季节冻土区土钉支护边坡地震反应动力特性分析

为了更科学地评价地震荷载作用下土钉支护季节冻土边坡的抗震性能，基于热-动力理论控制方程，应用大型非线性有限元软件ABAQUS，建立带有黏弹性人工边界的地震荷载作用下土钉支护季节冻土边坡的数值模型，对比分析夏季和冬季这两个典型季节时的加速度响应、位移响应以及土钉轴力响应。结果表明：无论是夏季还是冬季，加速度峰值随着季节冻土边坡高程以及激振加速度峰值增加而增加，在夏季时刻的季节冻土边坡坡顶位置处达到最大。此外，在不同地震波峰值加速度作用下，相同位置处的位移响应峰值却有明显的不同，同一地震烈度地震波激震时，夏季的季节冻土边坡坡顶位移最大，表明地震荷载对夏季的季节冻土边坡坡顶破坏效应最为明显，土钉轴力具有高程放大效应和坡面放大效应，季节冻土边坡坡底至坡顶的土钉端部轴力峰值逐渐增大。文中数值模拟模型及结论可为制定地震荷载作用下土钉支护季节冻土边坡抗震设计提供一定的参考。     

地震作用下边坡动力响应及影响因素研究

利用ANSYS有限元软件建立了边坡数值模型,并结合汶川地震实例分析了边坡的共振特性、动力响应变化以及地震动三要素对边坡动力响应的影响,对汉源县高烈度异常现象从共振的原因做出了解释。通过分析发现:边坡的共振主要由前5阶固有频率被激发引起,坡体阻尼和地震波频率对共振作用有显著影响。边坡体对输入地震波低频部分存在放大作用,对高频能量具有滤波作用。坡体加速度和位移响应随高程增加而增大,沿水平方向从左至右,位移减小,加速度先增后减。坡体峰值加速度放大系数随频率的增加而减小,随持时变化不明显;坡体位移随振幅和持时增加而增大,随频率增大而减小;弹性范围内,加速度和位移动力响应绝对量随振幅增大呈明显的线性增长关系,而位移、加速度放大系数保持不变;坡面陡坎处动力响应突变效应明显。     

基于FLAC3D预应力锚杆抗滑桩支护边坡地震响应分析

建立预应力锚杆抗滑桩支护边坡三维模型,通过坡面监测点分析地震作用下边坡坡面监测点位移、加速度响应以及地震过程中抗滑桩所受剪力与弯矩的受力规律。结果表明:地震作用下边坡坡面产生永久位移,最大水平位移发生在边坡中下部;与无支护边坡相比,预应力锚杆抗滑桩支护边坡能有效抑制坡面峰值加速度PGA放大系数。地震作用下抗滑桩随地震历时的增加受力不断变大,最后趋于稳定,其中剪力呈现倒"S"型,桩身弯矩呈现"S"型。研究结论对预应力锚杆抗滑桩支护边坡的抗震设计有一定参考价值。     

地震动参数对边坡地震响应的影响规律

选取了具有不同峰值加速度、频谱和持时的6组地震动加速度时程作为输入,基于有限元数值模拟方法建立了二维均质边坡有限元模型,模拟分析了不同地震动作用下边坡模型的加速度和位移响应,揭示了地震动峰值加速度、频谱和持时对土坡地震响应的影响作用及其规律.研究结果显示:地震动峰值加速度、频谱和持时对土坡地震响应均有显著的影响,其中,边坡坡脚处和坡肩处的变形位移随地震动峰值加速度、特征周期和持时的增大而增大,坡体临空面各点的峰值加速度放大系数呈现随输入地震动特征周期的增大而增大、随输入地震动峰值加速度的增大而减小的规律.研究结果可为地震作用下边坡稳定性设计及防治研究提供参考.      

