近断层速度脉冲地震动引起的边坡永久位移预测模型

基于小波分析方法,从NGA数据库的3 551条地震记录中选取189条速度脉冲地震动,地震动均转换成发生最强脉冲的方向。基于Newmark方法,分析了近断层速度脉冲地震动作用引起的边坡永久位移值。结果表明：近断层速度脉冲地震动对边坡产生特殊的破坏作用,表现在滑动位移值大、滑动体破坏力强等方面;边坡永久位移值与速度脉冲地震动的峰值速度具有高度相关性,位移值较大时尤为明显。建立了基于单变量形式的峰值速度及双变量形式的峰值速度、峰值加速度两种边坡永久位移预测模型,模型简单实用,与回归数据具有很好的相关性,前者更适用于预测对实际工程影响较大的永久位移值,且离散性较小。提出的预测模型为考虑近断层地震动速度脉冲特性影响的边坡永久位移值的概率地震灾害分析提供了基础。     

土工结构地震滑动位移统计分析

土工结构在地震荷载下的滑动位移是评估结构安全性能的重要参数。采用一种新型的地震波选择方法,在强震数据库中选择修改地震波,以有效地在结构动力分析中引入不同特征地震波的影响。通过一个简单的土工结构地震滑移模型,系统地分析了结构基本周期和滑动面屈服系数对地震滑移概率及相应滑移距离的影响,并提出了滑动体在不同地震场景和基本周期条件下的滑移概率和累积滑动位移的统计模型,对基于性能的土工结构抗震设计具有重要的参考意义。     

小型土石坝加密抗液化离心机振动台试验研究

地震作用下土石坝液化易导致坝坡失稳滑移等严重后果,加密法是常用的抗液化手段之一。针对坝趾压重与坝壳翻压两种坝身加密加固方法,开展了离心机振动台试验,分析了不同加密型抗液化处理的小型土石坝坝坡地震响应规律。试验结果表明,由于高水头作用下坝坡底部土体软化,未处理坝坡加速度放大系数沿高程先减小后增大,而加密坝坡加速度放大系数沿高程逐渐增大,且坝坡表面处加速度存在表面放大现象。坝趾压重和坝壳翻压提高了坝身有效应力,降低地震产生的超静孔压比,有效防止土体液化。未处理坝坡在峰值加速度为0.24g地震作用下即发生坝趾液化现象,而加密坝坡在峰值加速度为0.24g和0.45g下均未发生液化。未处理坝坡整体侧向位移大,加密处理后,在峰值加速度为0.24g下坝坡整体表现为竖向位移。坝趾压重区坝趾水平位移明显减小,坝壳翻压区坡顶沉降减小了50%。试验结果验证了坝趾压重和坝壳翻压的抗液化效果,为小型土石坝抗震加固设计提供了参考。     

A practical method for identifying parameters in the seismic design of embankments

The effect of heterogeneity of soils on a seismic design procedure based on residual displacement according to safety factors is examined. Although soils are heterogeneous in nature, at present the seismic designs of embankments implement the assumption that soils are homogeneous. In this study, a seismic reliability analysis using a Monte Carlo simulation and considering the heterogeneity of soil strength was applied to the Newmark sliding block method. The data of the analysis in this study were based on in-situ soil test results of actual airport embankments. This paper indicates a rational and practical approach to modifying the actual heterogeneous soil conditions into homogeneous design parameters for the Newmark sliding block method in homogeneous ground conditions.     

A correlation for permanent earthquake-induced deformation of earth embankments

Seismic design of earth dams and embankments is mainly controlled by the permanent deformation that may be induced directly or indirectly because of the design earthquake. Simple design charts, such as those developed by Yegian et al. [Yegian, M.K., Marciano, E.A., and Ghahraman, V.G. 1991. Earthquake-induced permanent deformations: Probabilistic approach. J. Geotech. Eng., 117, 35–50.], Hynes-Griffin and Franklin [Hynes-Griffin, M.E., and Franklin, A.G. 1984. Rationalizing the Seismic Coefficient Method. Miscellaneous Paper GL-84-13, US Army Corps of Engineers Waterways Experiment Station, Vicksburg, Mississippi.], Makdisi and Seed [Makdisi, F.I., and Seed, H.B. 1978. Simplified procedure for estimating dam and embankment earthquake-induced deformations. J. Geotech. Eng., 104, 849–867.], and Sarma [Sarma, S.K. 1975. Seismic stability of earth dams and embankments. Géotechnique, 25, 743–761.], are often used to obtain a preliminary estimate of the permanent, earthquake-induced deformation of earth dams and embankments. Comparison of permanent deformations estimated from these procedures with observations from 122 published case histories on performance of earth dams and embankments during past earthquakes indicate that the estimated permanent earthquake-induced deformations were, in general, smaller than the observed deformations. However, the observed permanent deformation, D_avg, was found to relate to the ratio of yield acceleration, a_y, and the peak horizontal ground acceleration, a_max. The scatter in the observational data, upon which the D_avg–a_y/a_max relationship is based, can be partly explained by the variations in the ratio of the fundamental (elastic) period of the earth structure, T_D, and the predominant period of the earthquake ground motion, T_p, and the magnitude of the earthquake, M_W.     

