• Volume 43,Issue 5,2021 Table of Contents
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    • >Earthquake Research
    • Preliminary analysis results of fixed-point monitoring on soilgas along the northern margin fault of West Qinling

      2021, 43(5):1001-1007. DOI: 10.3969/j.issn.1000-0844.2021.05.1001

      Abstract (388) HTML (0) PDF 14.86 M (1379) Comment (0) Favorites

      Abstract:According to the previous study on the historical earthquakes and the recurrence cycle and elapsed time of paleoearthquakes along the northern margin fault zone of West Qinling, a great potential risk of strong earthquakes exists in the fault. Therefore, it is of great practical significance to strengthen the fixed-point monitoring and earthquake prediction of current tectonic activity of the fault. In this paper, according to the profile concentration distribution (variation) characteristics of gas escaping from the fault, three stations for continuous observation on fault soil gas were newly built in the Tianshui section. Then the concentration observation of fault gas (H2, CO2, Rn, CH4) was carried out to analyze the spatial difference of deep gas characteristics in different sections of the fault zone and their variation characteristics with time. In this way, the stress adjustment and seismicity in southeast Gansu were monitored. The analysis of preliminary observation data showed that the background value is relatively stable under normal conditions, and the change patterns of the same measurement item at different measurement points are similar and synchronous, indicating that the observation data are true, reliable and comparable. The synchronous abnormal change of measured item at different measuring point may reflect the regional stress adjustment and change, thus providing a reference criterion for earthquake tracking and prediction.

    • Variation and pre-seismic anomaly characteristics of the lithosphericmagnetic field in Hebei Province and its surrounding areas

      2021, 43(5):1008-1013. DOI: 10.3969/j.issn.1000-0844.2021.05.1008

      Abstract (168) HTML (0) PDF 10.03 M (816) Comment (0) Favorites

      Abstract:In this paper, the semi annual variation of the lithospheric magnetic field in Hebei and its surrounding areas was obtained by using the data of mobile geomagnetic vector from 156 observation points of North China in autumn 2019, and the overall variation characteristics of lithospheric magnetic field in the study area were analyzed and summarized. Furthermore, the local variation and anomaly characteristics of lithospheric magnetic field before the Huai'an, Hebei MS3.4 earthquake on December 3, 2019 and the Fengnan, Hebei MS4.5 earthquake on December 5, 2019 were studied. The results showed that the epicenter of Fengnan MS4.5 earthquake was located in the turning area of vector H, the high value area of negative anomaly of total intensity F, the high gradient zone of negative anomaly of element D and the high value area of Z value. The Huai'an MS3.4 earthquake occurred in the area where the amplitude of vector H weakened and turned, the positive area near the zero value line of element D and the low value area where the Z value changed.

    • Development and application of an integrated management systemfor basic data of underground fluid network in Tianjin

      2021, 43(5):1014-1023. DOI: 10.3969/j.issn.1000-0844.2021.05.1014

      Abstract (163) HTML (0) PDF 12.97 M (787) Comment (0) Favorites

      Abstract:With the support of the monitoring and forecasting department and the technical management group of underground fluid discipline of China Earthquake Administration, a comprehensive management system for basic data of underground fluid network was developed in this paper. The system has the functions of basic information quality inspection, geochemical background survey, water level inspection and calibration, assessment list and declaration, station change and stop observation, feedback on subject quality assessment, etc. For its applicability to underground fluid stations, provincial underground fluid networks center, and national underground fluid networks center, the system can provide technical support for data collection and filing, instrument operation and maintenance, data tracking and analysis, data anomaly verification, and product output services, thus laying a good foundation for monitoring, forecasting, and scientific research.

    • Characteristics of regional stress field and static Coulombstress changes among strong earthquakes in Xinjiang area

