In this paper, five survey lines of soil radon were set up along the fault F₅. Combined with the data of geological survey and shallow artificial earthquake, the results showed that the detection results of soil radon in the study area have a clear indication for the fault location, fault type and characteristics, and fault activity. Soil radon detection shows the location of fault F_5-1 and fault F_5-2. There is a certain correspondence between the abnormal shape of radon concentration and the characteristics of fault. The relative activity of the two branch faults of F₅ fault in the Suqian section of the Tanlu fault zone is preliminarily judged using the concentration intensity of soil radon as index.

Abstract:The Changping-Fengnan fault is the largest fault in the Zhangjiakou-Penglai fault zone. It is a buried active fault discovered through interpretation of satellite remote sensing images. The study of the Quaternary activity of the Fengnan-Fengnan fault is of great significance to understand the activity characteristics of the Zhangjiakou-Penglai fault zone. To further investigate and confirm the existence, spatial position, property, and tectonic features of the Changping-Fengnan fault, based on the interpretation of satellite remote sensing images of the general spatial position of the fault, two shallow seismic survey lines were laid for high-resolution seismic exploration. Using the abovementioned working methods and selecting the appropriate data processing techniques, the clear imaging of underground structure and fault structure within the control range of the survey line were obtained. The results showed that the Changping-Fengnan fault is an S- and NWW-trending strike-slip normal fault. The shallow seismic profile reveals that the buried depth of the fault is 80-100 m, and the latest active age is estimated to be late Pleistocene based on the borehole data near the survey line. By interpreting the deep seismic reflection data across the Changping-Fengnan fault, the deep structural features of the fault are obtained, and the Mesozoic and Paleozoic strata and crystalline basement were dislocated downward. The results of this paper provide reliable seismological data for the evaluation of the existence and activity of the Changping-Fengnan fault.

Abstract:Dachuan-Shuangshi fault is located in the southern segment of the front-range of the Longmenshan fault, which is hidden under the terrace of Minjiang River in Dujiangyan area of Chengdu. To a certain extent, it affects the evaluation of both seismic risk and seismic capacity along the southern segment of the Longmenshan fault zone. Therefore, it is important to study the underground distribution characteristics and activity of Dachuan-Shuangshi fault in preparing disaster avoidance strategy and recovery planning. The effective disaster management planning helps in selecting sites for major projects in Dujiangyan City. Based on the field geological survey, shallow seismic reflection profile, high-density resistivity profile, and borehole joint profile are arranged along the vertical fault direction. Various methods are used to reveal the precise spatial distribution location, near-surface structural morphology, buried depth of upper breakpoint, and the activity of Dachuan-Shuangshi fault. This fault passes through the west bank terrace of Minjiang River in Dujiangyan area. It is a reverse fault inclined to NW with a dip angle of 60°-70° in the shallow layer of the surface and 20°-30° near the surface. The upper breakpoint extends upward to the Quaternary gray-brown clay and brown-yellow coarse sand-gravel beds with a burial depth of about 3.5 m. The study shows that the Dachuan-Shuangshi fault near the urban area of Dujiangyan has the Holocene activity characteristics.

Abstract:This study analyzes and summarizes eight types of environmental factors disturbing electromagnetic instruments in the Xinjiang region based on measurements obtained from data tracking and analysis products from 2008 to 2018. After analyzing the interference causes, specific typical events are determined, and the data curve shape and variation characteristics of various environmental interference events are investigated. This study provides effective examples and references for data tracking analysis at stations using the same observational means in the Xinjiang region. Furthermore, the causes of the eight environmental disturbance factors and the characteristics of data curve changes in the Xinjiang area can be used as a reliable base and as a reference for the further extraction of earthquake precursor anomaly information and earthquake predictions.

Abstract:This paper analyzed geoelectric field observation data at Gufeng, Sitan, and Pingcheng stations from an electromagnetic, satellite ground-based, comparative observation system. Results showed that:(1) The normal diurnal variation was clear from geoelectric field data at the three stations. (2) During the occurrence of a geomagnetic storm, geoelectric storm changes were recorded in all directions of the geoelectric field, and the maximum variation amplitude of the geoelectric field was significantly larger than that of the normal diurnal variation. (3) Impending anomalies before the earthquakes, recorded by the geoelectric field at Sitan station, agreed well with earthquake occurrence in time and space.