岩层倾角对顺倾向边坡地震效应的影响

利用FLAC3D软件模拟地震作用下不同岩层倾角的顺倾向边坡,对比坡面峰值加速度放大系数、峰值位移、地震作用结束后坡体剪应变增量的变化规律,探讨岩层倾角对顺倾边坡地震效应的影响。研究表明:(1)在水平地震波作用下,坡面水平峰值加速度放大作用随岩层倾角增大而线性减小;(2)当岩层倾角小于软弱岩层内摩擦角时,坡面峰值位移较小且变化规律受岩层倾角影响不明显,当岩层倾角大于软弱岩层内摩擦角且小于30°时坡面峰值位移增大,大于60°时减小;(3)岩层倾角小于坡角时,残余剪应变增量最大值集中在坡面中下部软弱岩层处,反之,剪应变增量最大值出现在整个坡面并呈弧形区。     

组合支护结构作用下反倾层状岩质边坡加速度响应振动台试验研究

设计并完成一个1∶30的大比例尺高陡反倾层状岩质边坡的振动台模型试验,坡体内部有6个软弱泥化夹层,研究在组合支护体系作用下EL Centro地震波和汶川-清屏地震波激振下泥化夹层含水量发生变化时边坡的加速度动力响应规律。试验结果表明:(1)坡面X、Z向加速度放大系数均具有非线性高程放大效应,但前者大于后者;(2)泥化夹层含水量的变化对坡面加速度放大效应影响显著,注水后X向减小而Z向增大;(3)支护体系作用下边坡临空面放大效应的现象受限制,预应力锚索抗滑桩以下边坡基本不存在加速度放大效应;边坡分级支护可有效降低X向加速度放大系数的高程增大效应,但对Z向会产生不利作用;(4)边坡的破坏模式为上部受软弱夹层滑动牵引而发生倾倒-拉裂变形,导致顶部框架梁有可能最先发生破坏,且破坏类型可能以绕坡顶为支点向坡体内侧转动,引起上部的锚索产生拔出破坏。     

卵石土场地地震反应特征振动台试验研究

为研究卵石土场地地震反应特征,基于四川成都典型卵石土场地,通过振动台模型试验研究卵石土场地在不同地震波、不同地震强度激励下的加速度峰值放大系数、加速度频谱反应及动土压力反应,并且对其场地地震反应非线性效应及土体动剪应力-动剪应变关系进行分析。结果表明：卵石土场地表层土层对地震波具有明显的放大效应,加速度峰值放大系数介于1～1.4之间,下部土层放大效应较小,加速度峰值放大系数介于0.9～1.2之间。卵石土场地对地震波具有低频放大,高频滤波的作用,滤波频率上、下限随激励强度的增大逐渐向低频方向移动。激励强度较小时,土体尚未破坏,动土压力在地震过程中逐渐增大;随着激励强度的增大,动土压力反应明显增大,表现出骤减后逐渐增大的现象。在激励强度较小时(SN1),中部土体最先进入非线性反应阶段,地震波在中部土层能量损耗最大;激励强度较大时(EL3),土体均发生了较大变形,土体最大动剪应变达到1.7%,此时卵石土场地对地震波的放大作用明显减弱。     

黄土边坡动力响应分析

运用有限差分软件FLAC3D,建立了某一黄土边坡三维模型,首先对其在地震作用下的动力响应规律进行了总结,然后探讨了地震动参数对黄土边坡动力响应的影响。结果表明：黄土边坡对地震波存在垂直放大和临空面放大作用;当输入地震波振幅或频率增加时,坡面监测点加速度放大系数随坡高增加呈＂增加→衰减→增加＂的三段形态;速度放大系数随坡高的增大而增大,并在坡顶达到最大值;位移放大系数随振幅和频率的增加而增加;地震持时对加速度、速度峰值的影响不大,但坡体位移随持时的增加而显著增加。强震作用下的最大剪应变增量区域的位置和形状表明,黄土边坡的破坏模式仍是沿着某一弧形潜在滑动面失稳破坏。研究结果有助于进一步揭示黄土边坡在地震作用下的失稳机制,为黄土地区边坡抗震设计与防灾减灾提供参考。     

含泥化夹层反倾岩质边坡动力响应的大型振动台试验

针对含泥化夹层反倾岩质边坡制作相似比为1∶30的试验模型进行大型振动台试验,研究泥化夹层饱水前(天然含水状态)和饱水状态下边坡的加速度和位移响应规律,探讨边坡的破坏模式。试验结果表明:泥化夹层饱水后坡面水平向加速度放大系数小于饱水前;泥化夹层饱水前和饱水后随着相对高度的增加,坡面水平向加速度放大系数呈现非线性增加的趋势,其整体上大于坡体内部的加速度放大系数;坡面位移从下至上在泥化夹层饱水前,呈现出非线性增长特性;饱水后位移呈先增大后减小,临近坡肩处坡面最大,坡面呈现鼓出形态。泥化夹层饱水前,在幅值为0.3g的地震波作用下坡体仅出现坡肩局部掉块;饱水后,输入地震动幅值≥0.4g时,坡体先出现坡肩的局部掉块,随后坡体沿中上部的饱和泥化夹层滑动剪出,与此同时,坡体中上部出现纵向裂隙并与水平裂隙贯通,坡顶被震碎。     