      2021, 43(5):1024-1036. DOI: 10.3969/j.issn.1000-0844.2021.05.1024

      Abstract (247) HTML (0) PDF 36.60 M (965) Comment (0) Favorites

      Abstract:Based on the focal mechanisms of 828 MS ≥ 3.0 earthquakes occurring in the Xinjiang area since 1900, we adopted the method of damped regional-scale stress inversion to obtain the characteristics of regional stress field in Xinjiang. The results revealed that the main types of focal mechanisms in Xinjiang are thrust and strike-slip, and the maximum horizontal principal compressive stress is in nearly SN direction along with local tension and shear. Then, according to the characteristics of regional stress field and spatial distribution of strong earthquakes in the region, we calculated the Coulomb stress changes among strong earthquakes in Tianshan, Kashi-Wuqia, and Kunlun-Altun areas. It is concluded that the strong earthquakes in Tianshan area has little influence on the occurrence of subsequent earthquakes. Kashi-Wuqia area is a strong earthquake prone area, and the epicenters are densely distributed along with obvious earthquake triggering or delay effect. There is little effect between earthquakes in Kunlun-Altun area, except the triggering effect of the Yutian MS7.3 earthquake in 2008 on the subsequent Yutian MS7.3 earthquake in 2014. Finally, we also calculated the Coulomb stress changes of surrounding faults caused by strong earthquakes, and the results showed that the Coulomb stress increased along the middle segment of western Boluokenu Fault, the west segment of Kazikearte Fault, the west segment of Muji Fault, and the west segment of Hetian Fault, suggesting the increasing seismic risk.

    • Geomagnetic anomalies prior to the JiuzhaigouMS7.0 earthquake in 2017

      2021, 43(5):1037-1044. DOI: 10.3969/j.issn.1000-0844.2021.05.1037

      Abstract (154) HTML (0) PDF 9.42 M (683) Comment (0) Favorites

      Abstract:The continuous measurement data of Songpan (SPA), Chengdu (CDP), and Tianshui (TSY) magnetic stations in 2017, which are 64, 254, and 238 km away from the epicenter of Jiuzhaigou MS7.0 earthquake, were analyzed in this paper. Geomagnetic anomalies recorded by SPA before the MS7.0 earthquake mainly showed that the cumulative change of long-term vertical component had reached 40 nT since May 2017. There were also short-term step changes, up to 10 nT. No obvious anomalies showed in the magnetic field of CDP and TSY. According to the detailed inspection of raw data, it is found that the difference between the last observation value of many observation days at SPA and the first observation value of next day is more than 1 nT. Therefore, it is considered that the anomaly in the observation data before Jiuzhaigou earthquake is caused by the anomaly of observation system. The statistical results of diurnal variation in vertical component of the three stations revealed consistent with each other in different time, indicating that there is no obvious abnormal change of geomagnetic vertical component in a short time before the earthquake, and the difference of magnetic field at the three stations is resulted from the different properties of underground medium. An alternation of positive and negative anomalies in the lithospheric magnetic field was shown in the west area of epicenter, which may be related to the seismogenic process of Jiuzhaigou earthquake

    • Evidence of new activities along the westernmargin fault zone of the Ganjia Basin

      2021, 43(5):1045-1053. DOI: 10.3969/j.issn.1000-0844.2021.05.1045

      Abstract (209) HTML (0) PDF 47.42 M (878) Comment (0) Favorites

      Abstract:In the west margin of the Ganjia Basin, which is located at the western end of the northern margin fault of West Qinling fault, three nearly SN-trending faults (east branch, middle branch, and west branch) were developed, showing an arc landform ladder with high west and low east. Based on the interpretation of high-resolution satellite remote sensing images, geological and geomorphological survey, UAV aerial measurement, and profile cleaning and 14C dating, evidences of new activities in late Quaternary were found along the west margin fault zone of the Ganjia Basin. The new fault activities were characterized by different levels of fault scarps, faulted terraces and diluvial platforms, and right-lateral gullies and terraces. The profile and scratch of faults revealed that the western margin fault zone of the Ganjia Basin has the property of dextral thrust, and the latest stratum of fault dislocation is Holocene. According to the UAV measurement and dating data, the average horizontal right-lateral slip rate of the west branch of the west margin fault of Ganjia Basin since the middle Holocene is estimated as 0.89 mm/a, while the average vertical slip rate is 0.30 mm/a.

    • Characteristics of frequency field anomalies beforethe Wenchuan earthquake in 2018

      2021, 43(5):1054-1061. DOI: 10.3969/j.issn.1000-0844.2021.05.1054

      Abstract (133) HTML (0) PDF 6.29 M (505) Comment (0) Favorites

      Abstract:The earthquake frequency field is a mathematical method to describe the temporal and spatial characteristics of seismic frequency. Taking the area near the epicenter of Wenchuan MS8.0 earthquake on May 12, 2008 (30.0°-33.0°N, 101.5°-105.5°E) as the research area, the time variation characteristics of typical field time factors of frequency field were analyzed with the expansion method of natural orthogonal function. When the typical fields corresponding to the first eight eigenvalues were taken, the fitting accuracy reached 0.936 8, and six typical fields showed abnormal changes, accounting for 0.691 1 of the total field. The anomaly occurred in September 2004 at the earliest, that is, 3 years and 7 months before the main shock, and more than 1 month before the main shock at the latest, showing the characteristics of short-term and imminent anomaly. The results showed that the seismic frequency field method can ideally extract the anomalies before the Wenchuan MS8.0 earthquake.

