大型振动台试验土质边坡模型材料相似性及评价

大型振动台模型试验是边坡动力响应和破坏模式研究的重要手段,其中相似材料的选择是决定试验能否成功的关键。以黄土地区2类典型边坡为研究对象,在对滑坡体原状土样开展室内土动力学测试的基础上,提出6种相似比条件下振动台模型试验相似材料的配比方法;对2种相似比条件下相似材料的参数进行量纲分析,依据相似判据、相似准则的约束,以模糊数学理论进行优化,并提出大型土质边坡振动台试验的材料相似性评价体系。     

高边坡在水平动荷载作用下的动力响应规律研究

高岩石边坡在水平动荷载作用下的动力响应规律是有关工程界十分关心的问题。本文通过大量的数值模拟分析对边坡的动力响应规律进行研究，发现了高岩石边坡在水平动荷载下动力响应的加速度、速度、位移三量放大系数等值线在边坡剖面上分布的规律性特点。对于一定的岩土体材料，当边坡高度在一定时，边坡动力响应的加速度、速度、位移三量会随着边坡角度的增大而减小；当边坡的角度一定时，边坡动力响应的加速度、速度、位移三量会随着边坡高度的增加而放大；边坡的下覆岩层的材料特性对于边坡的动力响应的加速度、速度、位移三量的放大作用的影响具有一定的规律性；边坡动力响应的加速度、速度二量受动荷载的特征周期影响较位移明显，具有一定的规律性。边坡的边缘部位对振动的反应幅值较之内部存在放大现象，坡度决定了三量分布的等值线方向的走向。其结论性成果体现了高岩石边坡的地震动力响应特征，为高边坡工程提供理论基础和实践依据。     

含软弱夹层岩质边坡的模态分析及其对边坡地震动力响应影响的初步研究

本文以含软弱夹层岩质边坡作为研究对象,基于数值软件ANSYS的模态分析给出了含不同倾角与厚度软弱夹层边坡的前5阶固有频率与振型,并分析了夹层倾角和厚度对边坡固有模态的影响。接着,结合已有的大型振动台模型试验结果,在小应变范围内讨论了边坡的固有模态与其动力响应特性之间的关系。结果表明:(1)在夹层倾角相同时,含较厚软弱夹层边坡固有频率低于含较薄软弱夹层边坡;(2)在夹层厚度相同时,随着倾角增加,夹层从反倾变化到顺倾,低阶(1、2)固有频率也逐渐增加,而高阶(3、4、5)固有频率则呈下降趋势;(3)从第3、4阶开始,边坡变形受夹层影响增强;(4)基于加速度傅里叶谱比分析得出的边坡响应放大频率与边坡前5阶固有频率范围接近,加速度和位移响应在夹层及以上部位响应强烈,与边坡前5阶振型较为一致,预示了边坡的共振响应。需要指出的是,本文得出的结论尚且不能用于准确解释边坡在大变形及破坏阶段的动力响应特征,但可为边坡动力特性及共振响应的深入研究提供思路。     

地震作用下黄土边坡动力响应的时频特征分析

地震作用下黄土边坡的动力响应特征与变形失稳机制是具有重要理论与实践意义的课题,但从动力响应频谱特性方面开展的研究还相对较少。以大型振动台模型试验获得的黄土边坡地震动峰值加速度数据为基础,通过分析其变化规律,着重从频谱特性的角度分析,讨论黄土边坡的动力失稳机制。进一步通过对坡面不同高程测点、边坡内部垂直方向以及水平方向上测点的加速度时程进行绝对加速度反应谱分析,从频谱变化角度提出黄土边坡的动力失稳机制。研究表明,黄土边坡在地震动作用下的响应过程可以分为三个阶段：弹性阶段、塑性阶段与破坏阶段;黄土边坡进入破坏阶段时均会伴随反应谱峰值的增幅或者主周期的变化,在弹性阶段反应谱加速度峰值增幅与输入地震动幅值增幅一致,进入塑性阶段后反应谱峰值增幅比输入地震动幅值增幅小;研究提出将反应谱首峰的凸显情况作为坡体破坏程度的判断依据之一。     

