• Volume 37,Issue 3,2015 Table of Contents
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    • >Earthquake Engineering
    • Centrifuge Model Test on a Buried Pipeline Crossing Reverse Fault Considering Soil-structure Interactions

      2015, 37(3):639-642. DOI: 10.3969/j.issn.1000-0844.2015.03.0639

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      Abstract:Buried pipeline systems are usually referred to as lifeline systems due to their support of human daily life and economic development, energy-transportation and water-transmission. The primary hazard for buried pipelines during earthquake events is permanent ground deformation (PGD). However, an important factor to control the response of the buried pipeline to PGD is the interaction between the soil and the pipeline. In this study, a centrifuge model test was conducted to investigate the effect of PGD on a pipeline. The normal pressure of the interface between pipeline and soil was measured using the smart tactile pressure sensor system, and other important parameters such as PGD, strain rate, pipeline diameter, the orientation of the pipeline and soil types were also tested to determine the influence on soil-pipeline interactions. All of the PGD, pipeline-PGD orientations, pipeline diameters, and soil types were key factors affecting the interaction between soil and pipeline. The results of this research could be used in the aseismic design of pipelines passing through the PGD.

    • Seismic Response of Long-period Structures Based on the Instantaneous Energy Spectrum Obtained by the Hilbert-Huang Transform

      2015, 37(3):643-647. DOI: 10.3969/j.issn.1000-0844.2015.03.0643

      Abstract (1052) HTML (0) PDF 2.27 M (1447) Comment (0) Favorites

      Abstract:To reveal the failure mechanism of long-period structures, we obtained the instant energy spectrum by the Hilbert-Huang transform (HHT), and analyzed the structure's displacement response based on the theory of simple harmonic seismic response. The transient response of a MDOF system was also calculated based on a harmonic earthquake response analysis. Notable characteristics on long-period structures were different from short-period structures, based on analyses of the transient vibration patterns of a long-period (e.g., 15 layer) building. First, the time of peak displacement response on the structure was always observed to be later than the time of peak value of earthquake energy. Second, the displacement response was mainly controlled by the transient response in low order modals. Third, the first order modal displacement hysteresis lasted the longest, and the hysteresis mainly depended on the natural vibration period of the structure. The conclusions showed that demolition and collapse of long-period structures due to the strong earthquake did not happen at the greatest density of earthquake ground motion.

    • Influence of the Vertical Seismic Wave on the Seismic Response of an Large-span High-section Y-shaped Column Subway Station

      2015, 37(3):648-654. DOI: 10.3969/j.issn.1000-0844.2015.03.0648

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      Abstract:In this study, the Y-column subway station of the Xinhua Street Station in public areas of the Beijing Metro Line 6 was used as an engineering background to develop a numerical model with the FLAC3D finite difference program. The model was used to analyze and research the seismic response characteristics of the large-span high-section Y-shaped column subway station under only ground horizontal vibrations as well as under a combination of both horizontal and vertical seismic waves. The results showed that compared with inputting only one-way seismic waves, the peak acceleration and stress value of the station increased and the relative horizontal displacement decreased under the two-way seismic coupling. When the strength of the seismic wave input increased, the impact rate of vertical ground motion showed a decreasing trend. Under the combined action of the two-way seismic waves, the vertical displacement of the Y-shaped column fork branch was significantly increased under the same conditions and the vertical displacement of the measuring point was more uniform, whereas the vertical displacement of the measuring point in the one-way horizontal motions was quite different. Compared with the one-way horizontal motion, the vertical seismic wave input was less affected by the horizontal-direction vibration characteristics law among each measuring point.

    • Free Vibration Analysis of a Mindlin Plate-beamon a Winkler Elastic Foundation

      2015, 37(3):655-659. DOI: 10.3969/j.issn.1000-0844.2015.03.0655

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      Abstract:In recent years, short-and medium-length floating-slab tracks have become commonly used in railway engineering. These tracks are of a model type between a Winkler foundation beam and a Winkler foundation plate. For this type of wide-beam structure, a more suitable theory is required that both ensures calculation accuracy, as does the plate theory but also provides a simple analytical process, such as that of beam equations. In this study, the governing equations of the Mindlin plate are degraded and the dynamic equations for wide-beam structures are obtained:this is called the Mindlin plate-beam theory. Although the equations of the Mindlin plate-beam theory appear similar to the equations of the Timoshenko beam theory, the coefficient of bending stiffness is different and retains the direct influence of the Poisson's ratio parameters. This means that lateral deformation can be considered in the Mindlin plate-beam theory. The stiffness of the elastic foundation is also considered, and the equations are extended accordingly. For general analysis, the variables and parameters in this study are normalized and the expressions for both the vertical displacement and flexural rotation angle of a wide beam are obtained. Based on the boundary conditions, the dynamic characteristic equation for a simply supported wide beam is finally derived, and the normalized frequencies for the wide beam can be calculated through certain root searching programs. In this study, different kinds of boundary conditions are considered using the same procedure. To illustrate the wide-beam theory described herein, several numerical examples are used and the natural frequencies of a Mindlin plate-beam on a Winkler elastic foundation are compared with the results of a Timoshenko elastic foundation beam and a Mindlin elastic foundation plate. The results demonstrate the accuracy of the present equations. The effects of the height-to-length Poisson's ratios and elastic foundation stiffness are considered and the following conclusions are obtained from the numerical results:(1) For a simply supported wide beam, the first three frequencies of the plate-beam model show good agreement with those based on the Mindlin plate model. The discrepancy of the results from the two beam models increases with the width of the beam as compared to those of the Mindlin plate. However, the fundamental frequency of the Mindlin plate-beam theory still remains in good agreement with the plate theory; (2) the natural frequencies obtained from the Mindlin plate and Mindlin plate-beam theories will increase with the Poisson's ratio for a wide beam on an elastic foundation and those obtained from the Timoshenko beam theory will decrease. This result means that the relative error of the beam-plate and Mindlin plate will further reduce for a larger Poisson's ratio; and (3) the equations derived here are suitable for wide-beam analysis, can incorporate the effect of beam width, and are especially suitable for a wide foundation beam with a relatively large Poisson's ratio. The numerical examples based on this approximation theory are in good agreement with the Mindlin plate theory, while the equations and calculation process are much simpler.

    • Study on Seismic Robustness of Structure

      2015, 37(3):660-666. DOI: 10.3969/j.issn.1000-0844.2015.03.0660

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      Abstract:In the last decade because of the frequent occurrence and great harm brought by the progressive collapse of structures, this problem has attracted increasing attention in the engineering field and has become a hot research issue worldwide. Progressive collapse is defined as a situation where the local failure of a primary structural component leads to the collapse of the whole structure. A safe and robust structure is able to bear the required loads to prevent complete collapse. Researchers have suggested a number of ways to ensure that buildings of significant size can absorb local damage and resist progressive collapse. However, the source and magnitude of the loads may differ, so it is impossible to design and construct structures that can guarantee absolute safety. Although much work has been done in the field of structural robustness, the term used for structural property prevents progressive structural collapse and is still in the exploration stage. So far, there is no clear definition or accepted parameters to quantitatively evaluate structural robustness. In this study, we describe the progressive-collapse resistance robustness of a frame structure and propose a target-oriented component vulnerability coefficient in combination with an internal force feature of the frame structure during the collapse process. Additionally, we improve an existing structural robustness coefficient. Furthermore, we verified the practicability of our proposed method by computing a finite element model of a reinforced concrete frame structure using the finite element analysis software, SeismoStruct V6.5. Our results show that structural robustness is relative and can be enhanced by reducing the member vulnerability coefficient of important columns. Under the same load, the vulnerability coefficient of the frame columns can be segregated as the middle, side, and corner columns, and the member importance coefficients have the opposite values. Components with large vulnerability and important coefficients should be protected to ensure structural robustness.

