Abstract:On the ninetieth anniversary of the Gulang, Gansu M_S8 earthquake, in this paper, we retrospectively investigate and discuss the prediction of great earthquakes. We used two indexes, the block border zone and high mountain indexes, to research the location of the 1920 Haiyuan M_S8.5 earthquake and the 1927 Gulang M_S8 earthquake. We discuss the year of earthquake occurrence of the 1927 Gulang M_S8 earthquake based on the relationship of the 25-year cycle for great earthquakes in China and the maximum solar background activity. Our retrospective study of these indexes provides a valuable reference for the study of earthquake ground motion and seismic risk regions for the prediction of great earthquakes.

Abstract:To study the seismic behavior of asymmetrical steel-reinforced concrete columns, nonlinear numerical analysis was carried out based on the quasi-static test of 12 columns with a T-shaped steel section. The concrete, steel, and reinforcing bar elements were simulated by using the Solid65, Solid45, and Link8 modes of the finite element software ANSYS, respectively. The model of multi-linear kinematic hardening (MKIN) was fully adopted for analyzing the concrete, whereas the model of bilinear kinematic was adopted for analyzing the steel and reinforcing bars. Constant axial compression and lateral cyclic loading were applied on the models. Failure mechanism, bearing capacity, ductility, and energy dissipation ability were also investigated. Three failure modes were observed in the experiment process, including bending failure, shear bond failure, and shear diagonal compression failure. In addition, axial compression ratio, shaped steel ratio, and shear span ratio were analyzed to determine the effects on seismic performance. The results indicated that the asymmetrical steel-reinforced concrete column possessed a plump hysteresis loop, which showed good ductility and energy dissipation ability. For the hysteretic curves, the load and displacement increase linearly in the early stage but increase nonlinearly in the elastic-plastic stage; moreover, residual deformation appears after unloading. The numerical simulation agreed well with the results of the experiment before the peak load. With increased axial compression ratio in a certain range, the peak load increased but the corresponding displacement decreased; moreover, the bearing capacity improved and the slope became steep, thus indicating poor ductility. The bearing capacity, stiffness, and ductility of the specimens improved with the increase of the shaped steel ratio, which mitigated the performance degradation after the peak load. Furthermore, the peak load obviously increased, and the corresponding displacement was kept constant. The shape of the curve was roughly the same. Meanwhile, with the increase of shear span ratio, the initial stiffness of the specimens decreased and the ascending branch became particularly smoother. The corresponding displacement of the peak load slightly increased. The declining branch also became gentle and the ductility improved, which had a significant effect on failure mode.

Abstract:With the rapid development of rail transportation in China, high-speed and heavy-load railways have become the trend of development in this field. In such systems, it is important to consider the interaction process between the train and the bridge, along with the influential factors, when a train passes through a bridge. In this paper, a 156-m long simply-supported steel truss bridge of the Huang Han-hou New Yellow River Railway is taken as an example. A dynamic model of the train-bridge was constructed considering a wheel-rail relationship. Serpentine movements and track irregularity were used as self-excited excitation sources of the train-bridge system. The finite element software ANSYS and UM (Universal Mechanism) were used to simulate the train-bridge coupled vibrations. The influence of the bridge structure of the portal frame, wide-span ratio, curve of the steel truss and track irregularity, as well as the marshaling coaches on the train-bridge coupled vibrations were discussed with the numerical simulations. The results showed that the gantry of the steel truss bridge had greater influence on the acceleration. As the line radius of the curved steel truss bridge increased, the dynamic responses of the train became smaller, thus affecting wheel-rail force. Moreover, with increasing wide-span ratio, the lateral stiffness of the bridge increases, and the bridge lateral vibration became smaller. When the track conditions became worse, the dynamic responses of the train increased considerably and the comfortable and stability worsened. The findings indicate that the full empty grouping and empty-weight mixed grouping schemes are harmful to the coupled system of a train-bridge, which should be avoided in practical operation.

Abstract:Rainfall is one of the important factors that induce landslide sliding and landslide stability.At present,the research on the influence of rainfall on the tunnel landslide orthogonal system without the supporting structure is still lacking.In order to study the action mechanism of rainfall on the tunnel landslide orthogonal system under different intensity of rainfall,and study the characteristics of slope deformation and the stress characteristics of the tunnel without the supporting structure,the influence mechanism of rainfall for the Tunnel-Landslide Orthogonal system by large geological mechanics simulation model test is researched.With the four different stages of rainfall,the changing characteristics of longitudinal of tunnel and the variation characteristics of circumferential stress of tunnel with different cross sections,and the changing characteristics of the displacement of the sliding body at different locations and different cross sections also are analyzed.The results show that:(1) The rain can lead to the cross-sectional of slope broke,and form a new glide plane which result in the landslide slipped.(2) With the increasing of water content of sand,the strain of tunnel has obviously sudden changed,and the longitudinal strain of tunnel near the mountain is bigger than the longitudinal strain of tunnel near the river.(3)Rainfall makes stress of the tunnel uneven change;And the stress of tunnel bottom is greater than the stress of the top,the stress near the mountain is larger than the stress near the river under the tunnel landslide orthogonal system,and shows that necessary drainage measures are indispensable.And it is indicated that the rainfall can cause the movement of the sliding body,cause the uneven stress and deformation of the tunnel,which is very unfavorable to the safety of the tunnel structure.This experiment can provide some reference for the landslide and tunnel anti slide design in the abundant water area.