考虑进洞高程效应的黄土隧道洞口段地震动力响应特征研究

通过大型振动台模型试验并采用Midas-GTS有限元软件进行模拟计算,研究黄土隧道洞口段在地震作用下的动力响应特征、破坏过程和地震波在模型中的传递规律,分析影响黄土隧道洞口段地震动力响应的主要因素。结果表明:边坡沿弧形开裂面的垮塌受坡脚剪切和坡顶拉裂的共同作用;边坡会对其卓越频率内的地震波产生明显放大效应,且在1/2坡高以上放大效应出现饱和现象;隧道临空面是影响隧道洞口段地震动力响应的主要因素。考虑进洞高程效应时隧道洞口段抗震设防长度可取距洞口5倍洞径范围。振动台模型试验与数值计算在位移、加速度、应力三个响应特征上吻合较好,证明二者结果合理可靠。研究成果可为隧道工程设计和地下结构抗震理论研究提供有益参考。     

地震作用下均质土坡动力特性的振动台试验研究

设计并完成比例尺1∶100的边坡振动台模型试验,讨论模型的相似关系、传感器的布置及模型的建造,并编制相应的动荷载加载方案。通过输入不同类型、不同幅值、频率的动荷载,分析模型边坡在地震作用下的动力响应规律以及地震动参数对边坡动力特性和动力响应的影响。试验结果表明,在坡体的表面和坡内的竖直方向上,加速度放大系数均随着高程增加而明显增大。当输入不同压缩比的地震波时,压缩比越大坡体的动力响应越明显,即随着输入动荷载的频率增加,越接近土体的自振频率加速度放大效应越明显;在坡体的同一高程处,坡面的加速度放大系数略大于坡体内的加速度放大系数,表现出一定的趋表效应,同时随着输入地震波振幅的增加,加速度放大系数整体出现递减的趋势。实验结果分析有助于揭示土质边坡在地震作用下的失稳破坏机制,为今后边坡工程的抗震设计提供积极的参考。     

土边坡地震反应及其动力稳定性分析

本文建立了计算土边坡地震反应及评价其动力稳定性的一个数值分析模型，将上边坡在动力作用下的应力状态简化为自重应力状态和附加动力状态的叠加，并对这两个应力状态分别进行研究。本文用时域集中质量显式有限元方法结合多次透射公式，研究了无限域中边坡在动力作用下的位移场和应力场，提出了土边坡动力稳定性的定量评价方法。     

水平地震作用下黄土多级高填方边坡动力响应规律及稳定性分析

为研究水平地震作用下黄土多级高填方边坡动力响应规律及稳定性，本文以某高填方边坡工程为背景，利用GeoStudio2012有限元分析软件建立模型进行分析，并对比分析多级高填方边坡与单级填方边坡动力响应结果。计算结果表明，边坡坡面和挖填交界面上动力响应规律表现为:位移幅值基本随着高程的增加而增加；速度幅值随着高程的增加先增大后减小再增大；加速度幅值随着高程的增加有减小趋势；多级高填方边坡动力响应规律与单级填方边坡动力响应规律不同，单级填方边坡位移幅值、速度幅值、加速度幅值均随着高程的增加递增；地震波在坡体内传播时，随着高程的增加具有滞后性。边坡稳定性随着地震加速度峰值的增大有所下降，相比静力作用，水平地震作用下边坡稳定性下降明显。本文相关研究可为西北地区黄土高填方边坡工程抗震提供一定理论依据。     

单面边坡的两种动力反应形式及其临界高度

把单面边坡的动力反应分为高边坡动力反应和低边坡动力反应两类. 研究了两种不同动力反应形式临界边坡高度的影响因素. 量纲分析表明弹性条件下边坡动力反应临界高度Hthre与构成边坡材料的动弹性模量Ed的平方根成正比,与边坡材料的密度ρ成反比,与边坡动力输入的特征周期T成正比. 结合弹性波动理论,利用大量数值模拟和统计分析得到了Hthre的表达式. 当边坡的高度大于Hthre时,边坡的动力反应呈现高边坡动力反应规律,当边坡的高度小于Hthre时,边坡的动力反应呈现低边坡动力反应规律.     

边坡模型相似材料配比试验研究

针对边坡模型试验相似材料配比问题,系统总结了国内外常用的岩体及边坡相似材料配比研究现状:相似材料的配比对物理力学参数特性的影响很大,而不同学者采用的材料及配比方案差异较大,使得边坡模型试验的成果难以得到全面的推广;目前,重晶石粉、石英砂、石膏、甘油、水能模拟自然界中大多数类型的岩体,是进行边坡模型试验的理想材料.采用三因素四水平的正交试验法,对16组不同配比相似材料进行力学试验,通过极差和方差敏感性分析得出结论如下:重晶石粉含量与密度成正比,石膏含量对密度影响不显著;抗压强度与石膏含量呈正相关关系,甘油占比对抗压强度影响明显,呈现先略微增大后急剧降低的特征;弹性模量与甘油和重晶石粉占比呈负相关关系;抗拉强度与甘油占比呈负相关关系,与石膏占比呈正相关关系;随着石膏含量的增加内聚力呈现增大的趋势;内摩擦角呈现出随重晶石粉含量增加而减小的趋势.该问题的研究对边坡模型试验相似材料的配比具有一定的指导意义.     

Centrifuge modeling of a dry sandy slope response to earthquake loading

This paper presents results of a series of centrifuge models of dry, sandy slopes excited by earthquakes and cyclic waves under 50g centrifugal acceleration to investigate the dynamic performance of slopes. Test results of four model slopes with different profiles stimulated by the adjusted El Centro earthquakes with various peak accelerations reveal the response amplification mechanism of the slope. By calculating the response spectra of recorded acceleration time histories, it was observed that the different frequency contents of the input event were amplified to different degrees. The model slope showed a completely different response under the cyclic wave with a constant frequency and amplitude in that the spectral amplification factor curves had no prominent peak values. These findings suggest that dynamic centrifuge tests excited with a real ground motion are able to better reflect the response characteristics of a slope rather than the tests with cyclic loading.     

Identification and imaging of soil and soil-pile deformation in the presence of liquefaction

1 Introduction Soil and soil-structure systems exhibit complex response patterns during earthquake-induced liquefaction. These patterns depend on geotechnical properties, in-situ stress conditions and interaction with subsurface structural elements. Seismic records of full- scale systems during case histories provide a valuable source of information on the associated response mechanisms. However, the response of these systems is commonly monitored at sparsely distributed locations only, mostly…     

Mitigation of the seismic motion near the edge of cliff-type topographies

Concentration of damage of buildings near the edge of hard or dense cliff-type topographies has been observed during a number of recent earthquakes. These observations have been interpreted by numerical dynamic analyses that illustrate the amplification of accelerations near the edge of slopes. The paper studies the effect of mitigating these accelerations using anchors both experimentally and numerically. The main issue is that if the part of the slope in which topographic amplification occurs is connected to that in which the acceleration is less, then the accelerations have to become more uniform. The experimental study involves dynamic centrifuge tests at the Cambridge University facility both with and without anchors. The numerical procedure was verified by the seismic response of the centrifuge tests. It was then applied to the study of the effect of anchors of a typical field case, the Aegion slope, under two different input motions. In all cases anchors were found effective in mitigating the seismic motion near the edge.     

砂土自由场地震响应的离心机试验研究

离心机模型试验是研究岩土地震工程问题的有效手段。本文使用层状剪切箱,通过干落法制备了均匀的砂土模型,进行了离心机振动试验;观测了振动过程中孔隙水压力的发展,土体的加速度响应、侧向变形以及竖向沉降。结果表明,土体的运动和变形与孔隙水压力的发展密切相关,但离心机中的试验现象和现场观测的现象存在显著区别。研究结果增强了对振动过程中土-水之间相互作用机理的理解,同时为自由场地震响应分析方法的验证提供了基础数据。     

Experimental p-y curves for liquefied soils from centrifuge tests

The present study aims to obtain p-y curves(Winkler spring properties for lateral pile-soil interaction) for liquefied soil from 12 comprehensive centrifuge test cases where pile groups were embedded in liquefiable soil. The p-y curve for fully liquefied soil is back-calculated from the dynamic centrifuge test data using a numerical procedure from the recorded soil response and strain records from the instrumented pile. The p-y curves were obtained for two ground conditions:(a) lateral spreading of liquefied soil, and(b) liquefied soil in level ground. These ground conditions are simulated in the model by having collapsing and non-collapsing intermittent boundaries, which are modelled as quay walls. The p-y curves back-calculated from the centrifuge tests are compared with representative reduced API p-y curves for liquefied soils(known as p-multiplier). The response of p-y curves at full liquefaction is presented and critical observations of lateral pile-soil interaction are discussed. Based on the results of these model tests, guidance for the construction of p-y curves for use in engineering practice is also provided.     

Centrifuge modeling of batter pile foundations under sinusoidal dynamic excitation

Batter pile (or inclined pile) foundations are widely used in civil engineering structures. However, their behavior under dynamic loadings is not yet thoroughly understood. This paper presents an experimental work on the behavior of batter and vertical piles considering dynamic soil-pile-superstructure interactions. A series of dynamic centrifuge tests were performed using sinusoidal excitations. The influence of the base shaking (frequency content and amplitude) and of the height of the center of gravity of the superstructure is investigated. Seismic responses are analyzed considering the pile cap displacements and forces (total base shear, overturning and residual moments, axial forces). It is found that in certain cases batter piles play a beneficial role on the dynamic behavior of the pile foundation system. This novel experimental work provides an important database on the behavior of batter pile foundations under dynamic loadings.     

Centrifuge modelling of flexible retaining walls subjected to dynamic loading

This paper outlines the results of an experimental program carried out on centrifuge models of cantilevered and propped retaining walls embedded in saturated sand. The main aim of the paper is to investigate the dynamic response of these structures when the foundation soil is saturated by measuring the accelerations and pore pressures in the soil, displacements and bending moment of the walls. A comparison among tests with different geometrical configurations and relative density of the soil is presented. The centrifuge models were subjected to dynamic loading in the form of sinusoidal accelerations applied at the base of the models. This paper also presents data from pressure sensors used to measure total earth pressure on the walls. Furthermore, these results are compared with previous dynamic centrifuge tests on flexible retaining walls in dry sand.     

基于拟动力法的抗滑桩加固边坡地震稳定性分析

地震力作用下土质边坡动态稳定性研究对实际边坡工程有着重要的意义。采用拟动力法结合简化毕肖普法研究坡顶抗滑桩加固土质边坡在地震力作用下的动态稳定性。尽管拟静力法是目前处理地震力最为广泛的方法之一,但其局限性在于无法考虑地震力随时间变化且忽略了地震波在土体中的传播。而拟动力法采用正弦波模拟地震波在土中传播,并考虑地震波从坡脚传递到坡顶的相位差以及阻尼力对边坡稳定性的影响,通过边坡安全系数的变化揭示土质边坡在地震力作用下的稳定性变化规律。将得到的结果与拟静力法进行对比,突出了拟动力法的优势。最后,考虑水平地震加速度系数、加速度幅值放大系数以及土体内摩擦角对边坡稳定性的影响,以期对实际工程提供理论借鉴。