    • Upper Bound FEM to Analyze the Ultimate Aseismic Capability of Earth-rock Dams

      2015, 37(3):667-671,692. DOI: 10.3969/j.issn.1000-0844.2015.03.0667

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      Abstract:An upper bound limit analysis finite element method is developed to study the ultimate aseismic capacity of earth-rock dams. Considering the large value of the internal friction angle and the non-linear shear strength parameters of earth-rock materials, a static form, which is the corresponding dual problem of the second-order cone programming for upper bound limit analysis, is formulated with constraints based on the yield criterion, flow rule, boundary conditions, and the energy-work balance equation. The upper bound solution of ultimate aseismic capacity is then iteratively obtained by a state-of-the-art interior-point algorithm. The proposed method is applied to the seismic stability problem of a typical earth-rock dam. The results indicate that the earth-rock dams designed according to code have strong seismic capabilities, as the influence of vertical earthquake load is considered. These results also demonstrate the high calculation accuracy and practical value of the proposed method.

    • Three-Dimensional Numerical Simulation of Embankment Seismic Liquefaction Using Adaptive Time-Stepping Method

      2015, 37(3):672-677. DOI: 10.3969/j.issn.1000-0844.2015.03.0672

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      Abstract:Three-dimensional (3D) numerical simulation of a large model is a time-consuming process due to the huge number of elements and nodes. This is particularly true for seismic behavior analysis in which the accuracy is limited by the size of the time increment. In this study, the temporal discretization error estimator and time increment adaptive adjustment method is proposed on the basis of the numerical platform for seismic liquefaction analysis of saturated soil. The proposed method is successfully applied in 3D embankment seismic response analysis. The temporal discretization error estimation includes errors in soil skeleton displacement and pore water pressure. These two types of errors are combined to form a mixed error as an effect of pore water pressure error. The time increment is adaptively adjusted by the relationship of mixed error and the given error tolerance. Through a numerical example of 3D embankment, it is determined that the adaptive time-stepping method can be used to improve the accuracy of small time increments. The results of this method are comparable to those obtained using highly efficient but time-consuming large time increments.

    • >地震科学技术
    • Application of Gassmann Equation-based Fluid Substitution Method to the Research of Reservoir-induced Earthquakes at Shanxi Reservoir

      2015, 37(3):678-686. DOI: 10.3969/j.issn.1000-0844.2015.03.0678

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      Abstract:By analyzing the relationship between seismic P-wave velocity, velocity ratio, and rock porosity and saturation in the Shanxi reservoir, the fluid substitution equation method based on the Gassmann equation was used to estimate the rock porosity and fluid diffusion rate in the reservoir's earthquake source region. The results show that the rock of the epicentral area is always close to the water-saturated state. The changes in P-wave velocity and the velocity ratio from decreasing to increasing reflect that the rock in the epicentral area changes from increasing porosity (decreasing saturation) to increasing saturation. The velocity ratio gradually increases from the minimum value to the maximum value because of the changes in rock conditions from unsaturated to saturated. Moreover, the fluid diffusivity of the Shanxi reservoir is 1.44×104 cm2 s-1 to 0.84×104 cm2 s-1, which is consistent with that of the South Carolina reservoir in the United States, the Acu reservoir in Brazil, and the Xinfengjiang reservoir in Guangdong, China. Further, the maximum rock porosity in the source area is 8.7%~2.0%, which is consistent with the average value of porosity of new rhyolite porphyries in the Shanxi reservoir dam site measured by the East China Investigation and Design Institute by lab testing of the physical and mechanical properties of the rock.

    • Time-space Dynamic Evolution Characteristics of a Gravity Field in the Middle Area of North China

      2015, 37(3):687-692. DOI: 10.3969/j.issn.1000-0844.2015.03.0687

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      Abstract:Employing the mobile gravity data from 2009 to 2013 as the foundation,mobile gravity observation data of the middle region of North China from 2009 to 20l3 were analyzed,and time-space dynamic evolution characteristics of the gravity field were studied.The change of the gravity field is closely related to the tectonics of active faults.The resulting gravity data showed that the changes in gravity anomalies in North China are severe.In the northern portion of the Shanxi graben zone,centered at the border region in Shanxi,Hebei, and Inner Mongolia,the gravity variation showed a large area of negative anomalies.The entire survey area showed a large area of negative changes in the local area with a gravity gradient formation,which reversed the recent changes,indicating a further increase in regional seismic hazards.This potential guide to earthquake prediction has important practical significance.

    • Location of Future Large Earthquakes in Jiangsu Segment of Tanlu Fault Zone Based on the Crustal Velocity Structure

      2015, 37(3):693-701. DOI: 10.3969/j.issn.1000-0844.2015.03.0693

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      Abstract:The Tancheng-Lujiang Fault Zone (simplified as the Tanlu Fault Zone) is the biggest in east China. In 1668, an M8 earthquake occurred along this fault zone in Tancheng, Shandong Province, China. Seismologists are focusing on the most likely location of the next major earthquake along this fault, particularly in the areas near Shandong and Jiangsu provinces. The multiphase travel time inversion (MUTI) algorithm was developed to invert the three-dimensional crust velocity structure of the Shandong-Jiangsu segment of the Tanu Fault Zone and its adjacent area (30°~37° N, 113°~122° E). The crust can be divided into three layers, the upper (10~15 km thick), the middle (10~15 km thick) and the lower (10~12 km thick). The segmentation of the shallow velocity structure is consistent with that of fault activity, and indicates that the area from Xinyi to Sihong comprises the active fault block section. There is a low velocity layer at a depth of 20~25 km in the Tanlu Fault Zone from Linshu to Dingyuan and its eastern area. A low velocity layer can also be found in the middle crust of the source region of the 1668 Tancheng earthquake. In this study, we present the variation of Moho depths in Suqian, Siyang, Shuyang, and Tancheng. The Wuxi-Suqian fault, the Hongze-Goudun fault, and the Jiashan-Xiangshui fault all intersect with the Tanlu Fault Zone, and the intersection area of these faults may be dangerous. By comparing the depth velocity structure features of the Jiangsu segment along the Tanlu fault zone with the source area of the 1668 Tancheng M8 earthquake, combined with data regarding seismic activity, the active fault block, the low velocity layer in the middle crust, the depth variations of the Moho, and the fault intersections, the area of next large earthquake can be estimated for the Jiangsu segment of the Tanlu fault zone. The most likely position is 33.4°~34.1° N and 118.2°~118.8° E, in Suqian, Shuyang, Siyang and Sihong in particular. The estimated maximum magnitude is 8.

    • Characteristics and Tectonic Activities of Faults in Zhangjiakou-Xuanhua Basin

      2015, 37(3):702-709. DOI: 10.3969/j.issn.1000-0844.2015.03.0702

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      Abstract:An active fault leads to disaster in the world, and within the general development of disasters, an active fault's frequency and the damage it causes is based on the degree of the fault layer, and gradually intensifies. In recent years, earthquake prediction research and engineering construction developments have vigorously promoted the study of active faults. The Zhangjiakou-Xuanhua Basin, situated in the intersection of the Zhangjiakou-Bohai fault zone and the Shanxi seismic tectonic zone, is a typical Cenozoic extensional fault-depression basin. There are many active faults in this basin, which control the basin's development and evolution. However, there is scant research on the active faults in the Zhangjiakou-Xuanhua Basin, and existing research is confined to a few areas. As such, a systematic analysis of this area's active faults, the identification of quantitative information regarding active faults, and a better understanding of the characteristics of this basin's long-term activity is important in theory and practice. Based on an analysis and reorganization of relevant information from detailed field investigations and shallow seismic exploration, this study describes the geometric characteristics and tectonic activities of the active faults in the Zhangjiakou-Xuanhua Basin. The faults for which there are research data include the Zhangjiakou, Wanquan, Ximalin-Shuiquan, and Yanghe faults. The results showed that:The Zhangjiakou fault strikes mainly to the northwest and east-west, dipping to the north, and extending over 70 km. As a major geological and geomorphologic boundary, the Zhangjiakou fault controls the geotectonic movement in this region, in which its southern side is characterized by Late Quaternary unconsolidated basin deposits, and its northern side by Mesozoic volcano debris and Pre-Mesozoic metamorphic rocks in the form of lower mountains and hills. The Zhangjiakou faults are mainly high-angle inverse strike-slip faults with some normal strike-slip faults. The activity of the central segment of the Zhangjiakou fault is stronger than that in other segments. Since the late Pleistocene, the average vertical slip rate along a single fault is over 0.07~0.30 mm/a, while the total vertical slip rate over the entire fault is as high as 1.33 mm/a. The Wanquan fault lies in the northwest of the Zhangjiakou-Xuanhua Basin, striking mainly northeast or north-northeast, dipping southeast, and extending over 15 km. It is a major geological and geomorphic margin, controlling the neotectonic movement in this region. On the southeast side of the Wanquan fault there are Late Quaternary unconsolidated deposits, forming a basin or deposition; but on the other side there is Mesozoic volcano debris, forming lower mountains and hills. The Wanquan fault is a normal fault with southeast-dipping at a medium-high-angle. This fault was active in the Quaternary. Since the middle-late time of the late Pleistocene, the average rate with vertical slip of a single fault has been about 0.03~0.3 mm/a, but the fault has multiple slipping surfaces, and a total large-rate with vertical slip is yet to be estimated. The Ximalin-Shuiquan fault is located in the southwest of the Zhangjiakou-Xuanhua Basin, and can be divided into four sections. The fault strikes mainly northwest, with high-angle inverse strike-slip fault or normal strike-slip fault characteristics. The latest active time of the Ximalin-Shuiquan fault is in the late Middle Pleistocene. The Yanghe fault is a subsurface fault, and its active time was in the Middle Pleistocene. The fault strikes mainly northwest, and controlled the Yanghe River's flow direction and terrace development. The fault strikes mainly northwest, with high-angle slip fault characteristics.