    • Simulation study on the influencing factorsof stress field in echelon fault

      2021, 43(5):1062-1071. DOI: 10.3969/j.issn.1000-0844.2021.05.1062

      Abstract (125) HTML (0) PDF 22.16 M (967) Comment (0) Favorites

      Abstract:In this paper, the fault contact pairs with viscoelastic mechanical parameters were established by using the finite element method. Through the comparative analysis method, factors affecting the tectonic stress field and the distribution state of the echelon fault were analyzed by changing the geometric spacing and viscosity coefficient of the fault. The stress drop and stress-strain relationship caused by earthquake during the instability process of the echelon fault were simulated, as well as the angle relationship among the first, second, and third principal stresses and fault.

    • Interference of load variation on the vertical pendulumobservation at Shexian seismic station

      2021, 43(5):1072-1076. DOI: 10.3969/j.issn.1000-0844.2021.05.1072

      Abstract (118) HTML (0) PDF 3.78 M (405) Comment (0) Favorites

      Abstract:In this paper, the operation of the vertical pendulum instrument at Shexian station in Handan City, Hubei Province, from 2011 to 2016 was analyzed, and the internal accuracy was calculated. The effects of load changes of surrounding project construction on the vertical pendulum were calculated by using the particle, two-dimensional, and three-dimensional load models. The results showed that the load change has no significant effect on the data of vertical pendulum at Shexian station. The results of two-dimensional and three-dimensional load models tend to be consistent. It is concluded that the inner accuracy of the vertical pendulum becomes bad during the period of ground breaking.

    • Co-seismic response characteristics ofWuji well in Hebei Province

      2021, 43(5):1077-1086. DOI: 10.3969/j.issn.1000-0844.2021.05.1077

      Abstract (149) HTML (0) PDF 5.60 M (611) Comment (0) Favorites

      Abstract:Obvious anomalies of Wuji well in Hebei Province, which generally occurred within 3 months before earthquakes, were obtained through the wavelet transform analysis in this paper. The minute data of digital water level of Wuji well and the global M ≥ 5.0 seismic data from 2011 to 2018 were analyzed. The results showed that Wuji well has good co-seismic response ability to global M ≥ 7.0 earthquakes, and the response forms to different earthquakes are oscillatory water-level seismic waves. Well-aquifer observation system, seismic magnitude, and well-hypocenter distance are important factors affecting the effect of water-level seismic wave recording. The type of focal mechanism may influence the effect of water-level seismic waves. A further analysis of the relationship between water-level seismic wave and seismic wave showed that R wave causes the largest change of water level. The wavelet transform results showed that there is obvious high-frequency abnormal information in the detailed analysis of water level before large earthquakes. In this paper, the previous research on the mechanism of water level oscillation was comprehensively analyzed, and the relevant mechanism was preliminarily discussed in combination with the specific situation of Wuji well.

    • Mechanism of borehole strain precursor anomaly at Fengjie station: results from stress transfer in regional stress field

      2021, 43(5):1087-1094,1102. DOI: 10.3969/j.issn.1000-0844.2021.05.1087

      Abstract (134) HTML (0) PDF 37.51 M (872) Comment (0) Favorites

      Abstract:Nowadays, the mechanism of borehole strain precursor anomaly at Fengjie station is not clear. In this paper, combined with other observation data and historical background information, the reliability and physical significance of the anomaly were compared and analyzed, and the precursory anomaly mechanism was further analyzed by finite element simulation method. The results showed that the trend change of borehole strain at Fengjie station, which is consistent with other nearby observation data, is a record of changes in regional stress field. Fengjie station is located in the eastern margin of Sichuan depression of Yangtze platform. Numerical simulation results showed that the substrate of Yangtze platform is hard and has good stress transmission. The lithology at the edge of Yangtze platform is relatively soft, easy to deform under stress, and sensitive to the stress at the other end of the platform. Therefore, the abnormal trend change of borehole strain at Fengjie station is the result of stress transfer in regional stress field.

    • Application of integrated geophysical methods in detectionof piedmont buried faults: a case study of theWeishan-Changshan south slope fault

      2021, 43(5):1095-1102. DOI: 10.3969/j.issn.1000-0844.2021.05.1095

      Abstract (156) HTML (0) PDF 17.31 M (1464) Comment (0) Favorites

      Abstract:In view of the complex and difficulty in the detection of piedmont buried faults, the Weishan-Changshan south slope fault was taken as an example in this paper. Combined with data of composite drilling geological section, the accurate location and activity of the buried section of the Weishan-Changshan south slope fault were studied by using shallow seismic exploration, high-density electrical exploration, and other geophysical methods, and the accurate location and occurrence of the fault were determined. The study results showed that the buried segment of Weishan-Changshan south slope fault in Tangshan city behaves as a south-dipping normal fault with an inclination of about 78ånd a fault distance of about 3 m, and the up-breakpoint of the fault is at depth of about 19 m. The buried segment of the fault in Tangshan city is a middle Pleistocene fault, and not active since the late Pleistocene.

