Earthquake Engineering

• Discussion on the story drift ratio limits of shear wall structures in seismic fortification areas with 8.5 degree earthquake

  JI Jing, LIN Haoyu, FU Hao, WU Zinan, HAN Xiaolei

  2023(2):251-259, DOI: 10.20000/j.1000-0844.20211012001

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  Abstract:

  To meet the requirements of the story drift ratio limits of structures impacted by small earthquakes, the section sizes of many vertical members are large, especially in seismic fortification areas with high seismic activity. In addition to meeting the requirements of comfort and normal use of decorative structures and mechanical equipment, the main purpose of controlling the story drift ratio under a small earthquake is to ensure that the structure will not collapse under a large earthquake. According to the data of 128 strong earthquake waves in Kashgar, Xinjiang (intensity 8.5 degrees) and local projects, and by referring to the provisions of different codes on story drift ratio limits, six shear wall structural models are designed by taking the story drift ratio and height as control parameters. The seismic performance evaluation method based on member deformation is used to study structural safety under large earthquakes. Results indicate that the six shear wall structures meet the requirement of “no collapse under large earthquakes” under the action of an 8.5- degree earthquake and possess a reasonable yield energy dissipation mechanism under twice the impact. The limit value of the elastic story drift ratio of the shear wall structure in Kashgar (Xinjiang, China) can be relaxed to 1/500 under small earthquakes.

• Experimental study on the dynamic characteristics of Zhoushan marine soft clay under different loading frequencies and cyclic stress ratios

  WANG Jinbao, XIONG Feng, LIU Xiaolin, WANG Yajun, NIAN Tingkai

  2023(2):260-269, DOI: 10.20000/j.1000-0844.20210830003

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  Abstract:

  Soft clay in different regions shows different dynamic characteristics. In this research, a series of undrained triaxial tests were carried out on the soft marine clay in the Zhoushan area using the Wille dynamic triaxial apparatus. The influence of different dynamic loading frequencies and cyclic stress ratios (CSRs) on the dynamic stress- strain- pore pressure and softening index of the soft clay were studied. Results indicated that the area corresponding to the stress- strain hysteretic curve under low- frequency loading is larger than others, and the curve is inclined to the strain axis. As the number of cycles increases, the softening degree of the clay increases (the softening index decreases), and a large cumulative plastic strain and residual dynamic pore pressure are generated under high CSRs. Under low- frequency loading with many cycles and high- frequency loading, it is necessary to pay attention to the influences of CSRs, in addition to the changes in accumulated plastic strain and residual dynamic pore pressure of soil caused by different values of confining pressure and axial deviatoric stress. Reducing the CSR can reduce the influences of different frequency loadings on the dynamic characteristics of the soft clay foundation. In addition, the cumulative plastic strain and residual dynamic pore pressure measured in the experiment are fitted with related correction models to obtain consistent fitting results. The results help as a reference for the application of Zhoushan marine soft clay in actual projects.

• Influence of the diaphragm wall on the dynamic responses of subway station structures under different site conditions

  ZHAO Mi, JIA Zhifu, ZAN Zihui, HUANG Jingqi, DU Xiuli

  2023(2):270-278,295, DOI: 10.20000/j.1000-0844.20210812003

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  Abstract:

  The open excavation method has always been adopted for subway station construction, wherein the diaphragm wall serves as a supporting structure in the foundation pit, following which the diaphragm wall continuously operates with the subway structure. In previous studies, the diaphragm wall was assumed to have a positive impact on earthquake resistance, and it was usually neglected in the seismic analysis of subway structures. However, the influence mechanism of the diaphragm wall on the seismic performance of subway structures must be further studied. Based on the finite element method of near- field wave motions and the viscous- spring artificial boundary condition, the dynamic responses of a typical two- story and three- span subway station structure with and without the diaphragm wall were compared and analyzed. Furthermore, the influence characteristics and mechanisms of the diaphragm wall on the seismic responses of subway station structures under different site conditions were investigated. Numerical results indicated that the diaphragm wall, which can reduce the overall inter- story displacement of a station structure, is beneficial to the seismic resistance of the side wall and the middle column in the bottom layer. However, the diaphragm wall also magnifies the bending moment and normal stress at the connection between the roof and floor and the side wall. The influence of the diaphragm wall on the internal force and normal stress of the middle column end in the top layer and the middle- span plate end of the structure is related to the site condition. In detail, it has a decreasing effect under hard and medium hard site conditions and a slightly increasing effect under soft site conditions. A possible reason for the response mechanism is that the diaphragm wall increases the lateral stiffness of the structure, thereby reducing the lateral deformation of the station structure. However, the diaphragm wall restricts the side wall deformation, thus increasing the bending moment and internal force at the connection between the roof and floor and the side wall.

• Nonlinear vibration control of isolated curved girder bridges based on the sequential optimal control algorithm

  LI Ximei, WANG Jiancheng, DU Yongfeng, MU Bohai

  2023(2):279-286, DOI: 10.20000/j.1000-0844.20200924002

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  Abstract:

  Various control measures need to be taken to ensure the safety of isolated curved girder bridges as they produce large elastic- plastic deformation under strong earthquakes. The classical Bouc- Wen model was used, and the nonlinear dynamic equation for isolated curved beam bridges considering the upper structure’s eccentricity was established to solve the dynamic response of the structure under rare earthquakes. In view of the large elastic- plastic deformation of isolated curved girder bridges under rare earthquakes, the nonlinear vibration control equation was established. After equivalent linearization treatment for the equation, sequential optimal control (SOC) and classical linear optimal control (COC) were used to study the vibration control of the bridge. The results show that under rare earthquakes, the lower structure and isolation layer of the curved bridge enter the plastic stage, and a small amount of residual displacement is generated. Both the SOC and COC can effectively reduce the horizontal and residual displacements of the isolated curved girder bridge under elastic- plastic conditions and also effectively restrain its torsional effect. Compared with the COC, the SOC algorithm can greatly reduce the peak response of the curved bridge.

