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1.
目前相关规范主要依据工程场地单点的测试数据进行砂土液化判别,而实际的三维土层结构可能非常复杂。研究土层结构对砂土液化的影响机制,有利于提高砂土液化判别结果准确度。分析2008 年5 月28 日发生的松原MS地震和2010—2011 年新西兰坎特伯雷地震序列中砂土液化点的分布,结果显示:砂土液化点主要位于高弯度河流的沉积相地层,凹岸侧蚀、凸岸沉积形成的边滩具有典型的二元结构,其顶部分布的黏土类不透水层有利于下伏饱和粉细砂等易液化土层的超孔隙水压累积;而辫状河流沉积相中,上覆黏土类不透水层间断分布特征明显。针对河流不同沉积相的土层结构建立简化场地模型,使用FLAC3D 进行砂土液化数值模拟,揭示出不同土层结构中超孔隙水压力的累积、消散和渗流过程机制,结果表明,河流沉积相土层结构对砂土液化场点的分布和地表变形具有显著影响。在合理的工程地质分区基础上,现有的液化判别方法有必要考虑场地的土层结构的影响。 相似文献
2.
Konstantinos I. Andrianopoulos Achilleas G. Papadimitriou George D. Bouckovalas 《Soil Dynamics and Earthquake Engineering》2010
This paper presents the constitutive relations and the simulative potential of a new plasticity model developed mainly for the seismic liquefaction analysis of geostructures. The model incorporates the framework of critical state soil mechanics, while it relies on bounding surface plasticity with a vanished elastic region to simulate the non-linear soil response. Key constitutive ingredients of the new model are: (a) the inter-dependence of the critical state, the bounding and the dilatancy (open cone) surfaces on the basis of the state parameter ψ, (b) a (Ramberg–Osgood type) non-linear hysteretic formulation for the “elastic” strain rate, (c) a discontinuously relocatable stress projection center related to the “last” load reversal point, which is used for mapping the current stress point on model surfaces and as a reference point for introducing non-linearity in the “elastic” strain rate and finally (d) an empirical index of the directional effect of sand fabric evolution during shearing, which scales the plastic modulus. In addition, the paper outlines the calibration procedure for the model constants, and exhibits its accuracy on the basis of a large number of laboratory element tests on Nevada sand. More importantly, the paper explores the potential of the new model by presenting simulations of the VELACS centrifuge tests of Models No 1 and 12, which refer to the free-field liquefaction response of Nevada sand and the seismic response of a rigid foundation on the same sand, respectively. These simulations show that the new model can be used successfully for the analysis of widely different boundary value problems involving earthquake soil liquefaction, with the same set of model constants calibrated on the basis of laboratory element tests. 相似文献
3.
液化条件对地表动力响应影响的有效应力动力分析 总被引：2，自引：2，他引：0
本文根据上海市区的典型地层分布及其力学参数,选取和构造了若干计算剖面,利用Biot动力固结方程和亚塑性边界面模型的排水有效应力动力分析方法,计算了地下水位、粉砂层厚度及其埋深等对地表峰值加速度和位移的影响,得到了一些有意义的结果。 相似文献
4.
考虑地基土液化影响的高层建筑地震反应分析 总被引：5，自引：0，他引：5
为了研究地基土液化对高层建筑地震反应的影响，本文简要介绍了分时段等效线性有效应力动力分析方法，且将其中的等效线性化方法改进为逐步迭代非线性方法，并利用ANSYS程序的参数化设计语言将这一分析方法并入ANSYS程序中，最后分析了考虑液化时桩基-高层建筑体系的地震反应。认为对于单层砂土-桩基-高层建筑体系来说，砂土的液化对上部结构地震反应有较大的影响；而对于本文采用的上海土-桩基-高层建筑体系来说，砂土层的液化未对上部结构的地震反应产生明显的影响。 相似文献
5.