Abstract:To develop scaling laws for source models, two data sets of global parameters are compiled from the data of reference [3] with modified and supplied by the NGA data bases. These data include parameters of 189 and 204 earthquakes, among which 127 from reference [3], 31 modified from NGA, 31 and 46 newly collected respectively from the two versions of NGA data bases. Empirical and semi-empirical relations between moment magnitude and four source global parameters; the area, width, and length of the rupture plane; and the average slip on the plane are presented for three rupture types and five (three) magnitude intervals. The result coefficient values of the relations do not differ significantly from those in reference [3], and the largest relative differences are 12.4% and 8.4%. The deviations of data to the relations appear to decrease, i.e., the larger the data set, the more stable the statistical relation. To demonstrate the effect of the improvement in this paper, high-frequency ground motions at four near fault points are synthesized by means of source models established for a M7.0 strike slip shock with the scaling laws. The results show higher mean spectral amplitudes and peak values than those determined by reference [3]. The relative differences of the means are about 4.6%~23.0% and decrease with increasing distance.

Abstract:In this paper, coseismic GPS data and the multisurface function are first used to calculate the coseismic surface strain caused by the M_S8.0 Wenchuan earthquake that occurred on May 12, 2008 based on a piecewise data fitting method. The accuracy of the calculations is assessed, and the variation characteristics of surface strain related to the earthquake are analyzed. Calculation of coseismic strain changes revealed that the strain results obtained by piecewise fitting way are more precise than those determined by overall fitting. The calculation results of the two fitting methods feature the same order of magnitude, and the spatial distributions of the two images show some similarity. Compared with the results of the overall fitting method of multidimensional functions, the coseismic surface strain expansion and compression zones determined by the piecewise fitting method are more concentrated in the spatial distribution image. The results of this paper were compared with those of numerical simulation, and findings indicated that the calculation results of piecewise fitting are reliable. Coseismic strain appears to reflect the energy release characteristics and ground destruction distribution of the Longmenshan fault. The Wenchuan earthquake caused intense crustal shortening in the northern region of the Longmenshan fault zone. After the earthquake, the Longmenshan sub-block and the Sichuan basin sub-block moved in opposite directions with high speed over a short period of time. In the near-field region, several major aftershocks occurred in some areas where the coseismic horizontal displacement is amplitude. The coseismic surface strain highlights the right lateral slip characteristic of Wenchuan earthquake and the characteristics of uneven compression at the northwestern side of the Longmenshan fault zone are demonstrated. The results show different strain attenuation characteristics at both sides of the Longmenshan fault. Taken together, findings in this study may be used to determine the characteristics of horizontal crustal movement caused by the M_S8.0 Wenchuan earthquake in a more intuitive manner.

Abstract:The air-gun source, first invented in the 1960s, is mainly used in the field of oil exploration. It has high precision, good repeatability, and is non-polluting; thus, it has gradually become an important artificial source in geophysical detection area. The earthquake administration of Fujian Province efficiently completed the construction of its air-gun source system and has successfully carried out a series of air-gun explosion experiments in 2014 and 2015, thus providing valuable observation data for further research. Considering that the experimental conditions of the air-gun array and the explosion conditions directly affect the explosion performance, researchers have designed a series of air-gun explosion experiments under different experimental conditions. After each experiment, the explosion capability must be quickly analyzed to determine an optimal operating condition for the consecutive explosion issue. At present, the whole analysis work is completed by manual work. This process requires a lot of work, time, and effort, so analysts need to work overtime. Thus, this process is not only inefficient but also subjective because different analysts may provide different results. Considering the further application of this repeatable source, a new method based on the correlation coefficient method is proposed to automatically analyze and display the distribution of air-gun trigged stations. Analysis results show that the new method obtains the same results as the artificial judgments. The K24 and K36 experiment results show better explosion effect. Moreover, over 70 stations received the signals of single firing, with signals that can be recorded by stations beyond 200 km. After repeating the firing for 50 times, over 90 stations received the signals, which can be recorded by stations beyond 226 km. The automatic detection method provides a faster and more objective way to demonstrate the distribution of the trigged stations, thus significantly contributing to the air-gun explosive effect evaluation process. The automatic detection method was successfully applied in subsequent experiments carried out in the Mianhuatan Reservoir (Longyan, Fujian) and Shihuangfeng (Wuping, Fujian).