Abstract:In this paper, we planned and improved the ant colony algorithm to quickly and accurately obtain the near-surface stratum structure. The ant colony algorithm is the simple algorithm, which has the advantages of fast operation efficiency and high precision. In this paper, the model data and the measured data indicated that the improved ant colony algorithm applied in Rayleigh wave inversion can achieve a better balance between the fast convergence rate and accuracy, and the solution has high credibility. This algorithm was divided into two ways, global search and local search, which can effectively avoid the generation of local optimal solution and thereby promoting the solution rapidly converge to the global optimum. Finally, the effectiveness and versatility of the improved ant colony algorithm in the inversion of near-surface shear wave velocity were verified using the artificial Rayleigh wave data and real observation data. Moreover, by comparing with the genetic algorithm, it was found that the improved ant colony algorithm has the advantages of high efficiency and accuracy.

Abstract:The M_L3.8 earthquake that occurred on October 1, 2013, in Rushan at 12:07 is located in Shandong Province's northeast section. Then the earthquake swarm activity was formed. A total of 13 000 seismic records were obtained in the seismic network at Shandong so far. The largest earthquake on May 22, 2015, is M4.6. During 2011-2014 we collected the teleseismic waveform from Rushan station to calculate the receiver functions, then we calculated the crustal thickness and velocity ratio in the focal region and its adjacent regions. The results showed that the lateral heterogeneity of the crustal velocity structure in the study area is high, and the receptor functions observed differently in different azimuth. There is an obvious difference between the source area and the adjacent area. In the middle and lower crust of source area, there is an obvious low-velocity zone but high-velocity zone in the middle and lower crust of its neighboring areas. We used the receiver functions stacking method H-k to determine the crustal thickness and wave velocity ratio of the seismic source area and adjacent area. The results showed that the thickness of the crust is 31 km, and the wave velocity ratio is 1.74. Many earthquakes above M_L3.0 occurred in the high and low-velocity junction regions. It was inferred that the occurrence of the Rushan earthquake swarm may be due to the upper crust rupture caused by the heterogeneity of matter within a small scope.

Abstract:In this study, by collecting teleseismic data recorded by 238 and 350 stations in the northeastern and southeastern margins of the Tibetan Plateau, respectively, we used the shear wave splitting method to measure two splitting parameters at each station:polarization of fast wave and splitting time. Subsequently, the upper mantle anisotropy beneath the northeastern and southeastern margins of the Tibetan Plateau was obtained. The results can be summarized as follows:In the Qilian, Alsxan, and northern part of the Ordos Block, the fast wave direction is NNW-SSE, which is significantly different from the near NE-SW direction of surface displacement field measured by GPS, and the average delay time in this region was 0.85 s. In the Songpan-Ganzi fold belt and western part of the Qiangtang Block, the fast wave direction tends to rotate clockwise, which is consistent with the direction of surface displacement field measured by GPS, and the average delay time in this region was 1.24 s. In the junction of the Qinling orogenic belt, eastern part of the Songpan-Ganzi fold belt, and southern part of the Ordos Block, the fast wave direction shows a disorder distribution, which is inconsistent with GPS direction, and the average delay time in this region was 1.08 s. In the northern part of the Sichuan-Yunnan Block, the fast wave is in the near N-S direction, which is consistent with the direction of surface displacement field measured by GPS, and the average delay time in this region was 0.925 s. In the southern part of the Sichuan-Yunnan Block, the fast wave is generally distributed in the near E-W direction, which is distinct from the direction of surface displacement field measured by GPS, and the average delay time in this region was 1.065 s. After comprehensive analysis, we suggested two conclusions:1) in the Songpan-Ganzi fold belt, western part of the Qiangtang Block, and northern part of the Sichuan-Yunnan Block, the crustal and deep deformations are coupled, and 2) In the Qilian Block; Alsxan Block; northern part of the Ordos Block; junction of the eastern part of the Songpan-Ganzi fold belt, Qinling orogenic belt, and southern part of the Ordos Block; and the southern part of the Sichuan-Yunnan Block, the crust and mantle are likely decoupled.