• Seismic damage model of prestressed segmental bridge piers considering the self- centering influence

  ZHANG Yuye, QIAO Ning, JIANG Dingzhi, YUAN Wancheng

  2023(2):287-295, DOI: 10.20000/j.1000-0844.20210914002

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  Abstract:

  Prestressed segmental bridge piers have a good self- centering capacity under earthquakes. However, existing damage models cannot accurately evaluate the seismic damage of such piers. Thus, studying the seismic damage model of prestressed segmental bridge piers is crucial. Based on the self- centering characteristics and damage mechanisms of prestressed segmental bridge piers, the self- centering performance characterization method was first simplified in this study. Then, the self- centering correction factor was used to correct the hysteretic energy dissipation of bridge piers under an earthquake, and a seismic damage model was obtained, taking into account the self- centering performance of bridge piers. On this basis, the damage states of the prestressed segmental bridge piers were divided, and the applicability of the damage model and the damage classification method was verified. Results revealed that an obvious correlation existed between the self- centering performance and the energy dissipation damage of prestressed segmental bridge piers. The proposed model and classification method considering the self- centering performance of piers are suitable for different prestressed segmental bridge piers. This study can lay the foundation for quantitatively evaluating the damage degree of prestressed segment bridge piers under earthquakes.

• Numerical study of the deformation and failure of layered soil slopes with multiple sliding surfaces under earthquakes

  SONG Jian, LU Zhuxi, XIE Huawei, WU Kaili

  2023(2):296-305, DOI: 10.20000/j.1000-0844.20210812002

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  Abstract:

  Landslides caused by earthquakes pose a great threat to life, the environment, and the economy. Present studies on slope stability under earthquakes mainly focus on the failure modes of single sliding surfaces, while studies on slope stability with multiple potential sliding surfaces are comparatively obscure. A numerical simulation is conducted on the seismic stability of different slopes by using the finite difference software FLAC. The evolution process of sliding surfaces and the distribution characteristics of permanent deformation of homogeneous soil slopes, layered soil slopes, and soil slopes with weak interlayers under different earthquake intensities are compared and analyzed. Results reveal that the sliding surface of homogeneous slopes caused by earthquakes exhibits a single sliding surface, and the increase in seismic intensity only leads to an increase in permanent deformation along the sliding surface. For heterogeneous slopes, seismic action may also trigger local sliding deformation at the soil interface, and the sliding surface initially formed under seismic action is consistent with the most dangerous sliding surface corresponding to the minimum safety factor obtained under static conditions. In addition, a complex interaction exists between the shallow and deep slope deformations and failures caused by earthquakes. If the shallow sliding occurs first, further increase in ground motion can easily induces deep slope sliding; if the deep sliding occurs first, then plastic deformation affects the propagation of seismic inertia force to the upper slope body; thus, the further sliding deformation of the shallow slope is relatively difficult to trigger.

• Characteristics and cause analysis of saturated soft loess in Xianyang City

  WANG Qiyao, SHI Wei, HAN Zhenxing, SHI Hang

  2023(2):306-310, DOI: 10.20000/j.1000-0844.20201105007

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  Abstract:

  As a type of specific saturated loess, saturated soft loess is extremely unfavorable for engineering construction. Based on large amounts of survey data and testing results, this paper summarizes the spatial distribution characteristics and physical and mechanical properties of saturated soft loess in the Xianyang urban area. Furthermore, it analyzes the cause of saturated soft loess from the collapsibility of loess and the historical trend of groundwater level. Results indicate that the saturated soft loess in the Xianyang urban area is mainly distributed in the central and eastern parts of the second terrace, with an average porosity ratio of 0.85 and a compression modulus of 5.07 MPa, which has a large porosity ratio and compressibility and low strength. The main internal factor for the formation of saturated soft loess in Xianyang is the special structure of loess, and the main external environmental factor is the rise in water level caused by large- scale irrigation projects since the 1970s.

• Quantitative relationship between the collapsibility coefficients and physical indexes of loess

  REN Wenbo, HU Shaolei, LIU Yunlong, LI Jiajia, LI Lei

  2023(2):311-318, DOI: 10.20000/j.1000-0844.20201102006

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  Abstract:

  Collapsibility is an important engineering property of loess. In this study, the relationship between collapsibility and physical property indicators is first discussed in the context of the loess microstructure, and then the soil parameters of the collapsible loess in the Luoyang area are obtained on the basis of the Environmental Geological Survey of Central Plains City Group. Fi-nally, the correlation between the collapsibility and physical property indicators of loess is quantitatively analyzed using MATLAB. The results are as follows: (1) Among the physical property parameters related to collapsibility, the loess collapsibility coefficient in the Luoyang area is closely related to the void ratio, dry density, and plasticity index; the degree is in the order of void ratio, dry density, and plasticity index; (2) MATLAB is used to analyze the quantitative relationship between loess collapsibility coefficients and physical property indexes, and the fitting formula of the functional relationship between them in the study area is obtained; (3) Combined with the collapsible mechanism of loess, the rationality of the fitting formula is demonstrated by comparing the measured value with the predicted value. The research method used in this paper also has an enlightening significance for the prediction of the loess collapsibility coefficient in other areas.

• Loading- wetting model test on the compacted loess foundation and calculation of its collapsible deformation

  SUN Lei, HU Haijun, YAN Ruimin, DANG Jinqian, ZHANG Aijun, LUO Yasheng

  2023(2):319-328, DOI: 10.20000/j.1000-0844.20200518003

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  Abstract:

  To study the collapsible deformation development of the compacted loess foundation and the reliability of existing calculation methods for collapsible deformation, the indoor loading- wetting model test was carried out on the compacted loess foundation in Yangling. The collapsible deformation was calculated using the one- dimensional collapsibility coefficient method, chord modulus method, and tangent modulus method. The calculated results were then compared with the measured results. The experimental results show that collapse deformation occurs quickly after the foundation is wetted and then reaches stability. Due to non- self- weight collapse, collapse deformation occurs mainly in the top layer of the loess foundation. Calculated results of the three methods show that under a small load, the collapse deformations calculated by the one- dimensional collapsibility coefficient method without considering lateral extrusion are close to the measured values, while the deformations calculated while considering the modification factor of lateral extrusion are greater than the measured values. Under a large load, the collapse deformations calculated by the one- dimensional collapsibility coefficient method with and without considering the lateral extrusion are far less than the measured values. The chord modulus obtained from the in- situ loading test is unsuitable for calculating the collapse deformation of the compacted loess foundation. Since the elastic deformation of the initial yield surface is not well considered, the collapse deformation calculated by the tangent modulus method is greater than the measured value.

