• Volume 39,Issue 4,2017 Table of Contents
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    • >地震工程
    • Effect of Window Hole on Seismic Response of Ancient Masonry Pagoda

      2017, 39(4):587-591,616. DOI: 10.3969/j.issn.1000-0844.2017.04.0587

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      Abstract:Using the Kuiguang Tower in Dujiangyan city, Sichuan province as our engineering background, we used ANSYS software to establish a solid finite element model and analyzed the effect of a window hole on the stress distribution law of the control section of this ancient masonry pagoda. To do so, we conducted a time-history analysis and also identified the damage mechanism of the tower during the 2008 Wenchuan earthquake. The results show that the first and tenth floors of the tower (at the transformation from double to single layers) are seismically weak. Stress concentration occurs near the window of the ancient masonry pagoda, and the maximum and minimum principal stresses of the outer wall are significantly higher than those at the inner edge of the wall, with the stress near the window about 2-3 times that far away from the window. At the symmetry axis section of the main tower perpendicular to the direction of earthquake excitation, we found the shear stress to concentrate at the top of the window, thus revealing the top of the window as a weak spot with respect to strong earthquakes.

    • Analysis of Influence of Vertical Earthquake Action on theSeismic Response of Liquid Storage Tank

      2017, 39(4):592-599. DOI: 10.3969/j.issn.1000-0844.2017.04.0592

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      Abstract:The earthquake safety of large storage tanks is a matter of great concern today. In this study, we used ANSYS software to establish a finite element model of the tank-liquid coupled system and consider the nonlinear contact effect between the tank bottom and foundation. We selected the El-Centro earthquake wave in the north-south and vertical directions, which is typically selected as input, for our analysis of the tank-liquid coupled system. Then, we investigated the seismic response of the storage tank in two cases-under horizontal earthquake excitation and under simultaneous horizontal and vertical earthquake excitation. Our study results show elephant-foot deformation to occur within 1.2 m of the tank wall bottom, which produces a larger relative horizontal displacement in the tank wall bottom in the case with simultaneous horizontal and vertical earthquake excitation. In addition, we observed there to be some influence on the hoop stress, axial compressive stress on the tank wall, and base shear of different degrees under simultaneous horizontal and vertical earthquake excitation, but little effect on the vertical shaking of the liquid. We observed some obvious nonlinear uplift and permanent slippage at the tank wall bottom under the simultaneous horizontal and vertical earthquake excitation. The influence of vertical excitation on the tank response is unfavorable and cannot be ignored. Thus, the seismic design of storage tanks should consider the impact of vertical seismic-wave excitation. These research conclusions provide a reference and basis for the future seismic design of vertical storage tanks.

    • Seismic Response Analysis of Immersed Tunnel underOblique Incidence of Seismic SV Wave

      2017, 39(4):600-608. DOI: 10.3969/j.issn.1000-0844.2017.04.0600

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      Abstract:With development over time, the immersed tunnel is becoming increasingly important. This tunnel is generally built in underwater environments and requires special considerations with respect to its design and safety factors. Researchers around the globe have conducted many studies on this type of structure and have found that it can be affected by the liquefaction of the foundation and hydrodynamic pressure due to earthquake, the interaction between soils and structures, and the oblique incidence of seismic waves. In this paper, we use the time-domain wave method coupled with a viscous-spring artificial boundary condition and the equivalent stress input method to obtain the oblique incidence of shear-vertical (SV) waves. The half-space numerical results demonstrate this method to have good precision. We then applied the proposed method to investigate the seismic response of the Haihe immersed tunnel subjected to the oblique incidence of seismic waves. The simulation results show that the dynamic responses of the immersed tunnel subjected to the action of obliquely incident seismic waves clearly differ from those due to vertically incident seismic SV waves. With increases in the incident angle, the stress on the immersed tunnel increases, and a larger stress point appears in the four corners of the tunnel and in the connection between the partition wall and the bottom plate and the roof, with the middle partition wall being the weakest point. With increases in the incident angle, the relative maximum horizontal displacements of the side wall and partition wall increase, and the displacement of the middle partition wall is the greatest. With increases in the incident angle, the vertical acceleration rate of the tunnel structure increases significantly. Therefore, seismic research of immersed tunnel structures should consider the effect of obliquely incident seismic waves.

    • Dynamic Responses of Single Earthen Sites Under Seismic Loads:A Case Study of the Liufuzhai Watchtower in Shandan, China

      2017, 39(4):609-616. DOI: 10.3969/j.issn.1000-0844.2017.04.0609

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      Abstract:Earthen architecture is one of the oldest forms of construction. It is composed of construction materials made from unfired earthen materials, including adobe, rammed earth, and a host of other earthen components and construction techniques that vary with varying cultures and regions. Numerous single earthen sites remained in the northwest region of China. However, these cultural relics have not been preserved well. The physical and chemical properties, as well as the mineral compositions and textural characteristics of the soils, are the intrinsic factors that determine the form of weathering, whereas the natural environment is the driving force promoting the damage process. Among them, the structural failures induced by earthquakes are a form of the most serious problems which affect the preservation of the sites. It is worthwhile to provide any effort to achieve a convincing explanation of the distress causes and to propose interventions that are safe and respectful of the history of the sites. To better protect the single earthen sites, FLAC3D software was applied to analyze the dynamic response of the Liufuzhai Watchtower under seismic loads and the seismic-induced displacement, stress and the acceleration amplification effect of seismic wave was investigated. The results indicate that the Watchtower produces a certain permanent displacement, which is mainly vertical displacement under seismic loads. Meanwhile, there is a tensile stress concentration which is close to the tensile strength in the fissure of the Watchtower. The amplification effect of seismic acceleration strengthens with the increase of height, especially for the vertical acceleration. The fissure has a strong adverse effect on the vertical displacement. Meanwhile, the acceleration amplification factor on the fissure is the largest. However, the fissure can weaken the amplification effect of adjacent points. This case study provides an innovative approach to predict the stability of cultural sites when an earthquake occurs; in particular, it is suitable for earthen sites in Northwest China.