Abstract:In this study, 315 real-time transmission stations in Fujian province were accessed in the active air-gun source detection experiment. The noise levels of the network were estimated in three bands:1-10 Hz, 0.1-1 Hz, and 10-60 s. First, the background noise records during 240 h were counted to obtain the MODE line of the noise level at each station. Then, the area ratio of the global high-noise model line and low-noise model line to the MODE line was used to quantify the noise level of the network. Based on the different color standards, we divided the noise levels of the network into 10 levels for estimation, and thereby got the high-quality stations. The influence of background noise on the explosive effect of the air gun was further studied. It is confirmed that the receiving capability of the station is closely related to the background noise. We analyzed the environmental noise levels of different station bases and concluded that the environmental noise levels from low to high are fixed base, encrypted base, mobile base, and undersea base. The detection ability of the air-gun source signals would be efficiently improved by the noise assessment of the network, which would also provide an important reference for the maintenance of high-quality stations.

Abstract:In this paper, the digital records of 290 M_L ≥ 2.5 earthquakes recorded in the Jinggu M6.6 earthquake sequence are used to calculate source parameters. Results show that the seismic moment M₀ is 10¹²-10¹⁶N·m, the corner frequency f_c is 3-16 HZ, the apparent stress is 0-15 MPa, the mean value is 2.14 MPa, and the median value is 1.39 MPa. A certain correlation was also found between the source parameters, and the spatial distribution of aftershocks in the Jinggu earthquake sequence can be divided into northern, middle, and southern sections. The distribution of apparent stress is south > middle > north. This finding indicates that the stress level in the southern section of the source area is the highest after the main shock occurred, which may be the root cause of the subsequent M5.8 and M5.9 strong aftershocks that occurred in the southern section. Apparent stress in the southern section is "gradually rising-maintaining stability" before the strong aftershocks occurred. In the northern and middle sections where no strong aftershocks occurred, the temporal change in apparent stress is a rapid adjustment in the early stage, which then gradually changed to the average value in each region. Such changes indicate that in a short period before the occurrence of strong aftershocks, the local stress in the southern section first increased and then maintained a "locked" state of a relatively high value until the occurrence of strong aftershocks. Therefore, the spatial distribution of apparent stress in the source area has an indication of the possible location of strong aftershocks, and its temporal variation has a certain correlation with the occurrence of strong earthquakes in the seismic sequence. The temporal and spatial variations of apparent stress have important indications for subsequent seismic activities and can provide a corresponding reference for the space-time determination of strong aftershocks.

Abstract:Based on the demand of Yunnan seismic network for continuous rate improvement, along with the current network framework and the existing network access conditions, a transmission scheme based on wired channels and supplemented by wireless channels was designed through router debugging and server configuration. This study provides a choice for improving the operation rate of Yunnan seismic network.

Abstract:In this study, we used an outdoor testing method to draw a two-dimensional contour map, and we normalized the wavelength and double-pile variables to analyze the vibration of the surrounding soil when a Rayleigh wave passes through a double pile. The results show that the vibration in the soil strengthens between and in front of the piles, with the greatest vibration intensity in the soil is between the piles and at the pile angle. Increases in the ratio of the pile length to wavelength strengthen the vibration of the soil between and in front of the piles, and also improve the vibration-isolation effect of double piles. When the ratio is in the range of 0.691-0\^781, the variation range of each point is gentle. An increase in the pile spacing causes double piles to lose their mutual influence. When the ratio of the pile spacing to wavelength is between 0\^34 and 0.42, the A_r value of the soil between, in front of, and behind the piles approaches 1, i.e., there is no vibration strengthening or attenuation. Increasing the pile diameter can improve the vibration-isolation effect of double piles, whereby as the ratio of the pile diameter to the wavelength increases, the A_r values of the soil between and in front of the piles increase slightly. An increase in the distance of the vibration source strengthens the vibration-isolation effect of double piles. As the ratio of the vibration-source distance to the wavelength increases, the A_r value of soil in front of the pile decreases by about 0.13, that between the piles decreases by about 0\^068, and that behind the pile decreases by approximately 0.108. The vibration-isolation effect is also enhanced, but the amplitude of this enhancement is small.

Abstract:The reasonable spacing between anti-slide piles and the load transfer mechanism was investigated in this study. First, the calculation formula of the rupture angle with the skewback of a soil arch supported by a pile body was deduced from the fracture surface with the skewback supported by the side friction. Second, the logarithmic spiral method was introduced to determine the slip depth of soil between piles. The calculation model was established based on the soil arching effect to solve the expression of reasonable spacing between anti-slide piles considering the slip depth of the soil between piles. Finally, the major influencing factors of the net spacing between anti-slide piles were analyzed, including the landslide thrust, the cohesion, and the width and height of the anti-slide pile section. The results showed that the skewback of the soil arch supported by the pile body and pile side friction was more in line with the actual stress state; moreover, under this condition, the ring thickness and vector height of soil arch, which increased with the pile depth, were less than those of the soil arch supported by the pile body but more than those of the soil arch supported by the pile side friction.