编制完全耦合的三维排水有效应力动力反应分析程序，对可液化地基进行三维地震响应分析，探讨了不同土性参数、不同土层构成和不同附加压重等因素对可液化地基抗液化性能的影响。结果表明：在地震荷载作用下，天然饱和砂土地基中的超孔隙水压力随深度的增大而增大；在不同深度处，超孔压峰值到达的时刻比地震加速度峰值到达的时刻要晚；随输入地震加速度的减弱，深层处的超孔压开始消散或基本保持不变，浅层处的超孔压保持不变或略有上升，这一现象与土性参数、输入地震荷载的情况等因素有关；土性参数对土体本身的抗液化性能有重要影响，初始孔隙比越小，相对密度越大，土体的抗液化能力越强；附加压重有利于地基抗液化能力的提高；随着附加压重的增大，超孔压比减小；附加压重对地基中超孔隙水压力的增长有明显的抑制作用。 相似文献
6.
In this study, the effectiveness of liquefaction countermeasures for residential houses was explored using a fully coupled dynamic effective-stress finite element procedure. Numerical analyses were conducted on two wooden houses that were damaged to different degrees due to dune liquefaction during the 2007 Niigata Chuetsu-offshore earthquake. House A, which was only improved by horizontal drainage pipes to lower the ground water level, was completely destroyed; however, house B, which was improved by a horizontal drainage system, soil–cement mixtures, and steel-pipe piles, was slightly deformed. Numerical results show that the effects of the sand dune slope on the damage to the two houses were somewhat different. For house B, it was found that the steel-pipe piles were more effective. Two countermeasures generally led to a greater degree of reduction in both lateral and vertical displacements of house B than only a single countermeasure employed. In addition, the combined implementation of steel-pipe piles and soil–cement mixtures was the most effective among the cases with two countermeasures. 相似文献
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东圳水库大坝位于福建省莆田市城厢区,该水利枢纽处于华南沿海地震带北段,由于水库建设时我国尚未有抗震设防烈度标准,因此亟需对其抗震稳定性进行复核。以东圳水库大坝为原型,结合已有的地震资料,选用Byrne液化模型,采用FLAC3D软件,研究了在50年超越概率10%、5%和2%地震作用下坝体填料的液化特征及最终位移情况。结果显示,在地震作用下,坝体上游砂砾石填料会发生局部液化,且液化区随着地震强度的增大而增加,但尚未出现大面积连续液化区;坝体填料发生液化后,产生了有限度的塑性变形,其变形量也随着地震强度的增大而有所增加;除坝顶较小区域外,坝体总位移量相对较小,对大坝整体稳定性不会产生显著影响。研究结论可以为大坝的抗震加固和治理措施的选择提供依据和参考。 相似文献
9.
S. Bernardie E. Foerster H. Modaressi 《Soil Dynamics and Earthquake Engineering》2006,26(11):1038-1048
The destructive 1999 Chi–Chi earthquake (Mw 7.5) was the largest inland earthquake in Taiwan in the 20th century. Several observations witness the non-linear seismic soil response in sediments during the earthquake. In fact, large settlements as well as evidence of liquefaction attested by sand boils and unusual wet ground surface were observed at some sites. In this paper, we present a seismic response simulation performed with CyberQuake software on a site located within the Chang-Hwa Coastal Industrial Park during the 1999 Chi–Chi earthquake in Taiwan. A non-linear multi-kinematic dynamic constitutive model is implemented in the software. Computed NS, EW and UP ground accelerations obtained with this model under undrained and two-phase assumptions, are in good agreement with the corresponding accelerations recorded at seismic station TCU117, either for peak location, amplitudes or frequency content. In these simulations, liquefaction occurs between depths 1.3 and 11.3 m, which correspond to the observed range attested by in place penetration tests and other liquefaction analyses. Moreover, the computed shear wave velocity profile is very close to post-earthquake shear wave velocity profile derived from correlations with CPT and SPT data. Finally, it is shown that in non-linear computations, even though a 1D geometry is considered, it is necessary to take into account the three components of the input motion. 相似文献
10.
A revised magnitude scaling factor (MSF) relationship for CPT-based and SPT-based liquefaction triggering analyses is presented in this paper. The revised MSF relationship incorporates functional dependency on the soil characteristics [represented by clean sand equivalent penetration resistances in the present form] as well as on earthquake magnitude. The revisions in MSF are based on the examination of cyclic testing results for a broad range of soil types and densities, analyses of strong ground motion records to develop relationships for the equivalent number of loading cycles for different soil properties, and the synthesis of those results into an MSF relationship suitable for implementation in practice. A separate study [2] showed that use of the revised MSF relationship in CPT-based and SPT-based liquefaction triggering procedures is well-supported by the case history databases. Other factors known to fundamentally influence the MSF are discussed. 相似文献
11.