    • Dynamic Response Analysis of a Subway Station UnderSeismic Action in the Loess Area of Northwest China

      2017, 39(4):617-622,631. DOI: 10.3969/j.issn.1000-0844.2017.04.0617

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      Abstract:Based on the explicit finite method of the ADINA software and the 32-CPU parallel computing cluster platform, a nonlinear seismic response calculation model of the interaction between the foundation soil and the station structure is established to study its nonlinear seismic response to the El-Centro, recorded Kobe ground motions, and the Lanzhou artificial waves under frequent seismic activity. Using the subway station of the subway line 1 in Lanzhou as an example, the results indicate that the vibration mode of the subway structure is similar to the foundation soil and the shape of the acceleration versus time-history curves of the midpoint of the ceiling, middle, and bottom of the subway station are all basically similar. Also, as the buried depth increases, the horizontal displacement of the center pillar and side wall decreases; the surface ground around the subway station produces a different degree of settlement. The settlement away from the subway station in the 7.5-m range is particularly serious because it led to partial damage around the buildings.

    • Seismic Behaviors of Bottom-business Multi-storyMasonry Structure with Winged Columns

      2017, 39(4):623-631. DOI: 10.3969/j.issn.1000-0844.2017.04.0623

      Abstract (690) HTML (0) PDF 7.77 M (1737) Comment (0) Favorites

      Abstract:In China, it is a common phenomenon that severe disaster occurs in weak earthquakes. One important reason of casualty and loss is the severe damage and collapse of buildings. The bottom-business multi-story masonry structure is the most severely damaged building form. In the Wenchuan earthquake, 80% of these types of buildings were ruined, while the bottom-business multi-story masonry structure is very popular in the small and middle towns in the south of China. According to inadequate statistics, about two million such buildings exist in China, which are inhabited by 120 million residents. Thus, it is necessary to study the earthquake resistant mechanism of this building structure and the methods to reinforce the existing buildings to reduce the damages caused by earthquakes. Through investigating the post-earthquake sites, it is found that in the same meizoseismal area, individual bottom-business multi-story masonry structures have shown very good seismic performance. The difference between these buildings and other bottom-business multi-story masonry buildings lies in the fact that winged walls and winged columns were added to the side of the columns in the longitudinal wall of the bottom floor. This structural measure raises the earthquake resistant capacity of the building and reduces the rigidity difference between the front and back vertical walls in the bottom floor; i.e., it reduces the earthquake load difference between the longitudinal walls to contain the damage rate of this building to as low as the middle of the XI zone. To study the influence of the wing column in the bottom of the front longitudinal wall on the collapse-resistant capacity of multi-story masonry structures, shake table tests of 1/5 scaled masonry structure models, with and without wing columns, have been conducted. The damage progression, acceleration amplification factor, relative displacement and strain at typical positions were compared and analyzed. The results show that the damage state, the inter-story displacement and the inter-story drift ratio of the model with wing columns were much lower compared with the model without wing columns. It indicates that the collapse resistant capacity of bottom-business multi-story masonry structures with wing columns would be better than the original structure.

    • Impact of Beam Restriction on Seismic Damage Modeof Abutments in Liquefied Ground

      2017, 39(4):632-638. DOI: 10.3969/j.issn.1000-0844.2017.04.0632

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      Abstract:As a key connection structure in modern transportation networks, bridges are readily affected by earthquakes. Abutment failures not only cause the loss of function, but also lead to damage of entire bridge structures. To further research the influence of beam constraints on abutment damage in liquefied ground, in this paper, we investigate earthquake damage to the Shengli Bridge in the 1976 Tangshan earthquake, use UWLC software to conduct a numerical simulation analysis of the earthquake damage to the Shengli Bridge, and compare our results with the actual seismic damage. We found the numerical simulation results to be generally consistent with those of the actual seismic damage, which indicates that the UWLC finite element software has a good fitting ability. We numerically simulated the influence of the restraint force of the beam and the thickness of the liquefied layer on abutment damage modes with and without a pile foundation. The results show that under earthquake action, bridge abutment breakage is more serious. Unlike the gravity abutment with no pile foundation, we found the damage modes of abutments with a pile foundation to be forward-collapse failure, mainly because the pile foundation restricts the horizontal movement of the abutment bottom. The post-seismic displacement of abutments with a pile foundation is less affected by the restraint force of the beam than that of abutments without a pile foundation. For the gravity abutment, the liquefied sand layer has a certain filtering effect on the middle and high seismic-wave frequency bands, which reflects the damping effect of the liquefied layer. For pile-foundation abutments, the damping effect is not obvious due to the pile-soil-platform interaction.