Deterministic approach to the seismic hazard of dam sites in Kızılırmak basin,Turkey

Dams constructed on the seismically active regions have a high-risk potential for downstream life and property. Strong ground motion can result in instability of the dam and strength loss of foundation. Active faults within the foundation of dam have the potential to cause damaging displacement of the structures. Appropriate design measures should be considered to obtain rational solution to the problem of catastrophic release of water from the reservoir, and especially to resist earthquake loads. Safety concerns for dams under the earthquake loads involve the seismic hazard evaluation of dam site for the overall stability of structure. Various types of analyses can be used, ranging from a simplified analysis to more complex procedures based on ground motion parameters and response spectra. This paper briefly evaluates seismic hazard analyses for dam structures, and introduces the analyses for thirty-six dams with height ranging from 15 to 195 m in Kızılırmak basin, Turkey. The seismic hazard analyses have indicated that peak ground acceleration varies within a wide range (0.09–0.45 g) for the dam sites of the basin.     

地震动加速度幅值对土坡失稳后滑坡体大小及致灾范围的影响

地震滑坡的致灾范围是判断滑坡能否会对已有建构筑物造成损失、确定预警疏散范围的重要依据,因此对地震土坡破坏后的滑坡体大小和致灾范围进行研究具有重要的意义.本研究基于SPH动力分析方法,结合弹塑性本构模型和固体力学控制方程建立了地震土坡破坏的动力分析模型;通过设置振动边界粒子和自由场边界粒子,实现了地震动加速度的施加以及自...     

桩板式抗滑挡墙地震响应的振动台试验研究

汶川地震路基震害调查表明,在顺层或堆积体边坡中的桩板式抗滑挡墙具有良好的抗震性能。为了更好地了解该结构的抗震性能和优化抗震设计方法,以大型振动台模型试验为手段对其进行研究。为明确地震作用下桩板式抗滑挡墙的地震响应特性,试验采用缩尺的卧龙台站实测地震波对模型激励。试验结果揭示了土压力沿桩身分布规律、桩体位移和边坡岩土体加速度的地震响应特征。研究表明,地震土压力沿桩身呈非线性分布,竖向地震荷载对水平加速度有放大效果。所以,双向加载时的地震土压力比水平单向加载时大,但二者差距在地震基本烈度VII、VIII度区域不显著。滑坡推力、滑床对桩的土体抗力和桩身位移均与输入地震动峰值加速度成正比,即随着地震动峰值加速度的增加,加速度放大比增大;滑动面材料剪切强度折减,滑坡推力、土体抗力和抗身位移均增大,且增大速率加快。此外,结合试验成果,建议了桩板式抗滑挡墙设计时地震综合影响系数Cz的合理取值,对应地震基本烈度VII、VIII、IX度区分别为0.2、0.35、0.4。试验结果有助于揭示该结构抗震机制,也为其抗震设计提供了可靠依据。     

Performance-based assessment of earthquake-induced catastrophic landslide hazard in liquefiable soils

This paper outlines a methodology for evaluating the likelihood of catastrophic landslide occurrence on gentle slopes in liquefiable soils during earthquake. The approach is based on a modified Newmark sliding block model of assessing the earthquake-induced undrained landslide displacements for conditions of no shear stress reversals on the sliding surface. By employing the shear resistance-displacement relationship from undrained monotonic ring shear tests, the simulation model incorporates the sensitivity of computed displacements to variations in yield acceleration. The proposed approach involves an examination of undrained seismic slope performance under various horizontal seismic waveforms scaled to different specific values of the peak earthquake acceleration. An example problem illustrates how the proposed methodology may be used to demarcate, based on the magnitude of permanent seismic displacement, the levels of low, moderate and high risk of catastrophic landslide on a gentle slope in a saturated cohesionless soil susceptible to liquefaction during earthquake.     

