液化地基自由场振动台模型试验研究

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。     

Probabilistic evaluation of liquefaction potential under earthquake loading

This paper presents a procedure to perform the risk analysis for ground failure by liquefaction. The first part of this study describes the differential equation of a smooth hysteretic model to characterize the behavior of the soil under random loading. The parameters of the proposed model to represent the experimental relationship are discussed. The second part of this study is to develop a method to calculate the probability that a specified volume of soil will liquefy at a given depth in the deposit. The liquefaction is defined as the result of cumulative damage caused by seismic loading. The fatigue life of soil can be determined on the basis of the N---S relationship and Miner's cumulative damage law. The rain-flow method is used to count the number of cycles of stress response of the soil deposit. Finally, the probability of liquefaction is obtained by integration over all the possible ground motion and the fragility curves of liquefaction potential. The sensitivity of the reliability against liquefaction to soil system parameters is also examined.     

新疆巴楚地震液化宏观现象的对比分析

2003年2月24日新疆巴楚-伽师地区发生6.8级地震,出现了唐山、海城地震后近30年我国最具规模的砂土液化现象。本文通过现场调查和资料分析,并与以往大地震液化比较,提出了此次地震液化宏观现象的认识,包括液化分布特征、喷水冒砂形态、液化震害和工程地质条件等几个方面。结果表明,此次地震液化宏观现象与我国以往几次大地震有很多不同,具有很大的研究价值。     

Modeling granular soils liquefaction using coupled lattice Boltzmann method and discrete element method

In this paper, a novel coupled pore-scale model of pore-fluid interacting with discrete particles is presented for modeling liquefaction of saturated granular soil. A microscale idealization of the solid phase is achieved using the discrete element method (DEM) while the fluid phase is modeled at a pore-scale using the lattice Boltzmann method (LBM). The fluid forces applied on the particles are calculated based on the momentum exchange between the fluid and particles. The presented model is based on a first principles formulation in which pore-pressure develops due to actual changes in pore space as particles׳ rearrangement occurs during shaking. The proposed approach is used to model the response of a saturated soil deposit subjected to low and large amplitude seismic excitations. Results of conducted simulations show that at low amplitude shaking, the input motion propagates following the theory of wave propagation in elastic solids. The deposit response to the strong input motion indicates that liquefaction took place and it was due to reduction in void space during shaking that led to buildup in pore-fluid pressure. Soil liquefaction was associated with soil stiffness degradation and significant loss of interparticle contacts. Simulation results also indicate that the level of shaking-induced shear strains and associated volumetric strains play a major role in the onset of liquefaction and the rate of pore-pressure buildup.     

砂土地震液化后大位移室内试验研究探讨

砂土地震液化引起的地面大位移会对结构产生灾难性的破坏，这已引起了人们的重视，但对其进行研究时间较短。作者在大量阅读有关资料的基础上，详细介绍了液化后地面大位移研究的室内试验设备、试验方法、试样的制备、试验的主要规律及国内的研究现状，并对试验技术和结果进行了探讨，指出以室内试验为基础提出液化后的本构模型及实用计算方法是今后工作的重点。     

A discontinuous Galerkin method for seismic soil–structure interaction analysis in the time domain

A technique for modeling transient wave propagation in unbounded media is extended and applied to seismic soil–structure interaction analysis in the time domain. The technique, based on the discontinuous Galerkin method, requires lower computational cost and less storage than the boundary element method, and the time‐stepping scheme resulting from Newmark's method in conjunction with the technique is unconditionally stable, allowing for efficient and robust time‐domain computations. To extend the technique to cases characterized by seismic excitation, the free‐field motion is used to compute effective forces, which are introduced on the boundary of the computational domain containing the structure and the soil in the vicinity of the structure. A numerical example on a dam–foundation system subjected to seismic excitation demonstrates the performance of the method. Copyright © 2003 John Wiley & Sons, Ltd.     

地震波正演模拟中无单元Galerkin法初探

无单元Galerkin法作为一种新型有限元开始应用于地震勘探领域.地震波正演模拟结果的好坏取决于基函数类型、节点分布、节点编号方式、稳定条件以及边界条件等因素,通过对各个因素的分析可知:基函数的阶数越高,结果精度越高,但数据量和运算量就越大;不同的基函数联合使用时,会带来数值计算上的误差;节点可以不均匀分布,但必须满足空间采样要求;合理的节点编号有利于节约数据量和减少运算量;采用衰减边界条件,能有效克服无单元Galerkin法在边界上处理的难点.以上分析结果,对无单元Galerkin法在地震波正演模拟中的应用具有一定的指导意义.     