• Restoration method of the original topography of ancient seismic landslides in loess areas

  WU Liangjie, BO Jingshan, PENG Da

  2023(2):329-337, DOI: 10.20000/j.1000-0844.20211006002

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  Abstract:

  Restoration of the original topography is the basis for the study of ancient seismic landslides in loess areas. The No.1 landslide in the Pangou Group, Sanhe Village, Pingfeng Township (Xiji County, Ningxia Hui Autonomous Region) was taken as an example in this paper. Satellite remote sensing interpretation and field survey were adopted to collect the current topographic data of the landslide. Based on the principle of equal volumes of landslide bodies before and after sliding, MATLAB was used to restore the original topography of the No. 1 landslide using 3D surface interpolation technology. The surface shape of the restored landslide's original topography is generally convex, with a slope distribution range of 12°—15°. Finally, the rationality and feasibility of the restoration results were demonstrated by the slope distribution range of the loess geomorphic units and the landslide stability calculation. Results provide a novel approach for the restoration of the original topography of ancient seismic loess landslides that lacks the topography data before sliding, thus providing important theoretical significance and engineering application value for related studies.

• Liquefaction characteristics and parameters of pore- water pressure model for Malan loess

  DAI Yan, DENG Longsheng, MAO Wei, FAN Wen, LI Pei

  2023(2):338-345,361, DOI: 10.20000/j.1000-0844.20211020001

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  Abstract:

  The growth characteristics of the pore- water pressure of loess and the associated models and parameters are important for evaluating the liquefaction of loess sites under seismic loads. In this paper, the liquefaction characteristics, applicability of typical pore- water pressure models, and value ranges of parameters for the loess in the Dongzhi tableland of Qingyang City (Gansu Province, China) were studied via a series of liquefaction tests under different soil properties and loading conditions. Three types of pore- water pressure growth curves of saturated remolded loess under dynamic loading have been discovered, and their applicability to various pore- pressure models is verified via a comparison, and the value ranges of parameters for models with better applicability are provided. The parameter α of the Seed model ranges from 1.09 to 1.84, parameter β of the A- type curve model ranges from 1.70 to 2.52, and parameter θ of the power function model ranges from 1.13 to 1.75. The models are verified by the pore pressure curve of the loess in the Longxi area. Results reveal that the parameter range of these models has regional characteristics. For Longxi loess, the fitting parameters of the Seed model, A- type curve model, and power function model are 0.91, 8.32, and 3.51, respectively.

• Quantitative evaluation of 1D seismic response analysis methods of soil layers based on dynamic time warping

  QI Wanwan, SUN Rui

  2023(2):346-354, DOI: 10.20000/j.1000-0844.20220729002

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  Abstract:

  To quantitatively evaluate the gap between the calculated acceleration response spectra of 1D soil seismic response analysis methods and the actual records, 2 418 groups of acceleration response spectra calculated by four 1D numerical simulation methods (i.e., DEEPSOIL, SHAKE2000, SOILQUAKE, and SOILRESPONSE) were collected in this research. Based on the actual records of KiK- net in Japan, the applicability of the dynamic time warping (DTW) algorithm for quantitatively evaluating the response spectra gap was verified, and the DTW distances between actual records and calculated acceleration response spectra of different sites and different peak ground acceleration (PGA) intervals were compared and analyzed. Results revealed that on class Ⅱ sites, when PGA is less than 0.2g, the average DTW distances of the four methods have a slight gap, and when PGA is larger than 0.2g, the average DTW distance of the SOILQUAKE method is smaller than others. On class III sites, when PGA is less than 0.2g, the average DTW distance of the DEEPSOIL method is smaller, and when PGA is larger than 0.2g, the average DTW distance of the SOILRESPONSE method is smaller than others. On class IV sites, when PGA is less than 0.1g, the average DTW distance of the DEEPSOIL method is smaller, and when PGA is larger than 0.1g, the average DTW distance of the SOILRESPONSE method is smaller than others. On different classes of sites, the DTW distances of the four methods increase as PGA increases, and the growth rate of the DTW distance for the SOILRESPONSE method is lower than the three other methods on classes Ⅲ and Ⅳ sites. DTW distance can accurately and effectively reflect the gap among the spectra, thus providing a new method for quantitative evaluation of 1D soil seismic response analysis methods.

• Shear post- yield stiffness of metal rubber bridge bearings

  LI Dawei, XIA Xiushen, ZHANG Yongqiang, MA Jianxing, LUO Hui

  2023(2):355-361, DOI: 10.20000/j.1000-0844.20220511001

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  Abstract:

  Based on the overlapping area method and Haring theory, the formula for the shear post- yield stiffness of metal rubber bridge bearings with a circular cross- section was obtained in this study. The shear post- yield stiffness in the formula is proportional to the compressive stress and the bearing diameter and inversely proportional to the bearing height, where two coefficients α and β are to be determined. The relationship between the shear modulus and compression modulus of large- size metal rubber bridge bearing specimens was obtained through compression and compressive- shear tests, and coefficient α was approximately 1.3. Referring to the influence law of compressive stress, bearing diameter, relative density, and shape factor on the shear post- yield stiffness of the bearing in the shear test, the formula of the dimensionless coefficient β was evaluated. Furthermore, a practical simplification of the theoretical formulation was performed according to coefficients α and β, and the theoretical calculation results of the post- yield stiffness were compared with the experimental results. Results showed that the practical calculation formula, which agrees with the test results, is reasonably accurate. This formula can be used for the calculation of the post- yield stiffness of metal rubber bearings under compression- shear conditions.