Seismic behaviors of soil slope in permafrost regions using a large-scale shaking table

Large-scale shaking table model tests were carried out to study the dynamic behaviors of slopes and failure mechanism of landslide in permafrost regions. The model slope was constituted of silty clay layer stacked on an ice layer with 8° surface slope. Acceleration, displacement, and pore pressure were measured subjected to vertical and horizontal seismic loadings. The horizontal wave has a stronger influence on the failure of the model than the vertical wave motion, and the natural frequency of vibration in the horizontal direction decreased obviously at the failure state. The model slope has three components of different nonlinear mechanical properties, which are the soil layer, soil-ice interface, and ice layer. The amplification factor of peak ground acceleration is obviously smaller at the soil-ice interface than that at the soil and ice layer. The acceleration responses are nonlinear because of the nonlinear soil properties and degradation of modulus with increasing horizontal acceleration. Especially, excess pore pressure generation was observed near the soil-ice interface of the slope subjected to higher input acceleration, which resulted in the decrease of the effective stress. Failure surface appeared to be the soil-ice interface, which was consistent with the field observations of landslides in permafrost regions. Slope failure could be defined based on the massive movement of the slope, characterized by integral sliding pattern along the soil-ice interface without the distinct deformation inside the sliding body. The results show that the sliding of the slope with soil layer at gentle gradient is mainly triggered by the combined action of horizontal seismic wave, existence of soil-ice interface, and pore pressure generation in permafrost regions.     

基于简化 Newmark位移模型的区域地震滑坡危险性快速评估以汶川MS 8.0级地震为例

以汶川MS8.0级地震重灾区的11县市为例,初步提出了基于简化Newmark位移模型的地震滑坡危险性应急快速评估方法。利用汶川地震即时地震动参数、工程地质岩性经验分组及地形坡度数据,借助ArcGIS空间数据建模工具编制了地震滑坡危险性快速评估流程模块。计算了区域浅表层饱和岩土体斜坡的静态安全系数Fs、临界加速度ac,并借此分析了地震滑坡易发性。利用经验式获得了汶川地震Arias强度和区域滑坡位移DN分布,实现了汶川地震重灾区地震滑坡危险性的快速评估,为应急救灾决策提供了参考。通过对比评估结果和震后滑坡调查成果,可知数十处灾难性滑坡绝大部分位于-高危险区的龙门山主中央断裂带两侧约20km地带中,显示了评估方法的可靠性; 同时,分析指出了空间数据精度及更新不足导致局部评估结果欠佳的局限性,并提出了改进建议。     

考虑强度退化效应的堤坝抗震稳定性评价方法

考虑土的动强度随振动孔隙压力上升的衰减效应,将拟静力极限平衡分析和滑动体位移分析相结合,提出了堤坝抗震稳定性评价方法.首先,基于土工动力有限元分析,确定坝坡潜在滑动土体的平均加速度时程,进而,基于拟静力概念,采用极限平衡分析,确定坝坡的安全系数随时间的变化历程,其中当安全系数瞬时小于1时,表明坝坡在地震中处于瞬时超载状态,采用Newmark刚体滑块模型估算瞬时超载所产生的滑动位移,将各个超载阶段的滑动位移叠加,求得设计地震动作用下堤坝边坡的累积滑移量,根据这种方法所进行的数值计算与分析表明,考虑强度循环退化效应后所得到的坝坡滑移量更为合理.     

地震作用下堆积体边坡的坡面变形与失稳机制

地震作用下堆积体边坡的动力响应特性十分复杂,单一抗震安全系数不足以评价其动力稳定性。通过大型振动台试验,研究了连续多级地震荷载作用下,地震波的类型、卓越频率及峰值加速度对堆积体边坡坡面永久位移的影响,并初步分析其失稳机制。试验结果表明,相同峰值加速度下振动型地震波比冲击型地震波更容易产生坡面永久位移,地震波卓越频率对坡面永久位移也有重要影响;堆积体边坡在峰值加速度apeak=0.2g时开始有大颗粒石砾滚落,对应的坡面永久位移在apeak=0.2g～0.3g之间开始产生并显著增大,另外利用考虑坡面几何形态变化的改进Newmark法对坡顶的永久位移进行了估算。通过坡面永久位移评价堆积体边坡的动力稳定性有一定合理性。     