    • Experimental study on the construction of underground fluid precursorarray with Ningbo hydrogeological monitoring well network

      2021, 43(5):1103-1111. DOI: 10.3969/j.issn.1000-0844.2021.05.1103

      Abstract (178) HTML (0) PDF 4.21 M (463) Comment (0) Favorites

      Abstract:The water level and water temperature of Beilun and Cixi wells from Ningbo hydrogeological monitoring well network were observed for the experimental study. The pressure efficiency of water level, the rainfall load effect, and the tidal factor of the two wells were calculated and compared with those of Zhuangshi well. The results showed that:(1) The water level changes of three wells have a good correlation in time and space, and there is a good genetic correlation between water level anomaly and its influencing factors. (2) The rainfall load factor of Cixi well is about an order of magnitude smaller than those of Zhuangshi and Beilun wells, which may be related to the location of Cixi well. (3) The wells are located in the Ningbo Basin with multiple aquifers, which makes it possible to carry out observation and basic research of different aquifers in the same structure. Qualified seismic precursor monitoring wells can be selected from the network for the construction of seismic precursor fluid array in the Ningbo Basin.

    • Traffic capacity assessment and selection of earthquakeevacuation routes in small mountainous cities: a case study of Dongchuan urban area

      2021, 43(5):1112-1122. DOI: 10.3969/j.issn.1000-0844.2021.05.1112

      Abstract (164) HTML (0) PDF 14.78 M (671) Comment (0) Favorites

      Abstract:Safe and short seismic evacuation route is an basic guarantee for improving the level of urban resilience governance in the new era. Earthquake evacuation routes during disasters could reduce urban casualties and provide options of emergency evacuation for urban residents. Dongchuan District in Kunming, a small mountainous city, is affected by the Xiaojiang earthquake fault zone, resulting in frequent earthquake disasters, and the urban earthquake fortification intensity is as high as 9 degrees. In this paper, the influencing factors of post-disaster seismic evacuation routes in Dongchuan urban area were systematically analyzed, and the traffic capacity of evacuation routes were evaluated. The relationship between population concentration point and seismic shelter for evacuation was established based on ArcGIS. Then, the selection of multiple seismic evacuation routes was studied with the genetic algorithm. The results showed that many rural internal roads around the city and old urban roads in Dongchuan urban area do not meet the post-earthquake evacuation requirements. There are some service blind spots in the seismic shelters for evacuation, and some communities are lack of evacuation routes to connect with the seismic shelter for evacuation. Some selected paths which meet the evacuation requirements will take a long time. In case of disaster, the shortest path shall be given priority.

    • Frequency band response characteristics of Xianyou well waterlevel before and after drilling disturbance in July 2017

      2021, 43(5):1123-1128,1141. DOI: 10.3969/j.issn.1000-0844.2021.05.1123

      Abstract (121) HTML (0) PDF 11.26 M (804) Comment (0) Favorites

      Abstract:In this paper, the methods of wavelet transform, correlation analysis, and harmonic analysis were used to analyze the variation characteristics of Xianyou well water level in each frequency band before and after being disturbed by well drilling and pumping in July 2017. The results showed that the serious well drilling and pumping disturbance has a significant influence on the full frequency of water level. After the interference tends to be stable, the intermediate frequency band basically recovers, but there are still many strong signals in the low frequency band, and the response capacity of M2 tidal strain is slightly decreased, indicating that the intermediate frequency band of Xianyou well water level is an effective monitoring band for stress change after being disturbed. The research methods and results of this paper can provide reference for interference analysis and anomaly extraction of water level data.

    • >地震工程
    • Water migration test on the moisture field and temperature fieldof sandy soil embankments in seasonal frozen area

      2021, 43(5):1129-1133. DOI: 10.3969/j.issn.1000-0844.2021.05.1129

      Abstract (116) HTML (0) PDF 4.99 M (485) Comment (0) Favorites

      Abstract:Based on the actual environment of embankment projects along the Heilongjiang mainstream, the distribution of temperature field, water field, and stress field of typical sandy soil samples from the embankment under freeze-thaw cycle were tested by the water migration experimental device. The test results showed that the damage of concrete highway at the top of embankment is related to the uneven settlement of embankment. The temperature change causes the gradient change of moisture content in embankment foundation, resulting in the change of stress field, and there is a linear relationship between the temperature gradient and moisture content gradient. The stable freezing depth of foundation reaches 1.12 m. Combined with the measured data, a thermo-hydro-mechanical coupled model for embankment foundation in seasonal frozen soil area was established. Finally, the practicability of the model in embankment projects was proved by a simulation analysis with the ANSYS finite element software.

    • Calculation methods for rebound deformation of foundationpit bottom considering unloading deformation modulus

      2021, 43(5):1134-1141. DOI: 10.3969/j.issn.1000-0844.2021.05.1134

      Abstract (115) HTML (0) PDF 1.42 M (602) Comment (0) Favorites

      Abstract:Aiming at the rebound deformation of soil at the bottom of foundation pits caused by excavation unloading, the characteristics of soil elastic modulus changing with the unloading stress path during excavation was first considered, then the calculation formula of soil deformation modulus under unloading stress path was derived. Considering the change of stress at the excavation surface of foundation pit below the ground surface, based on the Mindlin stress solution, the additional stress of soil at the bottom of rectangular foundation pit caused by excavation unloading was calculated. The rebound deformation of the soil at the bottom of foundation pit caused by excavation was calculated by the layer-wise summation method. Combined with some engineering examples in the existing literature, the heave deformation of pit bottom caused by excavation was calculated by this calculation method, then the calculation results were compared with the actual monitoring data. The results showed that the proposed method can effectively predict the heave deformation of pit bottom caused by excavation, thus it can be used as an effective prediction method in this field.

    • Dynamic characteristics of seismic response of soilnailed slopes in seasonal frozen areas

      2021, 43(5):1142-1149. DOI: 10.3969/j.issn.1000-0844.2021.05.1142

      Abstract (95) HTML (0) PDF 9.28 M (550) Comment (0) Favorites

      Abstract:To scientifically evaluate the seismic performance of soil nailed slopes in seasonal frozen areas, based on the theory equation of thermal-dynamics, a numerical model of soil nailed slope with viscoelastic artificial boundary in seasonal frozen area was established under earthquake load by using large-scale nonlinear finite element software ABAQUS. The acceleration response, displacement response, and axial force response of soil nails in summer and winter were compared and analyzed. The results showed that whether in summer or winter, the peak acceleration increases with the increase of the slope elevation and the peak value of excitation acceleration, and reaches the maximum at the top of slope in summer. In addition, under the action of seismic waves with different peak acceleration, the peak displacement responses at the same position are obviously different. When seismic wave with the same intensity is excited, the largest displacement shows at the top of slope in summer, indicating that the seismic load has the most obvious damage effect on the top of slope in summer. The axial force of soil nails has elevation amplification effect and slope amplification effect. The peak value of axial force at the end of soil nails gradually increases from the bottom of slope to the top. The numerical simulation model and conclusions in this paper can provide some reference for the seismic design of seasonally frozen soil slope supported by soil nails under seismic load.

    • Proportion of granite similar material used inlarge-scale shaking table tests

      2021, 43(5):1150-1159. DOI: 10.3969/j.issn.1000-0844.2021.05.1150

      Abstract (156) HTML (0) PDF 7.88 M (515) Comment (0) Favorites

      Abstract:To study the dynamic response mechanism of large-scale granite earthquake landslides, it is important to develop and prepare granite similar material for shaking table model test. In this paper, iron ore powder, quartz sand, and barite powder were selected as aggregates, gypsum as adjusting material and rosin alcohol solution as binder. The orthogonal test with 4 factors and 5 levels was designed, and the range analysis and multiple linear regression fitting were performed on the test results. On this basis, the influences of various factors on the physical and mechanical properties of granite similar material and the empirical equation of the similar material proportion were obtained. The results show that the density of granite similar material increases with the increase in the ratio of iron powder and barite powder in aggregate. With the increase of binder concentration, the compressive strength, elastic modulus, and cohesion of granite similar material significantly increase. With the increase of gypsum content, the density, compressive strength, and internal friction angle all decrease. The empirical equation of similar material proportion obtained from the test can provide a reference for the preparation of similar granite material or other similar materials.