Abstract:This paper describes the dispersion characteristics of first-period P waves recorded by seismic stations near Datong window by measuring the medium quality factor (Q_m) and analyzing Q_m variations before and after the occurrence of earthquakes near and far from Datong window. By applying this method to the SZZ record of the Datong window earthquake sequence from 2001, we obtained the following results: before 3 earthquakes near the Datong window and 6 earthquakes far from the Datong window, the Q_m was the high values over 1 times mean square error; but Q_m returned gradually the background after these earthquakes. However, after eliminating the influences of epicentral distance and depth, large anomalies were still observed and small anomalies disappeared before the earthquakes. Furthermore, the corresponding rate of earthquake decreased from 0.9 to 0.5. Compared with the frequency of Datong window, the Q_m could better reflect earthquake probability. The results of YAY showed that before 1 earthquake near the Datong window and 2 earthquakes far from the Datong window, the Q_m were the high values over 1 times mean square error, and false and omitted cases were observed. Minimal changes to the curve were observed after eliminating the influences of epicentral distance and depth. Preliminary analysis suggested that the short-term high-value anomalies of Q_m before earthquakes recorded by the SZZ and YAY stations could directly reflect the seismogenic process. However, the Q_m recorded by the two stations obviously different before the same earthquakes. Two reasons may explain this phenomenon. The small earthquakes measured by Q_m differed between the two stations as these stations were located in different geological and tectonic positions. The SZZ station was located inside the Datong basin, while the YAY station was located in its eastern border. This difference could lead to the different deep medium and broken medium through by seismic wave ray paths and, therefore, marked variations in Q_m values. The length and width of Datong window were 60 and 5 km, respectively, so high-value anomalies were limited in this area. From the results of Q_m, for the moderate earthquakes which are not only near the Datong window but also far form Datong window, the amplitude of anomaly was almost the same and the distribute range had little change. As such, determining the variation of deep anomalies near or far from Datong window by using the spatial anomaly distribution is difficult. The Datong window showed high-value anomalies before the far-field earthquake of the Shanxi seismic belt because this window is located to the north of the same continental rift. However, the reason why it had high-value anomalies before the earthquakes of Zhangjiakou-Bohai seismic belt which were a few hundred kilometers away, it was possible that the "Y" type of low wave velocity anomaly from Datong volcanoes to below Bohai had played an important role in transmission.

Abstract:This article discusses the geochemical features of the fault gas radon (Rn) in the Jiangsu section of the Tanlu fault zone. The Rn concentration across the fault was measured at four locations: Chonggang, Xiaodian, Qiaobei, and Hezhuang. Measurement results showed that the Rn concentration anomaly contrast in the Jiangsu section of the Tanlu fault zone was 2.05~5.73. The Rn concentration was mainly distributed in and near the fault zone and showed a good correlation with seismic activity.

Abstract:In this paper, we report our preliminary research on the dynamic triggering function of the Nepal M_S8.1 earthquake with respect to microearthquake activity in the Kashi-Wuqia intersection area. We also discuss the triggering influence of the earthquake on activities at the Kashi-Wuqia intersection area based on observation data from the Xinjiang regional digital seismic network station. In this study, we used the discrete wave number method and performed envelope function waveform analysis, spectrum analysis, and β statistical test methods. The results show that after the Nepal 8.1 earthquake, the dynamic stress change produced at the Kashi-Wuqia intersection area exceeded the dynamic stress triggering threshold. Using the envelope function method, we determined that after the Nepal 8.1 earthquake, at least eight microearthquakes occurred at the Kashi-Wuqia intersection area before the arrival of a seismic surface wave. Six of these microearthquakes had not yet been identified by the regional seismic network or any single station location. Our β statistical results show that after the Nepal 8.1 earthquake, the seismic activities at the Kashi-Wuqia intersection area obviously changed, especially on the day of the earthquake, with the daily frequency of seismic activities being about ten times that in the month prior to the earthquake. Twenty-five days after the Nepal 8.1 earthquake, the seismic activities at the Kashi-Wuqia intersection area strengthened significantly. After comprehensive analysis, we consider that the Nepal 8.1 earthquake had a certain dynamic triggering function with respect to the microearthquake activity that occurred in the Kashi-Wuqia intersection area. The triggering time included not only the immediate dynamic stress trigger after the passage of the surface wave, but also the delayed dynamic stress trigger, which may have remained in a subcritical state with the stress of the Kashi-Wuqia intersection area. Fault rupture may require further accumulation or dynamic stress changes to affect the fault instability rate. Instability may be present long before dynamic stress ends despite the absence of any weakening.