Seismic Retrofit of Gravity Retaining Walls for Residential Fills Using Ground Anchors

Failure of several gravity retaining walls in residential areas built on reclaimed land, during the October 23, 2004 Chuetsu earthquake in Niigata Prefecture, Japan, determined the authorities to consider the seismic retrofit of the walls in order to mitigate future similar disasters in the urban environment. This study addresses the effectiveness of ground anchors in improving the seismic performance of such retaining structures through a sliding block analysis of the seismic response of an anchored gravity retaining wall supporting a dry homogeneous fill slope subject to horizontal ground shaking. Sliding failure along the base of the wall and translational failure along a planar slip surface of the active wedge within the fill material behind the wall were considered in the formulation, whereas the anchor load was taken as a line load acting on the face of the gravity retaining wall. The effects of magnitude and orientation of anchor load on the yield acceleration of the wall-backfill system and seismically induced wall displacements were examined. It was found that for the same anchor orientation, the yield acceleration increases in a quasi-linear manner with increasing the anchor load, whereas an anchor load of a given magnitude acting at various orientations produces essentially identical yield accelerations. On the other hand, the computed earthquake-induced permanent displacements of the anchored gravity retaining wall decrease exponentially with increasing magnitude of anchor load. Additionally, the influence of backfill strength properties (e.g., internal friction angle) on the seismic wall displacement appears to diminish considerably for the anchored gravity retaining wall. A dynamic displacement analysis conducted for the anchored gravity retaining wall subjected to various seismic waveforms scaled to the same peak earthquake acceleration revealed a good correlation between the calculated permanent wall displacements and the Arias intensity parameter characterizing the input accelerogram.     

Analysis on mechanism of landslides under ground shaking: a typical landslide in the Wenchuan earthquake

A high steep rock hill with two-side slopes near National Road 213 is used as a prototype in this paper. The full process from initial deformation to sliding of the slope during ground shaking is simulated by a new discrete element method—continuum-based discrete element method. Then, the seismic responses of a high steep rock hill with two-side slopes are researched from the base of time, frequency and joint time–frequency domain using Hilbert–Huang transform and Fourier Transform. The findings are: first, the stress concentration phenomenon occurs at the top of the sliding mass, and then some tension and shear failure points appear, which expand from the top toward the toe of the sliding mass along the structural plane. At the same time, the number of tension failure points gradually increases. Then the toe of the sliding mass fails, and shears out from its toe which results in the landslide. If the material parameters are under the same conditions, the landslide in the middle of the slope occurs before that at the foot of slope, and the starting time of landslide and the arrival time of the peak ground acceleration are synchronous or the former slightly lags behind the latter. The difference of distribution and dissipation of earthquake energy in the sliding body and sliding bed is the major influence factor to induce the landslide. When the accelerations are small, the instantaneous frequency of accelerations between sliding bed and sliding body is generally consistent, the energy transmittance coefficients of the sliding structural plane and the controlled frequency band of the energy all range in a limitation; with the increase of the seismic intensity, the instantaneous frequency and the energy transmittance coefficients gradually decrease, and then they are steady within the lower limitation. At the same time, the controlled frequency band also shifts gradually from high frequency band to the lower one. Based on the input seismic wave, the peak acceleration amplifies as the increase of elevation, regardless of the monitoring points on the steep slope, gentle slope side or inside of the slope. Generally speaking, amplification of the vertical peak acceleration is stronger than that of the horizontal peak acceleration, and amplification of the peak acceleration on a steep slope is stronger than that on a gentle slope, and that of inside of the slope is the weakest amplification.     