    • >地震科学
    • Review of Mid-long Term Prediction for Jiuzhaigou MS 7.0 Earthquake in Sichuan Province

      2017, 39(4):639-644. DOI: 10.3969/j.issn.1000-0844.2017.04.0639

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      Abstract:In this study,the Diebu,Gansu MS5.9 earthquake,which occurred on January 8,1987,was regarded as the symbolical earthquake based on the review of the "activity in quiescence" and "quasi-activity in quiescence" methods and the analysis of the 10-year seismic risk area in the North-South seismic belt designated by the State Seismological Bureau in 1989. Then three places in the northern section of the North-South seismic belt,where earthquakes with magnitudes in the range of 6~7 may occur,were identified using the time scale of mid-long term prediction,one of which is the Jiuzhaigou area in Sichuan Province. Based on the discussions of some problems in the mid-long term prediction,the following conclusions are derived:(1) The Jiuzhaigou MS7.0 earthquake verifies that "activity in quiescence" is a feasible method to predict earthquakes,and the method has been optimized in this study. (2) Based on the "activity in quiescence" method and the analysis of the 10-year seismic risk area in the North-South seismic belt,the precursors can be distributed into quiet and active periods,and the precursors in the quiet period may be more significant in predicting earthquakes.

    • Earth-resistivity Anomalies before the Jiuzhaigou MS 7.0 Earthquake in Sichuan Province

      2017, 39(4):645-651. DOI: 10.3969/j.issn.1000-0844.2017.04.0645

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      Abstract:Before the occurrence of MS7.0 earthquake near Jiuzhaigou county in Sichuan province, the earth resistivity measured in shallow wells at Pingliang seismological station, which is situated approximately 360 km from the epicenter, showed an abnormal trend for a year. The anomalous amplitude of NS and EW measuring channels showed annual variation rates of 1.1% and 0.6%, respectively, which were larger compared with the background value (0.6%~0.4% of the normal annual variation). The anomalous change was analyzed by a joint anomaly verification team comprising the China Earthquake Network Center, Earthquake Administration of Ningxia Hui Autonomous Region, and Earthquake Administration of Gansu Province from June 27 to 29, 2017. The analysis results revealed that change occurs in the resistivity of the underground medium, which is the seismic precursory anomaly. Twenty hours prior to the earthquake, the NS and EW channels showed daily variation rates up to 8.9‰ and 1.5‰, respectively. After the mainshock, the measured value basically returned to the background value. This study has a positive research value in predicting earthquakes.

    • Strong Motion Records and Its Characteristics in JiuzhaigouMS 7.0 Earthquake on August 8, 2017

      2017, 39(4):652-656. DOI: 10.3969/j.issn.1000-0844.2017.04.0652

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      Abstract:An MS7.0 earthquake occurred on August 8,2017,at Jiuzhaigou county,Sichuan province.66 strong motion stations installed in the provinces of Sichuan,Gansu,Shaanxi and Ningxia have been fully triggered,and 198 groups of three-component acceleration records in the main shock were obtained by NSMONS.In this study,the distribution of 198 groups of three-component acceleration records within different epicenter distances were first calculated after a conventional analysis.The basic characteristics of this earthquake were analyzed based on the acceleration time-history curves of two typical stations.Then,the attenuation relation of PGAs and spectral accelerations within different distances were analyzed by comparing the observed data with Italy08 GMPE (ground motion prediction equation).Finally,combining drilling data of engineering sites,the spectral ratio curves were calculated based on the strong motion data from two typical stations.It is found that the horizontal to vertical (H/V) spectral ratio method can well reflect the response characteristics of actual site situation.

    • Preliminary Discussion on the Focal Mechanism Solutions and Seismogenic Structure of Menyuan MS 6.4 Earthquake on Jan. 21, 2016 in Qinghai

      2017, 39(4):657-661. DOI: 10.3969/j.issn.1000-0844.2017.04.0657

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      Abstract:According to Chinese seismological station net determination, a MS6.4 earthquake occurred at 01:13, Beijing time on Jan. 21, 2016 in Menyuan county of Qinghai province. By the end of Feb. 11, 475 aftershocks of ML ≥ 1.0 had occurred in the seismic region of the Menyuan 6.4 earthquake, including 4.0~4.9 level 1 and 3.0~3.9 level 17 times. The largest magnitude of ML4.4 occurred at 01:18 on Jan 21, and the Menyuan earthquake caused heavy economic losses. The CAP method is one entire profile inversion method, its inversion result has an advantages of relatively small merit which relies on the speed model and the earth's crust lateral change. The core idea is as follows:we split the seismic broadband waveform data into Pnl and surface wave parts, calculate the objective error function of the observed and the theoretical seismograms, perform the grid search in the assigned parameter space, and search the focal mechanism and the focal centroid depth of the two global minimum variances. In the paper, using the wave data from "the fifth" Seismological Network of Gansu province and Qinghai province, we adopted the CAP method to obtain the focal mechanism of the 6.4 earthquake occurred at Menyuan on Jan. 21, 2016. The results show that the focal character of the earthquake is thrust, MW 5.9 and the focal depth of the event is 9 km. The nodal plane I parameters of the best double-couple are strike 339°, dip 49°, and rake 111°, respectively. The strike of the nodal plane is the same trend with the strike of the Lenglongling fault; the characteristics of the dip are according to the properties of the Lenglongling fault. The nodal plane has been identified to be representative of the seismogenic fault plane. Analysis considers that the occurrence of Menyuan 6.4 earthquake has osculating correlation with the activity of the fault.

    • A Study on the Extraction Method of Direct Wave and Reflected Wave in Loran-C Signal

      2017, 39(4):662-666. DOI: 10.3969/j.issn.1000-0844.2017.04.0662

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      Abstract:Determining the difference in arrival time between direct waves and reflected waves in the Loran-C signal is crucial for effectively using it for ranging.Based on the analysis of waveform characteristics of the measured waves and theoretical waves in Loran-C signal, it is considered that the direct wave signal included in the measured Loran-C signal is consistent with that in the theoretical signal.Therefore, the theoretical direct wave signal can be removed from the measured Loran-C signal via waveform subtraction, then the difference in arrival time between direct waves and reflected waves can be calculated by using cross-correlation method.

