共查询到19条相似文献，搜索用时 187 毫秒
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基于地震模拟振动台试验,配制3组不同平均粒径和3组不同细粒含量的6个砂土模型,通过埋置于砂土内部的传感器监测模型内部不同位置的超孔隙水压力等指标,分析砂土模型内部的超孔隙水压力时程曲线及孔压比时程曲线,归纳出地震波加载峰值、砂土平均粒径、细粒含量及埋置深度等因素对饱和砂土液化特性的影响规律。试验结果表明:随着地震波加载峰值的增大,砂土模型液化程度逐渐增大,液化势逐渐增大,抗液化强度逐渐减小;随着砂土埋置深度的增加,砂土细粒含量的增加,砂土平均粒径的增加,砂土模型液化程度逐渐减小,液化势逐渐减小,其抗液化强度逐渐增大。同时,试验结果还表明,砂土液化各影响因素对砂土液化的影响程度依次为地震波强度＞砂土埋置深度＞砂土平均粒径、细粒含量。试验结果可为后续数值模拟的参数选取提供支持,为研究其他因素对砂土液化的影响提供参考。 相似文献
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本文利用二维信息分配概念及模糊近似推论公式对砂土震动液化势进行了定量研究。文中利用日本学者时松孝次收集的世界各地100个地点的砂土震动液化势资料建立了应力比(τd/σ_0~1)、修正标准贯入击数(N_1)和砂土震动液化势之间的模糊关系(R),并结合作者收集的45个地点的砂土震动液化势资料对该方法进行了验证,其成功率达82%达到了今人满意的程度。 相似文献
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1976年唐山地震期间,附近一些地区出现了砂土液化现象。本文根据工程勘探中的实例及实验数据,进行了砂土液化作用的统计和综合预测。文章中采用贝叶斯准则下的逐步判别分析方法,对唐山地区已知液化地点和非液化地点,作了五种检验计算,挑选出准确度及可靠性最高的变量模式。从而,对于当地震为Ⅷ度烈度时的砂土液化进行了预测。五种预测结果相同,互相印证,可靠性高,分组最大后验概率大多在0.99以上。在此条件下,外推预测结果可信。工程实践中,迫切需要对砂土液化进行综合性预测,而一般采用地质学或试验方法,仅能对砂土液化作单因素或少量因素下的预测,本文提出了综合性的通用预测方法,为砂土液化统计预测提供了新途径。砂土液化是平原地区的一种重要地震灾害。国内外多次大地震中,都曾因饱水砂土受到地震作用,引起孔隙水压增高及砂粒间的结合力和摩擦力降低,而使砂层发生液化状态的流动,并伴随有地基承载能力降低或失效。1964年以来,新潟地震及阿拉斯加地震时,由砂土液化造成了罕见的灾害。激发了各国、尤其是美国和日本对砂土液化预测的研究。但还多是单因素或少量因素影响下的分析方法。未能进行综合分析及推断。采用数理统计方法,可以综合分 相似文献
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砂土液化是一种重要震害现象。近年来,关于影响砂土液化各因素的研究愈发引人注目。但常用的实验及地质学方法,仅限于研究单一或少量因素与液化间的关系。而缺乏对形成砂土液化的多种条件的综合性分析。笔者采用数理统计的方法,对唐山地震时,影响砂土液化发生的十五个因素进行了综合性分析。初步认识了它们的相对重要性 相似文献
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饱和砂土地震液化判别的分形插值模型 总被引：1，自引：0，他引：1
借鉴分形基本理论,提出了基于分形插值模型的饱和砂土地震液化判别方法.该方法首先选取影响饱和砂土地震液化判别的7个主要因素,根据分类标准,采用在每级标准中随机内插的方法,得到40个标准样本,用于构建饱和砂土地震液化判别的分形插值模型;其次根据最大似然分类原则确定每个饱和砂土地震液化判别指标的评价分维数;然后利用加权求和法计算样本的综合评价值,并根据样本综合评价值与经验等级之间的关系建立分形插值评价模型;最后,进行了实例分析结果表明:该模型的评价结果合理、客观,计算得到的每个样本具体得分值,即使对属于同一级的样本也可以给出其地震液化程度的顺序,为饱和砂土地震液化评价工作提供了一种新的研究方法与思路. 相似文献
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《世界地震工程》2010,(Z1)
将液化及液化后状态的砂土视为流体状态,研究发现液化及液化后砂土是一种剪切稀化非牛顿流体。对于液化前高孔压状态下的流动特性也值得探讨。根据落球黏度计的原理,开发了饱和砂土液化前流动特性的模型试验装置。在模型箱中铺设饱和砂土,模型箱底部与一水箱相连,提高水箱高度可以使模型箱中的饱和砂土产生超孔压。模型箱的砂土中埋设一个可以水平拉动的钢球,通过监测钢球水平运动的速度和所受的阻力来计算砂土的表观黏度,得到饱和砂土液化前高孔压状态下的流动特性。试验中考虑了超孔压比、钢球运动速度对结果的影响。试验表明,饱和砂土在液化前高孔压状态下,表观黏度均随着应变率的增大而减小,呈现出剪切稀化非牛顿流体特性,同时随着超孔压比的提高,表观黏度也逐渐减小。 相似文献
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砂土地震液化问题是岩土地震工程学的重要研究课题之一。在分析模糊神经网络原理的基础上,利用减法聚类算法对自适应模糊推理系统进行优化,并建立了砂土地震液化的模糊神经网络模型。然后,将该模型用于实际工程的砂土液化判别中,并与传统砂土液化判别方法结果进行对比。判别结果表明:文中建立的模糊神经网络模型具有较强的学习功能,用于砂土地震液化判别中是可行的和有效的。 相似文献
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从简单场地条件下砂土液化的判别入手,系统介绍一般场地液化判别的基本步骤,重点分析在复杂工程场地条件下,如何全面考虑各种因素以合理选取地震液化判据。文中结合某大桥地基土液化判别实例,多方位探讨判别特殊重大工程地基土液化的有效方法,讨论了液化深度问题,与此同时,尚考虑到液化和滑塌等地质灾害的相关效应 相似文献
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桩贯入地基过程的动画仿真 总被引：1，自引：0，他引：1
本文通过三维显式有限元计算结果，对混凝土桩打基的过程进行了三堆动力反应分析，褡完成了此过程的动画仿真研究，研制成可携带的录相带工匠仿真动画，形象，生动，直观地再现了桩贯入地基过程中撞击波在桩体，地基中的传播，桩体与地基间的相对接触，滑移及桩锤与桩头部间的接触撞击过程。 相似文献
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Pre-shear history has been shown to be a critical factor in the liquefaction resistance of sand. By contrast to prior experimental studies in which triaxial shear tests were used to examine the effects of pre-shear on the liquefaction resistance of sand, hollow cylinder torsional shear tests were used in this study to avoid the influence of the inherent anisotropy that is inevitably produced during the sample preparation process because of gravitational deposition. A series of cyclic