Abstract:There is a complicated stress state in Yunnan and the main research object in this paper is the Luquan seismic zone. The Luquan seismic belt is located in the Xiaojiang fault zone in the southern section of the North-South Seismic Belt within China's borders. The complexity of the stress field of the Luquan seismic zone gives it great research value as the focal-mechanism solution in the area contains a great amount of information about the focus of earthquakes. In this paper, we use the seismic moment tensor of the Yunnan Luquan earthquake and the focal mechanism solution of its main shock and aftershocks from the inversion of previous scholars, and refer to the Global CMT Catalog for the focal mechanism solutions of several earthquakes based on the Luquan earthquake. We transform the seismic moment tensor into a focal mechanism solution and then use a stress-field inversion program to invert the focal mechanism solution and obtain the stress field of the Luquan earthquake and surrounding areas. Then, we compare the differences between the two stress fields. We found the principal compression stress field of the hypocenter in the Yunnan Luquan earthquake to be in the NNW-SSE direction. Also, we found the principal compression stress to be equivalent to the principal extensional stress, and that of surrounding areas to be in the NW-SE direction. Furthermore, the facture surface of faults, mainly down strike-slip faults have a large slope angle and the principal compression stress is in a dominant position. However, we found Yunnan to be primarily affected by the principal compression stress in the NNW-SSE and NW-SE directions, given the impact of its location and the longitude and latitude of its surrounding areas. Therefore, in general, Yunnan is affected by compression stress in the NW-SE direction, with some areas affected by compression stress in the NNW-SSE direction. These research results can be used to analyze the mechanism of earthquakes and the seismic geological background and formation conditions of the faults in the area. They also have some significance in promoting relevant research on the geodynamic environment in the Yunnan region.

Abstract:We used the vertical component of data from 62 flow stations recording continuous background noise to determine the possible interaction of surface-wave-related functions and Rayleigh-wave-phase velocity dispersion curves in southeastern Gansu (32.2°~33.5°N, 102.7°~105.5°E). We used the ray-tracing surface-wave-dispersion direct inversion method for five observation stations within a 20-km shear wave velocity distribution image depth range. The results show that there is a correlation between shear wave velocity corresponding to a 5-km depth and lateral variations in the thickness distribution of the deposited layer in the surface fault zone. In addition, the northern West Qinling fault zone is mostly a low-speed zone. Also, the Zhangxian and Lintao Basins belong to one type of characterization of the deposited thick layer (the last a few kilometres). About a 10-km depth corresponds to the shear wave velocity in the south margin fault of Lingbei Xiqin. The Lintan-Dangchang fault in the Lixian-Luojiabao area is between the low-fracture velocity zone, with light covered mountains-stacked high speed around the Northern Piedmont fault zone. There is a block structure of high and low rendering features near the Diebu-Bailong River Ling fault at about a 15-km depth. At about a 10~18-km depth range, the speed gradually increases with depth and the magnitude of the change is about 0.2 km/s.

Abstract:In this paper, Seismological Network (2007-12-01-2013-12-31) data from Hubei and its surrounding areas are analyzed via the seismic anisotropy method. Shear-wave splitting parameters from 16 stations are obtained. The results show some S-wave splitting phenomena in Hubei and its surrounding areas, and that the dominant directions of fast shear-wave polarization are the northeast and or nearly northsouth directions and there is no first advantage of polarization direction obviously. The stress field of the stations may be the comprehensive result of regional tectonic background stress environments and induced local fractures. Complex local structures may affect the shear-wave splitting results by reducing the dominant polarization direction, which is not in accordance with the strike of the main active faults. Significant differences between the regional principal compressive stress and dominant polarization direction may also affect the results.

Abstract:The Subei Fault is located in the western part of the Yema River-Daxue Mountain fault, which is located in the northeast of the Tibetan Plateau. This fracture is about 17 km long, trends northwest 40°, and crosses the Altyn Tagh Fault in the Subei area. The conventional view is that the power of the Altyn Tagh Fault with a high slip rate (about 10 mm/a) was absorbed by the Tanghe Nan Shan fault, the Yema River-Daxue Mountain fault, the Changma fault, and so on. Some of this power was also tranversed to form a thrust fault, after which the slip rate of the Altyn Tagh Fault decreased to 1~2 mm/a. There has been little formal research and no systematic study made of the late Quaternary activity along the Subei Fault. Using high-resolution satellite imagery and systematically studying the Subei Fault area, we generated complete geology maps of the Subei area at a scale of 1∶25,000 and some maps at a scale of 1∶5,000. In addition, we completed other tasks, including a trench study, ¹⁴C sample dating, and measurements made by small unmanned aerial vehicles (sUAVs). Our conclusions are as follows: The Subei fault is a Holocene thrust fault that has exhibited multiple-staged activity since the late Quaternary, based on the structure transform mode put forward by Xu Xiwei in 2003. Moreover, our study shows the sUAV to have broad application prospects. We can rebuild a digital elevation mode based on hundreds of pictures collected by sUAVs with a very high precision. Using this technology, we can also build digital orthoimages any places we wish. Using digital elevation models (DEMs), we chose typical landforms and extracted their profiles to show the altitude of the scarps. We compared the altitudes measured by the DEM profile with measurements by the laser range finder, and found the measurement results to be basically the same. Combining several fault profiles along the Subei Fault and that of a trench excavated in Xishuigou, we determined that the Subei Fault is mainly a thrust fault, with linear and continuous scarps along the fault.