    • Study of the Optimal Excitation Effect of Air-gun SourceExperiments in Nanyi Reservoir, Fujian Province

      2017, 39(4):667-676. DOI: 10.3969/j.issn.1000-0844.2017.04.0667

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      Abstract:Waveform data with optimal signal-to-noise ratios are required in air-gun active-source experiments, so excitation experiments must be performed under various operating conditions. By comprehensively analyzing the characteristics of station records to identify conditions that yield an optimal excitation effect, we can lay the foundation for subsequent fixed-point excitation experiments. In this study, we used three methods——single-shot analysis, superposition analysis, and the coefficients of signal-to-noise ratios——to comprehensively analyze the excitation effects of air-gun source experiments under different operating conditions in Nanyi Reservoir, Fujian province. We then determined the optimal condition. We also evaluated network noise to further verify this optimal condition. The results indicate that the optimal condition in Nanyi Reservoir is a water depth of 25 m, an air-gun array sinking depth of 12 m, and an air-gun array size of 7 m×7 m. In addition, the excitation time of this optimal operating condition does not occur in a low-noise moment, which verifies the good stimulation effect of this condition and the reliability of the results.

    • Co-seismic Response of Well Water Level and Temperature inYunnan Area to the Nepal MS 8.1 Earthquake in 2015

      2017, 39(4):677-685,712. DOI: 10.3969/j.issn.1000-0844.2017.04.0677

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      Abstract:The co-seismic response of underground fluid wells to the 2015 Nepal MS8.1earthquake and its aftershock MS7.5 in the Yunnan area were recorded. Based on observed data, this paper analyzes the spatial distribution, anomaly shape, anomaly amplitude, and anomaly start and end times in the appropriate wells. The results show that the co-seismic responses were mainly concentrated in the southeast of the Sichuan-Yunnan rhombic block, the east of the Yunnan-Myanmar arc block, and the west of Yunnan area. The anomaly shapes of the co-seismic responses of water level and temperature in the same well are complicated and multiple. The observation items in a single well show consistency and are unconnected to earthquake magnitude, epicenter distance, and azimuth. The well's ability to record earthquakes is connected to the resolution of the observation instrument, well aquifer condition, and so on. The co-seismic response anomaly amplitude shows a certain quantitative relationship with magnitude and epicenter distance. In recent years, seismic activity has shown a "quiet-active-quiet" characteristic and small earthquakes have been clustered in the Yunnan area. In the near future, there is a risk of moderate-strong earthquakes in the west-northwest and southwest of Yunnan.

    • Relationship between Crustal Deformation Field Changes in the Peripheryof Kangding Area During 2011-2014, the Lushan 7.0 Earthquake,and Two Subsequent Earthquakes in Kangding

      2017, 39(4):686-691. DOI: 10.3969/j.issn.1000-0844.2017.04.0686

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      Abstract:Based on highly precise GPS data, this paper investigates the relationship between the Kangding earthquakes (MW6.3 and MW5.8, in November 2014) and the changes in crustal movement and strain energy in the surrounding area. First, the data was collected from continuous GPS observation sites in the Kangding seismic and surrounding regions (99.6°-105.2°E, 27.8°-33.0°N). We then calculated the velocity at the observation sites and determined the crustal movement and principal strain rate fields for specific grid points (0.4°×0.4°) using the fitting calculation of a rigid-linear elastic motion equation. Second, based on the obtained results, we discuss the movement field characteristics and strain field changes in the Kangding seismic region and explore their relationship with earthquake preparation. The results show that the study area is associated with strain energy accumulation prior to the Lushan MS7.0 earthquake in 2013. In contrast, the area exhibits strain energy release and adjustment after the Lushan earthquake. It is proposed that the Kangding earthquakes are a product of tectonic adjustment in the study area.

    • Discussion of Small Earthquake Relocation in the Area of the 1927 Gulang M8 Earthquake

      2017, 39(4):692-697. DOI: 10.3969/j.issn.1000-0844.2017.04.0692

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      Abstract:Based on the data recorded by 67 stations in the Gansu digital seismic network and its adjacent seismic network from 2000 to 2015, we relocated 4 592 small earthquakes that occurred at the epicenter of the 1927 Gulang M8 earthquake and in its adjacent areas via a double-difference earthquake relocation algorithm. The results show that the eastern and western segments of the Huangcheng-Shuangta fault zone exhibit different mechanical motion properties. While the western segment is primarily dominated by thrust faulting, and earthquakes occurred mainly in the footwall of the fault, and in the eastern segment earthquakes mainly occurred in the hanging wall of the fault. Moreover, we first found a conjugate fault located in the middle segment of the Huangcheng-Shuangta fault that nearly perpendicular to the main fault. Based on the inversion of fault parameters of these small earthquakes, we also found that this high dip-angle fault mainly exhibits right-lateral strike-slip faulting with a minor tension component.