    • Determination of ground motion parameters for the thicksilt site based on SOILQUAKE software method

      2021, 43(5):1160-1167. DOI: 10.3969/j.issn.1000-0844.2021.05.1160

      Abstract (473) HTML (0) PDF 13.05 M (752) Comment (0) Favorites

      Abstract:Taking a thick silt site in Binhai District of Tianjin as an example, the equivalent linearization method (LSSRLI-1) and the analysis method of soil earthquake response (SOILQUAKE) were used to calculate the earthquake response of soil layers under seismic ground motions of different fortified levels. The results showed that:(1) Compared with the results of the new zonation map, the equivalent linearization method may underestimate the seismic action of the thick silt soft site, or even underestimate the fortification intensity of the site; (2) The method of software SOILQUAKE can still show a certain amplification effect in determining the design seismic parameters of soft site, especially under strong earthquakes, it overcomes the phenomenon that the design spectrum is obviously low and wide in the calculation of soft site, which can provide a reference for the determination of fortification parameters of major projects in soft site; (3) The design ground motion parameters of soft site determined by the method of software SOILQUAKE are greatly superior to the results of the new zonation map. Considering the coordination with relevant seismic fortification codes, a large number of strong earthquake records need to be further input, calculated and verified for other types of soft sites, so as to be better applied to actual projects.

    • Seismic performance of spandrel columns strengthened by jackets based on the incremental dynamic analysis

      2021, 43(5):1168-1175. DOI: 10.3969/j.issn.1000-0844.2021.05.1168

      Abstract (96) HTML (0) PDF 12.11 M (626) Comment (0) Favorites

      Abstract:The Jinhua Bridge in Deyang City was taken as an example to analyze the actual seismic damage of spandrel columns, then using the nonlinear calculation model under the action of earthquake, an IDA-based method for evaluating the seismic performance of spandrel columns strengthened by reinforced concrete jackets was established. The analysis results showed that the shear-span ratio has a significant effect on the seismic performance of spandrel columns. The column with high shear-span ratio is relatively poor in seismic performance, and the spandrel column is a vulnerable component under earthquake action. The seismic performance of spandrel columns strengthened by jackets is improved obviously:the vulnerability is significantly reduced, and the ductility is improved to a certain extent. The analysis results are consistent with those of seismic damage survey, which can provide a reference for the seismic evaluation of spandrel columns.

    • Experimental study on shear behavior of metal rubber bearings

      2021, 43(5):1176-1182,1196. DOI: 10.3969/j.issn.1000-0844.2021.05.1176

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      Abstract:To study the shear performance of a kind of metal rubber bearing, the influences of vertical pressure and horizontal shear deformation on the shear performance of metal rubber bearing were analyzed by quasi-static tests under three kinds of compressive stress. Through the analysis of test data, the empirical formula of the correlation between the bearing shear performance and the compressive stress was established, and a trilinear restoring force model which can approximately simulate the test curve was proposed. The results showed that with the increase of bearing shear deformation, the equivalent stiffness and energy consumption of the bearing increase and the equivalent damping ratio decreases, while the yield force basically remains unchanged, and the hysteretic curve gradually changes from shuttle shape to anti-S shape. When the shear strain is greater than 25%, the stiffness hardening phenomenon appears. With the increase of compressive stress, the energy consumption, yield force, equivalent stiffness and equivalent damping ratio of the bearing increase.

    • Effect of site factors on the characteristics of offshore groundmotions based on strong motion observation records

      2021, 43(5):1183-1189. DOI: 10.3969/j.issn.1000-0844.2021.05.1183

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      Abstract:Present research on strong motion records show that the characteristics of offshore ground motions are obviously different from those of onshore ground motions, but it is difficult to further determine the influencing factors of offshore ground motions. Based on previous research, the differences of ground motion characteristics between adjacent offshore stations during the same earthquake were compared and the reasons were analyzed. The strong motion records from six offshore stations and adjacent onshore stations with different site conditions were selected in the K-NET of Japan. The V/H PGA ratio, amplification factor spectrum, and V/H spectral ratio of strong motion records from different stations were analyzed, then the ground motion characteristics from six offshore stations and the difference of ground motion characteristics between offshore and onshore stations with different site conditions were studied. The results showed that:(1) there are obvious differences in offshore and onshore vertical ground motions;(2) the ground motion characteristics of different offshore stations, which are greatly influenced by site factors, also have great difference and obvious regularity;(3) the characteristic period of offshore horizontal seismic response spectrum is large, and the spectral curve is between those of medium hard-soil and soft-soil sites.