    • Regional Crustal Deformation, Tectonic Geomorphology and Seismogenic Tectonic Model of the Northwestern Tibetan Plateau:Case Studies of the 2008 and 2014 Yutian (Xinjiang) MS7.3 Earthquakes

      2015, 37(3):710-723. DOI: 10.3969/j.issn.1000-0844.2015.03.0725

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      Abstract:To understand clearly the geomorphologic characteristics and seismogenic structure of the Yutian MS7.3 earthquakes of 2008 and 2014, the regional tectonic geomorphic features of the Karakoram-Western Kunlun-Kangxiwa region are analyzed using digital elevation model data. The tectonic environment and crustal kinematics of the northwestern Tibetan Plateau, where the earthquakes occurred, are discussed by combining data on active faults and GPS velocity field relative to the Tarim rigid block. The geological background of the Western Kunlun block, which is surrounded by the Karakoram, Kangxiwar, and Longmu Lake-Bangda Lake faults, is discussed. The seismic activity and seismogenic environment of the southwestern segment of the Altyn Tagh fault are studied. In this study, the topographic and tectonic geomorphologic characteristics near the seismogenic region are analyzed using terrain profiles to reveal the relation between the regional geomorphologic characteristics and the seismogenic structure. The deformation characteristics and seismogenic process of the middle and upper crusts are discussed on the basis of the regional tectonic geomorphology and crustal deformation obtained from the GPS velocity data. Finally, the evolutionary process of the Kerya River extension rift and geodynamic background is discussed. It is suggested that the 2014 Yutian MS7.3 earthquake was related to the coseismic static Coulomb stress and lower-crust viscoelastic relaxation that were part of the post-seismic processes of the 2008 Yutian MS7.3 earthquake. Moreover, the occurrence of these earthquakes may be related to the crustal thinning of the Tibetan Plateau.

    • Long-term Observation Data of Geo-electrical Resistivity at the Yanqing Station, Beijing

      2015, 37(3):724-730,771. DOI: 10.3969/j.issn.1000-0844.2015.03.0739

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      Abstract:The Yanqing station in Beijing has observed geo-electrical resistivity for almost 30 years.This station started observing the Geo-electrical resistivity in 1969 and a technological transformation of this observation site occurred in 1988.The station has roughly conducted normal observations since 1988.However,some environmental interference has occasionally occurred in the station's electrode-arranging region.This station is one of the few stations affected by environmental interference in the Beijing,Tianjin,and Tangshan areas.The quality of geo-electrical resistivity observation data has had relatively high standards for a long time.The reliability of geo-electrical resistivity observations since 1988 at the Yanqing station was analyzed. The normalized variation rate method was applied to process long-range geo-electrical resistivity observations.Data from seven medium or strong earthquakes that occurred near Beijing were integrated to study the relationship between geo-electrical resistivity and earthquakes.The results showed that the abnormal changes in geo-electrical resistivity observations demonstrated two characteristics of apparent resistivity changes.The first characteristic was an observation that appeared for a medium or short period and abnormal changes continued before the medium earthquakes occurred.The second characteristic was observed as an observation that had a long term of about 1 year and continued to have higher or lower abnormal changes before strong earthquakes occurred.This revealed a compact temporal correlation between the abnormal changes and strong earthquakes.The geo-electrical resistivity observation at the Yanqing station has the ability to reflect strong earthquakes near the station.Therefore,the observations provide a frame of reference for long-term or short-term earthquake prediction in nearby areas.In addition,the geo-electrical resistivity observations changed abnormal while strong earthquakes were occurring at long distances from the station in or around China.This showed that the geo-electrical resistivity observation at the Yanqing station can also be used to study earthquake prediction over long distances.The normalized variation rate method was applied to process the monthly observations of geo-electrical resistivity.This is an effective method to extract long-term or short-term geo-electrical resistivity data for abnormal changes.The abnormal changes that cannot be identified from the monthly data series can also be easily discovered through this normalized variation rate process.

    • Regional Crustal Deformation Analysis before and after the Minxian-Zhangxian Earthquake

      2015, 37(3):731-738. DOI: 10.3969/j.issn.1000-0844.2015.03.0731

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      Abstract:With the establishment of the Crustal Movement Observation Network of China (CMONOC) and the China Tectonic Environment Monitoring Network (CMTEMN),earthquake coseismic displacement can be obtained through global navigation satellite system (GNSS) data processing and analysis.The calculated results can provide basic research data for further study on seismic dynamics characteristics and determination of future earthquake trends.Using the GNSS data processing results from CMTEMN and CMONOC,together with the coordinate time series from the continuous observation stations,the baseline time series between two stations and the velocity and deformation fields were investigated in this study.In addition,the global positioning system deformation field of the northeastern margin of the Qinghai-Tibet plateau before and after the Minxian-Zhangxian Earthquake was analyzed.The results showed that the coordinate time series of the GNSS stations showed no noticeable change before the Minxian-Zhangxian Earthquake,and there were no prominent anomalies before the earthquake.The earthquake caused different levels of permanent co-seismic displacement of various stations,the maximum of which was as much as 16 mm This GSMX station,which is near the epicenter in the Lintan-Dangchang fault,exhibited a noticeable coseismic displacement.The GSWD station had no coseismic displacement.Similarly, the GSLX station,which was far from the epicenter,also experienced no displacement.The strain change of the three stations proved that the east-west strain was primarily linear,and there was no noticeable imminent anomaly before the earthquake removal of the coseismic step.The north-south strain exhibited a cycle and a half phenomenon,which was related to a corresponding year cycle in a single point,so this was not an obvious imminent anomaly prior to the earthquake.In addition to the obvious linear change,the north-east shear strain showed specific cycles,but no obvious anomalies before the quake,and these were restored to their original displacement after the quake.The GNSS baseline length change was based on the unity of the reference frame,so it was unaffected by the reference benchmark,therefore,it would objectively reflect the dynamic changes of the relative motion between two stations.Therefore,the GNSS baseline time series analysis was used to extract the crust movement microdynamic information as one of the direct routes.In this study,three stations close to the epicenter formed a triangular mesh,crossing the epicenter and the Lintan-Dangchang fault zone.Using the GSWD station as a reference, the statistical baseline series of the GSMX and GSLX stations were analyzed,and the results showed that there was no significant change of the baseline before and after the earthquake and no obvious anomalies;In addition,the long baseline time series across the Lintan-Dangchang fault was calculated employing six stations on either side of the seismogenic tectonic,forming five baselines.The results were same with the short baseline,before the earthquake,the baseline did not exhibit an obvious precursory change phenomenon,and the baseline change caused by the earthquake was not obvious in totality.There were signs of a clockwise motion near the Alashan and Qilian structural belt,where the direction of movement was south west on the east side and north west on the west side.The magnitude of the movement was within 7,which may explain why the push movement to the north in the western region was greater in the eastern area.In addition,due to the extrusion of the Ordos block in the east of the research area,the direction of movement of the edge of the block at the southeastern end in this region was to the southwest and its velocity was approximately 5 mm/a,The movement of the block was diminished in the western portion.The primary direction of the principal compressive strain from 2011 to 2013 was from the SE to NW,the region of maximum strain exhibited zonal distribution and was located in the southern part of the research area.