    • Time Symmetric Characteristics of MS ≥ 7.0 Earthquakes in theSichuan-Yunnan Region and Cycle Interpretation

      2017, 39(4):698-705. DOI: 10.3969/j.issn.1000-0844.2017.04.0698

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      Abstract:The ability to predict the time-trend of earthquakes through seismic time symmetric characteristics is a significant step in earthquake disaster prevention and reduction. To verify the research approach of seismic time symmetry and reveal the mechanisms involved in seismic time symmetry characteristics, time symmetry characteristics and trends of MS ≥ 7.0 earthquakes are analyzed and assessed by applying different methods such as commensurability calculations, the butterfly structure diagram, and the commensurability structure system. The seismic time symmetric characteristics are then explained in relation to types of cycles, such as the seismic energy releasing cycle, lunar right declination, and the sunspot cycle. Results show that:(1) the earthquake (MS ≥ 7.0) sequence in the study area has evident time symmetry characteristics, and there are strong earthquake signals in 2017 with a random probability of occurrence of 65.5%; (2) the time symmetry characteristics of MS ≥ 7.0 earthquakes provide a good intuitive expression of seismic energy releasing cycle; (3) the time symmetry characteristics of MS ≥ 7.0 earthquakes results from the varying effects of superposition of lunar right declination and sunspot cycles, and the extremum of lunar right declination is the main trigger for strong earthquakes (MS ≥ 7.0).

    • >场地地震效应及动力响应
    • Numerical Simulation of the Earthquake Liquefactionof a Roadbed in a Plateau

      2017, 39(4):706-712. DOI: 10.3969/j.issn.1000-0844.2017.04.0706

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      Abstract:The roadbed in a plateau is impacted by seasonal freezing and thawing; compared with those of plains, of the liquefaction factors of roadbeds in a plateau are more complex. Taking Qinghai S308 knot ancient qumarleb section of highway roadbed deformation for example, reducing the roadbed in the earthquake devastated by FLAC3D process simulation software, the following conclusions can be made:(1) In the absence of groundwater conditions, slope obvious plastic vibration strength yield is 0.6g, plastic yielding occurs first in the subgrade fill thinner ends. (2) If the sand is completely saturated with water, liquefaction gradually occurs with increasing amplitude. When the amplitude is less than 0.3g, the sand layer is not liquefied. At an amplitude of 0.4g, the sand layer liquefies 5 s later. At amplitudes greater than 0.5g, the vibration from the beginning, there have been liquefied. Saturated sand embankment power (3) the underlying failure mechanism is:saturated sand layer near the surface of the yield →yield zones in saturated sand layer through→yield saturated sand layer to the middle layer is completely saturated sand expansion→yield first, fill the rear area damage undermine→fill fill-sand interface extends down→fill rear surface cracking yield expansion in the destruction zone backfill. At the final destruction, filling cracks in the rear of the large-scale yielding, but filling the front remains intact.

    • Effect of Rayleigh Damping Matrix on SeismicResponse Analysis of Deep Soft Soil

      2017, 39(4):713-718. DOI: 10.3969/j.issn.1000-0844.2017.04.0713

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      Abstract:This paper deals with the effect of the Rayleigh damping matrix on site response analysis in the time domain. We introduce the fundamental theory of time domain analysis and summarize several methods for constructing a damping matrix. In our study, we to developed a series of numerical models to simulate wave propagation through an elastic medium after using the finite difference method to consider the intensity and spectral characteristics of the input motions. We adopted a full Rayleigh damping and selected five methods to determine the high frequency. The results show that damping models have a significant influence on acceleration and spectral acceleration, and their degree of influence is related to the frequency characteristics of the input motions. When the fundamental site frequency is close to the predominant frequency of the input motions, it is feasible to determine the damping matrix based on this consideration only. However, the peak ground acceleration and spectral value are underestimated when the predominant frequency of the input motion is high or far higher than the fundamental site frequency. In time domain analysis, damping considerations should include the site frequency and frequency characteristics of the input motions.

    • Estimation of Site Amplification Effect in North Chinafrom Ambient Seismic Noise

      2017, 39(4):719-724. DOI: 10.3969/j.issn.1000-0844.2017.04.0719

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      Abstract:Site amplification of the strong motion of earthquakes is a subject of considerable interest. However, other data are required to produce site amplification factors when available strong motion data are lacking, and this application has been proven to be reliable and practicable. Seismic array observations now cover almost the entire Chinese continent and supply abundant data. Our method is applied in the North China array. Assuming that the seismic stations in a network or array are driven by a forcing function derived from the ambient noise field, each site will respond differently depending upon the elastic and anelastic properties of the underlying medium. With the Steven-Taylor method, the F-K spectrum of ambient noise is regarded as the input and the auto-power spectrum is the response; the ratio between the response and input can thus represent site amplification. In this study, we use the F-K spectrum of the cross-correlation function of ambient noise to deprive the velocity and azimuth of energy extremum, which is different to that in the Steven-Taylor method. We then correct the Fourier spectrum for all stations according to the velocity and azimuth, and the input power spectrum is computed from the stack and average of all the Fourier spectrum. The ratio between the power spectrum of each station and the maximum of frequency-wave number spectrum of ambient noise can then be adopted to estimate site amplification. This method is used to estimate site amplification of the North China array in a period from 10 to 20 s, and the ratio between maximum and minimum amplification is about 7. The sediment thickness of the plain region is basically consistent with that of the Bohai Bay Basin, and site amplification factors of the plain after standardization are found to be larger than those in the mountain region. This study therefore provides an available method to estimate site amplification.