In this study, two different earthquake input models are introduced, i.e. massless foundation model and viscous-spring boundary input model considering radiation damping. Linear elastic and nonlinear contraction joint opening analyses of the 210 m high Dagangshan arch dam under construction in China are performed using the two different earthquake input models. First, the responses of the three-dimensional (3-D) canyon without the dam are analyzed, respectively, with massless-truncated foundation and with viscous-spring boundary; second, linear and nonlinear analyses of the dam–foundation system are performed and compared by using the two input models. Hydrodynamic effects are considered using finite element discretization for incompressible reservoir fluid. It is concluded that stresses and displacements and contraction joint opening in the dam are significantly reduced both in linear and nonlinear analyses when using viscous-spring boundary model. Interestingly, in the case of linear analysis of the Dagangshan, the massless foundation input model with a relatively higher damping ratio of 10% leads to a comparable response of the dam to that using viscous-spring boundary model. In addition, the maximum tensile stresses from nonlinear analysis are 10–25% larger than that of the corresponding linear cases due to a partial release of the arch action. 相似文献
12.
地震波是一种随机的、不规则作用的动荷载脉冲,可分为振动型和冲击型。不同类型的地震波会对砂土液化和变形等产生重要影响,而传统的砂土震陷计算方法往往忽视这种因素,只考虑最大加速度幅值。通过编写UMAT子程序,在非线性有限元软件ABAQUS中开发亚塑性砂土边界面模型,对不同地震波类型下不同相对密度的砂土进行动单剪试验模拟,得到一系列砂土剪应变及竖向应变的时程曲线,并与室内试验结果进行对比分析。研究表明:在同一工况下,同类型的地震波引起的砂土竖向应变相近,不同类型引起的竖向应变差异明显;振动型地震波比冲击型引起的竖向应变更大。 相似文献
13.
This paper investigates the effect of nature of the earthquake on the assessment of liquefaction potential of a soil deposit during earthquake loading. Here, the nature of the earthquake is included via the parameter V, the ‘pseudo-velocity’, that is the gross area under the acceleration record of the earthquake at any depth below the ground surface. By analysing a number of earthquake records from different parts of the world, a simple method has been outlined to assess the liquefaction potential of a soil deposit based on the pseudo-velocity. For many earthquakes occurred in the past, acceleration records are available or can be computed at the ground level or some other depth below the ground surface. Therefore, this method is a useful tool at the preliminary design stage to determine the liquefaction potential before going into a detailed analysis. Validation of the method is carried out using a database of case histories consisting of standard penetration test values, acceleration records at the ground surface and field observations of liquefaction/non-liquefaction. It can be seen that the proposed method has the ability to predict soil liquefaction potential accurately, despite its simplicity. 相似文献
14.
The model presented in the companion paper is validated in both the linear and nonlinear cases under steady-state single frequency harmonic and transient ground motions. The crest acceleration responses of the Santa Felicia earth dam subjected to the 1971 San Fernando earthquake and of the Long Valley earth dam subjected to the strongest of the 1980 Mammoth Lake earthquakes are computed and compared with the motions recorded at the site. Acceleration time histories for the solid and fluid phases in both horizontal and vertical directions, as well as stress-strain and pore water pressure-strain time histories for points along the height of the dam are presented. The ability of the model to simulate the occurrence of liquefaction in a dam is also demonstrated. 相似文献
15.
应用FLAOD实现自由场液化数值模拟试验.试验结果验证了砂土液化典型特征:超静孔隙水压升高,有效应力降低,体积压缩积累增大.证实了液化的隔振作用:砂土在液化状态变为流体,不能传递剪力,液化时砂土位移、速度、加速度振幅显著降低,剪应力降低,动水向上渗流,土体向下沉降,水平残留不可恢复位移.球压应力、有效压应力、动水压力满... 相似文献
16.
饱和砂土液化是由地震引起的一种最常见的工程地质现象,也是造成重大地震灾害的主要原因之一。由于成因的复杂性和所造成灾害的严重性,饱和砂土液化一直是土动力学和岩土地震工程研究领域的重要课题。针对饱和砂土液化问题,基于开源地震工程数值计算平台OpenSees,对材料库中的4种砂土本构模型进行数值计算。采用二维u-p单元模拟土颗粒位移和孔隙水压力,分析和对比4种模型在循环动力荷载作用下的加速度、超孔隙水压力、位移、剪应力-剪应变和平均有效应力路径方面的响应结果。研究结果表明:(1)砂土对输入加速度表现出一定的放大效应,对于不同的模型,该放大效应存在一些差异;(2) Stress Density模型在循环动力荷载作用下易产生永久变形;(3)在循环动力荷载作用下,PDMY模型和CycLiqCPSP模型的强度逐渐降低,直到完全消失;(4) Stress Density模型和Manzari Dafalias模型在循环动力荷载下表现出明显的剪胀效应。研究成果对砂土液化的数值模拟问题具有重要的理论价值,可为饱和砂土的液化模拟和砂土本构模型的选取提供参考。 相似文献
17.
基于谐波入射下的波动理论频域精确解,导出线性时域精确解,并在Matlab环境中编制相应的计算程序;选取8个简化的中硬场地剖面,用LSSRLI-1、精确解和SHAKE2000三种方法计算各场地在不同输入条件下的地震反应。结果表明:程序计算所得地表反应谱和土体剪应变分布与SHAKE2000结果一致;LSSRLI-1方法得到的地表反应谱与前二者结果一致;LSSRLI-1方法在某些情况下得到的土体剪应变分布与另外二者结果存在较大偏差,该偏差对地表反应谱有着不可忽略甚至非常显著的影响。 相似文献
18.
液化地基自由场振动台模型试验研究 总被引：4，自引：0，他引：4
进行了液化场地自由场振动台试验,试验采用柔性容器以减小边界影响,采用上覆黏土层的饱和砂土作为模型土。试验中再现了液化场地土的震害现象。得出的主要规律有:随着振次的增加,地基的频率迅速降低,阻尼比迅速增大;砂土对地震动起滤波作用;土体的加速度峰值反应在高度上呈"K"形分布;当最初加速度峰值到达前,砂土层中的孔压比存在负值;震后土中振动孔隙水压力不一定随振动的停止而立即开始消散,在短期内可能继续增长。 相似文献
19.
遮帘式板桩码头作为一种新型的板桩结构型式,其抗震性能研究是设计建造过程中的重要环节。在FEM-FDM水土耦合计算的平台上引入循环弹塑性本构模型,借助FORTRAN编程软件形成饱和砂土动力液化分析的数值方法,可有效模拟饱和砂土在地震动力作用下的非线性及大变形特性,同时也可模拟砂土液化流动对遮帘桩和前墙的动土压力。研究表明:地震作用下可液化土层超孔隙水压力比增长并发生较大的水平流动变形,对前墙的水平破坏大于竖向破坏;前墙剪力最大值位于海床与前墙交界处;遮帘桩剪力最大值位移与前墙底平行的位置;后拉杆拉力逐渐变大,前拉杆拉力逐渐变小。通过对板桩码头地震液化灾害的分析,可为抗震和抗液化设计提供参考依据。 相似文献
20.
The joint between concrete slab and rockfill is designed as welded contact in the classical modeling of concrete-faced rockfill (CFR) dams and earthquake response of the CFR dams is determined by this method. In this study, linear and nonlinear response of Torul CFR Dam including interface element between concrete slab and rockfill were investigated for the duration of strong seismic excitation. The finite element analyses were performed by employing both cases, empty and full reservoir, to research the effect of the reservoir water on the earthquake response of the dam. The reservoir water was modeled with fluid finite elements by the Lagrangian approach. The Drucker-Prager model was used in nonlinear analyses for concrete slab, rockfill and soil materials. According to finite element analyses, displacement and stress components were increased by hydrodynamic pressure. The nonlinear response of the concrete slab was monitored about the peak ground acceleration (pga). This study reveals that the size of sliding zone increases with increasing acceleration amplitudes. 相似文献