Abstract:Based on the displacement rate of GPS stations in Shanxi rift zone from 1999 to 2007, the changes of maximum principal stress and maximum shear stress at the depth of 10 km in the crustal zone of Shanxi rift zone were calculated with the Green function method, and the results were compared with regional geological structure, strong earthquake activities, and focal mechanism solution. The study results showed that strong earthquake activities in Shanxi rift zone is controlled by regional tectonic stress field. Nowadays, the seismic activity level is relatively high in the region with strong stress field variation, and the seismic focal mechanism is consistent with the variation characteristics of tectonic stress field. The variation of tectonic stress field and strong seismicity are also affected by the strong earthquake activities in tectonic-related areas. The activities of moderate and strong earthquakes along the Yuanping section in Xinding Basin to the Shilingguan uplift since 2009 may be related to the Wenchuan M8.0 earthquake. A high background stress level shows in southern Shanxi, especially Yuncheng Basin, so further attention should be paid to the seismic hazard in the area.

Abstract:Earthquake events can be divided into natural earthquakes and non-natural earthquakes according to the generating mechanism. Collapse earthquakes belong to the common earthquake events in non-natural earthquakes. In this paper, we selected 50 collapse earthquakes in Pingliang area of Gansu Province and 50 natural earthquakes in southeastern Gansu Province, and 30 earthquakes to be measured in the same area. The convolution neural network, an advanced image recognition method in computer field in recent years, was selected to identify two types of seismic events. 80% of the total number of waveform channels was set as the classification threshold of seismic events, that is, more than 80% of the waveform channels were "0" or "1". Seismic events were taken as the original images, and the most representative feature points in the images were extracted. Then the feature points were classified and compressed by the pooling layer, and the most representative image features were extracted to output the recognition image. The results showed that final classification accuracy of collapse earthquakes is 86.7% and that of natural earthquakes is 93.3%, and the total recognition rate is 90%. The results can provide a reliable reference value for future classification of collapse earthquakes in Pingliang area.

Abstract:Based on the observation data from Liaoning Digital Seismic Network since 2001, we used the Wadati method of single station to calculate the average wave velocity ratio of 34 stations in Liaoning Seismic Network, and focused on the spatial distribution characteristics of wave velocity ratio in Liaoning area. The results showed that the spatial distribution of wave velocity ratio in Liaoning area has laterally heterogeneities. The average wave velocity ratio in Xialiaohe basin is lower than that in the whole Liaoning area, while the wave velocity ratio in western and eastern Liaoning is significantly higher than that in Xialiaohe basin and the average value of Liaoning area. It is also found that M≥5.0 earthquakes in Liaoning area mostly occurred in the low-value zone of wave velocity ratio or the transition area of high to low value. The calculated average wave velocity ratio of each region has a certain reference value for future analysis of wave velocity ratio changes in Liaoning area.

Abstract:Through the analysis of the data recorded by the Yry-4 component strain gauge, the water level gauge, and the seismograph at Linxia seismic station, it is found that before the Wenchuan M_W7.9 earthquake on May 12, 2008, both of the pre-slip seismic phase Xp and the tremor seismic phase Tp were recorded by the above three instruments in a similar period. In this paper, based on the summary of the record characteristics of Xp and Tp phases, the physical mechanism of pre-slip and tremor phase recorded before the earthquake was confirmed and explained by the results of indoor small-scale stick slip experiments. The results showed that: on April 18 and May 6, 2008, two large-scale pre-slip dislocations occurred on the block where Linxia station is located, and N tremors were accompanied before and after the pre-slip. These two large-scale pre-slip dislocations may be related with the Wenchuan M_W7.9 earthquake.

Abstract:Based on the hyperspectral remote sensing data, the influencing factors of CH₄ and CO were analyzed and applied to the abnormal determination in Beijing-Tianjin-Hebei region. The correlation coefficient between hyperspectral gas in different terrain and water vapor, temperature, long wave radiation, and air pressure were calculated. It is found that the correlation coefficients on land and ocean have different characteristics. There is a strong negative correlation between CH₄ and Co, and the correlation coefficient in basin is greater than that in mountain area and plain area. The results showed that CH₄ concentration in terrestrial environment is greatly affected by meteorological factors such as water vapor, temperature, and air pressure, while CO has low correlation coefficient with the parameters due to the influence of marine sources. The recent hyperspectral gas anomaly in Beijing-Tianjin-Hebei region is extracted by RST algorithm. It is found that there is an obvious high-value anomaly in June in the border area of southwest Beijing and Hebei. Through the test of regression equation, it is more likely that the anomaly is caused by meteorological factors, which provides a basis for the earthquake tracking and judgment.