    • Analysis of Applicability of Standard Penetration Test Methodfor Evaluating Sand Liquefaction Potential in Tianjin

      2017, 39(4):725-730,737. DOI: 10.3969/j.issn.1000-0844.2017.04.0725

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      Abstract:With reference to the evaluations of the typical saturated silt liquefaction potential in the Tianjin area, along with an adjustment in the seismic fortification criterion, in this paper, we discuss the applicability of the standard penetration test method for evaluating soil liquefaction. We collected a great volume of engineering drilling data and investigation results pertaining to the 1976 Tangshan earthquake, compared and analyzed the evaluation results of three methods used in the seismic design codes of China. The results show that the method in the Code for Seismic Design of Buildings (GB50011-2010) has the highest degree of safety in evaluating the liquefaction potential in the Tianjin area at seismic fortification intensities of 7 degrees (0.15g) and 8 degrees (0.20g). This method's accuracy ratio is highest in liquefied areas, but its misjudgment ratio in non-liquefied areas is also high, and the degree of liquefaction determined by this method is more severe than the facts. The accuracy ratio of the method used in the local Code for Investigation of Geotechnical Engineering in liquefied areas is also high, close to that of the current seismic design code, but its misjudgment ratio in non-liquefied areas is relatively reduced compared to the previous method. The degree of liquefaction determined by this method is in good agreement with the facts, which will not only ensure safety, but also reflect a certain degree of economy, making it more suitable for evaluating the silt liquefaction potential in the Tianjin area.

    • Study on the Calibration Method of Micro Earth Pressure Sensors

      2017, 39(4):731-737. DOI: 10.3969/j.issn.1000-0844.2017.04.0731

      Abstract (706) HTML (0) PDF 1.24 M (635) Comment (0) Favorites

      Abstract:Micro earth pressure sensors are often used to measure the earth pressure within a soil mass or the earth pressure acting upon the boundaries of buried structures in centrifuge model tests. As pressure is a contact measurement, disturbances to the soil become inevitable when the sensors are embedded in it; these disturbances affect the soil stress distribution and promote artificial boundary conditions or soil arching. Considering this problem, calibrating each sensor is necessary before the test is conducted and measurements are made. Traditional calibration methods using solution or gas as the calibration medium cannot accurately reflect working conditions. Thus, in this work, a system designed to calibrate micro earth pressure sensors for centrifuge model tests is proposed. Multiple sensors are calibrated in the laboratory considering two working conditions:with a rigid backrest and without the backrest. Water, silty clay, or Fujian standard sand are used as the calibration media. Calibration coefficients are then obtained to establish the relationship between output voltage and earth pressure. The results show that the loading and unloading segments are relatively linear when the calibration medium is water; when the medium is sand or silty clay, however, highly non-linear behavior and large hysteresis are noted. The hysteresis ratio R is defined to evaluate the hysteresis quality, and computed results indicate that the calibration media and sensor types are the two major factors affecting valves of R. A number of factors that may affect the calibration results of the sensors are then discussed. The material properties and geometric characteristics of the sensors, the preparation of the foundation soil, changes in soil compactness and soil strength due to preloading and cyclic calibration, the calibration medium, and the working state were found to exert the most significant influences on the calibration coefficients. Therefore, to enable correct measurement of earth pressure, the calibration conditions, especially the calibration media and the working state, must be as similar as possible to the test conditions, and all sensors should be calibrated individually.

    • >工程动力响应分析
    • Analysis of Bearing Capacity and HystereticPerformance of Reinforced K-Joint

      2017, 39(4):738-743. DOI: 10.3969/j.issn.1000-0844.2017.04.0738

      Abstract (787) HTML (0) PDF 4.58 M (960) Comment (0) Favorites

      Abstract:The K-type tubular joint is one of the most widely used nodes in steel pipe structure engineering because of its simplified intersecting lines and good precision. The investigation on damaged steel structures caused by major earthquakes showed that the design and construction of connection nodes were flawed. Since the node is a key part of the structure and dissipates seismic energy, a research on strengthening the steel structure joint is necessary. The overlapped K-point of a steel tubular section is prone to cause local buckling and tearing on the main tube wall. Herein, a new strengthening K-type joint is proposed; the concrete poured between the main tube and internal tube was used to stiffen the K-joint. Compared with the method of filling concreate in the main tube, this enhanced node can not only keep the building beautiful but also reduce the structural weight. Using the finite element software ANSYS, the ultimate bearing capacity and hysteretic performance of unstiffened and stiffened joints are analyzed. Compared with pre-strengthening nodes, the failure mechanism under static and reciprocating loads is investigated. The results show that a stiffened joint can effectively improve the mode of failure, reduce stress concentration near the joint and enhance rigidity and bearing capacity of the joint. The unreinforced joint shows a complete hysteresis curve; however, when compared with the reinforced joint, the bearing capacity of unreinforced joint is much worse. The ultimate bearing capacity of the joint can gradually increase to reduce the inner tube size. When the inner tube size is reduced to a certain value, the bearing capacity of the node does not change.

    • >地基与构筑物土动力
    • Experimental Study on the Dynamic Properties of Sliding ZoneSoil of a Landslide under Varying Water Content