Abstract:Based on dynamic triaxial tests, in this paper, we present the results of research on the dynamic modulus, damping ratio, and shear strength of undisturbed and remolded earthen-site soils in the Hexi area, Gansu Province. We then use numerical simulation to analyze the dynamic responses of earthen-site soil under the action of destructive earthquakes. The results indicate that the dynamic stress and dynamic strain of both undisturbed and remolded earthen-site soils show a nonlinear relation in the elastic range, fitting the hyperbolic model. With increases in the dynamic strain, the dynamic elastic modulus is decreased. In the same strain range, the increasing trend of the damping ratio of the remolded soil is obviously higher than that of the undisturbed soil. Under the same conditions, the cohesive force of the undisturbed soil is slightly higher than that of the remolded soil. To a certain extent, the strength of an earthen-site is restored by consolidation, but the seismic performance of the soil should be strengthened when earthquake strikes.

Abstract:Chord modulus method is used to establish chord modulus function considering the basic physical properties of loess and the combined effects of additional stress. Layer-wise summation method is applied to calculate the deformation of the loess foundation. Good prediction results are obtained in the engineering practice of the Guanzhong loess area in Shaanxi Province. However, a different result is obtained when analyzing the settlement of foundations in other loess areas, such as Lanzhou. The contradicting results could be due to the neglect of the structural characteristics of loess under natural conditions. Using chord modulus method, this study evaluates the relationship between the structural index of loess and the compressive modulus, void ratio, and water content. Four soil samples were collected in the urban area of Xi'an, and a large amount of load test data was employed in the analysis. The results validate the theory of structural parameters in the settlement calculation of foundation settlement.

Abstract:The sliding distance of an earthquake landslide is significantly different from that of a gravity landslide. Scientific prediction of the sliding distance of seismically-induced landslides in loess regions is an effective way to reasonably assess the risk and minimize the hazards of such landslides. Based on 400 groups of field survey data of loess landslides triggered by the 1920 Haiyuan earthquake and 67 sets of verification data, feasibility and suitability of the back propagation (BP) neural network model for predicting sliding distances of seismic landslides was demonstrated. Comparison of the results of BP neural network algorithm with those of traditional multiple linear regression and multiple nonlinear regression showed that the BP neural network was a superior predictor of real-life situations. This study can be used to predict landslide slip of loess earthquakes.

Abstract:The current status of research on liquefaction failure in underground structures is not ideal. It is necessary to analyze the soil liquefaction potential of underground structures such as subway tunnels. In this paper, the anti-liquefaction safety of the Taiyuan metro tunnel was analyzed using four methods, i.e., those used by Tokimatsu and Yoshimike, Seed, the Japan Road Association, and the Chinese code. The overall liquefaction risk level of the site was evaluated. Based on the dynamic shear-stress ratio of vibration liquefaction, the anti-liquefaction safety factor, the relationship between the standard penetration test number and volumetric strain, and the liquefaction settlement deformation of the shield tunnel were evaluated. By the adoption of the anti-liquefaction technique of secondary grouting of the shield tunnel in silty sand and the clay silt stratum, it is suggested that secondary grouting of a cement-based suspension be used to reinforce the foundation of the Taiyuan Metro to improve its anti-liquefaction ability and reduce the deformation associated with liquefaction-induced settlement.

Abstract:A series of cyclic triaxial tensile tests were conducted on K₀-consolidated saturated clay with cyclic stresses of equal amplitude. The results showed that the dynamic shear modulus G is related to both the cyclic shear strain γ_cy and the cumulative strain γ_p. To further study its impact, we conducted cyclic triaxial tensile tests under progressive loading, the results of which showed that as the cumulative strain increases, the initial dynamic shear modulus G_max gradually decreases. Using G_max as a normalized parameter under a certain confining pressure, we established the G/G_max-γ_cy relationship, which has good applicability at other confining pressures. The cumulative strain and confining pressure have little effect on the damping ratio, and the damping ratio can be considered to have a unique correspondence with the vibration shear strain. The relationship between the dynamic shear modulus and damping ratio was established in a set of cyclic triaxial tensile tests, and this relationship can be applied in cyclic triaxial tensile tests with other stress combinations.