Abstract:Since cross-fault means have been determined for nearly 40 years, the Sichuan area has accumulated rich observational data. The Sichuan region is an earthquake-prone area and, in recent years, the Sichuan Province experienced the Wenchuan and Lushan earthquakes, which were greater than magnitude 7. These huge earthquakes resulted in a great human casualty toll and property losses. As such, conducting earthquake prediction research has great significance. There have been many studies in this field and some important achievements. In this paper, we provide an overview of Sichuan earthquakes above 7.0 before which site anomalies have been observed. We also summarize the methods with which anomaly conditions were verified prior to the two large local earthquakes. In a recent analysis, an unusual approach involving cross-fault monitoring data was used, in which the authors found the faulting rate to reflect raw-data anomalies that eventually became abnormalities. On this basis, we introduce a wavelet analysis method for determining the presence of abnormality prior to an earthquake. We analyzed two trends in wavelet decomposition entries and found earthquake occurrence to correspond with abnormal wavelet decomposition. Finally, based on our analysis of raw data and wavelet decomposition, we propose the analysis of cross-fault earthquake precursory data as a reference for future research of earthquake abnormalities. In this paper, we statistically analyze horizontal and vertical anomalies greater than those of the M_S7.0 earthquake in Sichuan Province and use wavelet analysis to analyze long-term observation data. We conclude that the cross-fault monitoring data shows good ability to reflect earthquake occurrence. At present, there are many methods for monitoring earthquakes and in recent years, earthquakes have frequently occurred. Our proposed comprehensive method for conducting retrospective earthquake research provides a very useful prediction tool.

Abstract:Considering that seismic soil pressure is the key to an efficient seismic design of an underground tunnel, seismic soil pressure on an underground tunnel in the axial direction is studied by indirect boundary element method. First, the time domain problem is transformed to discrete frequency domain problem by Fourier transform. Next, the free-field ground motion is calculated, and the scattered field is simulated by a set of fictitious loads combined with the Green' s functions of uniformly distributed load acting on an inclined line. The values of these fictitious loads are determined from the displacement boundary conditions of the underground tunnel. Then, the seismic soil pressure in the axial direction is obtained by utilizing these fictitious loads. Finally, the seismic soil pressure is transformed back to time domain by inverse Fourier transform. The proposed method is verified by comparing its results with those of the analytical solution. Based on the model of a rigid underground tunnel soil layers over elastic bedrock, the amplitude and distribution of the seismic soil pressure are analyzed through parametric studies. Several findings are obtained. (1) For the underground tunnel, the kinematic interaction plays a major role while the inertial interaction has little effect. (2) The dynamic soil-tunnel interaction (SSI) only has minimal effect on the distribution of the seismic soil pressure, but it can significantly affect the amplitude of the seismic soil pressure; moreover, the peak of the seismic soil pressure can be significantly amplified compared with the relevant free-field soil stress. (3) The distribution of the seismic soil pressure is similar with that of the free-field soil stress, which is nearly linear distribution. Furthermore, the seismic soil pressures on the top and the bottom of the underground tunnel are in opposite direction, whereas the seismic soil pressure on the bottom of the underground tunnel is large. (4) Finally, the burial depth of the underground tunnel affects the amplitude and the distribution of the seismic soil pressure. Furthermore, the amplitude of the seismic soil pressure increases with the augmentation of the burial depth. A simplified estimation method is proposed for analyzing seismic soil pressure in accordance with its basic law. The simplified method is based on free-field seismic response analysis, which does not require the calculation of the dynamic soil-tunnel interaction. The method can be utilized to estimate the design load for underground tunnel seismic design in the axial direction.

Abstract:The results of seismic hazard analysis are significantly influenced by the seismicity parameters in the potential seismic source zones (PSSZ) and the attenuation relations of the seismic ground motion. According to the PSSZ map used to prepare the fifth-generation seismic zonation map of China, and by the use of two magnitude interval types (type I, type II), we established the self-edit and the fifth-generation seismic zonation map's spatial distribution functions of the PPSZ, respectively. By combining these with four groups of attenuation relations of the horizontal peak ground acceleration (PGA) on the Qinghai-Tibet plateau and its peripheral areas, we computed the PGA of the rock sites for a 10% probability of exceedance in 50 a (10% P.E in 50 a) (return period of 475 years) for 81 points along the Qinghai-Tibet Engineering Corridor (QTEC). To do so, we used the China probabilistic seismic hazard analysis method and empirical equations to translate the general site PGAs from the rock site PGAs. Then, we compared the results with the archive limits of the fifth-generation seismic zonation map of China. These results show that the PGAs with attenuation relations of the horizontal PGA in western China are greatest, in Yunnan region are smallest, and in the Sichuan-Tibet region and northeastern Tibetan plateau are in the middle. When attenuation relations are known, the PGAs computed by self-edit spatial distribution functions are generally slightly larger than those computed by the spatial distribution functions of the fifth-generation seismic zonation map. In the area of the PSSZ, in which the upper limit magnitude is 8.5, and its nearby area, the magnitude interval types of the spatial distribution functions significantly influence the results of the seismic hazard analysis. Our comprehensive analysis shows the calculation results to be relatively ideal when using the self-edit spatial distribution functions of type II and the PGA attenuation relations in the Sichuan-Tibet region. Lastly, using this relatively ideal parameter combination, we computed the rock site PGAs of the grid points (0.05°×0.05°) in QTEC and used empirical equations to translate the rock site PGAs to general site PGAs. Then, with the aid of arcGIS, we drew the rock site and general site PGAs for the 10% P.E in 50 a zonation maps of the QTEC.