砂土液化大变形本构模型及在ABAQUS软件上的实现

基于Yang和E lgam al等人提出的砂土液化大变形本构模型,对该模型的建立过程进行了详细的推导,基于新的嵌套屈服面硬化规则,对原有模型的硬化规则的不连续性做了改进,把该本构模型扩展应用到三维液化大变形的数值分析中,实现了基于ABAQUS大型商用软件计算平台上砂土液化大变形的计算子程序的开发,基于该计算平台和开发的本构模型,对动三轴试验体系中砂土试样的液化过程进行了数值试验分析,给出了试验过程中试样的竖向动位移、整体竖向应力应变关系滞回曲线和动孔压时程曲线的数值计算结果。文中初步验证了该模型在ABAQUS上开发的子程序的可靠性和数值计算模型的可行性,模型的可靠性及其子程序的稳定性还需通过试验结果和数值计算结果的对比分析与进一步验证。     

液化场地桩-土-桥梁结构动力相互作用振动台试验研究进展

本文在全面归纳与总结液化场地桩－土－桥梁结构动力相互作用振动台试验及与之相关领域的国内外研究进展基础上，直接针对我国桥梁工程中的主要震害问题，提出在我国开展液化场地桩－土－桥梁结构动力相互作用振动台试验研究的必要性，并阐述作者对液化场地桩－土－张桥梁结构动力相互作用振动台试验中若干问题的认识。     

场地土液化引起的地下管道上浮反应研究

本文利用虚功原理,建立了场地土液化引起的地下管道的上浮反应分析模型,用弹性地基梁来模拟地下管道,并考虑了土的非线性约束作用、管道的初始变形、液化区长度、管道的初始轴力等的影响。采用非线性增量有限元法,对场地土液化引起的地下管道的上浮反应进行了研究,给出了部分计算结果。     

Probability density evolution method for seismic liquefaction performance analysis of earth dam

To investigate the seismic liquefaction performance of earth dams under earthquake loading, we present a new methodology for evaluating the seismic response of earth dams based on a performance‐based approach and a stochastic vibration method. This study assesses an earthfill dam located in a high‐intensity seismic region of eastern China. The seismic design levels and corresponding performance indexes are selected according to performance‐based criteria and dam seismic codes. Then, nonlinear constitutive models are used to derive an array of deterministic seismic responses of the earth dam by dynamic time series analysis based on a finite element model. Based on these responses, the stochastic seismic responses and dynamic reliability of the earth dam are obtained using the probability density evolution method. Finally, the seismic performance of the earth dam is assessed by the performance‐based and reliability criteria. Our results demonstrate the accuracy of the seismic response analysis of earth dams using the random vibration method. This new method of dynamic performance analysis of earth dams demonstrates that performance‐based criteria and reliability evaluation can provide more objective indices for decision‐making rather than using deterministic seismic acceleration time series as is the current normal practice. Copyright © 2016 John Wiley & Sons, Ltd.     

A case-based reasoning method of recognizing liquefaction pits induced by 2021 MW 7.3 Madoi earthquake

Earthquake-triggered liquefaction deformation could lead to severe infrastructure damage and associated casualties and property damage. At present, there are few studies on the rapid extraction of liquefaction pits based on high-resolution satellite images. Therefore, we provide a framework for extracting liquefaction pits based on a case-based reasoning method. Furthermore, five covariates selection methods were used to filter the 11 covariates that were generated from high-resolution satellite images and digital elevation models (DEM). The proposed method was trained with 450 typical samples which were collected based on visual interpretation, then used the trained case-based reasoning method to identify the liquefaction pits in the whole study area. The performance of the proposed methods was evaluated from three aspects, the prediction accuracies of liquefaction pits based on the validation samples by kappa index, the comparison between the pre- and post-earthquake images, the rationality of spatial distribution of liquefaction pits. The final result shows the importance of covariates ranked by different methods could be different. However, the most important of covariates is consistent. When selecting five most important covariates, the value of kappa index could be about 96%. There also exist clear differences between the pre- and post-earthquake areas that were identified as liquefaction pits. The predicted spatial distribution of liquefaction is also consistent with the formation principle of liquefaction.     

不均匀场地土液化引起的地下管道上浮反应研究

本文采用非线性增量有限元迭代法,对不均匀场地土液化引起的地下管道的上浮反应进行了研究,考虑了液化土3种不均匀的情况,给出了一些计算结果。     

地震作用下液化场地变截面桩与等截面桩的动力响应对比分析

为研究液化场地变截面桩的动力响应,依托翔安大桥实体工程,采用有限元软件,建立变截面桩－土和等截面桩－土相互作用模型,模拟液化场地变截面桩及等截面桩在地震作用下的振动反应,分析在地震作用下变截面位置不同的变截面桩及等截面桩的动力响应特征。结果表明:地震作用下,液化土层不同深度处的孔压比变化规律基本相同,均从0逐渐增大最后趋于稳定;变截面桩的桩身加速度和桩身位移均大于等截面桩,且桩顶加速度峰值出现的时刻均滞后于桩底;在饱和砂土层处,桩身位移变化趋势均较陡;变截面桩的桩身弯矩峰值和桩身剪力峰值均大于等截面桩,且其峰值出现的位置较等截面桩深;地震作用下,变截面桩及等截面桩的弯矩与剪力均在安全范围之内;液化场地变截面梁桥桩基础抗震设计时,应着重分析液化土层与非液化土层分界面以下的抗弯能力设计及液化土层中抗剪能力设计。     

Kostadinov与Yamazaki液化识别方法的可行性剖析

研究具有代表性的Kostzadinov and Yamazaki液化识别方法的可行性,特别是对软土和液化场地的识别能力.选择包含了13个软土场地的52个场地实际地震纪录,分析结果表明,该方法识别成功率随场地类别变软而显著降低,对中硬、中软和软土非液化场地成功率分别为100％、70.6％和46.2％,对液化场地成功率为6...     