      2017, 39(4):744-749,758. DOI: 10.3969/j.issn.1000-0844.2017.04.0744

      Abstract (1169) HTML (0) PDF 1.32 M (956) Comment (0) Favorites

      Abstract:The Xieliupo landslide is in an active and ruptured fault zone, and its growth and movement are controlled by the active fault. Historically, the combined effect of earthquakes and rainfall has repeatedly activated the landslide, causing severe damage to life and property. Hence, it is important to evaluate the dynamic stability of the Xieliupo landslide for mitigation of the hazards. The sliding zone soil, viewed as one of the major components of a landslide, is always perceived as a key factor in keeping the landslide stable and steady. To investigate the dynamic properties of the sliding zone soil of the Xieliupo landslide, remolded specimens of various water contents are tested on a cyclic triaxial apparatus under consolidated and undrained conditions using a step-by-step method to increase the dynamic load. The test results show that the dynamic elastic modulus of the sliding zone soil decreases exponentially with the increase of shear strain under constant water content. As the water content increases, the dynamic elastic modulus of the slip soil also decreases continuously under the same confining pressure and its deterioration velocity increases with increased water content. It seems that there is a threshold water content (around the plastic limit) in describing the variation of maximum elastic modulus with water content. The maximum dynamic elastic modulus of the slip soil, calculated from the cyclic triaxial test results, initially reduces slowly with water content, but when the water content is above the plastic limit, it abruptly decreases with further increase of the water content. Additionally, the relationship between dynamic elastic modulus and dynamic strain under different water content could be perfectly normalized, referring to the maximum dynamic elastic modulus. The damping ratio of the slip soil increases with shear strain and under the same confining pressure, the damping ratio increases as the water content increases. The relations between damping ratio and dynamic shear strain of the slip soil could also be normalized based on the maximum damping ratio. Based on the analysis of the cyclic triaxial test results, it can be concluded that the backbone curves of dynamic stress against strain for the sliding zone soil of the Xieliupo landslide could be described using the conventional hyperbolic model.

    • Numerical Simulation of Soil Pressure Characteristics of GravityRetaining Walls during Earthquake

      2017, 39(4):750-758. DOI: 10.3969/j.issn.1000-0844.2017.04.0750

      Abstract (699) HTML (0) PDF 5.43 M (1024) Comment (0) Favorites

      Abstract:The soil pressure characteristics of gravity retaining walls under seismic action are an important consideration in the retaining wall design. In the seismic design codes of many countries, including China, the seismic soil pressure of a retaining wall is calculated using the Mononobe-Okabe formula. Previous studies have identified many limitations with respect to some of the assumptions of the Mononobe-Okabe formula, which has led to results that are inconsistent with actual situations. As such, the reliability of this method must be further examined. In their detailed studies of the soil pressure characteristics of retaining walls, researchers have improved the pseudo static method, developed the pseudo dynamic method, and introduced model experimentation and numerical analysis, which have greatly improved the accuracy of the calculated results. However, most research has considered maximum earthquake intensity, but not the impact of the time-history variation of seismic waves on the soil pressure behind the wall. In this study, we used numerical simulation to establish a series of monitoring points on the back of the retaining wall and then obtained time-history curves of the acceleration and soil pressure strength. Based on these time-history curves, we then analyzed the distribution characteristics of soil pressure strength, calculated the total soil pressures, and obtained the overturning moment of the toe of the wall. Finally, we compared the soil pressure distribution, total soil pressures, and overturning moment of the toe of the wall with those calculated by existing methods and codes. The results show that the peak acceleration of each monitoring point occurs at the same moment, but the peak soil pressure does not. Some existing methods do not consider the time-history change of peak soil pressure strength, thereby yielding a bigger result than is practical. In low seismic intensity conditions, the total soil pressures and overturning moments calculated by codes tend to be conservative, whereas in high intensity conditions they tend to be dangerous.

    • >工程地质及施工
    • Particle Flow Simulation of Zonal Disintegration inDeep Tunnel Surrounding Rock

      2017, 39(4):759-766. DOI: 10.3969/j.issn.1000-0844.2017.04.0759

      Abstract (664) HTML (0) PDF 27.21 M (755) Comment (0) Favorites

      Abstract:With the development and utilization of deep resources, there is an increasing number of problems associated with deep rock masses. In environments characterized by high stress, high water pressure, and high temperature with more complex crack deformations (including zone cracks, rock blasts, splits on side walls, and plastic fluids), deep rock masses exhibit different corresponding characteristics than those of shallow rock masses. In this study, to precisely describe the deformation laws of deep rock masses, we used PFC software to examine the macro-responses of deep rock masses by micro-scale stimulation. The results show that with increased depth, temperature, and pressure, the plastic damage in shallow surrounding rock becomes crack damage in deep surrounding rock, with crack zones and alternating zonal disintegration with depth. The spacing of the crack zone is related to the rock mass properties and depth. In the cross section of tunnels, the first crack zone appears in the haunch of the arch and then at the arch springing line, eventually becoming an entire crack zone. If pressure is exerted on the surface of the surrounding rock, the crack zone will decrease and move into the deep area. As such, a pre-stressed anchor can effectively improve the bearing characteristics of surrounding rock and reduce the number of cracks. These results agree with model-test data and also reflect the deformation law of deep rock masses. These conclusions provide a valuable reference for the design and construction of deep underground engineering projects.

    • >活动构造
    • Interpretation of Fault Characteristics in Funiu Mountains,Western Henan Based on ASTER GDEM

      2017, 39(4):767-773. DOI: 10.3969/j.issn.1000-0844.2017.04.0767

      Abstract (656) HTML (0) PDF 36.34 M (841) Comment (0) Favorites

      Abstract:GIS terrain analysis technology based on ASTER GDEM data and LANDSTAT image data provides information about hill shade, slope, aspect, river systems, planation surfaces, together with 3D visualization. In this study, such information is combined with results of previous research to extract and analyze the main fault structures in the Funiu Mountain region. Most faults trend NW-SE are clearly shown in shadow maps with 45° and 225° azimuths. Areas that show different gradients are generally located at the junction of mountains and always indicate strong fracture activity. The asymmetric distribution of the river system also shows a response relationship with fault structures. Two planation surfaces with elevations in the range of 1 350~1 400 m and 1 100~1 200 m, respectively, are extracted through terrain analysis and are located in two adjacent stable blocks. The tectonic activity between the two blocks is obviously different, and it is thus easy to identify the F3 fault. In addition, twelve faults are interpreted through a comprehensive comparative analysis. Overall, this method has a higher accuracy in determining and analyzing large faults than small faults; accuracy of the latter cannot be totally verified due to incomplete previous research data. This method can assist in identifying small faults that have not yet been discovered, but it can only be used in surface topography analysis and not in a qualitative analysis of structures as further study is required to meet such requirements.