• Seismic response analysis of inter- story isolation structures considering SSI under three- dimensional far- field long- period ground motions

  ZHOU Wangwang, LIU Dewen, ZHAO Jie, CHEN Lihao, LIU Yang, WAN Feng

  2023(2):362-371, DOI: 10.20000/j.1000-0844.20210802001

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  Abstract:

  Earthquake excitation is a kind of complicated multi- dimensional motion, so it is not safe and accurate enough to only consider horizontal earthquake excitation. Unlike ordinary ground motions, far- field long- period ground motions have characteristics such as long period, long duration, and rich low- frequency components. They will have adverse effects on structures with large isolation periods. The soil- structure interaction (SSI) is particularly complicated and needs further discussion. Therefore, a large chassis inter- story isolation structure was established in this paper. Under the excitation of three- dimensional ground motion, the different effects of ordinary earthquakes and far- field long- period earthquakes on the inter- story isolation structure were discussed, and the different effects of SSI on the structure were analyzed. The results show that the seismic response of three- dimensional long- period far- field ground motion on the inter- story isolated structure is far greater than that of ordinary ground motion. When the SSI effect is considered, the structural response increases with increasing soil softness. Three- dimensional isolation bearings were set to solve the problems of traditional horizontal isolation bearing under three- dimensional far- field long- period ground motion, i.e., story drift ratio and bearing displacement beyond limits. The analysis results show that the isolation effect of three- dimensional isolation bearings is better than that of traditional horizontal isolation bearings.

• Comparative study on three identification methods of the nonlinear time- varyin process: a case study of the 2021 Fukushima earthquake in Japan

  CHEN Changlong, LIU Qifang

  2023(2):372-381, DOI: 10.20000/j.1000-0844.20211110002

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  Abstract:

  Based on the records of six KiK- net stations in the 2021 Fukushima earthquake (M_JMA7.3), the nonlinear time- varying process of the site was studied using the moving- time- window deconvolution method, moving- time- window spectral ratio method, and moving- time- window autocorrelation function method. Then, the threshold and degree of nonlinearity were analyzed. Results show that the ability of the three methods to identify the nonlinear time- varying characteristics of the site differs. The moving- time- window deconvolution method can easily obtain a more stable nonlinear time- varying response for soil, but the degree of nonlinearity is low. The method reflects the change of average wave velocity from the surface to the underground. For shallow soils with a strong wave impedance ratio, the nonlinear degree of identification results derived from the moving- time- window spectral ratio method and moving- time- window autocorrelation function method are strong. These two methods cannot provide stable nonlinear time- varying results of shallow soils with a low wave impedance ratio. The strongest nonlinear moments identified by the three methods are basically the same and are located near the peak acceleration of the whole record. The nonlinear threshold values of the six stations identified by the three methods are about 40-140 gal, and the shear wave velocity drops between 16% and 53%, indicating that the degree of site nonlinearity is high.

Earthquake Research

• Construction of "underground cloud maps" based on airgun active source of Gansu

  ZHANG Yuansheng, QIN Manzhong, ZHONG Meijiao, ZOU Rui, ZHANG Weidong, ZHOU Tao, GUO Xiao, LIU Xuzhou, LI Shaohua

  2023(2):382-386, DOI: 10.20000/j.1000-0844.20230202004

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  Abstract:

  Based on the continuous development of the technical system of airgun active source on land, the evolution process of seismic waves' physical parameters (wave velocity and vP/vS) can be presented in the form of meteorological cloud map by using the techniques of seismic tomography and computer image display, so as to achieve the purpose of "reading cloud maps and recognizing weather underground". On the basis of the results of "underground cloud maps", we can study the seismogenic process and mechanism of earthquakes, deeply understand the temporal and spatial evolution characteristics of seismic wave velocity and vP/vS in epicentral area before and after strong earthquakes, and also summarize and extract universal seismic precursor parameters and indicators. The results of the study have important scientific significance for further improving the efficiency of earthquake prediction.

• Research progress on injection- induced earthquakes

  HUANG Yuanmin, MA Shengli, LI Xiaohui

  2023(2):387-400, DOI: 10.20000/j.1000-0844.20220708006

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  Abstract:

  The characteristics, mechanisms, and maximum possible magnitude of injection- induced earthquakes are important to study for induced earthquake prevention, risk assessment, and disaster reduction strategy formulation. This paper systematically collates the main understandings and disputes of injection- induced earthquake research at home and abroad. The results indicate that the maximum possible magnitude of an induced earthquake, which is affected by water injection parameters such as injection pressure and cumulative injection volume, is determined by geological conditions such as fault size and stress state. The reliable method for identifying induced earthquakes depends on a series of evidence chains, including the time- space correlation between earthquakes and water injection, the parameters of the statistical model, and the analysis of fault activation. When a hydraulic connection exists between the fault and the fluid reservoir, the pore pressure disturbance is the main induction mechanism; when the fluid pathway is unavailable, the change in pore elastic stress caused by the volume deformation of the rock matrix plays a dominant role. In addition, the chemical action of fluid and the triggering effect of small earthquakes may also play an important role in injection- induced earthquakes. This study provides a scientific reference for studying the mechanism of injection- induced earthquakes and the mitigation of destructive induced earthquake disasters.

• Co- seismic deformation filed and fault- slip distribution of the Menyuan MS6.9earthquake on January 8, 2022, constrained by GNSS observations

  XU Shuang'an

  2023(2):401-409, DOI: 10.20000/j.1000-0844.20220824002

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  Abstract:

  On January 8, 2022, an MS6.9 earthquake occurred in Menyuan County, Qinghai Province. It is another strong earthquake occurred in this region after the 2016 Menyuan MS6.4 earthquake, and determining the rupture distribution of this earthquake has great significance for analyzing the seismic damage risk in this area. Based on the observation data from 12 continuous global navigation satellite system (GNSS) stations and 17 mobile stations in the epicenter and its surrounding areas, the GNSS static co- seismic deformation field of 29 stations within 100 km of the epicenter was obtained and the co- seismic slip distribution of the MS6.9 earthquake was inverted. Results show that the maximum deformation observed by near- field GNSS reaches 1.3 m. The optimal rupture model shows that the main rupture zone of the earthquake is concentrated at the depth of 0-10 km; the sliding rupture is exposed to the surface, and the maximum slip is up to 4.07 m; the inverted seismic moment is about 1.1×10¹⁹ N·m, corresponding to MW6.7. The earthquake rupture to the surface is the direct cause of the destruction of infrastructure in this region.