Abstract:The dynamic response of two-phase saturated porous media is of great significance in the field of earthquake engineering. The solution to this problem is complicated due to the dynamic coupling between the solid and liquid phases. So, its volatility is very large using general numerical software, and the results are generally not ideal. Hence, it greatly hinders the speed of the numerical methods for the study of the two-phase coupling problem. In this paper, the advantages of COMSOL in solving the multi-field coupling problem is utilized, to provide the wave equation characteristics of the Biot-saturated porous medium u-U coupled mode, using a series of differential operators and matrix transformation. Then, the wave equation of the derivative is obtained, based on the generalized partial differential equation model in the COMSOL Multiphysics module to solve the converted wave equation, and the improved infinite element boundary is applied to the simulation of the infinite domain dynamic problem. To prove the scientific nature of this method, the following methods are used to verify the accuracy of the method. By comparing with the analytical solution of the dynamic response of a saturated porous medium, the feasibility and correctness of the proposed model is verified, and based on this method, the relationship between the screening efficiency of the open trenches in the saturated soil foundation and the Poisson's ratio and porosity of the saturated soil are discussed. Through the research and analysis in this paper, the solution to the numerical solution of the dynamic coupling equations of the saturated porous media is realized, and it can also provide some valuable reference for the design of the open trenches vibration isolation in the saturated soil foundation. On the other hand, it also provides some valuable reference for practical engineering applications.

Abstract:Based on experiments related to the dynamic characteristics of intact loess in Lanzhou, Gansu Province, in this paper, we investigate the prediction of the seismic subsidence of loess under earthquake load. We analyzed the relationship between shear-wave velocity and the seismic subsidence coefficient for different water-content intervals and the functions was polynomial-fitted. In a similar manner, we analyzed water content and the seismic subsidence coefficient at different shear-wave velocity intervals. By analyzing the relationship between shear-wave velocity and water content, we established a new method for evaluating the characteristics of the seismic subsidence of loess by associating shear-wave velocity with water content. We then used this method to predict the seismic subsidence of loess in the Yongdeng earthquake. The results indicate that the seismic subsidence coefficient increases with increasing water content at certain shear-wave velocity intervals and decreases with increasing shear-wave velocity at certain water-content intervals. We determined the absolute seismic subsidence ability to characterize the potential seismic subsidence ability that remains constant in different external loess conditions, as reflected by the shear-wave velocity. We also determined the absolute seismic subsidence coefficient to be proportional. We found water content to influence the release of the potential seismic subsidence ability. We used a case example to demonstrate the obvious practicality of this method.

Abstract:A large number of site seismic safety evaluations of major projects have recently been carried out in the Wuhan area, and, from these works, data on the shear-wave velocity of soil from the engineering geological borehole were collected. These data were obtained at different depths in the borehole. The area around Wuhan city was divided into four geological engineering zones according to rock and soil type. The first zone was analogous to the first terrace in the Yangtze and Hanjiang Rivers, and the second zone was analogous to the second terrace in these river. The third zone was analogous to the second terrace in the Yangtze and Hanjiang Rivers. The fourth zone was analogous to the exposed area before the quaternary bedrock. The statistical work in this paper included shear-wave velocity data of 8,305 measure points. In the first zone, 880 measure points of silty clay with depths ranging from 1 m to 52 m, 630 measure points of clay with depths ranging from 1 m to 54 m, 295 measure points of silt with depths ranging from 2 m to 42 m, 955 measure points of silt sand with depths ranging from 1 m to 48 m, 1,164 measure points of silty-fine sand with depths ranging from 1 m to 76 m, 1,433 measure points of fine sand with depths ranging from 1 m to 70 m, 804 measure points of medium-coarse sand with depths ranging from 1 m to 75 m, and 469 measure points of gravelly soil with depths ranging from 3 m to 72 m were made. In the second zone, 440 measure points of silty clay with depths ranging from 1 m to 36 m and 239 measure points of clay with depths ranging from 1 m to 42 m were made. In the third zone, 503 measure points of silty clay with depths ranging from 1 m to 36 m and 239 measure points of clay with the depths ranging from 1 m to 38 m were made. The maximum shear-wave velocity of all drilling boreholes exceeded 500 m/s. Thus, the depth of all drilling boreholes was consistent with the requirements of the engineering site seismic safety evaluation (GB17741-2015). By using three statistical models of the first-order linear equation, exponential equation, and unary polynomial equation of two degree, the empirical relationship between shear-wave velocity and depths of different conventional soil types in three geomorphic units were respectively obtained. Results showed an obvious correlation between shear-wave velocity and soil depth. Overall, the polynomial equation in one two-order showed the highest fitting accuracy. Comparison between the measured and predicted values showed very minor differences. This result indicates that the relationship between shear-wave velocity and soil depth is reliable and reasonable. Taken together, the results of this work could be used as a reference when shear-wave velocities are not tested for sites.