    • Inversion of Rayleigh Wave Dispersion Curves and Attenuation Coefficient Curves in Viscoelastic Medium

      2015, 37(3):739-742. DOI: 10.3969/j.issn.1000-0844.2015.03.0739

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      Abstract:Rayleigh waves always have a corresponding large amount of energy and a high signal-noise ratio that can be used for the inversion of mechanical information. In recent years, the Rayleigh wave method has been increasingly used in geophysical exploration, seismology, and ultrasonic non-destructive testing. To date, most Rayleigh wave applications are assumed to be in elastic media. However, media such as soil and rocks can show viscoelastic characteristics, and there will be an associated error if the medium is assumed to be elastic. Therefore, it is important to study the inversion of Rayleigh waves in viscoelastic media, and as yet there has been little research on this topic. In this study, we investigate the inversion problem of Rayleigh waves dispersion curves and attenuation coefficient curves, present a method to invert Rayleigh waves dispersion curves and attenuation coefficient curves, and analyze the error associated with this method.

    • Effect of Overlaying Rock and Soil Layers on Ground Motion Characteristics

      2015, 37(3):743-747. DOI: 10.3969/j.issn.1000-0844.2015.03.0743

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      Abstract:Several hundred strong motion records from two bedrock stations and two class Ⅲ stations from the KiK-Net in Japan were used to analyze ground motion features, the relationship between Fourier spectrum dominant frequency and magnitude or distance, and the effect of shallow surface rock and soil layers on ground motion. At the bedrock stations, both underground and at the surface, the Fourier spectrum dominant frequencies for three components decreased with increasing magnitude or distance, and exhibited similar values and distribution. However, at class Ⅲ sites, only the underground sites displayed a decrease in their three-component Fourier spectrum dominant frequencies over increasing magnitudes or distances. At these class Ⅲ sites, the Fourier spectrum dominant frequencies displayed significantly different values and distributions between the underground and surface ground motions, and the changes are different between the ground motions at stations with different soil conditions. These results indicate that hard bedrock has little effect on ground motion; however, an overlying soil layer on the bedrock has a profound and uncertain effect on ground motion characteristics.

    • >土动力学
    • Study on Deformation Characteristics of Saturated Silty Sand in Uni-and Bidirectional Cyclic Triaxial Tests

      2015, 37(3):748-753. DOI: 10.3969/j.issn.1000-0844.2015.03.0748

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      Abstract:When evaluating the dynamic characteristics of sandy deposits during earthquakes, the analysis method proposed by Seed is the one almost always adopted. In addition, a unidirectional dynamic cyclic triaxial test rather than a bidirectional one is often used by researchers to determine the dynamic characteristics of sandy deposits. The validity of these methods is called into question considering that the dynamic stress paths induced by uni-and bidirectional cyclic triaxial tests are not the same. In this study, a dynamic triaxial apparatus, capable of vertical and radial dynamic loading, was used to compare uni-and bidirectional cyclic triaxial tests on saturated silty sand. Comparison of the results showed differences in both the hysteresis loops and skeleton curves produced by each method; both deformation and energy dissipation were larger in the unidirectional test; this was found to be a result of spherical stress. A hyperbolic model that perfectly matched the skeleton curves for both sets of test results was then established. Finally, cell pressure was identified as the key factor affecting the test conditions, resulting in the difference between the two methods. A suggested initial cell pressure value is established and given for the tested material.

    • Test Study of the Influence of Moisture Content on Dynamic Characteristics of Residual Soil

      2015, 37(3):754-758. DOI: 10.3969/j.issn.1000-0844.2015.03.0754

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      Abstract:In this study, we chose the shallow residual soil from a constructional engineering site in Xiamen as our remolded specimen, and used the SDT-10 microcomputer control electro-hydraulic servo dynamic triaxial test system as the main test equipment. Under sine dynamic loading, we tested the dynamic characteristic curves and parameters of the residual soil's dynamic stress-strain, dynamic deformation times (number of loads), and dynamic modulus of elasticity with moisture contents of 10%, 15%, 20%, and 23%. The analysis of the test data indicates that the specimens showed viscoelastic-plastic behavior, and the higher the moisture content of the specimen, the greater the cumulative plastic axis deformation, but the most elastic modulus slowly decreases. The extent of the decrease in the most elastic modulus is not great when the moisture content of specimen increases from 20% to 23%.

    • Experimental Study on Dynamic Properties of Saturated Fine Sand in Jingjiang Levees

      2015, 37(3):759-764. DOI: 10.3969/j.issn.1000-0844.2015.03.0759

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      Abstract:Saturated fine sand is widespread under the Jiangling section of the Jingjiang levees, so a system test of the levees' dynamical properties is necessary. Using specimens built with reference to in situ test results with an estimated consolidation stress ratio Kc (approximately 1.6), we conducted a series of dynamical triaxial tests to study the dynamical elastic modulus, damping ratio, and dynamical strength. The results are as follows:(1) The relationship curves of the dynamic stress-strain of the specimens and the Hardin-Drnevich hyperbolic model assumption match well, and Hardin's formula is also a good fit with the relationship between the dynamic modulus/damping ratio and dynamic strain. In the actual compactness range of the specimens, the maximum dynamic modulus increases with increase in the confining pressure and compactness, and the confining condition is more sensitive. Furthermore, with the same confining pressure but different compactness, the fitting curves of the shear modulus ratio and the dynamic strain nearly coincide. In addition, the damping ratio decreases with increase in the confining pressure and compactness, and when the dynamic strain is 1%, the corresponding damping ratio for specimens with different conditions ranges from 0.15 to 0.21. (2) Under bias-consolidation conditions, we set a cumulative axial strain of 5% as the liquefaction standard. With increases in the confining pressure and number of dynamic cycles, the dynamic shear stress ratio decreases, and the maximum dynamic pore pressure ratio can only reach 0.8~0.9. (3) The dynamic friction and cohesion obtained by the total stress method decrease with increases in the number of dynamic cycles. In addition, the cohesion of the specimens is not approximately equal to 0, which indicates a viscosity characteristic of saturated find sand under dynamic action.

    • Effect of Randomness in the Cross-section Shape of Underground Lenticles on the Extreme of the Surface Dynamic Response

      2015, 37(3):765-771. DOI: 10.3969/j.issn.1000-0844.2015.03.0765

      Abstract (946) HTML (0) PDF 2.01 M (942) Comment (0) Favorites

      Abstract:The semi-analytical solution of SH-waves scattering by an arbitrary cross-section of an underground lenticle in half space is presented using the wave functions expansion method combined with the boundary discrete method. The Monte Carlo method was used to randomly generate 30 samples of the cross-section shape of the lenticle, and the effect of randomness in the cross-section shape on the surface dynamic response was studied by statistical analysis. It was observed that the randomness of the cross-section shape has a significant effect on the surface dynamic response around a lenticle in half space. When the variation coefficient of the inclusion radius is equal to 0.1 for a lenticle of elliptical shape, the maximum of the surface displacement amplitude is larger than that of the peak values observed for the elliptic solution with an average of 47.46%. The difference increases as the inclusion rigidity decreases, whereas the difference decreases as the inclusion depth increases.

    • Experimental Study of the Dynamic Characteristics of Tailings Silts

      2015, 37(3):772-777. DOI: 10.3969/j.issn.1000-0844.2015.03.0772

      Abstract (896) HTML (0) PDF 2.22 M (818) Comment (0) Favorites

      Abstract:Based on dynamic triaxial tests conducted on tailings silts under different consolidation conditions, the dynamic strength, and developing characteristics of dynamic pore water pressure of tailings silts were studied. The cell pressures used were 100, 200, and 300 kPa, and the consolidation ratios were 1.0 and 2.0. The results indicated that saturated tailings silts underwent liquefaction under isotropic consolidation conditions and did not experience liquefaction under anisotropic consolidation conditions. The failure criterion under the isotropic consolidation condition was the 5% double amplitude strain condition, and the criterion under the anisotropic consolidation condition was the 5% total strain condition. Under the same consolidation ratio, the relationship of τd/σd and Nf of different cell pressures could not be normalized. The relationship of τd/σd and Nf could be described by a logarithmic function. Under the same consolidation condition, the relationship of ud/σd-N/Nf was the same. Under the same consolidation ratio, the cell pressures had a certain influence on the relationship of ud/σd-N/Nf.When the consolidation ratio was Kc=1.0, the pore pressure developed characteristics that could be described by a power function, and the pore pressure developed characteristics under Kc=2.0 that could be described by a logarithmic function.