Seismic reliability analysis of earth slopes under short term stability conditions

Different models were developed for evaluating the probabilistic three-dimensional (3-D) stability analysis of earth slopes and embankments under earthquake loading. The 3-D slope stability model assumed is that of a simple cylindrical failure surface. The probabilistic models evaluate the probability of failure under seismic loading considering the randomness of earthquake occurrence, and earthquake induced acceleration and uncertainties stemming from the discrepancies between laboratory-measured and in-situ values of shear strength parameters. The models also takes into consideration the spatial variabilities and correlations of soil properties. The probabilistic analysis and design approach is capable of obtaining the 2-D and 3-D static and dynamic safety factors, the probability of slope failure, the earthquake induced acceleration coefficient, the yield acceleration coefficient, the earthquake induced displacement, and the probability of allowable displacement exceedance taking into account the local site effect. The approach is applied to a well known landslide case: Congress Street Landslide in Chicago. A sensitivity analysis was conducted on the different parameters involved in the models by applying those models to the Congress Street landslide considering different levels of seismic hazard. Also, a sensitivity analysis was carried out to study the sensitivity of computed results to input parameters of undrained shear strength, and corrective factors. A comparison was made between the different models of failure. The parametric study revealed that the hypocentral distance and earthquake magnitude have major influence on the earthquake induced displacement, probability of failure and dynamic 2-D and 3-D safety factors.     

液化场地桩-土-桥梁结构地震相互作用简化分析方法

液化场地桩-土-桥梁结构地震相互作用分析属于桩基桥梁抗震设计中的一个关键科学问题,而目前尚缺乏合理的简化分析方法。鉴于此,直接针对振动台试验,基于Penzien模型,建立了液化场地桩-土-桥梁结构地震相互作用的数值分析模型与相应的简化分析方法。通过振动台试验验证了数值建模途径与简化计算分析方法的正确性,可用于液化场地桩基桥梁结构地震反应的分析,并且特别考虑砂层中孔压升高引起的砂土承载力衰减效应,推荐了计算参数的合理选取方法;据此进行了桩径、桩土初始模量比、砂土内摩擦角、上部桥梁结构质量等重要参数对液化场地桩-土地震相互作用影响的敏感性分析。研究表明：在液化场地条件下,随桩径和桩土初始模量比的增大,桩的峰值加速度、峰值位移减小,而桩的峰值弯矩则增大;随砂土内摩擦角增大,桩的峰值加速度、峰值弯矩、峰值应力均增大,而桩的峰值位移则减小;随上部结构配重增大,桩的峰值位移、峰值弯矩均增大。     

Expansion of the Nishinomiya Built Environment Database

The Nishinomiya Built Environment Database, which can be used to analyze the disaster process of the 1995 Hanshin-Awaji Earthquake Disaster in Nishinomiya City, has been expanded with new data entries. The database contains the following very detailed datasets: (1) the urbanization area base map, (2) casualty data, (3) three sets of building damage data surveyed by the Nishinomiya City, the Architectural Institute of Japan and the City Planning Institute of Japan, and the Kobe University, (4) building property data based on the real estate tax roll, (5) photographs of the damaged buildings with the information on the place and orientation of the picture, and (6) the estimated distribution of the seismic ground motion. The seismic ground motion was simulated for the southern part of Nishinomiya City and two verification sites in Kobe City and Amagasaki City. In the simulation, the borehole data of public facilities were used to model the surface soils as one-dimensional layers, taking into consideration the fact that the spatial distribution of the sediment/basement interface forms a slope. The model of the fault rupture process simulated the characteristics of the seismic motion at basement level, and amplification effects of the surface layers were evaluated based on multiple reflection theory. The distribution of peak ground acceleration and peak ground velocity was estimated from acceleration response spectra at each borehole point. In addition, the relationship between simulated seismic ground motion and building damage was studied based on newly proposed band-passed spectrum intensity using the expanded database. This confirmed that detailed categorization is necessary in order to evaluate the fragility functions, especially for reinforced concrete structures. The database should provide fundamental information for identifying the relationship between the ground motions and the extent and pattern of building damage, or the pattern of the occurrence of casualties.Presently     

Slope Instability in Static and Dynamic Conditions for Urban Planning: the ‘Oltre Po Pavese’ Case History (Regione Lombardia – Italy)

The paper describes a method for the evaluation of slope instability for urban planning purposes, applied in the test area Oltre Po Pavese (Regione Lombardia, Italy). A statistic and a probabilistic approach have been applied for the estimation of landslide activations and for the definition of potentially unstable areas. The displacement has been obtained through a simplified dynamic analysis, using deterministic methods: first the critical horizontal acceleration coefficient (K_c) has been evaluated, second the displacement has been calculated using the K_c values and the seismic input values, such as peak ground acceleration (PGA) and Arias intensity (Ia), through empirical relationships between displacement and Ia values for different K_c values. The results can be used by the regional government to give to the municipalities of the area a guide for the selection of the zones to be studied with future and more detailed analyses.