• Electrical structure of the Tianjin—Tanggu segment of the Zhangjiakou—Bohai seismic belt and its importanceTianjin 300170, China)

  GAO Wuping, LIN Yi, ZHANG Wenpeng, XU Xinxue, YAN Chengguo, CAO Jingquan, LIU Hongyan

  2023(2):410-420, DOI: 10.20000/j.1000-0844.20211130003

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  The Zhangjiakou-Bohai seismic belt is a seismic fault zone in the northern part of North China. The Jiyunhe fault zone in its middle segment constitutes the western boundary of the Tangshan rhombus block, and it is considered the seismogenic fault of the Ninghe M6.9 earthquake in 1979. To effectively reveal the deep structure and seismogenic dynamic environment of this region, we conducted a magnetotelluric sounding profile in the Dagang—Yutian area, which directly crosses the epicenter of the Ninghe M6.9 earthquake and is almost perpendicular to the Zhangjiakou—Bohai fault zone. Detection results show that the electrical structure in the study area is layered vertically and partitioned horizontally. Additionally, the magnetotelluric sounding profile reveals the deep structural characteristics of some regional faults, i.e., the Haihe fault, Hangu fault, and Jiyunhe fault in the middle section of the Zhangjiakou—Bohai fault zone, in which the Hangu fault may be a deep fault that runs through the crust. The good correlation between the high and low resistivity gradient zones and the epicenters of the Ninghe M6.9 earthquake and the other two M6.2 earthquakes in Hangu suggests that the moderate- strong earthquakes in the study area are closely related to the development of obvious high and low resistivity gradient zones in the deep area.

• Application of microtremors to detect the secondary faults of the northern piedmont fault of Xizhou Mountain

  YAN Xiaobing, LIANG Ruiping, WANG Weijun, HAO Xuejing

  2023(2):421-430, DOI: 10.20000/j.1000-0844.20210818001

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  The northern piedmont fault of Xizhou Mountain is the seismogenic structure of the Dingxiang M7 earthquake in 1038. It may have one or more secondary faults in the basin, which may be very near Xinzhou city. This study uses the microtremor method to detect whether hidden secondary faults exist in the northern piedmont fault of Xizhou Mountain. The locations of approximately 17 remarkable breakpoints were obtained through the lateral change in resonance frequency and the relationship between bedrock depth and frequency. The results indicate that three obvious secondary faults exist in front of Xizhou Mountain, as well as the location of their breakpoints, relative offset, and corresponding strike distribution. This research provides basic data for earthquake prevention and disaster reduction in Xinzhou city.

• Development planning of urban emergency shelters based onANP- SWOT model: a case study of Lanzhou City

  JI Wanjing, WANG Jinping, SONG Shanshan, XUE Mingmei

  2023(2):431-440, DOI: 10.20000/j.1000-0844.20211026002

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  Reasonable planning and construction of urban emergency shelters can improve the city's disaster- resisting capability, enhance urban disaster resilience, and reduce casualties and property losses caused by disasters. On the basis of a detailed investigation on the construction status of emergency shelters in Lanzhou, the development planning was analyzed using the ANP- SWOT model. First, the SWOT analysis method was used to determine the internal advantages and disadvantages, external opportunities, and threats of emergency shelters in Lanzhou. Then, the ANP analysis method was adopted to build the network hierarchy of emergency shelters' development planning in Lanzhou. Finally, combined with expert consultation, the best development strategy was formulated through assignment and comparative analysis. Results show that the key problems restricting the development of emergency shelters in Lanzhou are uneven distribution, insufficient number, and lack of a special emergency plan. The best development strategy is to accelerate the standardization of emergency shelters in Lanzhou.

• Discussion on the correlation between the water- level anomaly of the Shiquan well and the Jiuzhaigou M7.0 earthquake

  WU Ming, YANG Xiaodong, LIU Jie

  2023(2):441-446, DOI: 10.20000/j.1000-0844.20210809002

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  Abstract:

  In this paper, we selected the integral point value data of the Shiquan fluid well water level in 7 years from 2014 to 2020 and combined them with the wavelet analysis method and regional structure analysis to study the possible reasons for the long- term abnormal change in the Shiquan well water level. The results show that the water- level anomalies of the Shiquan well mainly occurred after the Jiuzhaigou M7.0 earthquake on August 8, 2017. The wavelet analysis method is effective in extracting high- frequency abnormal information. The strengthening of regional fault activity after the Jiuzhaigou M7.0 earthquake or the change in aquifer permeability around the fault caused by the earthquake may be the direct cause of the long- term abnormal water level in the Shiquan well. The fault activity near the Shiquan section of the Yuehe fault deserves further attention.

• Construction of fixed- point observation stations of the soil gas along the northern margin fault of West Qinling

  ZHAO Jie, SU Hejun, GAO Shude, YANG Chao, GUO Yun, MENG Weibin, WANG Wenxi, TIAN Jie

  2023(2):447-456, DOI: 10.20000/j.1000-0844.20220408001

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  Abstract:

  In this paper, the design idea, construction content, and operation of three soil gas observation stations along the northern margin fault of West Qinling are introduced. Through an analysis of observation data in the past year, the background values of soil gas observed by the stations are considered stable, and the observation data are considered reasonable and reliable. The change patterns of the same measurement item at the three observation stations are similar and synchronous, and synchronous abnormal responses occurred before the Yuzhong M_S3.6, Maduo M_S7.4, and Menyuan M_S6.9 earthquakes. This finding shows that the soil gas along the northern margin of West Qinling potentially reflects the changes in regional tectonic stress. Furthermore, the construction scheme and technical indicators of fixed- point observation stations for fault soil gas provide a reference for establishing a fault soil gas observation network in the study area and lay a good foundation for further promotion and application.