    • Numerical Simulation of Soil Dynamic Response under Moving Loads

      2015, 37(3):778-781. DOI: 10.3969/j.issn.1000-0844.2015.03.0778

      Abstract (913) HTML (0) PDF 2.42 M (763) Comment (0) Favorites

      Abstract:A model of moving traffic vibration loads is developed on the basis of vibration mechanism analysis. Some factors related to vibration such as the speed or bumping motion of the train, the weight of the wheels, and the dispersion effect of the sleeper car are included in this model. A three-dimensional (3D) elastic-plastic finite element model of foundation soil is then established in ANSYS. The Drucker-Prager model is chosen to simulate the soil's non-linear characteristics. The bottom of the model is constrained within the horizontal plane. A 3D viscoelastic artificial boundary is adopted to simulate the bottom of the model and the boundary condition. Under moving traffic loads, the time-history curves of the displacement and the acceleration in various places in the foundation soil are calculated, and several conclusions are drawn. When the load is stationary, the displacement exhibits an abrupt change.However, as the load moves, the displacement maintains a stable value that decreases with distance from the track. When the load is just on, the acceleration also exhibits an abrupt change, with values trending closer to zero as the load moves. Therefore, train speed has little effect on vertical displacement and acceleration.

    • Effect of Seasonal Variations on the Dynamic Stress in Subgrade Soils Induced by Passing Trains and a Simplified Calculation Method on It

      2015, 37(3):782-788. DOI: 10.3969/j.issn.1000-0844.2015.03.0782

      Abstract (1030) HTML (0) PDF 6.05 M (1508) Comment (0) Favorites

      Abstract:Many railways were constructed in regions of China that experience seasonal freezing and thawing cycles in subgrade soils. Consequently, the dynamic stress distribution in subgrade soils induced by passing trains was observed to vary in different seasons. The research first focused on the development of a vertical train-track-subgrade coupled dynamic model, which considered the vibration of soil layers and the time histories of loading. Second on the effect of seasonal variations on the dynamic stress in subgrade soils, which was conducted by FEM computational simulations. Based on the results, the dynamic stress distribution and amplitudes were closely related to the frozen or thaw states of the subgrade soil. Third on the development of a simplified method for calculating the dynamic stress in subgrade soils induced by passing trains, which could be used in railway subgrade designs in seasonal frozen regions. The achievements of this research will be useful for optimizing the subgrade design method and completing the evaluation method of the long-term stability of the subgrade soil.

    • Experimental Study on the Cyclic Loading of Metro Trains

      2015, 37(3):789-793,802. DOI: 10.3969/j.issn.1000-0844.2015.03.0789

      Abstract (946) HTML (0) PDF 2.79 M (817) Comment (0) Favorites

      Abstract:Research on the dynamic characteristics of saturated soft soil has important significance for revealing the pore pressure, strength, and deformation mode of soft clay under subway loading. It can also provide a theoretical basis for the control of long-term settlement and the reduction of operational risk. Different forms of loading will bring different dynamic characteristic, so a study method must be identified that can reflect the true nature of subway train loads. In this study, we used the laboratory dynamic triaxial test to examine the dynamic characteristics of soil under a train load, and comparatively analyzed the effects of different dynamic loads. The results show that the biased sine wave can be used as a simplified train load wave. It also can ensure that only compressive stress exists in the soil during the process of loading, and it better simulates the cyclic loading of subways.

    • Comparison of Standard Penetration Test (SPT) Methods for Evaluating Seismic Liquefaction Potential

      2015, 37(3):794-802. DOI: 10.3969/j.issn.1000-0844.2015.03.0794

      Abstract (1268) HTML (0) PDF 2.18 M (909) Comment (0) Favorites

      Abstract:For the standard penetration test (SPT) method for evaluating seismic liquefaction potential,the liquefaction potential evaluation method recommended by the National Center for Earthquake Engineering Research (NCEER) is typically applied abroad;however,methods recommended by the code for geological investigation of water resources and hydropower engineering (GB50487-2008) and that for seismic design of buildings (GB50011-2010) are used domestically.These methods different in the following aspects:(1) earthquake liquefaction field investigation data;(2) liquefaction criterion;(3) method for reflecting the influence of earthquake magnitude;and (4) method for considering the influence of fines content.In this paper,the method recommended by NCEER is expressed by the curve of critical liquefaction blow count versus depth;a comparison is made between this curve and that determined by domestic methods.Under the same intensity,domestic methods tend to be safe for near earthquakes and distant earthquake with magnitude less than 7.5.For earthquakes with magnitudes of 7.5~8.5,critical liquefaction blow counts calculated by using the NCEER method are close to that calculated by domestic methods under specific acceleration,which tends to be safe depending on the specific acceleration.For distant earthquakes (design earthquake group 2),under the magnitude of M=8.0 and seismic intensity of Ⅶ and Ⅸ,the critical liquefaction blow counts calculated by the different methods are very close;under the intensity of Ⅷ,the NCEER method tends to be safe.For distant earthquakes (design earthquake group 3),the domestic methods tend to be safe with magnitude not more than 8.0.With the magnitude of M=8.5 and acceleration amax=0.3g,the critical liquefaction blow counts calculated by the different methods are close.The NCEER method tends to be safe with acceleration less than 0.3g,whereas the domestic methods tend to be safe with that more than 0.3g.For domestic methods,under distant earthquakes (design earthquake group 2),the critical liquefaction blow counts calculated by the different methods are close with a difference of less than 2.5 blow counts.The method used in the code for seismic design of buildings (GB50011-2010) tends to be safe with acceleration not less than 0.3g.The above research results can provide a reference for code revision of the aseismic design of hydraulic structures.

    • >岩土工程
    • Model Tests on the Cyclic Bearing Capacity of Suction Anchors in Soft Clay with Increasing Strength along Depth

      2015, 37(3):803-808. DOI: 10.3969/j.issn.1000-0844.2015.03.0803

      Abstract (971) HTML (0) PDF 3.51 M (1152) Comment (0) Favorites

      Abstract:A model test stratum with increasing strength along depth was prepared in a tank using the multilayer vacuum preloading method at the bottom. Bearing capacity model tests were conducted for suction anchors with two diameters and subjected to inclined static and cyclic loads at the optimal loading point using an electric servo loading apparatus developed by the authors for the lateral failure mode. Model test results showed that the cyclic displacement of the anchor did not obviously increase with the increase of the number of cycles during cyclic loads, and the failure of anchors was attributed to the cyclic cumulative displacements. The relative variation of cyclic bearing capacity for suction anchors in soft clay with increasing strength along depth was consistent with that of suction anchors in soft clay with uniform strength along depth. The cyclic bearing capacity was approximately 90% of the static bearing capacity when the number of cycles was 100, and the cyclic bearing capacity decreased to approximately 70% of the static bearing capacity when the number of cycles was increased to 2000. The variation of anchor diameter only changed the absolute cyclic bearing capacity, and did not affect the relative variation of the cyclic bearing capacity. The degradation of the vertical resistance was larger than that of the lateral resistance for suction anchors in soft clay with increasing strength along depth under cyclic loads, which was the same as that observed for suction anchors in soft clay with uniform strength along depth.

    • Stability Analysis of Earthen Slope Sites Reinforced with Wood Anchors

      2015, 37(3):809-815. DOI: 10.3969/j.issn.1000-0844.2015.03.0809

      Abstract (942) HTML (0) PDF 8.87 M (882) Comment (0) Favorites

      Abstract:The slope stability of a project section of the ancient city of Jiaohe reinforced by wood anchors was investigated using the strength reduction finite element method. The safety factor of stability of the reinforced slope was given under a static load and under earthquake forces. The influences of the wooden bolt length, anchorage angle, and other factors on the safety coefficient were also analyzed. Finally, the wood anchor reinforcement mechanism of the slope was analyzed, which determined the existence of several problems that should be resolved in the future design of reinforced wood anchor slopes. The research results may provide a reference for other soil slope projects reinforced by wood anchors.