Abstract:In recent years, many earthen archeological sites have been extensively damaged because of urban and traffic construction as well as the lack of effective measures to test and evaluate them. Based on the blasting vibration observation of the G7 highway, the attenuation analysis of peak particle acceleration and peak velocity is carried out to study the impact of blasting vibration on the earthen archeological site of the Mingshui military fortress that is adjacent to the blasting site. According to the observation and data analysis of vibration acceleration and speed in vertical and horizontal directions, the attenuation law of vibration peak particle acceleration of some particles is examined under different explosive capacities. Construction suggestions related to vibration control site and maximum explosive capacity near the highway blasting are given, and the related data of blasting construction near the earthen ruins are accumulated. Finally, the corresponding results and suggestions can provide reference to similar efforts to protect earthen ruins in the future.

Abstract:Site conditions can cause scattering and diffraction of seismic waves and therefore, the amplification and de-amplification of earthquake ground motions may occur. This study focuses on the influence of a weathered canyon on the ground motion that is key input to the seismic design of critical structures. In fact, the site effect of a weathered canyon is crucial to the seismic stability of engineering structures like dams and bridges. To reveal the influence of the weathered layers on the earthquake ground motions, an analytical model of a locally layered semi-circular canyon subjected to a cylindrical SH wave emanating from a line source is established. With the aid of the wavefunction expansion method and the region-matching strategy, a rigorous analytical solution to this problem is derived. The entire region of the half-space with a weathered canyon is firstly divided into three sub-regions. Then the wavefields for the sub-regions, in terms of the series of Bessel and Hankel functions with unknown complex coefficients, are constructed to satisfy the Helmholtz equation by means of the separation of variables method. The solution is finally obtained as the unknown coefficients are sought using the continuity conditions on the interfaces of the three sub-regions. It is worth noting that the wavefield coefficients are in an explicit form which can guarantee high efficiency of the solution. To clearly identify the amplification or de-amplification of the ground motion, the near-source amplification factor is calculated by normalizing the seismic response to the free field of the line source. Based on both results of the surface displacement amplitudes and the ground motion amplification factors for the weathered semi-circular canyons, it is found that the location of the near source is an important factor influencing the site effects. There will be more amplifications and reductions of ground motions within a certain area near the canyon if the source is located farther from the canyon site.

Abstract:In the actual hydraulic fracturing process, the fracture always extends along a direction perpendicular to the minimum stress. The distribution of the in-situ stress and the interaction between multiple fractures (stress shadow effect) play important roles in the formation of a complex fracture network. Based on the extended finite element method (XFEM), in this paper, we simulate the arbitrary propagation of fractures in porous media. Since we introduce the enriched degree of freedom based on the traditional finite element method (FEM), with which we can describe discontinuous displacement, the fracture can be propagated independent of the mesh. By introducing a one-dimensional flow assumption, we solve the lubrication equation, taking into account the flow of the fluid in the fracture. At the same time, we also consider the leak-off effect of the fracture on the matrix. We investigate the influence of the propagation pattern and stage distance on the fracture morphology under different perforation spacing in the actual construction. The results show the fracture in the middle is shielded when the stage spacing is too small. In addition, the fracture will turn due to the stress shadow effect.

Abstract:The stability of a layered rock slope is affected by many factors,such as slope height, slope angle, structural plane strength, and so on. The degrees of influence of such factors vary, and in most cases, depend on the comprehensive judgment generated from an actual engineering exploration. In an orthogonal experiment that features two main parameters (factors and levels), a factor refers to the set of elements that may directly affect the results of a test and may be single or multiple. The level of factor refers to the specific value of the human factors in the experiment. This paper analyzes the sensitivity of the main factor, which affects the stability of the rock slope and determines the composition of the primary factor as follows: the slope height H>slope angle β > structural surface cohesion C > structural surface friction angle φ > rock density γ > the dip angle α > block thickness h > rock cohesion. Next, we discuss the efficiency of the finite element method in determining slope accuracy, which is also an important factor that can affect the stability of a slope. By taking the numerical calculation of the rock slope of a typical single line sliding surface as an example, the influences of element mesh size and boundary condition on the safety factor of slope stability is analyzed. Some numerical simulation suggestions are proposed according to the calculation results, and these suggestions are used to improve the accuracy of the numerical calculation of the known sliding surface rock slope. In general, the common sliding surface application of 20~30 in the interface unit is enough, and the mesh size is roughly set at 2~3 m to meet the accuracy requirements. We also find that the smaller the mesh size is, the longer the time required, although the safety factor only showed a slight change. There should be at least three or four layer elements under the potential sliding surface to ensure the transition to the fixed support boundary. According to the preliminary forecast, in order to prevent the wave reflection at the interface, element size should be controlled in the λ/10~12 (where λ is the wavelength), because of the encryption unit within the analysis of dynamic stability of slope, thus increasing the scope of the model.