    • Influence of specimen thickness on laboratorydetermination of loess collapsibility indexes

      2021, 43(5):1190-1196. DOI: 10.3969/j.issn.1000-0844.2021.05.1190

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      Abstract:To study the influence of specimen thickness on the collapsibility indexes of loess, a series of collapsibility tests on loess specimens at different depths (from 1 m to 20 m) in a certain area of Xi'an were carried out using conventional high-pressure and modified consolidation apparatus, respectively. The results of indoor collapsibility tests on loess specimens with thickness of 2 cm and 8 cm were compared and analyzed. The conclusions showed that the collapsibility coefficients of specimens with different thickness are similar when the collapsibility of soil is weak or the pressure is small. The difference between two specimens is more and more obvious with the increase of pressure when the collapsibility of soil is strong, and the collapsibility coefficient of 8-cm specimen is much larger than that of 2-cm specimen under the same pressure. The stronger the collapsibility of loess, the greater the influence of specimen thickness on the collapsibility indexes (collapsibility coefficient, self-weight collapsibility coefficient, and initial collapsibility pressure). This conclusion can provide a basis for the adjustment of specimen thickness in indoor collapsibility test.

    • Seismic performance evaluation and damage degree controlof fiber reinforced concrete frame structures

      2021, 43(5):1197-1207. DOI: 10.3969/j.issn.1000-0844.2021.05.1197

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      Abstract:To study the damage degree control and the performance evaluation method of fiber reinforced concrete (FRC) frame structures, the ABAQUS finite element software was adopted to conduct a dynamic time-history analysis on several FRC frame models. The qualitative description and quantitative methods of limit states of various performance levels were studied, and the seismic performance of the structure was evaluated. According to the results, the FRC in the expected damage position can reduce the residual inter-story drift ratio, the maximum rotation angle of column end section, and the maximum residual rotation angle of column section, that is, the damage degree of the overall structure and members can be controlled. Then the limit values of column section angle, story drift ratio, and residual story drift ratio of FRC frame structure under different performance levels were given. Considering the characteristics of FRC material and the simulation results, this study suggested to select the residual inter-story drift ratio for performance evaluation. The FRC frame structure with a column-to-beam flexural strength ratio of 1.2, which considers the flange width of 8 times the plate thickness, can achieve the performance objective D.

    • Accumulative deformation characteristics ofloess under different loading modes

      2021, 43(5):1208-1213,1243. DOI: 10.3969/j.issn.1000-0844.2021.05.1208

      Abstract (141) HTML (0) PDF 1.33 M (383) Comment (0) Favorites

      Abstract:The dynamic characteristics of soil are mainly related to the stress condition, loading type, test control mode, load, and other parameters. Previous experimental study on the cumulative deformation of unsaturated loess under uniaxial dynamic stress loading can not truly reflect the stress state of soil. In this study, the WF-12440 dynamic triaxial-hollow cylinder torsional shear test system produced by WF Company, UK, was used to carry out a series of long-term repeated load tests of loess under unidirectional and bidirectional dynamic stress loads. The effects of different dynamic stress loading methods on the development characteristics of cumulative deformation of unsaturated loess. The test results showed that the softening index of loess decreases non-linearly with the increase of cycle times both under unidirectional and bidirectional loading. At the same cycle times, the softening index decreases with the increase of dynamic stress amplitude. Under different loading modes, the softening index decreases rapidly within 100 cycles, and the softening rate tends to be stable with the increase of cycles. Under the action of bidirectional load, when the axial dynamic load is small, the application of radial load will accelerate the softening degree of loess; with the increase of axial dynamic load, the effect of radial load on soil softening will weaken gradually. With the development of this study, it can be more accurate to evaluate the seismic subsidence of loess field or calculate the deformation of subgrade soil under different load coupling changes in Northwest China, so as to effectively control the overall stability of subgrade and the settlement after construction.

    • Design and implementation of the publishing system forWAMP-based earthquake science information database

      2021, 43(5):1214-1219. DOI: 10.3969/j.issn.1000-0844.2021.05.1214

      Abstract (123) HTML (0) PDF 9.41 M (675) Comment (0) Favorites

      Abstract:We emphasized the importance of the design concept of the public service publishing system for popular earthquake science information from the perspective of social public services. Based on the common software framework design ideas in the world, we analyzed the software framework structure of the public service publishing system for popular earthquake science information, developed a set of self-designed software framework, and realized the design pattern of Web+Apache+MySQL+PHP (WAMP). The system consists of the release module, the query module, and the processing module for earthquake science information. After deep optimization, the modules all have excellent operation performance.