    • Application of the Structural Model Under Stress and Moisture in Loess Slope Dynamic Stability Analysis

      2015, 37(3):816-822,833. DOI: 10.3969/j.issn.1000-0844.2015.03.0816

      Abstract (1014) HTML (0) PDF 6.99 M (1363) Comment (0) Favorites

      Abstract:The structural property of soil is derived from mechanical effects as well as the comprehensive effect of the spatial arrangement and bonding effects of soil particles. During the process of seismic loads, the structural parameters of natural loess slope are derived mainly from the combined effects of stress and deformation. Meanwhile, that parameters reflected the coordination between stress and deformation during the process of seismic load and the structural damage process of the loess during the seismic process. It was shown that using structural parameters to quantitatively determine the loess slope stability was more reasonable during the process, and its physical meaning was very clear. Second, analysis of the dynamic stability of the natural loess slope was used to verify the feasibility criterion by structural parameters, and this method could be used to quantitatively determine the location of slip surfaces and corresponding structural parameters.

    • Shaking Table Tests on the Acceleration Response of an Anti-dip Stratified Rock Slope with Composite Retaining Structure

      2015, 37(3):823-828. DOI: 10.3969/j.issn.1000-0844.2015.03.0823

      Abstract (1090) HTML (0) PDF 3.70 M (965) Comment (0) Favorites

      Abstract:Using large 1:30-scale shaking table model tests, we studied the dynamic response characteristics of acceleration of a high steep anti-dip stratified rock slope containing six siltized intercalations with a composite retaining structure, by inputting EL Centro and Wenchuan seismic waves in the X-and Z-directions, respectively. Test results show that:(1) The acceleration amplification coefficient grew nonlinearly with increasing slope height in both the X-and Z-directions, and the values of the former were greater than the latter. (2) The acceleration magnification effect at the slope surface is significantly affected by the water content variations of the siltized intercalation. The X-direction amplification on the water-soaked soft interlayer decreased in comparison with that of the initial conditions, however, the opposite was true in the Z-direction. (3) By the action of the retaining structures, the more restricted the magnification intensity of the slope free face, the more the amplification effect can be ignored where the altitude is less than 1/3 of the slope height. With respect to the elevation amplification effect of X-direction acceleration, a slope supported by hierarchical implementation is beneficial, but it is disadvantageous in the Z-direction. (4) The tilt-split model may be used as a failure model for a counter-tilt layer rock slope under earthquake conditions, which is controlled by the sliding of weak layers, particularly after rain. Damage is possible from the upper frame beam rotating around the slope crest, which can be pulled out using the pre-stressed anchor cable as a fulcrum.

    • Preliminary Analysis of the Influence of Longitudinal Non-uniform Distribution of Soil Parameterson the Seismic Response of a Shield Tunnel

      2015, 37(3):829-833. DOI: 10.3969/j.issn.1000-0844.2015.03.0829

      Abstract (1020) HTML (0) PDF 2.44 M (1171) Comment (0) Favorites

      Abstract:Soil is generally simplified as a uniform one-layer model or uniform multi-layer model in present research works, and the influence of soil parameters that may change along the longitudinal direction during seismic responses is usually neglected. With a focus on a practical engineering, a uniform soil-tunnel model and non-uniform soil-tunnel model were established and the internal structural forces and deformations were calculated and compared. The results showed that soil parameters that changed along the longitudinal direction had some influence on internal structural forces and deformation, but the degree of influence was not significant. The reasons were attributed to the small sizes of the tunnels, the small seismic wave amplitude, and the good soil conditions. The results of this study showed that more general seismic response laws should be discussed in future works, based on extensive parameter analyses.

    • Influence of CFG Piles Construction in Foundation Piton Surrounding Environmental Stability

      2015, 37(3):834-839. DOI: 10.3969/j.issn.1000-0844.2015.03.0834

      Abstract (1000) HTML (0) PDF 3.18 M (1096) Comment (0) Favorites

      Abstract:In underground engineering,the main structure with the basement is built with CFG pile composite foundation because the natural ground bearing capacity is insufficient.Because the construction length of the CFG pile is limited by the spiral drilling machine,CFG piles under the floor of the basement must be constructed after a part of the deep foundation pit is excavated.In certain deep foundation pit engineering with CFG pile construction,there is an obvious crack phenomenon on the ground surface around the foundation pit.In order to explore its causes,the deformation characteristics of the foundation pit are analyzed considering the action seepage when CFG piles are constructed in the foundation pit after part excavation.The analysis uses FLAC3D as the numerical simulation tool. The calculated results are compared with actual monitoring data of the foundation pit.Finally,the causes of cracks in the ground around the foundation pit during construction are studied.The results show that the rapid sampling effect in the foundation pit decreases the earth pressure in the passive zone of the foundation pit when CFG piles are constructed in the foundation pit after part excavation.The effect scope of earth deformation around a foundation pit is beyond the scope of monitoring which is twice the depth of the foundation pit.Therefore,the scope of monitoring of the ground deformation around similar foundation pits should increase appropriately on the basis of meeting the requirements of the National Standard.According to the calculation results,it is suggested that the scope of monitoring in similar foundation pit engineering should adopt the sum of the foundation pit excavation depth and the CFG pile length at the foundation pit bottom.Similar foundation pit engineering design should increase the length of the support structure and the depth of the waterproof curtain.Construction of CFG piles in foundation pits should be from the inside to the outside edge of the foundation pit with piling every a few piles.The construction time should increase appropriately.These measures will help to reduce the deformation of surrounding soil due to the construction of CFG piles in foundation pits after part excavation.

    • Quasi-static Analysis of Rotational Displacement in a Gravity Retaining Wall During Earthquakes and Tsunamis

      2015, 37(3):840-844. DOI: 10.3969/j.issn.1000-0844.2015.03.0840

      Abstract (974) HTML (0) PDF 1.63 M (1173) Comment (0) Favorites

      Abstract:The prediction of seismic rotational displacements in retaining walls under passive conditions is an important design aspect in earthquake-prone regions. In this study, a rotating block method was developed to calculate the rotational displacements of quay walls based on rigid foundations under seismic loading, and tsunami forces for the passive earth pressure condition. The proposed method considered the combined effects of seismic forces, hydrostatic, and hydrodynamic pressures and tsunami forces acting on the quay wall. The tsunami force was considered to be an additional force acting on the upstream face of the wall, and was calculated using a simple formula. Variations of different parameters involved in the analysis suggested the sensitiveness of the rotational displacements against the rotational slider of failure of the wall, which will provide a better guideline for design.

    • >土力学
    • A Practical Coupling Method for Analyzing Soil-structure Interaction

      2015, 37(3):845-850. DOI: 10.3969/j.issn.1000-0844.2015.03.0845

      Abstract (1025) HTML (0) PDF 4.43 M (1159) Comment (0) Favorites

      Abstract:A novel practical method is presented for the analysis of soil-structure interaction (SSI). In this method, the structure is modeled by nonlinear FEM (OpenSees), and the soil is modeled by a time domain solution that is transformed from a frequency domain analytical solution using a discrete time domain recursive filter. The boundary conditions of force and displacement between soil and structure are satisfied using Newton's method, and the coupling between the two substructures is based on CS integration techniques. We use structure and soil systems with a single degree of freedom, and study a real SSI example to determine the efficiency, accuracy, and applicability of the proposed method. Furthermore, we examine the differences between the conditions when considering and not considering SSI effects. This study proposes a practical method for nonlinear seismic analysis of SSI systems, and the research results provide valuable insights for engineering applications.