Abstract:A new large-scale, computer-controlled, compression-torsional multi-axial loading apparatus has been designed, developed, and tested. This apparatus integrates many geotechnical testing functions, such as cyclic triaxial and cyclic torsional shear. This apparatus has three main characteristics. First, it features specimens of two different sizes, which can be chosen according to the experimental requirements. The height of the larger specimen reaches 600 mm. Second, the loading degrees of freedom, including axial force, torque, inner pressure, outer pressure, pore pressure, and related displacements, can be controlled separately, which is useful in the study of soil behavior under complicated stress paths. Finally, the stress or strain path can be preprogramed into the computer before conducting tests and can also be controlled automatically during the tests. Test results show that the control accuracy of the apparatus can meet the requirements of geotechnical material tests.

Abstract:Microtremor, also known as microseism and ambient noise, refers to the tiny vibration of the earth. Its amplitudes range from about a few to a few hundred microns, and its frequencies range from about a few seconds to tens of Hz. Generally, microseisms refer to the low frequency waves produced by wind and ocean waves, whereas microtremors refer to high frequency waves created by mechanical vibration excitation, the boundary of which is about 1 Hz. The microtremor wave field is a complex time-varying field, and its main ingredient is the fundamental mode of the surface wave, a small amount of body wave, and high order surface wave. Fundamental mode Rayleigh waves dominates the vertical component, whereas Love waves dominate the horizontal component. Shear wave velocity structure is an important index for site condition and is considered an engineering site classification. Convenient and economic field near-surface velocity structure exploration methods have been the focus of research in the field of engineering seismic exploration. In the seismic active fault evaluation of near fault strong ground motion, a 3D underground structure model must first be established. Artificial or natural seismic exploration methods cannot meet the requirements, and some sites are also limited by existing buildings, deployment difficulties, and low resolution for the surface velocity structure. Meanwhile, blasting as a means of seismic exploration in urban areas have received increasingly less public acceptance. The drilling method is the most direct method to determine the soil ground velocity structure and soil dynamics parameters, but the high cost and limited drilling depth restrict its large-scale use. Compared with the above method, the Rayleigh surface wave method is economical, simple, and convenient; it has unique advantages in solving the abovementioned problem. Based on the generation of the Rayleigh wave signal as well as the collection and analysis methods, the surface wave method can be classified into two types: active detection method (SASW, MASW) and passive method (Spatial Autocorrelation Coefficient (SPAC), F-K). The microtremor survey method involves many steps and subjective judgment, and entails the necessary pre-processing of data, post-processing of the dispersion curves, and rapid on-site assessment tools for array. In order to facilitate technical engineering use, developing a visualization analysis software system is necessary. According to the need of microtremor data processing, we developed the software system (MSM-SPAC) for the SPAC microtremor survey method. The main functions include the design of the observation array, the azimuth distribution analysis of the array, data format conversion, selection of the effective interval of observation data, data signal filtering, re-sampling, SPAC coefficient parameter calculation, dispersion curve extraction, editing, merging, and project management. The software is user-friendly and easy to operate.

Abstract:The 16^th World Conference on Earthquake Engineering was held in Santiago,Chile in January 9-13,2017.The theme of this conference is "Resilience,the new challenge in earthquake engineering".The author had the honor to participate in this Conference.This paper gives a brief introduction to the general program of the conference,which includes 3 invited lectures,2 debates and 12 parallel sessions of special topics,and lastly shares the author's personal experience and thinking.These 3 invited lectures titled "Resilience,the new challenge in earthquake engineering","The quest for resilience in seismic design of RC buildings:The Chilean practice","Effects of Long-Duration Motions on Soil Liquefaction Hazards".And these 2 debates about "Performance-Based Design:Promises and Pitfalls?","Prescription of Seismic Demands:Probabilistic vs.Deterministic".And those 12 parallel sessions include topics:Assessment of the probability of structural collapse,Non-technical strategy on improving housing seismic safety in developing countries,Field investigation and Analysis of recent destructive earthquakes including 2015 Nepal earthquakes,Soil-structure interaction of deep foundation,Ground failure liquefaction,Earthquake-induced landslides in natural slopes,Geotechnical laboratory test and in-situ test,Seismic hazard,risk and earthquake risk management at city level,Resilience,Earthquake risk economy and insurance,The future of the city:planning for future earthquake risk,Management policies,etc.

Abstract: