块状岩体边坡地震滑动位移分析

岩体边坡在强震作用下往往会产生滑动残余位移。这种位移是边坡稳定性评价的重要参量。本文利用块体动力学原理推导出层状和块状岩体边坡地震滑动位移微分方程式, 并编制了相应的计算程序, 给出了实例的计算结果。     

地震作用下无衬砌黄土隧道围岩结构安全系数的计算探讨

为了得到无衬砌黄土隧道围岩结构在地震作用下的安全系数,借助有限元软件ANSYS,首先采用水平地震作用下的动力分析模型进行模态分析,得到质量阻尼系数和刚度阻尼系数;其次,输入地震波进行动力时程分析,得到模型顶点的最大水平位移;最后,采用静力分析模型,并考虑自重和左右边界上顶点水平位移最大时的侧向边界节点水平位移,通过不断折减围岩土体的抗剪强度参数,即黏聚力c和内摩擦角?,直到计算不收敛为止,从而得到无衬砌黄土隧道在地震作用下的安全系数。数值算例表明：所采用的方法是可行的,地震作用会使得围岩结构的安全系数降低,从而为以后黄土隧道围岩结构在地震作用下安全系数的计算及其工程应用提供了理论依据。     

多次冻融后格栅加筋黏土路堤工作性能分析

利用多次冻融后加筋黏土路堤相关试验参数对其进行有限元计算, 确定了加筋黏土结构各初始因素对其工作性能的影响规律, 并利用ABAQUS有限元计算软件对各种计算条件下的位移和应力进行求解, 确定了冻融循环后位移和应力的最大值. 结果显示: 增加加筋黏土路堤中的格栅层数可以减小冻融后加筋路堤的竖向和水平位移及土体剪应力最大值, 且格栅层数的增加对土体变形的影响强于对土体剪应力值的影响. 土体压实度的增大可以减小加筋路堤的竖向和水平位移, 同时引起土中剪应力数值的增大; 土体初始含水率的减小可以减小加筋路堤的竖向和水平位移, 同时引起土中剪应力数值的减小.     

Pseudostatic approach for seismic analysis of pile group

This paper evaluates a simple approximate pseudostatic method for estimating the maximum internal forces and horizontal displacements of pile group subjected to lateral seismic excitation. The method involves two main steps: (1) computation of the free-field soil movements caused by the earthquake, and (2) the analysis of the response of the pile group based on the maximum free-field soil movements (considered as static movements) as well as a static loading at the pile head, which depends on the computed spectral acceleration of the structure being supported. The methodology takes into account the effects of group interaction and soil yielding at pile–soil interface. The applicability of this approach has been validated by a similar approach for single piles and then verified by both experimental centrifuge models of pile-supported structures and field measurements of Ohba-Ohashi Bridge in Japan. It is demonstrated that the proposed method yields reasonable estimates of the pile maximum moment, shear, and horizontal displacement for many practical cases despite of its simplicity. Limitations and reliability of the methodology are discussed and some practical conclusions on the performance of the proposed approach are presented.     

Stochastic seismic slope stability assessment using polynomial chaos expansions combined with relevance vector machine

This paper presents probabilistic assessment of seismically-induced slope displacements considering uncertainties of seismic ground motions and soil properties.A stochastic ground motion model representing both the temporal and spectral non-stationarity of earthquake shakings and a three-dimensional rotational failure mechanism are integrated to assess Newmark-type slope displacements.A new probabilistic approach that incorporates machine learning in metamodeling technique is proposed,by combining relevance vector machine with polynomial chaos expansions(RVM-PCE).Compared with other PCE methods,the proposed RVM-PCE is shown to be more effective in estimating failure probabilities.The sensitivity and relative influence of each random input parameter to the slope displacements are discussed.Finally,the fragility curves for slope displacements are established for sitespecific soil conditions and earthquake hazard levels.The results indicate that the slope displacement is more sensitive to the intensities and strong shaking durations of seismic ground motions than the frequency contents,and a critical Arias intensity that leads to the maximum annual failure probabilities can be identified by the proposed approach.     

埋置简谐扭转荷载作用下广义Gibson饱和地基动力响应

考虑地基为饱和半空间,研究了广义Gibson饱和地基内作用简谐扭转动荷载时地基的动力响应问题。从Biot饱和地基固结理论出发,结合扭转振动的特点,建立了剪切模量随深度线性变化的饱和地基扭转振动的动力微分方程,通过Hankel变换求解此微分方程,给出了Hankel变换域内的切向位移和剪应力关于待定系数的表达式。根据饱和地基表面为自由表面,荷载作用面位移连续、剪应力差等于动荷载大小,波的辐射条件等边界条件求解出待定系数,借助Hankel逆变换给出地基内的位移和应力的表达式。通过数值算例研究发现:在同一水平面内,地基内的切向位移和剪应力曲线的实部和虚部都呈现出非常明显的波动变化规律;在竖向平面内,动荷载作用面上部区域内随深度逐渐增大时,地基内切向位移和剪应力曲线的实部逐渐增大,而在动荷载作用面下部区域则正好相反;扭转动荷载的影响范围主要是荷载作用面上下2倍半径区域。     

采空区上方建筑物地基附近的地表沉陷

根据载荷作用线上水平位移的特征和采空区上覆岩层破断后的结构形态,确定了位移边界条件;给出了采空区上方任意点的沉降位移、地表沉陷、地表水平位移以及建筑群引起的地表沉陷;探讨了在采空区和建筑物载荷的共同作用下地表的移动特性。研究结果表明:建筑物引起的地表沉陷与建筑物和采空区的相对位置有关;建筑物附近的地表下沉随着采空区上覆岩土层厚度的增加而减小,呈非线性变化;在沉降范围内,建筑物两侧地表的水平位移均匀分布,方向相向,均指向建筑物。      

Analysis of a rigid footing lying on three-layered soil using the finite difference method

A numerical procedure is described for the analysis of the vertical deformation and the stress distribution of the strip footings on layered soil media. Three layers of soil with different stiffness are considered with the middle soil layer the thinnest and most stiff layer. The soil media is discretized and using the theory of elasticity, the governing differential equations are obtained in terms of vertical and horizontal displacements. These equations along with appropriate boundary and continuity conditions are solved by using the finite difference method. The vertical and horizontal displacements, strains and stresses are found at various nodes in the soil media. Parametric studies are carried out to study the effect of the placement depth of the middle soil layer, the relative ratios of the moduli of deformation of the soil layers on the vertical displacement of the footing and the vertical stress distribution. These studies reveal that the middle thin but very stiff layer acts like a plate and redistributes the stresses on the lower soft soil layer uniformly. The displacement on the top and bottom of the middle soil layer is almost the same showing that the compression of the middle layer is negligible as it is very stiff.     

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.     

竖向入射S波作用下单桩水平地震响应简化解析方法

基于连续介质模型并考虑桩-土运动相互作用,将单桩视为一维线弹性梁,研究了竖向入射S波作用下的单桩水平地震响应问题。将竖向入射S波模拟为基岩水平位移,基于平面应变模型建立的土体控制方程,推导出地震作用下土体水平动力阻抗函数表达式。将土体阻抗代入单桩控制方程并联立桩-土接触条件及桩顶和桩底的边界条件,得出了竖向入射S波作用下单桩的地震响应解析解。通过将所得解与已有文献理论解和有限元结果进行对比,验证了该方法的合理性。基于所得理论解进行参数分析得出：桩-土模量比的增加可以明显降低桩-土运动相互作用因子的最小值,而较大桩身长径比以及土体滞回阻尼对桩-土运动相互作用因子的影响较小;对于桩顶水平地震放大因子来说,桩-土模量比的增加仅在高共振频率处抑制其幅值,较大桩身长径比对其影响较小,而滞回阻尼比的增加会显著抑制共振频率处的幅值;桩身地震响应仅在较小桩径比时受桩-土模量比的影响明显,并随桩-土模量比的增加而降低。     

带有复合摩擦阻尼系统的基础隔震结构分析

针对常规摩擦阻尼器的起滑力难以确定的问题,提出了复合摩擦阻尼系统（CFDS）,它由非线性硬弹簧和摩擦阻尼器串联而成。当地震较小时,摩擦阻尼器处于附着状态,非线性硬弹簧发挥作用,防止隔震层位移过大;当地震较大时,非线性硬弹簧的变形则保持不变,摩擦阻尼器处于滑动状态,通过摩擦阻尼耗散能量。建立了带有复合摩擦阻尼系统的基础隔震结构的运动方程,指出摩擦阻尼器处于附着和滑移2种状态下边界条件。据此研究了常规强震和近断层脉冲型地震动作用下复合摩擦阻尼装置对橡胶隔震结构的减震效果。仿真分析表明：安装复合摩擦阻尼系统,在显著降低隔震层位移的同时,对上部结构的层间位移和加速度均有一定的减震效果;并且,在整个运动过程中,摩擦阻尼器会在附着和滑移2种状态之间来回切换。详细研究了复合摩擦阻尼系统的３个参数对隔震结构的减震效果。结果表明：在不同地震波作用下,由于摩擦阻尼系统参数的变化导致隔震结构地震响应的变化趋势是不同的,因此最优参数的取值与输入地震波类型和地面加速度峰值有关,并且不存在使隔震层位移和上部结构加速度同时达到最小的最优参数,因此需要设定合适的控制目标以确定适当的阻尼系统参数。     

土钉墙开挖性状的有限元分析

土钉墙是粉砂土、黏性土等地区基坑开挖围护的主要形式之一。采用ABAQUS有限元软件建立土钉-面层-土体的相互作用模型,土体应用Mohr-Coulomb本构模型,土体与土钉间的接触性质为摩擦小滑移,在此基础上,得到了土体深层水平位移、面层位移、面层土压力和土钉轴力的分布形式和基本规律。计算结果表明：深层土体水平位移的最大值发生在墙顶靠下或者墙顶的位置;坑底水平位移从坡脚向坑中逐渐变小,在基坑开挖深度范围内,减小的速率较大,以后趋于某一稳定值;土钉轴力两头较小,中间较大,作用在面层上的作用力值远小于土钉轴力,该力与作用在面层上的作用力之和等于土钉轴力;土钉墙的面层土压力随着深度的增加,先增加到最大值后,再逐渐减小,每开挖一步面层土压力就会增加,且最大值向下移动。     

结构体系的一种新型半解析动力算法——地下结构动力分析的拉普拉斯积分变换解法

得到了地下结构在水平地震作用下的动力运动方程,利用拉普拉斯变换和结构的对接条件,得到了求解待定系数的超越方程。利用拉普拉斯逆变换得到了结构的位移表达式和确定拉普拉斯参数极点的方程。进一步研究发现,拉普拉斯变换参数s与结构频率ω之间存在某种特殊的关系:s2=?ω2。为了避免确定待定系数及拉普拉斯参数极点时求解复杂超越方程的困难,建议通过数值的办法先把结构体系的频率求出来,再通过拉普拉斯逆变换留数定理求解结构的位移和内力。     

Assessment of soil–pile–structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations

The role of the seismic soil–pile–structure interaction (SSPSI) is usually considered beneficial to the structural system under seismic loading since it lengthens the lateral fundamental period and leads to higher damping of the system in comparison with the fixed-base assumption. Lessons learned from recent earthquakes show that fixed-base assumption could be misleading, and neglecting the influence of SSPSI could lead to unsafe design particularly for structures founded on soft soils. In this study, in order to better understand the SSPSI phenomena, a series of shaking table tests have been conducted for three different cases, namely: (i) fixed-base structure representing the situation excluding the soil–structure interaction; (ii) structure supported by shallow foundation on soft soil; and (iii) structure supported by floating (frictional) pile foundation in soft soil. A laminar soil container has been designed and constructed to simulate the free field soil response by minimising boundary effects during shaking table tests. In addition, a fully nonlinear three dimensional numerical model employing FLAC3D has been adopted to perform time-history analysis on the mentioned three cases. The numerical model adopts hysteretic damping algorithm representing the variation of the shear modulus and damping ratio of the soil with the cyclic shear strain capturing the energy absorbing characteristics of the soil. Results are presented in terms of the structural response parameters most significant for the damage such as foundation rocking, base shear, floor deformation, and inter-storey drifts. Comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil–structure interaction amplifies the lateral deflections and inter-storey drifts of the structures supported by floating pile foundations in comparison to the fixed base structures. However, the floating pile foundations contribute to the reduction in the lateral displacements in comparison to the shallow foundation case, due to the reduced rocking components.     

双向增强体复合地基桩土应力比分析

针对双向增强体复合地基,由于桩体与桩间土变形不协调,导致路堤填土内部垂直变形有差异,应力状态发生变化。引入剪切位移法来分析路基填土中水平加筋体的变形和应力传递规律,在综合考虑填土力学性质（c, ）和水平加筋体作用的基础上,通过微元体平衡分析推导得到了桩土应力比、桩顶刺入量等计算公式。通过工程实例验证公式的可靠性,并综合分析了相关因素对桩土应力比的影响,得到了一些有益的结论。     