Abstract:In this paper, we first collected the seismic data of 76 fixed seismic stations in Tangshan and its neighboring areas from 2010 to 2018, then we inverted the source position and three-dimensional velocity structure of P-wave in the middle and upper crust of Tangshan and its adjacent areas by applying the method of double-difference tomography. The results showed that the change of P-wave velocity in shallow area is consistent with the distribution of surface geological structure and active faults. In the upper crust, the variation of P-wave velocity between the two sides of Tangshan fault is obvious, and the velocity structure of P-wave has significant lateral heterogeneity. There is a distinct low-velocity anomaly in the middle crust, which may be related to the intrusion of mantle source materials. After earthquake relocation, the distribution of epicenter position is more concentrated, and M_L＞3.0 earthquakes are mainly located in the high and low speed transition zone of P-wave.

Abstract:The middle section of Qilian Mountains is considered to be a key area where strong earthquakes might occur in recent years, but the earthquake situation in the study area is still unclear. Therefore, it is of great practical significance to study the anomaly characteristics of geoelectric observation data recorded by Shandan station in Zhangye City, Gansu Province. On September 16, 2019, an M_S5.0 earthquake occurred in Ganzhou District, Zhangye City, Gansu Province. Before the earthquake, there were obvious short-impending anomalies in the observation data of Shandan earth resistivity and geoelectric field, with an epicenter distance of 63 km. In this paper, the anomalies were analyzed and summarized, and they were considered to be reliable earthquake precursor anomalies after excluding the surrounding observation environment, observation system, natural environment, magnetic storm, and other factors. The abnormal forms of earth resistivity and geoelectric field observation data in different channels were also discussed. It is found that the earthquake occurred when the above-mentioned observation data had a turning change or the rising (falling) rate changed during the anomaly duration

Abstract:On Feb 3, 2020, an M_S5.1 earthquake occurred in Chengdu, Sichuan Province. The epicenter of the earthquake event is located on the Longquanshan fault zone, 38 km away from the center of Chengdu. As a rare earthquake event with M≥5.0 in the history of Longquanshan fault zone, a comprehensive analysis was carried out on the seismogenesis of this event: (1) The seismicity along the Longquanshan fault zone was discussed by collecting historical seismic data; (2) the location of main earthquake was relocated by using high-quality waveform data; (3) the seismogenic structure and fluid influence were analyzed through seismic tomography; (4) the relationship between the earth tide and the earthquake was analyzed by using the theoretical model of earth tide. The results showed that the M_S5.1 earthquake occurred in the northern part of Longquanshan fault zone with epicenter coordinate of (30.732°N, 104.529°E) and focal depth of 15.12 km. The source is located near the transition zone of high-low Poisson's ratio, accompanied by a wide range of low velocity anomalies. Furthermore, the change of shear stress caused by the earth tide on the fault plane is also considered to be closely related to the triggering of the earthquake, which indicates that the seismic risk of the northern part of Longquanshan fault zone has reached a high level before the earthquake. This study suggests that the deep fluid intrusion, the coseismic effect of strong earthquakes, and the comprehensive influence of specific seismogenic and tectonic environment may be the main factors leading to the triggering of this earthquake.

Abstract:On September 4, 2018, an M_S5.5 earthquake occurred in Jiashi, Xinjiang. In this paper, the CAP method was applied to calculate the focal mechanism solutions of the M_S5.5 mainshock and M_S≥3.0 aftershocks, and the result showed that the strike, dip, and rake angles of nodal plane Ⅰ and Ⅱ are 48°, 83°, 3°, and 318°, 87°, 173°, respectively. The azimuth and plunge of the principal compressive stress P axis are 3° and 3°, respectively, and the azimuth and plunge of the principal tensile stress T axis are 273° and 7°, respectively. The moment magnitude of the mainshock is M_W5.3. The double-difference location method was used to relocate 129 earthquakes with M_S≥1.5, and the focal mechanism solutions and relocation results were comprehensively analyzed. It is found that the earthquake distribution obtained from relocation result is consistent with that from the inversion result of CAP method, and the earthquakes are concentrated in the NEE direction. Therefore, it is considered that nodal plane I is the main rupture plane of this earthquake. After relocation, the average relative errors of NS, EW, and UD directions are 0.25, 0.23, and 0.09 km, respectively. The average travel-time residual is 0.026 s, and the focal depth is concentrated in 5-15 km. It is preliminarily determined that the 2018 Jiashi M_S5.5 earthquake may be controlled by the hidden fault near the Keping fault zone.

Abstract:In air-gun source detection, some effective signals are missing or seriously disturbed by random signals due to the influence of various interference factors. To reconstruct continuous and complete data, a missing signal reconstruction method based on compressive sensing is constructed according to the sparse characteristics of air-gun source signals in a Fourier transform domain. First, a numerical simulation is carried out, and the processing effect of this method is compared with that of the traditional interpolation method. The root mean square error and signal-to-noise ratio analyses of the reconstruction effect are carried out. Results show that the compressive sensing method has a high waveform coincidence, strong amplitude consistency, and clear and continuous phase axis and suppresses noise before and after reconstruction. In conclusion, the reconstruction effect of this method is better than that of the traditional cubic spline interpolation method. The method is applied to practical data, and the results show that the interfered effective signal can be well reconstructed.

Abstract:How to realize the parameterization of velocity pulse and analyze the characteristics of parameters is a problem worthy of further study. In this paper, 126 groups of near-fault pulse-like ground motion records were selected from the NGA-West2 database. The velocity pulse model was used to obtain the characteristic parameters of horizontal component based on the least square method. The effects of magnitude, fault distance, and site type on the pulse parameters were studied, and the characteristics of the pulse parameters of fault-normal component and fault-parallel component were compared. The results showed that the change rate of peak pulse value of fault-normal component with magnitude and fault distance is faster than that of fault-parallel component, and the site conditions have a great influence on the variation of peak pulse with magnitude and fault distance. There is a strong linear correlation between the half pulse period and the main pulse period, and the variation of them with the magnitude is different. With the same magnitude, the pulse peak moment in bedrock site is smaller than that in soil site. For the Chi-Chi earthquake, the small shape parameters are mainly concentrated near the rupture fault. With the increase of fault distance, the difference of pulse shape parameters between different components also increases.

Abstract:Earthquake intensity distribution is an important basis for the rapid assessment of disaster losses, emergency rescue, and restoration and reconstruction after the earthquake. At present, the seismic intensity circle is mainly drawn manually according to the intensity survey points obtained from field survey by using the GIS software. However, the traditional method is inefficient and time-consuming. In this paper, a method of automatic delineation of seismic intensity circle was proposed. First of all, the factors affecting seismic intensity mapping were fully considered. According to the aftershocks distribution and the types of seismogenic faults, the location of macro epicenter and the long axis direction of intensity circle can be determined. Then, the envelope was generated based on the maximum discrete intensity points. The statistical relationship between the maximum intensity and the area of intensity circle was taken as the constraint condition, and the maximum intensity circle was obtained by using the adaptive algorithm. Finally, combined with different discrete intensity points, other intensity circles were obtained by using the above-mentioned method, and the Jiuzhaigou M7.0 earthquake was taken as an example. The experimental results showed that the proposed method can automatically generate intensity circle, and the accuracy of intensity circle generated by discrete intensity points obtained from the fusion of multi-source disaster information in 28 hours after the earthquake is over 80%. The method effectively improves the delineation efficiency of earthquake intensity circle, and can provide support for the rapid development of earthquake emergency rescue work.

Abstract:To investigate the microscopic mechanism of sand liquefaction, this study proposes a time-effect relationship according to the generation rate of bubbles in indoor microbial denitrification test. Highly saturated sand samples were treated with microbiological method for 0, 2, 3, and 5 days. The samples were subjected to cyclic triaxial undrained shear tests by CFD-DEM coupling method under different working conditions. Changes in force chain distribution, vibration time, pore pressure ratio, axial strain, and mechanical coordination number of the samples during the load process were determined to study their liquefaction resistance. Numerical results show that the liquefaction resistance of the highly saturated sand samples containing microbial bubbles is higher than that of fully saturated sand. With increasing treatment time, the saturation degree of the samples decreases but their liquefaction resistance increases; moreover, the pore pressure ratio and axial strain increase slowly.