Abstract:To study the seismic slope stability of the proposed dagoba of Longquan Temple in Taishan, Taiyuan City, the landform, stratum, geological structure, and hydrological conditions of the site and its periphery were investigated. Firstly, combined with seven exploration wells, the possible instability mode of soil slope body at the tower site was determined, and the analysis and calculation of slope stability were performed. The results showed that the slope stability coefficient is 1.37 in natural state and 1.24 and 1.15 under the influence of 8 and 9 earthquake intensities, respectively. According to the Technical Code for Building Slope Engineering (GB 50330-2013), the slope at the tower site is stable and is not necessary to be treated. Secondly, combined with the exposure of three exploration trenches, the bedrock slope on the north side of the site was found to have experienced sliding. Based on the dip angle of sliding surface, the amount of sliding, and the characteristics of faulted strata, we considered that it is a special slope deformation and failure, i.e., a faulted rock mass, which is the intermediate type between collapse and landslide. According to the existing topography and geomorphology features, the faulted rock mass has been stable at this stage. Finally, we have provided suggestions and measures to prevent slope sliding, i.e., not to excavate the lower part of the slope but to drain the surface water to the main ditches on the east and west sides and to prevent the precipitation from infiltrating into the rock and soil layer, resulting in the loss of support at the lower part of slope and the instability of soil slope. Additionally, reinforcement should be applied to the loose rock mass of the upper slope to avoid the recurrence of collapse that will cause seismic and geological disasters to the proposed dagoba. The results of this study provide a scientific basis for the prevention of slope disaster and treatment of the proposed dagoba and reference for succeeding seismic stability research of other similar slope sites.

Abstract:Daning County is located at the southern end of Lüliang Mountain, Shanxi Province, with unique topographic and geomorphic characteristics of the loess plateau. The investigation of geological hazards was conducted in the area to determine the distribution, causes, and hidden dangers of disasters. Through the application of the relevant principles of geomorphology and remote sensing image interpretation, two large-sized and two medium-sized landslide bodies were detected and confirmed in the 0.3 km² (575 m×526 m) range of the two banks of the Yiting River. The characteristics of the four landslide bodies and their surrounding landform, as well as the change in the direction of the river course, are analyzed. We propose the following:(1) The four landslide bodies were formed in different geological periods. (2) One landslide body was obviously affected by a fault. (3) The three other landslide bodies were formed over a long period of time under the dynamic action of "gravitational collapse" and river flow direction. (4) The stress of three M_S8.0 earthquakes, i.e., the Hongdong and Linfen earthquakes (60 km from the area) and the Huaxian earthquake (more than 230 km from the area), aggravated the occurrence of the landslides. (5) Future studies should consider the possibility that landslides are accelerated by unconventional external conditions, such as heavy rainfall or earthquake stress.

Abstract:The dynamic characteristics of undisturbed red clay in Guiyang under cyclic loading were tested by a SDT-20 dynamic triaxial testing machine in the laboratory. Effects of confining pressure, consolidation stress ratio, and vibration frequency on the dynamic parameters of red clay were investigated. Results showed that the dynamic constitutive relationship of Guiyang red clay conforms to the H-D hyperbolic growth model. Dynamic elastic modulus decreases nonlinearly with increasing dynamic strain, and the damping ratio increases nonlinearly with increasing dynamic strain. In addition, confining pressure and consolidation stress have a significant influence on the dynamic parameters of red clay. Details are as follows:with increasing confining pressure and consolidation stress ratio, dynamic deformation and damping ratio decrease, and dynamic elastic modulus increases. Under the same conditions, if the vibration frequency is increased, the kinetic parameters will follow the same law as confining pressure and consolidation stress ratio, though not significantly. Based on the H-D model, the hyperbolic model parameters of undisturbed red clay in Guiyang are given. The empirical model of dynamic elastic modulus attenuation and damping ratio of Guiyang red clay under different test conditions is proposed by multiple regression analysis, and the corresponding fitting parameters are given.

Abstract:This study investigated the effects of moisture content and consolidation pressure on the dynamic properties and deformation behavior of intact loess under repeated cyclic loads. The British GDS bidirectional dynamic triaxial test system was used to simulate traffic loads, and a dynamic triaxial test was carried out on intact loess in Haidong area, Qinghai Province. The test results showed that under a single cyclic dynamic load, in the initial loading stage, the axial dynamic strain of intact loess significantly increased with an increase in the number of cycles; the increase rate gradually reduced, and the strain eventually became stable in the late loading stage. The moisture content and consolidation pressure had no significant impact on the axial dynamic strain of intact loess in the initial loading stage. However, when cycle number N exceeded 400, the axial dynamic strain of intact loess increased with an increase in moisture content and decreased with an increase in the consolidation pressure. With increasing number of cycles, the dynamic shear modulus of intact loess first decreased, then increased, and finally decreased; moreover, it significantly decreased with increasing moisture content. The dynamic damping ratio of intact loess first increased and then decreased with the increase in the number of cycles, and it increased with increasing moisture content. The test results showed that intact loess in Haidong area can easily undergo vibration deformation because of its large-void overhead structure.

Abstract:To study the compressive strength of concrete under the coupling action of different confining pressure and temperature, the control parameters of compressive strength σ_max of concrete were processed with no-dimensions according to the similar analysis principle, and related similarity criteria were obtained. The relationship between those similarity criteria was obtained by finite element calculation, taking C40 concrete as an example. Results show that (1) The compressive strength σ_max and residual strength increase with the increase of confining pressure, and the maximum deviator stress is linear with the confining pressure; (2) When the confining pressure is less than 20 MPa, the stress-strain curve can be divided into two sections, and when the confining pressure is greater than 20 MPa, the stress-strain curve can be divided into three sections, showing obvious yield; (3) The influence of temperature on compressive strength is obviously different under different confining pressure, and the maximum deviator stress and temperature are approximately linear; (4) Three dimensionless parameters (σ_max/E, F/E, and αθ) form a plane in the three-dimensional coordinate, which shows that σ_max/E has a linear relationship with αθ and F/E.

Abstract:To study the formation mechanism, slip characteristics, and sliding distance of the liquefaction-induced slip disaster in the Shibeiyuan area during the 1920 Haiyuan earthquake, drilling exploration, sampling, and trench excavation were conducted in the Shibeiyuan liquefaction and slip area. Shear wave velocity tests, particle analysis, and indoor dynamic triaxial tests were performed on boreholes and samples. The stratum distribution in the liquefied slip zone of Shibeiyuan area, the layer of liquefied soil during the earthquake, and the sand under different seismic intensities were then obtained. The comprehensive analysis results of drilling exploration, particle analysis, and dynamic triaxial test revealed the formation mechanism of liquefaction-induced slip disaster of the loess deposit in Shibeiyuan area during the Haiyuan earthquake. The liquefied sandy loess layer floated the first paleosol layer and the upper "dusting" unsaturated loess layer to move along the gentle slope under the combined action of its own weight stress and seismic force. The slip distance formula of the liquefied slip deposit was used to estimate the slip distance (i.e., 223.35 m), which is consistent with the actual situation. The results of this research provide a reference for the prevention of liquefaction and slip disasters in the loess deposit.

Abstract:After a destructive earthquake, the rapid assessment of earthquake disaster, as the core module of the earthquake emergency command technology system, provides important information services for the earthquake emergency command and decision making of government and emergency management departments at all levels. It is also an important support platform for earthquake emergency rescue and command and decision making. After decades of research in the field of earthquake emergency, the conditions for developing a new generation of rapid assessment system for earthquake disasters have been prepared. In this paper, based on the research foundation of the earthquake intensity attenuation model of different magnitudes, the evaluation model of casualties in different regions, and the design of earthquake emergency thematic map in Gansu Province, a new generation of rapid evaluation prototype system of earthquake disaster in Gansu Province is developed, which can automatically trigger a software, estimate the impact range of earthquake with different magnitudes, calculate the casualties of earthquake disaster personnel in different regions, automatically generate earthquake disaster assessment report, and improve the automation level of the system and the accuracy of calculation results. The software can improve the rapid response ability from an earthquake disaster and can provide more scientific and reliable information services for emergency rescue and command decision making from an earthquake disaster in Gansu Province.

Abstract:Due to the superposition of double disasters, post-earthquake fires cause massive loss of life and property and pose serious threats to human life. In this paper, we review the history of secondary fires associated with several major earthquakes. We summarize the occurrence and spread of post-earthquake secondary fires, and discuss the analysis and research methods most commonly used to study them. We also summarize and analyze evaluations of the risks and losses associated with post-earthquake secondary fires. Recent advances in the prevention and control of these secondary fires are discussed with respect to civil buildings, oil and gas chemical facilities, nuclear power plants, post-disaster resettlement sites, and forestry. We used the bibliometric method to search for entries in the CNKI database in the past two decades related to the theme "secondary earthquake fire," and analyzed the relationship between heat and earthquake events.