    • Analysis of Subgrade Stress State and Factors Contributing to Subgrade Damage From Heavy Haul Freight Cars

      2015, 37(3):851-856,861. DOI: 10.3969/j.issn.1000-0844.2015.03.0851

      Abstract (968) HTML (0) PDF 3.25 M (1179) Comment (0) Favorites

      Abstract:The damage of railway lines during heavy haul freight train passage is closely related to the stress state of the subgrade surface.In order to study the stress path in subgrade soils under moving trains,this study utilized a dynamic freight-railway model to analyze such stress on during freight train operations.The study investigated the effects of ballast layer thickness,axle load,speed,and other factors contributing to subgrade surface damage.The extent of subgrade stress and related damage were obtained using the Euler beam model to analyze the elastic half-space under one moving load.The stress path in soils under the moving load was analyzed.Based on the modeling,it was determined that the stress state changes from pure shear to triaxial shear and back to pure shear in one cycle.According to the stress path curves for different moving speeds,it was determined that,when the moving load is high,the horizontal shear stress increases dramatically.The results further indicate that the stress state changes from the initial state to pure shear,to triaxial shear,and back to pure shear.The principle axis of stress rotates 180°.However,it is more complex due to the interaction of the wheels.A ballast layer deeper than 0.5 m,train speeds exceeding 70 km/h,the modulus of the subgrade materials less than 160 MPa,and an axle load higher than 27 t,all of these factors may result in the plastic deformation within the subgrade surface.If the stress path reaches the failure line,the hypothesis of elasticity will be invalid.

    • Experimental Study of Post-liquefaction Strength and Deformation Behavior of Silt in the Hangzhou Bay

      2015, 37(3):857-861. DOI: 10.3969/j.issn.1000-0844.2015.03.0857

      Abstract (1039) HTML (0) PDF 2.28 M (1136) Comment (0) Favorites

      Abstract:The liquefaction behavior of marine silty soil is different from that of sandy soil under dynamic loading conditions. The samples of insitu marine silty soil in the Hangzhou Bay were analyzed with a special dynamic triaxial liquefaction test, which could possibly clarify post-liquefaction strength and deformation behavior. The results showed that the shear strain of silty soil could be divided into two parts:nonzero effective stress state and zero effective stress state, and the deformation law of marine silty soil was similar to that of sandy soil and also the shear strain when the nonzero effective stress state or zero effective stress state was subject to vibration frequency, cell pressure, and εmax. constitutive model on the post-liquefaction behavior of silty soil is proposed, which could express the post-liquefaction stress-strain response very well.

    • >地震监测与技术
    • Application of Differential GPS to the Geographic Azimuth Measurement in China Geomagnetic Field Monitoring Network

      2015, 37(3):862-866,883. DOI: 10.3969/j.issn.1000-0844.2015.03.0862

      Abstract (1434) HTML (0) PDF 1.65 M (1443) Comment (0) Favorites

      Abstract:This study introduces the principle and method for the use of differential global positioning system (GPS) in measuring azimuth in the China Geomagnetic Field Monitoring Network (CGFMN). We also present some azimuth measurement results and accuracy levels by geomagnetic observatories and geomagnetic survey stations, and offer some suggestions on how different geomagnetic observatories can measure azimuth in the future. We adopted two sets of differential GPS (model PROMAK 2 and PROMAK 100) including auxiliary devices antennas, cables, connected bases, and used one theodolite (model Mingeo) with an accuracy higher than 1 second. We installed the two differential GPS on two tripods, locating one near a mark (called station A) and the other alongside a fixed station room (station B) to measure the angle between geographical north (N) and a line AB (∠NAB).The entire measuring process ensures that the antennas and tripods remained stable and that the distance between stations A and B was more than 200 m. The GPS can receive satellite data until the transmission distance is more than 5 km, then the system turns off, and the above procedure is repeated. ∠NAB is computed using the two GPS data files using a special program. The theodolite was installed on a tripod near the mark to measure the angle between lines AP and AB (∠PAB, P is one of pillars), then it was moved to the pillar to measure the angle between the lines PA and PM (∠APM, M is one of marks). As such, the azimuth between geographical north (N) and the line from any pillar to any mark is determined through known angles. There are several methods for measuring azimuth. The proposed CGFMN azimuth measurement has the accuracy of the astronomical and differential GPS methods, less than 6″ of arc, which is higher than that of other equipment. Since 2001, the Lanzhou geomagnetic observatory has used differential GPS to measure the azimuth of 14 geomagnetic observatories and more than one thousand geomagnetic survey stations. Currently, the differential GPS method has replaced the CGFMN's astronomical method of azimuth measurement, using extensive GPS application. The main advantages of the differential GPS method over the astronomical method is that, in addition to having the same accuracy, it is free from the effects of weather conditions and human factors, all equipment can be operated easily by observers, and the data processing is completely computerized and has higher efficiency.

    • Application of Generalized S-transform in Ambient Seismic Noise Data Processing

      2015, 37(3):867-872. DOI: 10.3969/j.issn.1000-0844.2015.03.0867

      Abstract (960) HTML (0) PDF 4.60 M (1448) Comment (0) Favorites

      Abstract:In this study, we used the generalized S-transform method to improve the signal-to-noise ratio of ambient seismic noise data, and improved the efficiency of geophysical inversion. The S-transform method is a time-frequency representation of local spectral phase properties. A key feature of the S-transform method is that it can uniquely combine a frequency dependent resolution of the time-frequency space and absolutely reference local phase information. As such, the phase in a local spectrum setting can be defined, and this makes possible the production of many desirable wave characteristics. The scaling property of the Gaussian window is reminiscent of the scaling property of continuous wavelets, because one Fourier frequency wavelength is always equal to one standard deviation of the window. In this study, we introduce a variant of the original S-transform, which replaces f with λfp. In this variant, one standard deviation of the Gaussian window contains λfp wavelengths of the Fourier sinusoid at all frequencies. The generalized S-transform solves the defect in the analysis of non-stationary signals caused by the fixed form of the basic wavelet in the S-transform, and the time-frequency characteristics can better describe the non-stationary signals. We wrote a computer program for the generalized S-transform, and for ambient seismic noise we used data denoising. The results showed that the signal-to-noise ratio is greatly improved through the generalized S-transform denoising, and yields more accurate data for the inversion process. There have been few studies on the denoised processing of background noise data using the generalized S-transform, and the resolution of our processing results is better than that achieved by the ordinary S-transform.

    • >仪器研制
    • Development of VP-type Broadband Tide Meter

      2015, 37(3):873-877. DOI: 10.3969/j.issn.1000-0844.2015.03.0873

      Abstract (1057) HTML (0) PDF 3.49 M (827) Comment (0) Favorites

      Abstract:The VP-type broadband tide meter was developed by improving the circuit system, mechanical system, data acquisition system, and control system on the basis of VS vertical pendulum tiltmeter, a kind of seismological observation instrument used to record earth tides. A good design of the mode of oscillation circuit and zero circuit was needed to improve the circuit system, because it could simplify the instrument circuit, reduce the failure rate caused by electronic circuit, make the continuous operation stable. A reasonable mechanical instrument design, including the design of automatic zero adjustment mechanism and instrument chassis, can simplify the whole structure, make the weight and dimension of the instrument smaller, and easy to be transported and installed. The improvement of data acquisition system includes the improvement of sampling rate, the increase of sampling channel and data storage capacity, and the design of switch control channel. The automatic zero adjustment function was also added. Compared with traditional tiltmeters, VP-type broadband tide meter is easy to install and maintain, for it can store more data and realize remote auto zero. The most obvious advantage of it is that its response to high-frequency signal is sensitive by improving the circuit and mechanical systems, and it can record more seismic information to better service for the earthquake prediction.

    • Design and Implementation of an Intelligent Isolated Lightning Protection System for Seismic Stations

      2015, 37(3):878-883. DOI: 10.3969/j.issn.1000-0844.2015.03.0878

      Abstract (979) HTML (0) PDF 2.89 M (732) Comment (0) Favorites

      Abstract:To develop a system to protect the instruments of seismic stations from being damaged by lightning, we used a single-chip microcontroller as the core of the system to control the other chips and hardware. We used an industrial GPRS module to translate information from remote seismic stations to the seismic net monitoring center, and a WIFI module to transfer data between our system and a local wireless router. We used a magnetoelectric nano-electromechanical system (NEMS) sensor probe to detect the electromagnetic field (thunder). The connection status of the seismic signal line and the power line was controlled by the stepping motor of the single-chip microcontroller. In addition, we designed a system with a double internal 12 V DC switching power supply and a double inverter 220 V AC power supply for controlling the charging and discharging of the double storage batteries. When one storage battery is providing power to our system, the other is connected to the DC power for charging. This design ensures the complete isolation of our equipment from AC power. Furthermore, the system is able to transfer seismic data to the gateway using the wireless local area network, and simultaneously monitor changes in the electromagnetic space field with the NEMS sensor. The system can receive or control information from the monitoring center at any time, and can also control the connection status of the AC power and signal lines with the stepper motor. The double internal DC and AC power supply reduces the signal breakdown faults caused by power failure. This device can effectively protect seismic station instruments from damage by lightning, and improve the continuous operation ratio of seismic data.