液化土中管道上浮反应的影响因素研究

本文在以前研究的基础上,对场地土液化引起的地下管道上浮的影响因素进行了较为全面的研究,包括液化土的弹簧刚度、管道的初始变形、液化区长度、管道的初始轴力、管道材料、管道半径等的影响.得到了一些有益的结论.     

Wavelet analysis for relating soil amplification and liquefaction effects with seismic performance of precast structures

Precast concrete structures are preferred for facilities with large open areas due to easiness in construction. Such structures are typically composed of individual columns and long‐span beams, and are quite flexible and of limited redundancy. In this paper, nonlinear dynamic analyses of a typical such structure are conducted using as excitation 54 ground motions recorded on top of a variety of soils (hard, soft, and liquefied soil sites). The results show that liquefaction‐affected level‐ground motions systematically impose a greater threat to precast‐concrete structures in terms of seismic demand, even when low values of elastic spectral acceleration prevail, as opposed to soft‐soil records and even more to hard‐soil ones. Thus, elastic spectral acceleration appears to be an insufficient engineering demand parameter for design. Soil effects, the “signature” of which is born on ground motions, are first uncovered using wavelet analysis to detect the evolution of the energy and frequency content of the ground motion in the time domain. From this, the changes in effective (“dominant”) excitation period are noted, persuasively attributed to the nature of the soil, and finally correlated with the observed structural behavior. Copyright © 2016 John Wiley & Sons, Ltd.     

自适应时间步长法及三维堤坝地震液化数值模拟

三维大模型数值计算因巨大的单元和结点数目而非常耗时,在地震响应分析中受计算时间步长的限值则更加耗时。在饱和砂土动力液化计算平台上开发时域离散误差评估方法和时间步长自适应调整的计算程序,并成功应用于三维堤坝地震液化响应分析。时域离散误差包括土骨架的位移误差和单元孔压误差,通过定义孔压误差影响系数计算出混合误差,根据混合误差和设定的误差允许值进行计算步长的自适应调整。在三维堤坝地震液化数值模拟中,采用自适应时间步长法有效避免小步长精确但耗时、大步长省时而不精确的缺点。在大模型和超大模型计算中,最优调整每一步的计算时间步长,完美实现既节省时间又不失精度的时域离散策略。     

高层框支剪力墙结构地震反应分析的超元法

西方嵩层框支剪力墙结构地震反应分析的超元法，即将每榀框支墙中的上部剪力墙和落地墙简化处理成等效柱，底部框架简化处理成等代柱，楼板视为深梁，将连续分布的质量离散化，建立二维空间结构的“串并联质点系”振动模型，采用超级单元进行结构的地震作用计算及内力分析，此法计算简便并适用于结构竖向变刚度和考虑楼板变形等情况。     

耦合有限单元法扩边的直流电阻率勘探无单元Galerkin法正演

本文分析了目前直流电阻率正演模拟中的无单元Galerkin法（EFGM）和有限单元法（FEM）的优缺点,针对采用第一类边界条件需要足够大的计算域时EFGM计算成本高的问题,在计算域外围区域采用FEM扩边,提出了直流电阻率的无单元Galerkin-有限单元耦合法（EFG-FE）.采用具有Kronecker delta函数性质的径向基点插值法（RPIM）构造EFGM形函数,在外围区域将EFGM与FEM直接耦合,无需其他处理手段,消除了传统EFGM与FEM耦合中存在的界面耦合困难.EFG-FE将模型计算域分割为EFGM区域和FEM区域,模型核心区域采用EFGM计算,发挥EFGM灵活性、适应性强和高精度的优点,使得模型建立简单方便,对任意复杂地电模型适应性强,同时获得高精度模拟结果.在模型计算域外围采用快速扩展的FEM单元网格进行剖分,利用其数值稳定性和高效性,使用少量FEM节点和单元网格将计算域大范围扩大满足第一类边界条件,同时不大幅增加计算成本,进而提高计算效率.最后,通过不同正演方法的模型算例的模拟结果对比,验证了本文提出的EFG-FE有效可行,其模拟结果具有很高的模拟精度,且相比于采用第三类边界条件的EFGM提高了计算效率,具有更好的模拟性能.