• Design and implementation of the national seismic deformation data spatial application management platform

  BAI Zhuoli, WU Yongcai, YANG Bin, JIA Peng, XU Jing

  2023(2):457-464,437, DOI: 10.20000/j.1000-0844.20220119001

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  Abstract:

  By analyzing the disadvantages of traditional seismic data (site maps, the tectonic maps of geological fault activity, and the observation environment data of stations), i.e., cumbersome access, a single expression form, and a lack of information, this paper presents the overall design idea and function module implementation process of the “national seismic data spatial application management platform.” Meanwhile, taking a typical crossfault site as an example, a centimeter- level high- resolution 3D scene model was constructed for the existing two- dimensional plane seismic data based on tilt photogrammetry and structure from motion technology, and it was then implanted into the management platform. The results show that the 3D expression of seismic data can not only restore the field monitoring scene and fault occurrence but also extract the observation curve and quantitative parameters of active structures, thus bringing a new application experience to relevant scientific researchers and providing a new consultation mode for our traditional consultation.

• Late Quaternary activity characteristics of the middle segment of Dachaidan fault

  PANG Wei, HE Wengui, WU Zhao, ZHANG Bo

  2023(2):465-473, DOI: 10.20000/j.1000-0844.20210720001

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  Abstract:

  The geological and geomorphological characteristics of the Dachaidan fault since the Late Quaternary were obtained through the interpretation of remote sensing data, field investigation, and differential GPS survey. The results show that the Dachaidan fault, with a total length of about 135 km, shows an inverse “S” shape. According to the change of fault strike, geomorphic characteristics, and fault activity, the fault is roughly divided into three sections, with Wenquangou and Tataleng Rivers as dividing points. The nature of reverse thrust has been obvious in the northern and southern segments of the Dachaidan fault since the Late Quaternary, and the middle section is dominated by dextral thrust activities. The reversed and strike- slip displacements are different on different geomorphic surfaces, showing obvious multi- stage activity characteristics. The paleoseismic profile in the field revealed a paleoseismic event, which occurred after (2 402.5±57.5) a.B.P., indicating that the fault was strongly active in the Holocene, consistent with the frequent strong seismic activities in the region in recent years.

• Application and interpretability of deep learning methods in seismic event classification

  LU Xiaochen, YANG Liming, YANG Xingyue, WANG Zudong, WANG Weihuan, GAO Yongguo, YIN Xinxin

  2023(2):474-482, DOI: 10.20000/j.1000-0844.20220926001

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  Abstract:

  In this paper, four deep learning network models, i.e., the CNN, ResNet18, Vgg16, and Inception10 models, were used to classify blasting and seismic events, and the dataset used blasting events and natural seismic events recorded by the Fujian station network from 2016 to 2020. The gradient- weighted class activation mapping (Grad- CAM) algorithm was introduced into the four classification models to address the “black box” problem of deep learning network models, and a visualization of each model was obtained. The visualization diagram provides an intuitive view of the model's reliance weights for different waveform features when making classification decisions, thus providing a basis for the model’s interpretability and improving its credibility. Analysis of the visualization diagram shows that the CNN and Vgg16 models with better classification effects rely more on the seismic phase characteristics of seismic waveforms when making decisions and pay less attention to the pre- earthquake and post- earthquake bands. In contrast, the ResNet18 and Inception10 models are insufficiently sensitive to the seismic phase characteristics. The results obtained from a visual analysis of the models through the Grad- CAM algorithm well reflect the classification effect of the models, which is important for improving the models and selecting an appropriate classification model.

• Influence of line orientation on the detection effect of a microtremor linear array

  WANG Shun, LIAO Wulin, YAO Yunsheng, ZHANG Chi, LI Jinggang

  2023(2):483-490, DOI: 10.20000/j.1000-0844.20210922001

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  Abstract:

  As a recent geophysical prospecting technique, microtremor survey technology is economical, environmentally friendly, practical, and widely used in resource exploration and engineering geology. To study the influence of line orientation on the results of a linear array, the microtremor survey results of a multisession double- circular linear array, T- shaped linear array, and linear arrays in different directions were compared and analyzed using the small- scale dense array data measured by the Wuhan Central Seismic Station. The results show that the results of linear arrays in different directions are remarkably different: The measured phase velocity increases gradually with a change in line orientation from north to east, and the results are closest to those of the double- circular linear array at approximately NE45°. The numerical simulation results also show that the results of the linear array are good when the angle between the survey line and the centerline of the main noise source is within a range of 30°-55°, and the measured phase velocity increases gradually with an increase in this angle. When a main noise source is present near the survey area, the measured and simulated results show that an increase in observation time cannot overcome the deficiency of the orientation distribution of the linear array. Therefore, the possible noise source distribution near the survey area should be considered before a microtremor survey.

• Spatial and temporal distribution characteristics of soil gas radon concentration intensity in the mid- eastern segment of the Qilianshan fault zone and its seismic hazard analysis

  WAN Yue, SU Hejun, LI Chenhua, ZHOU Huiling

  2023(2):491-500, DOI: 10.20000/j.1000-0844.20221221003

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  Abstract:

  Based on the observation data of soil gas radon concentration from nine measurement points from 2016 to 2021, the spatial and temporal distribution characteristics of radon concentration intensity in the mid- eastern segment of the Qilianshan fault zone were analyzed. Combining this analysis with strong historical earthquakes, present seismic activities, and fault zone sliding rate, the seismic hazard zones of the mid- eastern segment of the Qilianshan fault zone were determined from a geochemical perspective. The study results show that the study area has stronger soil gas radon concentration intensity in the eastern segment than in the western segment, and the change characteristics of the time series show a decreasing trend. The spatial distribution characteristics of soil gas radon concentration intensity, historical and present seismic activities, and fracture sliding rate are well coupled. This study provides evidence of deep underground fluid activity in the study area, which is vital in tracing the faults and active segments with seismic risk.