    • Influence of top building load on the slope stabilityunder strong earthquakes

      2021, 43(5):1220-1227. DOI: 10.3969/j.issn.1000-0844.2021.05.1220

      Abstract (119) HTML (0) PDF 22.12 M (651) Comment (0) Favorites

      Abstract:To study the influence of top building load on the slope stability under strong earthquakes, combined with the distribution characteristics of typical buildings in loess areas, the damage characteristics of loess slopes were discussed through a series of model tests, then a three-dimensional slope model under building load with different distances to the slope was established with the finite element simulation software. By analyzing the total displacement nephogram, horizontal displacement nephogram, and maximum shear strain nephogram of the slope, the variation law of potential dangerous area of the slope was judged. The study results showed that with the increase in the distance of top buildings to the slope, the coincidence area between the top load deformation area and the potential sliding surface of the slope decreases, and it is no longer affected by the potential risk sliding surface of the slope 20 m away from the top of the slope.

    • Dynamic liquefaction of unsaturated loess: a case study of Dangjiacha landslide

      2021, 43(5):1228-1237. DOI: 10.3969/j.issn.1000-0844.2021.05.1228

      Abstract (161) HTML (0) PDF 18.96 M (726) Comment (0) Favorites

      Abstract:Due to the strong water sensitivity and dynamic vulnerability of loess, many strong earthquakes in loess areas have caused geological hazards such as liquefaction and landslides, resulting in serious casualties and property loss. Therefore, the liquefaction of loess with high water content under vibration can not be ignored. Based on previous studies, taking Dangjiacha landslide in Ningxia as an example, the liquefaction of high moisture content loess under vibration was studied in this paper. The field investigation results showed that the slip soil with high water content did not reach complete saturation (about 95%). Obvious liquefaction characteristics of "fluidization" were seen on the fresh core sample section. The performance and mechanism of liquefaction in the unsaturated loess layer of Dangjiacha landslide were analyzed with indoor tests and numerical simulation. The results showed that:(1) The mechanism of liquefaction in the unsaturated loess layer could be summarized as follows:the pore water pressure of saturated loess layer increases sharply under earthquake, while the growth response of unsaturated loess layer with high water content lags behind. As the pore water pressure dissipates upward, the groundwater percolates upward. When the average effective stress is close to 0, the liquefaction of unsaturated loess layer with high water content occurs. (2) The growth response of pore water pressure of loess with different saturation has time delay. According to the criterion of pore pressure ratio of liquefied saturated loess and Seed simplified discriminant method, it is confirmed that unsaturated loess layer with high moisture content in Dangjiacha landslide has a tendency for seismic liquefaction. The initial saturation ranges of soil liquefaction in the front and middle of the slope are 68.3%~100% and 73.8%~100%, respectively, and the soil in the rear edge of the slope will not liquefy.

    • Experimental study of the influence of compaction degree on dynamicstrength and dynamic pore pressure of desulfurization gypsum

      2021, 43(5):1238-1243. DOI: 10.3969/j.issn.1000-0844.2021.05.1238

      Abstract (108) HTML (0) PDF 2.91 M (395) Comment (0) Favorites

      Abstract:To study the effect of degree of compaction on the dynamic strength and dynamic pore pressure of desulfurization gypsum, a series of undrained dynamic triaxial tests were carried out on three groups of desulfurization gypsum, with compaction degrees of 0.85, 0.90, and 0.95. The confining pressures were 100, 200, and 400 kPa, respectively. Test results showed that, with increasing compaction degree, the connected skeleton of particles of desulfurization gypsum is more difficult to destroy, and the dynamic strength and dynamic pore pressure of desulfurization gypsum increase, though the latter increases slowly. The dynamic shear stress ratio and dynamic inner friction angle of desulfurization gypsum show a linear relationship with the compaction degree. The tested desulfurization gypsum can be classified as a low-liquid-limit silt. Curves of dynamic strength and dynamic pore pressure were similar to those of conventional silt, which can be regressed by power function and logarithmic function, respectively. Through verification with the F test method, the significance level of the statistical regression was "highly significant."

    • Seismic performance of intake tower structuresbased on endurance time method

      2021, 43(5):1244-1250. DOI: 10.3969/j.issn.1000-0844.2021.05.1244

      Abstract (158) HTML (0) PDF 6.41 M (778) Comment (0) Favorites

      Abstract:The seismic performance of intake tower structure is of great significance to the safety and operation of hydropower stations. The seismic performance of the high-rise independent intake tower structure of Shapai Hydropower Station was analyzed and evaluated subjected to three endurance time accelerograms (ETAs). The calculation results were then compared with the incremental dynamic analysis (IDA) results under natural ground motions, and the comparisons of the top displacement, the base shear, and the seismic damage history of the intake tower were performed. The case study results showed that compared with IDA method, the endurance time method can better analyze the seismic response of the structure and match the mean value of IDA results. The endurance time method can get the structure response under different dynamic strengths by using less time-history analysis, and the calculation results are accurate and efficient, thus providing a new method for the seismic performance analysis of the water intake tower structure.

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