    • Application of Joint Exploration with P-and SH-waves to theInvestigation and Research of Benchahe Fault Activity

      2017, 39(4):774-780. DOI: 10.3969/j.issn.1000-0844.2017.04.0774

      Abstract (749) HTML (0) PDF 14.00 M (836) Comment (0) Favorites

      Abstract:The Benchahe Fault has been received much attention and research interest because of its importance and complexity. However, in the absence of definite evidence, there is little consensus regarding its structure and spatial distribution; the fault activity, in particular, is ambiguous. Bedrock top surface depth is about 800~1 600 m in the area where our target is located; however, a single exploration method is unlikely to identify both deep and shallow targets at the same time and has limitations. To investigate the spatial location, characteristics, and activity of the Benchahe Fault, a high-resolution shallow seismic P-and SH-wave survey profile was carried out across the fault. Fine structures at different depths beneath the profile were obtained and the patterns and characteristics of the fault were determined. In particular, the SH-reflection profile revealed evidence of tectonic deformation. The results show that the Benchahe Fault is a normal fault that runs nearly EW, and dips to the N with a dip angle of 60~75°. Based on the sections, we can speculate that the up-breakpoint of the south branch of the fault dislocated the top surface of the Middle Pleistocene, and may have dislocated the bottom of the late Pleistocene stratum interface. In this paper, we show that this multi-level seismic exploration method is an effective means of locating buried faults and studying their activity in areas with thick overburden. Joint inversion of P-and SH-waves was effective for locating the buried fault in thick Quaternary sediments and determining its activity. While the two methods corroborate each other in the overlapping buried depth range, the SH-wave exploration method can compensate for near-surface layer and rift structure information that is lost in P-wave exploration.

    • >震灾防御
    • Relation between Different Building Types and Personnel Death in theHeavy Disaster Area of the Minxian-Zhangxian MS 6.6 Earthquake

      2017, 39(4):781-789. DOI: 10.3969/j.issn.1000-0844.2017.04.0781

      Abstract (683) HTML (0) PDF 22.61 M (739) Comment (0) Favorites

      Abstract:Ninety-five people were killed and 2014 people were injured in the Minxian-Zhangxian MS6.6 earthquake that occurred on July 22, 2013. Houses in rural areas were severely damaged. The damage ratio of houses in heavy disaster areas was more than 36.59%. The combined effect of the earthquake and continuous rain induced a large number of landslides, collapses, and other geological disasters, which resulted in serious losses of life and property in the disaster area. In this study, a considerable amount of basic data are obtained through the investigation of degree of damage for different building types, population, number of deaths, cause of death, topography, and geological hazards in the disaster area. Further, the causes of death attributed to the earthquake and the damage ratio of different building types are obtained through analysis. Multiple linear regression fitting is used to obtain the relation between death toll data and the damage ratio of houses in nine administrative villages in the heavily impacted disaster area. The relation is validated using similar data for the population and the damage ratio of houses but from different intensity areas. The results show that the total death toll calculated using this method is 16 more than the actual one with a total error rate of 17.02%.

    • Analysis of the Time Delay Effect in ModernEarthquake Early Warning Systems

      2017, 39(4):790-796. DOI: 10.3969/j.issn.1000-0844.2017.04.0790

      Abstract (826) HTML (0) PDF 4.21 M (682) Comment (0) Favorites

      Abstract:The problem of time delay in earthquake early warning (EEW) systems restricts their effectiveness. Shortening the delay time can significantly improve the efficiency and emergency response ability of EEWs. In this study, we analyze the delay factors, decompose the period from earthquake occurrence to the warning information release to many links, then calculate the specific delay time in each link. We then compare the warning level and radius of warning blind area in autochthonous, allochthonous, and mixed EEW models, and analyze each model's delaying effect. The results show that the time delay in EEWs mainly comprises delay in data transition and processing; with a minimum theoretical delay time of Δt=3.9 s, an average delay time of Δt=14.3 s in the mainstream EEW, and Δt=8.7 s in the most advanced EEW. Moreover, the time delay exerts influence on the radius of the blind area in a shallow earthquake and a positive relationship can be witnessed. For example, when Δt=8.7 s, the blind area radius is 52.2 km and when Δt=3.9 s, the largest blind area radius is only 23.4 km. The results indicate that effective shortening of delay time can not only improve the timeliness of earthquake early warnings, but also reduce the blind area.

    • >短文
    • Discussion on the Medium-term Prediction of Jiuzhaigou, Sichuan MS 7.0 Earthquake on August 8, 2017, by Means of Triplet Method

      2017, 39(4):797-798. DOI: 10.3969/j.issn.1000-0844.2017.04.0797

      Abstract (633) HTML (0) PDF 971.79 K (907) Comment (0) Favorites

      Abstract:Three strong earthquakes, which occurred in the Jiuzhaigou county and its adjacent areas in the 20th century, fit to the temporal triplet distribution with period of 40 years. It is predicted that a strong earthquake will occur again in 2018 based on the period with the 1976 Songpan earthquake as the starting point. In fact, the previous period of actual earthquakes in this area is 43 years, one more than 42 years, so the new period should subtract one year, which means the predicted strong earthquake should occur in 2017.

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