Abstract:Continuous rotation of the principal stress axis of a foundation soil element will occur under the action of seismic load, and different stress coupling modes have shown significant effect on the strength, pore pressure, and deformation of soil. In this paper, the cyclic shear tests on saturated clay in Tianjin coastal site under K₀ consolidation and different stress coupling modes are carried out using the hollow cylinder torsional shear apparatus GCTS. Deformation behavior and cyclic softening characteristics of saturated clay under bi-directional, three-directional, and four-directional coupled loading modes with the same stress paths are compared. The experimental results showed that, under the same dynamic strength, saturated clay is more easily destroyed under a four-directional coupled stress mode, and the deformation and softening characteristics under this mode develop more rapidly than under bi-directional and three-directional coupled loading modes under the same dynamic strength. The effect of the shear stress component on the softening deformation characteristics of samples is more significant.

Abstract:To study the failure possibility of frame-bent structures under near-fault earthquake, the nonlinear finite element analysis model was established based on a reinforced concrete frame-bent structure. 16 near-fault and 8 far-field seismic waves were selected, and the incremental dynamic analysis method was used to draw the vulnerability curves. The results showed that for far-field ground motions, five limit states of the structure (normal use, basic use, use after repair, life safety, and collapse prevention) are not beyond under 8-degree frequent and basic earthquakes, thus meeting the seismic requirement of "no damage under minor earthquake, repairable under moderate earthquake"; the probability of exceeding limit state of normal use under 8-degree rare earthquake is 2.08%, thus meeting the seismic requirement of "no collapse under major earthquake". For near-fault ground motions, the first four limit states are exceeded under 8-degree frequent earthquake; under 8-degree basic earthquake, the probability of exceeding the limit state of use after repair is 16.62%, and the probability of reaching the limit state of life safety is 2.40%; the probability of approaching collapse under 8-degree rare earthquake is 15.4%. The research results can provide reference for seismic risk assessment of frame-bent structures in near-fault area.

Abstract:Previous experimental data show that the soil parameters have great spatial variability, which can be effectively simulated by the random field theory. The traditional spectral representation method (SRM) can not accurately simulate the cross-correlation between the parameters of multidimensional-multivariate random field. A support vector machine (SVM) and SRM coupling method was proposed in this paper. As a general machine learning method based on statistical learning theory and the principle of structural risk minimization, SVM has many advantages in solving the problems such as limited training data, nonlinear and high-dimensional pattern recognition. The shear strength parameters of soil (cohesion c and internal friction angle φ) were taken as an example, and the experiment proved that there is a natural negative correlation between them. The results showed that the proposed method can not only effectively describe the auto-correlation of variables, but also accurately describe the cross-correlation between variables under limited training data. The study provides an effective method to simulate multidimensional-multivariate random fields with a limited training data.

Abstract:To improve the safety and stability of stick-slip fault tunnels in a meizoseismal area, the rigid and flexible compound anti-reducing dislocation technology for stick-slip fault tunnels was analyzed in this paper on the basis of the stick-slip fault F1 of Youyi tunnel in the Dujiangyan-Wenchuan highway. After structure reinforcement measures were taken to resist the influence of fault stick-slip dislocation, the anti-reducing dislocation effect of structural displacement is not obvious, and the average anti-reducing dislocation effect of structural internal force is between 23%-33%. Setting the dislocation reducing layer can help reduce the influence of fault stick-slip dislocation. The anti-reducing dislocation effect of vault settlement and sidewall convergence are over 20%, while the average anti-reducing dislocation effect of structural internal force is between 37%-47%, better than the structural reinforcement measures. Rigid and flexible compound measures have good effects; the anti-reducing dislocation effect of vault settlement and sidewall convergence is over 30%, and the average anti-reducing dislocation effect of structural internal force is more than 80%. The results can provide a reference for the design of seismic disaster prevention and control for stick-slip fault tunnels in meizoseismal areas.

Abstract:To analyze the vibration responses of high-speed railway subgrade and track under the coupling action of seismic load and train moving load, a dynamic model of track structure-subgrade-foundation considering the coupling input of earthquake-train moving load was established based on the dynamic interaction of track structure-subgrade-foundation. First, DLOAD subroutine and ABAQUS finite element calculation program were compiled to realize the coupling effect of seismic load and train moving load. Then, the numerical simulation was carried out to analyze the dynamic responses of pile-supported subgrade and free subgrade of high-speed railway under the coupling action of seismic load and train moving load, and the vibration response difference between them were compared. The numerical results showed that the coupling load has a significant effect on the dynamic response of pile-supported subgrade. Under the coupling load, the resonance phenomenon occurs on the pile-supported subgrade, which makes the vibration displacement amplitude of track and subgrade in pile-supported subgrade larger than that of free subgrade. The pile-supported subgrade will not affect the vibration frequency of subgrade system, but will change the vibration amplitude. The acceleration in the X direction of track on pile-supported subgrade, the vertical acceleration at the shoulder and toe of subgrade are reduced by 6.2%, 50%, and 28.6%, respectively.

Abstract:Using GCTS' resonant column system, we conducted a series of dynamic behavior tests of clayey sand to study the effects of relative compactness on the dynamic shear modulus and damping ratio of clayey sand. We also considered the influence law. The test results show the relative compactness to have an effect on the dynamic shear modulus, the dynamic shear modulus ratio, the damping ratio, and the maximum dynamic shear modulus. The dynamic shear modulus was found to increase with increases in the relative compactness. When the clay content is low, the dynamic shear modulus ratio was found to increase with increases in the relative compactness. When the clay content is high (≥16%), however, the dynamic shear modulus ratio was found to be hardly affected by the relative compactness. We found the damping ratio to decrease with increases in the relative compactness. The maximum dynamic shear modulus was found to increase with increases in the relative compactness, but the increase in amplitude differed with different clay contents. We established the relation between the maximum dynamic shear modulus and the relative compactness, and provide the relevant parameters.

Abstract:To study the influence of interface in layered foundation on the vibration isolation effect of open trench, three kinds of open trenches with different depths were selected by model test, i.e., less than the interface depth, equal to the interface depth, and more than the interface depth. Then, by changing the width and position of open trench and the excitation frequency, the influences on the vibration isolation effect of open trenches with three different depths were analyzed. The results showed that: when changing the width and excitation frequency, the change of vibration isolation effect of the open trench with depth equal to the soil interface is the least obvious; when changing the width and position of the open trench, the vibration isolation effect of the open trench with depth less than the interface is most affected; when changing the excitation frequency, the effect of the open trench with depth greater than the soil interface is most affected. If the remaining parameters are fixed and the trench depth is gradually increased, the A_r value will increase when the depth reaches the interface, which is affected by the excitation frequency. The lower the excitation frequency is, the greater the rising range is, and the rising range of low frequency is the longest. In conclusion, when choosing the vibration isolation trench, we should pay attention to the influence of above factors and reasonably design the vibration isolation trench to achieve the best vibration isolation effect.

Abstract:To study the dynamic response of running tunnels in liquefiable site, the dynamic responses of tunnel structures under uniform excitation, local liquefaction, and traveling wave excitation were analyzed by the FLAC^3D software. The calculation results showed that the liquefaction of foundation soil affects the stress state of tunnel lining, and the failure position of lining changes from the arch shoulder and arch foot in non-liquefied site to the invert arch and arch waist in liquefied site. Compared with the liquefaction site, when the tunnel passes through local liquefiable soil, the failure position extends to the whole section of lining. Compared with the uniform excitation, under traveling wave excitation, the principal stress of lining increases, the distribution of principal stress changes, and the torsion effect bears.

Abstract:The implementation premise for seismic ductility mechanism of building structures is that the basic design principles such as "strong column-weak beam" are carried out actually. In previous earthquakes, seismic damage of RC frame structures run counter to the seismic ductility mechanism. In this paper, the experiment and simulation study of the influence of slab and reinforcement on the formation of "strong column-weak beam" mechanism by using effective flange of beam were summarized. Based on SAP2000 software, pushover analysis were carried out on three models of RC frame structures, i.e., structure without floor, structure without floor but considering beam stiffness amplification, and structure with floor by using three lateral loading modes. The relationship curve of force and displacement, the order of plastic hinge, the top displacement, and inter story displacement were analyzed. The results showed that: the phenomenon of "strong column and weak beam" in pure frame structure without floor slab is the most obvious, followed by the model considering the beam stiffness amplification, and that in structure with floor slab is the least obvious. It is proved that the negative moment bearing capacity, stiffness, and other parameters reflecting "strong column and weak beam" and the occurrence order of plastic hinge have obvious corresponding relations with floor slab and in-plate reinforcement. The floor slab and reinforcement, which affect the overall deformation performance and plastic energy dissipation capacity of frame structures, are important influencing factors for the realization of seismic ductility mechanism. In subsequent structural design, it is suggested to consider the actual floor and reinforcement modeling for calculation and analysis.

Abstract:Basal sapping is the main factor of soil site collapse.Numerous research results on the sapping instability mechanism of earthen sites are mainly based on numerical simulation and theoretical analysis,and the researches on experiments of basal sapping with equal proportions are few.Based on the sapping investigation and research of rammed earth site, a 1∶1 rammed wall model was established in this paper,and the instability mechanism was studied by means of experiment and numerical simulation of wall basal sapping. The experimental results showed that:when the sapping depth is less than 20%,the wall stress changes little;when the sapping depth is more than 20%,the deviatoric stress appears and increases rapidly;when the sapping depth reaches 45%,the wall collapses.During the experiment,the stress redistribution on the wall mainly occurs in the sapping stage,and the stress change is not obvious after the sapping is stable.The collapse and failure process of the wall is very rapid,and the whole performance is rigid dumping.The stress-strain characteristics are consistent with the numerical simulation results.The research results can provide a reference for the basal protection of rammed earth sites.

Abstract:The section in underground structures with varying stiffness is the vulnerable location in seismic analysis. A finite difference method is adopted to study the seismic response of the connection between the station and the tunnel. The response of the connection of the station and tunnel, the deformation distribution of side wall around the connection, and the ground settlement distribution characteristics are analyzed. The influences of buried depth, ground motion characteristics, and stiffness of surrounding soil on the tunnel stress at the connection are particularly investigated. Results show that the middle part at the bottom of the end wall and the top and bottom parts of the end wall at the connection are sensitive to earthquakes. The presence of the end wall influences the deformation distribution of the side walls and ground settlement. The buried depth of the structures, seismic spectrum, and acceleration amplitude significantly affect the seismic response of the connecting tunnel. Additionally, the stiffness of soil around the metro station has an apparent effect on the stress distribution in the tunnel.

Abstract:The prediction model of permanent displacement, mainly used to calculate permanent displacement of seismic slope in hazard assessment of regional seismic slope, is based on the Newmark sliding theory, and is obtained by statistical fitting of a large number of measured seismic acceleration records. Aiming at the problem of the shear strength parameters of a sliding surface remaining unchanged in the Newmark theory, and the calculated displacement from the existing prediction model of permanent displacement being less than the measured displacement, two prediction models of displacement, including peak acceleration and Arias intensity, are established using the theory of dynamic critical acceleration. The rationality of the permanent displacement calculated by the model is discussed. It was found that the permanent displacement calculated by the proposed model is close to the actual displacement of an earthquake landslide. The model can solve the present problem wherein the predicted displacement is less than the measured displacement. On the basis of further discussion and development, this model can meet more theoretical applications in engineering practice, and provide new ideas for seismic risk assessment of regional slopes.

Abstract:To investigate the change law of shear strength parameters of iron ore tailings with the consolidation degree, this paper conducted a series of triaxial consolidation undrained (CU) tests on iron ore tailings with different consolidation degrees and different dry densities. The shear strength parameters and effective shear strength parameters of the tailings sand were obtained by the total stress method and the effective stress method, respectively. The analysis results showed that for tailings sand with the same dry density, as the consolidation degree increases, both the shear strength index and the effective shear strength index increase gradually. The change in the degree of consolidation has a small effect on the cohesion c and the effective cohesion c', and has a large effect on the internal friction angle φ and the effective internal friction angle φ'. φ and φ' have a linear growth trend with the increase of dry density, and the γ_d-φ curve and γ_d-φ' curve have a high fitting degree under different consolidation degrees. Therefore, in the stability evaluation and safety management of tailings dams, if we consider the shear strength variation of the tailings sand with the degree of consolidation, the stability analysis of tailings dams will be more in line with the actual situation.

