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天然地震作用下的饱和砂土液化问题是岩土地震工程研究的重要课题之一。目前,国内推荐使用的规范法是基于实际地震液化调查而建立的判别方法,方法本身缺乏理论基础。采用Finn液化本构关系建立了砂土液化数值分析模型,运用有限差分法的动力时程分析模块,分析了饱和砂土地基的地震液化问题。结果表明,将Finn本构模型应用于砂土液化分析,可以较好地给出地震作用过程中孔隙水压力和有效应力变化的规律。 相似文献
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地基液化导致沉箱码头破坏及地基加固方法的非线性数值分析 总被引:2,自引:0,他引:2
地震作用引发的地基液化,往往导致沉箱基础的破坏。本文基于Biot两相饱和多孔介质动力耦合理论,采用FE-FD耦合数值分析方法,对液化海床沉箱基础的地震反应进行非线性有效应力分析。在数值分析过程中,建立了以土骨架位移和超静孔隙水压力表达的us-pw动力固结方程和循环弹塑性本构模型,该方法能够很好地模拟地震作用下沉箱码头的动力特性及液化破坏的影响。通过数值模拟计算,分析了采用碎石桩进行置换砂区域的防液化加固方法,并就碎石桩处理区域的选择提出了建议。 相似文献
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坝基地震液化特性及动力稳定性分析 总被引:3,自引:1,他引:2
为了考虑水库大坝地基地震液化及动力特性,首先通过室内动三轴试验研究混黏土的粉土、粉砂在动荷载作用下的孔压累积特性,提出了选择双幅应变达到5%作为土样液化的标准;然后采用现场标贯试验和室内动三轴试验对水库坝基中的粉土、粉砂层进行了液化判别,并对判别结果进行了对比分析;同时在液化判别的基础上利用有效应力动力分析方法对坝基土体进行了考虑渗流和不考虑渗流的地震液化的非线性动力有限元分析,并将液化的判别结果与现场标贯试验、室内动三轴试验的判别结果进行对比,从中得出一些有益的结论可供类似工程参考。 相似文献
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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
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砂土液化造成了大量建筑物的破坏,但目前对砂土液化地基中地铁地下结构的地震反应研究相对较少,尤其对微倾斜液化地基中地铁地下结构地震反应的研究更为缺乏。基于有限单元法,采用已开发的砂土液化大变形动力本构模型模拟液化土层的剪切大变形,采用基于ALE(Arbitrary Lagrange-Euler)算法的有限单元网格动态自适应调整技术解决土体液化大变形发生后有限单元的畸变问题,建立了地面微倾斜液化地基中土体-地下结构非线性动力相互作用的数值分析模型,分析了地面倾角变化对地铁车站周围地基液化分布特征、车站结构周围土层侧移变形特征、地下结构上浮和应力反应的影响规律,揭示了微倾斜液化地基中地铁地下车站结构的地震反应特征。 相似文献
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在二维应力状态下,地震在土体中不仅产生水平剪应力τvh,而且引起一般情况不可忽略的竖向动正应力σv及水平动正应力σh,在研究地震触发砂土液化的应力条件及液化判别方法时尖考虑这三种动应力的联合作用,本文基于莫尔-库伦强度准则,采用总应力方法,能够考虑地震动水平剪应力τvh,竖向动正应力σv及水平动正应力σh共同作用的砂土液化判别准则,并且经北京密云水库白河主坝震害为例,说明了这种液化判别准则的有效性及其使用方法。 相似文献
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利用基于Biot的饱和多孔介质理论和砂土多重机构模型的动力分析有限元程序FLIP,对遭受M6.7地震的国外某深厚砂质覆盖层土坝进行有效应力动力分析,研究坝体和地基的动力反应特性及其超静孔隙水压力的分布规律。通过对坝体加速度和永久变形的计算结果与现场实测数据的比较分析,证明两者之间存在一定差异,但计算结果基本上反映坝体加速度与永久变形的实际分布特征,从而说明采用的数值计算方法和本构模型具有一定精度。根据计算结果可以得出:坝体无液化发生;坝底上游浅层地基可能会发生局部液化,但范围较小,可以不进行加固处理;坝趾附近浅层地基可能会发生较大范围的液化,因此须采取相应的抗液化加固措施。 相似文献
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M. Kawano K. Asano H. Dohi S. Matsuda 《Soil Dynamics and Earthquake Engineering》2000,20(5-8):493-507
The linear and non-linear responses of surface soil layers have been predicted through the simultaneous simulation test against the observed ground motions at the six sites in Kobe City during the 1995 Hyogo-ken Nanbu earthquake. The total stress analysis method and the effective stress analysis method have been applied for the rough and detailed verification of the predicted non-linear dynamic behavior at the PIS and RKI sites including the liquefaction phenomenon. The shear strain distribution along depth, the ratio of excess pore water pressure to initial effective stress, the liquefaction strength parameters to initial effective stress, and the stress–strain curve during the earthquake at the PIS site have been investigated when the predicted ground motion could simulate successfully the observed acceleration time histories and response spectra in the non-linear range. 相似文献
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An effective stress method is presented for analysis of seismic response and liquefaction of irregular ground including soil–structure interaction, based on an implicit–explicit finite element method. A pore water pressure is computed with iteration from the total stress considering an undrained condition. The simulated pore water pressure is in reasonably good agreement with the experimental data. The proposed method of analysis is compared with other well-known methods for a one-dimensional model, which is in good agreement. The present effective stress method is also applied to liquefaction problems involving a two-dimensional soil–structure model. The structure is modelled by not only a rigid model but also as a multi-degree-of-freedom system with bi-linear springs. The numerical results are considered to be significant from the viewpoint of earthquake engineering. 相似文献
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Three groups of dynamic triaxial tests were performed for saturated Nanjing fine sand subjected to uniform cyclic loading.
The tested curves of the excess pore water pressure (EPWP) ratio variation with the ratio of the number of cycles are provided.
The concept of the EPWP increment ratio is introduced and two new concepts of the effective dynamic shear stress ratio and
the log decrement of effective stress are defined. It is found that the development of the EPWP increment ratio can be divided
into three stages: descending, stable and ascending. Furthermore, at the stable and ascending stages, a satisfactory linear
relationship is obtained between the accumulative EPWP increment ratio and natural logarithm of the effective dynamic shear
stress ratio. Accordingly, the EPWP increment ratio at the number of cycles N has been deduced that is proportional to the log decrement of effective stress at the cycle number N-1, but is independent of the cyclic stress amplitude. Based on the analysis, a new EPWP increment model for saturated Nanjing
fine sand is developed from tested data fitting, which provides a better prediction of the curves of EPWP generation, the
number of cycles required for initial liquefaction and the liquefaction resistance. 相似文献