• The Late Quaternary activity characteristics of the Xigongyi-Lidian fault - with a discussion on the seismogenic structure of the Huining M7 earthquake in 1352

  cui jiao, wang ai guo

  DOI: 10.20000/j.1000-0844.20230102002

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  Abstract:

  The Xigongyi-Lidian fault is a northwest-trending fault developed in the central part of the Longzhong Basin. Based on interpretation of high-resolution satellite remote sensing images, geological and geomorphological surveys, UAV aerial surveys, profile cleaning and 14C dating, the late quaternary activity characteristics of the Xigongyi-Lidian fault are studied. The results show that the fault is 120km long and dips SW with angle 75-80°. The most recent active time of the western segment of the fault is late Holocene by thrusting with left-lateral slip, while the most recent active time of the eastern segment of the fault is late period of late Pleistocene by thrusting with left-lateral slip and normal slip partly. There are two paleo-earthquake event in the western segment at least during Holocene, which is before 10070±30a B.P. and during 5410±30a B.P. to 4520±30a B.P. respectively. According to UAV surveying and dating data of western segment of the fault, the average vertical slip rate in Holocene is 1.05mm/a and the maximum horizontal left-lateral slip rate since late period of late Pleistocene is 1.93mm/a. Integrated study of isoseismic line shape, meizoseismal area, fault size, new activity characteristics, ground surface relics and regional tectonic conditions indicates that the seismogenic structure of Huining M7 earthquake in 1352 is the western segment of Xigongyi-Lidian fault.

• PRECISE LOCATION AND TECTONIC SIGNIFICANCE OF THE 2021 AKSAI M5.5 EARTHQUAKE

  xueshanyu, XIE Hong, YUAN Daoyang, YIN Xinxin, SU Qi, ZHANG Zhengmo, CAI Mingyuan, WANG Liao

  DOI: 10.20000/j.1000-0844.20230116002

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  Abstract:

  On August 26, 2021, an M5.5 earthquake occurred in Aksai County, Jiuquan City, Gansu Province, which was a significant earthquake in the Western Qilian segment of the northeastern Tibetan plateau. In order to analyze the seismogenic structure of this earthquake and its significance, this study used the broadband seismic waveform data recorded by the regional seismographic network to inverse the focal mechanism solutions of Aksai M5.5 main shock and the M3.7 aftershock through the Cut-and-Paste(CAP) method. Furthermore, the study used the double difference location method(hypoDD) to relocate the earthquake events in Akesai area from January 1, 2021 to November 29, 2021. The results showed that Aksai M5.5 earthquake was a thrust activity. After relocation, the earthquake events were distributed intensively, the focal depth of Akesai M5.5 main shock was 14.1km and that of the aftershocks were minly distributed at 15~25km. Based on the integrated analysis of focal mechanism solution and the relocation results of seismic sequence, as well as the regional tectonic background, it can be confirmed that the Danghe Nanshan southern margin fault was responsible for this M5.5 earthquake. In the future, more attention should be paid to the risk of moderate to strong earthquakes in the Western Qilian Mountains.

• Three-dimensional velocity structure and relocation in Luding, Sichuan

  CAI Mingyuan, CHEN Jifeng, YIN Xinxin

  DOI: 10.20000/j.1000-0844.20230227003

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  Abstract:

  This paper uses the double-difference tomography method to perform seismic tomography and relocation of the source area of the Luding MS6.8 earthquake and the surrounding area based on the seismic phase data of 103990 earthquakes recorded by the Sichuan digital seismic network in this study area (27.5°N-31.5°N, 100°E-104°E). The results show that: (1) The aftershock sequence is mainly distributed on the southwest side of the Xianshuihe Fault, with a length of about 60 km. It is typically distributed in the northwest direction along the Xianshuihe Fault, with focal depths mostly concentrated at 5-15 km, exhibiting symptoms of increasingly deepening from north to south. According to the spatial distribution characteristics of the aftershock sequence and the location of the mainshock, the southeast section of the Xianshuihe Fault was proposed as the seismogenic fault. It was also found that there may be branch faults at the northern and southern ends of the aftershock sequence. According to the spatial distribution characteristics of background earthquakes, it is speculated that they may be foreshocks of the Luding mainshock. (2) The high-velocity anomaly body on the northwest side of the mainshock, which perhaps blocked the northwestward rupture of the Luding earthquake, combined with the weaker mechanical properties of the southeast section of the Xianshuihe Fault, whose sliding direction is the preferred propagation direction, leads to the inference that the Luding earthquake ruptured unidirectionally and in a southeastward direction. (3) The presence of a weak S-wave low-velocity layer and a high wave velocity ratio at a depth of 30 km below the source area of the Luding earthquake, and the existence of a significant high-conductivity and low-resistance layer in the lower and middle crust of the study area, and the Luding mainshock was located near the geothermal heat flow contour with a heat flow value of 65mW·m2, suggest that crustal fluids may have been present 30 km below the source area. At the same time, the Luding earthquake occurred at a high-low velocity junction where stresses tend to accumulate easily and release and rupture easily. It is inferred that the Luding mainshock accumulated a large amount of stress in the source area, together with the flow of crustal fluids into the seismogenic fault, led to the weakening of the seismogenic fault, and the combined effect of both eventually triggered the Luding MS6.8 earthquake.

• Ananlysis on the Relationship between the boundary intersection of Geomagnetic Low-point Displacement Anomaly and Earthquakes

  YANG Xingyue, LU Xiaochen, zhang fei jie, MEI Donglin, WANG Shuwang

  DOI: 10.20000/j.1000-0844.20220211003

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  Abstract:

  利用国家地磁台网中心产出的观测资料，研究了中国大陆地区低点位移现象与强震之间的关系，认为地磁低点位移异常与强震之间具有较好的关联性，多次5级以上地震发生前两月内会出现一次或多次低点位移异常，地震往往发生在低点位移异常分界线300km内。2022年1月8日青海门源6.9级地震前两月内出现了4次明显的地磁低点位移异常；2016年1月21日青海门源6.4级地震和2019年9月16日甘肃甘州5.0级地震前两月内均出现了3次明显的地磁低点位移异常。将多次低点位移异常分界线叠加到同一幅图上，会形成1个或多个交汇区域，发现地震发生在低点位移分界线的交汇区域附近。综合活动构造断裂分布，历史大地震发生情况，中长期预测的强震潜在危险区及年度全国地震危险区，进一步判断可能发震的区域，此项研究大大缩小了用地磁低点位移法预测地震发生地点的范围。

• Supplementary research on Baotou earthquake in Inner Mongoliain 849 A. D.