undrained shear tests were performed on sand samples that had experienced medium to large pre-shear loading. The test results showed that the liquefaction resistance of sand can be greatly reduced by its pre-shear history, and a pre-shear strain within the range from 0.1% to 5% can cause sand to be more prone to liquefaction. During the cyclic shear tests, the samples that had experienced pre-shear loading exhibited different behaviors when cyclic shear loading started in different directions, i.e., the clockwise direction and the counterclockwise direction. If the cyclic loading started in the identical direction as the pre-shear loading, then the mean effective stress of the sand was almost unchanged during the first half of the loading cycle; if the cyclic loading started in the direction opposite to that of the pre-shear loading, then the mean effective stress decreased significantly during the first half of the loading cycle. However, this anisotropic behavior was only remarkable during the first loading cycle. From the second cycle onward, the speeds of the decrease in the mean effective stresses in the two types of shear tests became similar. 相似文献
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Three dynamic centrifuge model tests were conducted at an acceleration of 80g to simulate the seismic responses of level sand deposits: an intra-silt layer was embedded in two of these sand deposits at different depths. The effects of a low-permeability intra-silt layer on the build-up and dissipation of excess pore-water pressure, surface settlement, and the related liquefaction mechanism were investigated. An intra-silt layer modifies the seismic response of the sand deposit, reduces the extent of liquefaction, and thus decreases surface settlement. The depth of the intra-silt layer is one of the factors influencing the seismic responses of the sand deposits. The magnitude of the surface settlement is proportional to the degree of liquefaction in the sand deposit. The high positive hydraulic gradients appearing in both the intra-silt layer and in the sand deposit lying on the intra-silt layer can break a thinner or weaker top layer and result in sand boiling. Our visual animation of the ratio of the excess pore-water pressure and the lateral displacement revealed that the liquefaction front travels upward during shaking and the solidification front travels upward after shaking. 相似文献
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During the 1999 Chi-Chi, Taiwan earthquake, many sand boiling phenomena were observed in central Taiwan, which caused severe ground settlement and structure damages. According to the installed accelerograms, the peak ground surface horizontal accelerations in the liquefaction-affected areas range from 774.42 to 121.3 gal. The writers carried out an extensive investigation of soil liquefaction in this earthquake. In this paper, we present results of the CPT exploration and post-earthquake liquefaction analysis. Two hundred and seventy five (275) cone penetration test data were collected from the liquefaction-affected areas, and 46 liquefaction case histories and 88 non-liquefaction case histories were derived that can be used to evaluate the accuracy of existing liquefaction evaluation models. In addition, the strength of the liquefied soils after earthquake and the implication of its liquefaction potential in the future event are discussed. 相似文献