    • >地震应急
    • Design and Implementation of Earthquake Emergency Thematic Map of Gansu Province

      2015, 37(3):884-889,900. DOI: 10.3969/j.issn.1000-0844.2015.03.0884

      Abstract (1068) HTML (0) PDF 6.26 M (972) Comment (0) Favorites

      Abstract:An earthquake emergency thematic map highlights and, as exactly and in as much detail as possible, displays one or more thematic elements in an earthquake-stricken area. Compared with an ordinary map, an earthquake emergency thematic map shows not only the current status and distribution of various elements of the earthquake area but also illustrates the dynamic change and development laws of various elements during the earthquake emergency rescue such as the dynamic changes of relief efforts after the earthquake, the distribution of relief supplies, and changes in the geological disasters. Earthquake emergency thematic maps includes maps of the earthquake, population, economy, traffic, housing estates, schools, hospitals, and geological hazards. During an earthquake emergency rescue, the earthquake emergency thematic map acts as an important output that allows an earthquake emergency office to respond effectively. It serves as one of the main basic maps to aid the government to take control and make decisions playing an important role in earthquake emergency rescue operations. A standardized and clear thematic map plays an important role in earthquake emergency command and rescue management providing timely and effective basic and disaster-related information. Its advantages are in providing rapid, visual, and large quantities of data. The computer mapping process of the earthquake emergency map involves basic data processing, overall and symbol designing, cartographic generalization, and map printing. In Gansu province, the available earthquake emergency maps were not standardized resulting in no timely output. In this study, we first classified, sorted, and preprocessed data from the earthquake emergency basic database of Gansu province (data transformation, topology error check, attribution edit, and others). Next, using the earthquake emergency thematic map concept as the basis, we built databases of different scales (50000), drew 16 thematic maps, and designed a product catalog in accordance with actual seismic demand. Then, we drew the Gansu province thematic map by region and divided the template into eight different magnitudes according to the seismic intensity attenuation relationships in Gansu province. Finally, we used fast-drawing software to rapidly output earthquake emergency thematic map drawings of local areas. As such, the standardization and production of thematic maps in our province will serve to promote the region's capacity and computer response speed in earthquake emergency mapping. In this study, we describe the design and implementation of the earthquake emergency thematic map of Gansu province. The clarity of expression regarding different earthquake magnitudes remains a problem in generating automatic thematic maps. In the future, we will explore ways to adjust the format size of maps and display the content during the automatic drawing process. This will make the content produced in thematic maps more specific to the actual needs of the earthquake emergency. In addition, with the rapid development of computer graphics technology, the product catalog of the earthquake emergency thematic map must be continually revised regarding symbol design modifications and display effects as well as to produce a more attractive, information-rich display on the thematic map template.

    • >技术交流与学习
    • Determination of Input Ground Motion at a Non-rock Site for Elastoplastic Analysis Based on a Scenario Earthquake

      2015, 37(3):890-895. DOI: 10.3969/j.issn.1000-0844.2015.03.0890

      Abstract (947) HTML (0) PDF 2.50 M (1027) Comment (0) Favorites

      Abstract:Acceleration time histories have a significant impact on the safety evaluation of key structures because earthquake duration and loading process contribute significantly to uncertainty in structural analysis. Thus, determining acceleration time histories for time history response analysis is a significant practical problem, particularly for non-rock sites. Epsilon (ε) is the number of standard deviations by which the ground motion is above or below the median-predicted motion for the attenuation relationship. This study clarified the role of ε in determining a scenario earthquake to obtain acceleration time histories. As an example, the seismic hazard at a real site is disaggregated into its contributions from discrete variables (M, R, ε) to determine a scenario earthquake. M is the surface wave magnitude and R is the projected epicentral distance along the minor axis of the equivalent ellipse. The target peak ground acceleration (PGA) and a consistent spectrum for the rock site with a 2% probability of exceedance in 50 years using probabilistic seismic hazard analysis were obtained. As the earthquake ground motion at the site increased, the number of potential seismic sources contributing to the probability of exceedance decreased. The fifth potential seismic source dominated the seismic hazard at the real site, given that the target probability of exceedance in 50 years is 2%, so the scenario earthquake was located in this potential seismic source. A sample space formed of M, R, and ε that may generate a PGA greater than or equal to the target PGA at the site was constructed. Thus, the normalized probability of the exceedance of the target PGA is the joint distribution of M, R, and ε. The mean and mode of M, R, and ε are the expected and the most likely event in the sample space, respectively. As the site is located near the geometrical center of the fifth potential seismic source, high-magnitude, near-field seismic events are a major contribution to the seismic hazard at the site. The predictive PGA of the mean and mode of M, R, and ε were computed using an attenuation relationship:the values are significantly larger than those of the target PGA. The difference between the mean/mode response spectra of M, R, and the target spectrum is obvious, especially for the acceleration response at low natural frequencies. For the computed response spectrum of the scenario earthquake fitted to the target PGA and consistent spectrum, the sample space was adapted so that the PGA of M, R, and ε computed from the attenuation relationship was approximately the same as the target PGA. Strong ground motion records were obtained from the NGA database based on the scenario earthquake for use in simulating aleatory uncertainty in rock ground motion. Stochastically generated soil profiles were used to investigate the uncertainty of the dynamic characteristics of soil and shear-wave velocity testing results. The strong ground motion records were combined with the soil profiles to create input files that were used to perform an equivalent linear site response analysis, which included an assessment of uncertainty in the amplification factor. Here, the amplification factor is the ratio between the response spectrum of soil surface acceleration and that of rock acceleration time histories. Thus, the distribution of the amplification factor of the spectrum was obtained. The response spectrum of the scenario earthquake was multiplied by the estimated amplification factor to act as the soil surface acceleration response spectrum. Although the scenario earthquake is neither the expected nor most probable event, its seismic influence field at the site exceeds the target PGA. By taking into account both the target PGA and consistent spectrum, in which all of the events in the fifth potential seismic source will generate ground motion at the site, the safety of important structures can be achieved.

    • Information Management System of Animals in Macroscopic Observation on the Basis of LabVIEW Technology

      2015, 37(3):896-900. DOI: 10.3969/j.issn.1000-0844.2015.03.0896

      Abstract (914) HTML (0) PDF 5.66 M (1257) Comment (0) Favorites

      Abstract:Animal abnormality is an important means of macroscopic observation. The purpose of this research is to build an information management system for animals, which will maintain general information on animal life for research. Using the serial communication modules and the LabSQL Kit provided by LabVIEW, the host computer could check and update the general information on the life of each animal in the access database through the ID number previously assigned to each animal. This system could help researchers in examining animal habits and provide a basis for the identification of precursory anomalous behavior in animals.

    • Application of the Alpha GUARD P2000 Portable Radon Monitor in Earthquake Prediction

      2015, 37(3):901-905. DOI: 10.3969/j.issn.1000-0844.2015.03.0901

      Abstract (1150) HTML (0) PDF 5.03 M (1486) Comment (0) Favorites

      Abstract:The technique of monitoring radon concentrations in groundwater has been used for earthquake prediction for nearly half a century. However, the upgrading of radon-monitoring devices has been very slow. Currently, the FD-105K electrometer and FD-125 radon-thorium analyzer are the most commonly used devices for measuring radon concentrations in water, but measurement errors may occur because the bubbling process is artificially conducted and the measured data are read by visual observation. This study presents an experimental study of the AlphaGUARD P2000 portable radon monitor, a more advanced device that can automatically perform the bubbling process and read data, avoiding errors caused by manual operation. The improved accuracy of this radon monitor helps to better detect radon anomalies prior to earthquakes. The AlphaGUARD P2000 is portable, battery-powered, and easy to use. It can be used in field observations, verification of anomalies, and measurements of radon concentration in soil for the observation of seismic subsurface fluids.

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