Abstract:Aiming at the foundation treatment of some new goods yards in Jazan, Saudi, this experimental study focused on the validity of reinforcing the poorly graded and loose foundation of coral reef sand through two vibroflotation compaction methods. Technique parameters were determined based on the engineering characteristics of dredged coral reef sand. First, the trial of the selected field area was completed, and the effect was verified by SPT test. The optimal vibroflotation technique was determined to guide the construction in a large area. The CPT test results were compared before and after the foundation reinforcement. A further liquefaction judgment was conducted using Iwasaki liquefaction index method. The settlement analysis on the improved foundation was conducted using limit equilibrium method (based on CPT) and Schmertmann's method (based on SPT). The results were then compared. The proposed scheme and construction technology were found to be reasonable and correct. The bearing and anti-liquefaction capacity of the reinforced foundation were improved effectively and satisfied the requirement of settlement control. The results can be used as reference for similar projects in the sea area of coral reef.

Abstract:There are a large number of underground cavities in the geotechnical engineering projects. These cavities will affect the propagation of seismic waves and thus arise site effects. In this paper, the numerical simulation method was used to analyze the effect of an underground cavity on surface wave propagation and site effect. The surface wave will be scattered and reflected when it encounters the underground cavity in the process of propagation, resulting in reflected surface wave propagating in the opposite direction and converted body wave propagating in the space. Then the energy in the middle and low part of far source side of the cavity will be greatly increased, on the surface and near the surface of far source side will be decreased, and the energy in the near source side will be slightly increased. The site effect of the cavity is generally decreased with the increase in cavity depth, and increased with the increase in cavity diameter. Generally speaking, the site effect of the horizontal component of ground motion is larger than that of the vertical component.

Abstract:To study the vibration isolation effect of wave impedance blocks (WIB) in the high-speed railway embankment, a simple principle test model of the railway embankment was developed. With different vertical distance between WIB bottom and embankment top, the attenuation law of vibration wave on the model surface under harmonic load was obtained, and the vibration reduction and isolation effect was analyzed. A three-dimensional dynamic simulation analysis model of the high-speed railway subgrade was constructed, and a comparative analysis was carried out to verify the rationality of the model. The study results showed that, when WIB is set in the bottom layer of subgrade bed of high-speed railway embankment, the closer to the top surface of embankment, the better the vibration reduction and isolation effect; the vibration isolation effect of WIB on the top surface of the bottom layer of subgrade bed is better than that on the surface of subgrade bed.

Abstract:Taking a typical loess tableland slope in Pingliang city, Gansu Province, as the prototype, a large-scale shaking table test was performed on the loess tableland slope with and without cracks to study the deformation and failure characteristics of the two slopes under different earthquakes. The results showed that the failure characteristics of the two slopes with different structures were significantly different under earthquakes of different intensities. The existence of cracks reduced the seismic stability of the cracked slope. With the increase in the input seismic amplitude, the deformation and failure process of the slope with and without cracks were obtained. The deformation and fracture of slopes with two structures included two patterns: toppling-tension or shear-slip. The deformation evolution of slopes was the result of the interaction of the two models.

Abstract:To meet the requirements of vibration speed control of precise instruments, a two-stage isolation measure combined by "group pile foundation + vibration isolation row pile" and air spring was proposed. This paper mainly studied the vibration isolation effect of row piles when moving vehicle passes. Dynamic parameters of the soil under small strain were first measured, then the road surface roughness was introduced by writing a subroutine of vehicle-pavement coupling unit (VRI), and a dynamic model of road-row pile-foundation was established based on the three-dimensional finite element method. The simulated vibration velocity was compared with the measured value through 1/3 octave filtering, and the vibration isolation parameters of piles were analyzed. The research results showed that the two-stage vibration isolation system can meet the control requirements of VC-E micro-vibration; The spacing and pile length of row pile, and the number of rows are the main factors affecting the isolation effect, and the vertical isolation effect is better than horizontal effect. The research results can provide useful reference for the design and construction of environmental micro-vibration projects in future.