Pseudostatic Seismic Response Analysis of a Pile Group in a Soil Slope

This paper presents a simple approximate pseudostatic method for estimating the maximum internal forces and horizontal displacements of a pile group located in a soil slope. The method is extension of an existing similar method developed by the authors for the case of a horizontal ground surface. The method employed for horizontal ground case involves two main steps: first, the free-field soil movements caused by the earthquake are computed; Then, the response of the pile group is analyzed based on the maximum free-field soil movements as static movements, as well as a static loading at the pile head, which depends on the computed spectral acceleration of the structure being supported. This newly developed methodology takes into account the effects of group interaction and soil yielding. Simple modifications are applied to take into account the effect of slope on seismic deformations of the pile group, making use of the Newmark sliding block method. The applicability of the approach and the developed program is verified by comparisons made with both experimental shaking table tests and the results of a more refined analysis of a pile-supported wharf. It is demonstrated that the proposed method yields reasonable estimates of the pile maximum moment and horizontal displacement for many practical cases, despite its relative simplicity. The simplifying assumptions and the limitations as well as reliability of the methodology are discussed, and some practical conclusions on the performance of the proposed approach are suggested.     

剪力键支护体系的构想及模型试验研究

针对深大基坑支护工程中存在的问题提出了一种新型的支护形式-剪力键支护体系,由竖直桩和斜向支撑的剪力键构成。通过模型试验,对剪力键组和单排悬臂桩组分别量测了不同开挖深度时的桩顶水平位移及桩身内力,同时进行了有限元的数值模拟。结果表明剪力键组的桩顶最大水平位移约为悬臂组的1/10,桩身最大弯矩值约为悬臂组的一半左右。剪力键支护体系具有更大的刚度,能够有效减小桩顶位移及桩身最大弯矩,且耗材相对较少,支护深度较大,占据空间较少,不影响主体地下室施工,可节约工期和成本,为深大基坑的支护提供了新的型式。     

非饱和土中端承桩水平振动特性研究

针对非饱和土中桩的水平稳态振动问题,采用三相多孔介质波动方程,考虑固、液、气三相材料间的惯性和黏性耦合效应以及基质吸力的影响,通过Helmholtz矢量分解及分离变量法解耦波动方程,并将基桩等效为能描述其剪切变形和转动惯性效应的铁摩辛柯（Timoshenko）梁模型,采用Novak三维连续介质模型对非饱和土中端承桩的稳态水平振动进行了理论推导,获得了桩顶水平频域响应解析解,讨论了饱和度对土层和桩顶阻抗的影响以及桩身位移、内力沿深度的分布规律。结果表明,随着土体饱和度的升高,土层复阻抗和桩顶动力阻抗增大,桩身位移和内力则相应地减小;饱和度,包括渗透系数在内的影响仅在土体接近准饱和时才得以发挥;频率较低时,短桩拥有较大的刚度因子。桩长越长,阻抗因子越大,而共振频率越低。当长径比超过10时,桩顶阻抗不再随长径比的增加而改变。     

A simplified approach for studying the influence of vertical accelerations on seismic response of slopes

ABSTRACT

A simplified approach is presented for estimating permanent displacements in slopes as a result of both vertical and horizontal seismic accelerations. A study of 52 earthquake records showed that the time difference between maximum horizontal and vertical accelerations varied between 0 and 10.3 s. The approach is illustrated for an earth dam embankment by analysing the effects of five of the above earthquake records. The approach combines a pseudo-static slope stability analysis for estimation of the critical (or yield) horizontal-vertical acceleration combinations, and a Newmark type displacement analysis. Guidelines are presented for conservative choice of soil strength parameters of saturated clays for use in the stability analysis. While permanent displacements of up to 40 cm were predicted without considering the vertical acceleration component, no additional displacement above 3.5 cm resulted when this component was included. The predicted additional displacement was consistently less than 10%, and in 50% of the analyses, vertical acceleration led to smaller predicted displacements. The simple approach may be applied in analysis for any slope using real earthquake records. Using existing, empirical expressions for permanent displacement, based only on horizontal accelerations, the effect of the vertical accelerations may be conservatively estimated by increasing the displacement by 10%.     

Horizontal displacements in Japan

Recent horizontal displacements in Japan are discussed by using the results of the first-order triangulation surveys. Large horizontal displacements are found in East Hokkaido, Tohoku, South Kanto, Tokai and Nankai districts (Fig.1). Crustal activity in these districts is also briefly discussed. The original triangulation survey in Japan neglected Laplace (azimuth) observations and consequently rotation and divergence around the assumed fixed point often appear as horizontal displacements. This is especially true in the central Japan where horizontal displacements result from cancelling the apparent rotation and divergence around the assumed fixed point (Fig.2).On the other hand, strain measurements avoid such shortcoming. Considering with the results of the first triangulation, the horizontal earth-strain can be calculated for every subsequent triangulation net. It is interesting that the velocity of the maximum shear strain is almost 2–3 · 10^/t7/year throughout Japan (Fig.3), even though the seismic activities show large regional discrepancies.