  YUAN Daoyang, LEI Zhongsheng, SI Guojun, LIU Xingwang, YU Jinchao, LI Hongqiang, CHEN Yanwen, SUN Hao, ZHANG Lijun

  DOI: 10.20000/j.1000-0844.20230202002

  Abstract(84) HTML(0) PDF(8.72 M)( 35) Collect

  Abstract:

  On October 20, 849 A. D. (Xinsi of October, the third year of Dazhong of Emperor Xuan in Tang Dynasty), a great earthquake occurred near Baotou city, Inner Mongolia Autonomous Region, causing serious earthquake damage such as the destruction of castles, military camps and houses and thousands of deaths. At present, the basic parameters such as epicenter location, intensity and magnitude of this earthquake are not unified. In this paper, the relevant historical data are systematically combed, and further verification is focused on the seriously affected towns such as Yunjia pass or Yunjia town, etc, where the location is in doubt.

• EXPERIMENTAL STUDY AND PERFORMANCE OPTIMATION OF NEW LOW-DAMAGE SELF-CENTERING CONCRETE FRAME JOINTS

  GENG Fangfang, DING Youliang, LI Yadong, LIU Wei

  DOI: 10.20000/j.1000-0844.20220803001

  Abstract(146) HTML(0) PDF(12.25 M)( 52) Collect

  Abstract:

  A low-damage self-centering precast concrete LDSCPC frame joints with replaceable mild steel damper is proposed in this study, and the pseudo-static tests of full-scale specimens were carried out for the seismic performance of the joint under earthquake and the performance recovery after replacing the mild steel dampers. Based on the connection tests, the parametric analysis and optimization design of the bolt preload, horizontal and vertical energy dissipation strips of the connection were carried out based on the ABAQUS refined finite element model. The research shows that the hysteretic characteristics and bearing capacity of the mild steel damper LT12 were the best, while the energy capacity of the mild steel damper LT14 was the best; Increasing the size and thickness of the energy dissipation strips of the mild steel damper can improve the energy dissipation capacity of LDSCPC frame joints at the early stage of loading and large deformation. Larger bolt preload of the bolts can significantly improve the energy dissipation capacity of LDSCPC frame joints. In addition, when the preload was 155 kN, the mild steel damper can almost achieve the ideal energy dissipation performance.

• Study on the base isolation effects of tubular-annular composite building structure

  quyaqing, renwenjing, qiu da peng

  DOI: 10.20000/j.1000-0844.20211126002

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  Abstract:

  It is possible for nuclear power plant located in near fault zone with the development of nuclear power plant construction. In this paper, 15 sets of far-field earthquakes ground records and 14 sets of near-field earthquake ground records are selected in terms of ATC-63 and the seismic fragility curves of isolated and non-isolated AP1000 nuclear plant shield building in terms of different performance indices are compared based on IDA and MSA methods. The effect of base isolation effect and the degree of aseismic safety margin coefficient improvement are evaluated. The results show that, base isolation of AP1000 nuclear island can play an effective role in reducing the slight damage, medium damage and severe damage probability of nuclear shield building subjected to near-field earthquake. The base isolation would deteriorate the collapse damage as the collapse probability of shield building with base isolation greater than without base isolation but there is still sufficient damage safety margin, so it is feasible to establish it in non bedrock field.

• Longitudinal deformation model and parameter analysis of railway under non-uniform frost heave

  guohan, wuweijiang, chipeihong, suxing, LIU Jun

  DOI: 10.20000/j.1000-0844.20220320001

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  Abstract:

  China is a country with a large distribution of frozen soil. Railway tracks in cold regions are generally affected by frost heaving of foundation soil. Previous studies focused on the frost heave characteristics of foundation soil, but paid less attention to the interaction between railway and foundation soil under longitudinal non-uniform frost heave deformation. Based on the beam theory of double-layer elastic foundation, this paper establishes the mechanical model of rail under rail foundation under the action of non-uniform frost heaving deformation, gives the analytical solution of the model, and analyzes the effects of interlayer elastic coefficient and frost heaving on track displacement and internal force combined with an example. The results show that the elastic interlayer can effectively reduce the frost heave deformation and stress response of the rail, which is conducive to the operation of the rail; The length of the transition section between the rail and the foundation under the rail, the shear force and bending moment at the concave convex bending section increase with the increase of frost heave displacement; The increase of the elastic coefficient of the interlayer will cause the influence of frost heaving force on the foundation under the track to gradually transfer to the track; The length of the transition section is only related to the amount of frost heaving. The calculation method and analysis conclusion proposed in this paper can provide scientific guidance for railway design, operation and maintenance in cold regions.

• Evaluation method of sand liquefaction based on SPT-APD-DDA

  HAO Shaolei, ZHANG Bing, XU Shiguang, LI Yuefeng, CHEN Mengrui, DENG Lixiong, GUO Wei

  DOI:

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  Abstract:

  There are a lot of uncertainties in the establishment of traditional normative methods，so a comprehensive research method is urgently needed to discuss the liquefaction discrimination in complex sites. Based on the emergency repair project of the immersed pipe in Baotou section in Shanghai，this paper first adopts the standard penetration test method (SPT) to qualitatively evaluate the sandy silt soil within 20 meters of the research area. Using the absolute difference percentage method (APD) proposed in this paper，35 groups of soil samples with accurate discriminant results and 14 groups with discriminant errors are divided. Secondly，referring to the theoretical thought of discriminant analysis and the theoretical thought of discriminant analysis， the physical and mechanical parameters such as average particle size D50, heterogeneous coefficient Cu，specific penetration resistance Ps，standard penetration point depth ds，groundwater burial depth dw and standard penetration hammer number N63.5 are added to the liquefaction evaluation. Using the soil samples with accurate discriminant results，a distance discriminant analysis model (DDA) suitable for the engineering geological characteristics of the research area is established to quantitatively evaluate the soil layers with discriminant errors or errors. Finally，choose the discriminant results based on the results of the "advantage combination". The research results show that the established comprehensive evaluation system for sand liquefaction is highly pertinent and adaptable to the research area. It is established that 37 groups of the 49 groups of sand and soil layers in the research area are liquefied. Through reasonable anti-liquefaction and subsidence measures，the steady progress of subsequent projects are guaranteed，which is stable for sand liquefaction in fields with similar geological conditions. The evaluation provides reference and reference.