Abstract:On September 12, 2018, a M5.3 earthquake occurred at Ningqiang County, Shaanxi Province. Thirty-nine strong motion stations located in this region were fully triggered by the main shock. A total of 117 records of three-component acceleration were obtained by NSMONS. In this paper, we first calculated the ground motion parameters of near-field stations and drew the contour map of peak accelerations near the epicenter. It is then found that the attenuation prediction model of Huo Jun-rong can better reflect the influence field of the earthquake by comparing the observed data with some commonly used ground motion prediction equations. Finally, we compared the acceleration response spectrum of 51GYD station with the design spectrum to summarize the basic characteristics of response spectra for this earthquake. The H/V spectral ratio method was applied to analyze the seismic response of the local site at 51GYD station and 62ZM array. Furthermore, the amplification effect of overburden soil on ground motion and the influence process of local topography on peak acceleration and peak velocity were studied.

Abstract:On April 20, 2013, and the M7 earthquake occurred in Lushan county, Sichuan Province. Based on the 2 106 sets of strong ground motion data, using the simplified attenuation relationship model based on NGA, the random effect method was used to obtain the PGA, PGV, and pseudo-acceleration response spectra (PSA) (damping ratio=5%) period from 0.01 s to 8 s. Through contrast with the attenuation relationship in other parts of Sichuan, this model can well predict the strong ground motion attenuation of Lushan aftershocks. The attenuation relationship on both the rock site and soft site is consistent in the short-term with the outcome of Lu Dawei's model. In the case of long periods, however, the outcome of this model in the soft site is larger than that of Lu Dawei's model and is lower at rock site than that of Yu Yanxiang's model. Therefore, when using the attenuation relationship derived from this paper, special attention should be paid to the influence of site and period.

Abstract:In recent years, the high-density resistivity method has been widely used in geological exploration and the evaluation of the stability of important project sites. In this paper, the high-density resistivity method and other methods were adopted to evaluate the seismic stability of the ADS facility site, a large-scale scientific facility project in China. This ADS facility is located in Huidong County, Huizhou City, Guangdong Province. Several high-density electrical profiles were developed for the site area, and resistivity profiles were drawn after two-dimensional inversion. Combined with the existing borehole and geological data, the distribution characteristics of the underlying faults were inferred and interpreted, followed by the investigation of the fault occurrence, thickness of the weathering layer, and hydrogeological conditions. To provide technical support for the design and construction of devices at the proposed site, we also studied the possible earthquake damage amplification of the faults near the site from future earthquake action. This comprehensive evaluation method can serve as a reference framework for the selection of similar sites for major national projects.

Abstract:Based on the data of 272 historical landslides from the national landslide catalog and 10 influencing factors, 3 representative quantitative methods, namely, information value model, logistic regression model, and artificial neural network based on frequency ratio model, were used in this paper to evaluate the landslide hazard risk in areas of Tangchang County, Zhouqu County and Wudu District in southern Gansu Province surrounding the Bailong River Basin. The results from these three models showed that the extremely high- and high-risk areas of landslide disaster are mainly distributed along the Bailong River valley. From the hazard zoning map, the result obtained by the artificial neural network model is found to be relatively reasonable, showing not only the trend of centralized distribution along the valley area but also the feature relatively independent to the landslide historical data, which is consistent with previous research results. The accuracy of the three models was tested according to the receiver operating characteristic curve, and the AUC values obtained were 0.818, 0.829, and 0.837, respectively, indicating that all three evaluation results have high reliability. Compared with the other two models, the artificial neural network model based on frequency ratio has better evaluation accuracy and can better predict and evaluate the landslide risk. Elevation, rainfall, lithology, and distance from the road are factors that have greater influence on the evaluation results than other factors, and the importance value of these four influencing factors accounts for 52.1%. The results of this study provide a reference for urban expansion and disaster prevention in the study area.

Abstract:This paper studies the disaster chain theory and discusses two academic concepts of disaster chain:one is the concept of "disaster to disaster",and the other is the concept of "reporting disaster with disaster".The latter is a concept of symbiosis,co-occurrence,and renewal of different disasters,and can be used to predict major disasters.