进洞高程对黄土隧道洞口衬砌和仰坡动力响应的影响

针对黄土边坡与隧道洞口段衬砌的相互作用问题,运用数值模拟的方法分析了以不同进洞高程进洞时黄土隧道洞口段衬砌的动力响应特征和洞口仰坡的动力稳定性。结果表明:进洞高程越大,洞口段隧道衬砌的位移响应与内力响应越大;随着进洞高程的增大,坡面位移放大系数在减小,不同进洞高程进洞时坡面位移放大系数均呈先增大后减小再增大的变化趋势。在0.2~0.6H时变化最为剧烈,0.4H左右时位移放大系数达到了最大值;不同进洞高程进洞时坡面中心和水平方向距离隧道结构1.5D处的坡面位移放大系数变化趋势基本一致,其大小关系为:纯边坡位移放大系数 < 有隧道结构中面位移放大系数 < 距隧道1.5D位移放大系数;随着进洞高程的增大,剪应变增量和坡面位移均在减小,坡面的稳定性在增强。该研究可为黄土地区隧道进洞高程的选择提供一定的参考。     

不同土压力模式下土钉受力特征探讨

土钉支护体系作为一种经济、有效的支护方式而得到广泛的应用。但关于土钉力计算的理论依然相对缺乏,远远落后于工程实践,严重制约了土钉技术的发展。基于杨光华提出的土钉力简化计算方法[1],以4种不同的土压力模式为背景进行简化,并对比分析不同土压力模式下的土钉力分布,结果表明:采用根据侧壁主动土压力与总土钉力相等并考虑施工过程的影响和增量法的土钉力简化计算方法简便,且采用三角形土压力分布模式与梯形土压力分布模式(二)较采用其他两种土压力分布模式简化计算得到的结果与监测结果更接近。     

Centrifuge modeling of seismic behavior of a slope in liquefiable soil

Two centrifuge tests were designed to improve the understanding the response of liquefied sandy slopes beyond initial liquefaction. A distinctive dilative behavior of the soil was observed near the slope where static shear stresses are present. The corresponding drops in the piezometric records and simultaneous negative upslope spikes in the acceleration records were measured in the transducer raw data. This dilative response became stronger as the input acceleration increased and tends to limit the downslope accumulation and thus reducing the permanent lateral displacements. Therefore, the maximum permanent displacement was smaller in the model with the larger input motion, because it developed a stronger dilative response. The dilative response was not observed away from the slope, where no static shear stresses are present.     

Current state of research on flow failure considering void redistribution in liquefied deposits

In liquefied ground, lateral flow is sometimes much larger than surface settlement and may exceed several meters even in a gentle slope of less than a few percent. It occurs not only during but also after earthquake shaking. Conventional laboratory soil tests using uniform sand cannot reproduce this phenomenon. Its mechanism is still poorly understood. In this paper, there is a major focus on the mechanism involving void redistribution or water film effects in layered sand deposits using recent findings obtained by different researchers on void redistribution and the associated lateral flow movement that potentially occurs in layered sand deposits. 1G shake table tests, 1D tube tests, torsional simple shear tests, in situ soil investigations, case history studies, etc. are used to develop an understanding of the lateral flow mechanism during liquefaction. Some of the major findings are; sand deposits in the field consist of sublayers with different particle sizes and permeability and readily develop water films by post-liquefaction void redistribution at sublayer boundaries. The water films may have served as sliding surfaces for large flow during the 1964 Niigata earthquake without the constraint of the dilatancy effect because the water films serve as shear stress isolators. The potential of this type of flow failure will be high for loose sand with relative density around 40% or less.     

不同厚度层状边坡动力响应的模型试验研究

采用振动台物理模拟试验方法,以4种不同覆土厚度的层状边坡模型为研究对象,水平输入振幅逐渐增大的正弦波加速度,分析了结构面上覆不同厚度土层对动力作用下边坡的稳定影响.研究了在动力作用下边坡的破坏位置和性质、破坏形式及最危险覆土厚度,验证了坡面放大效应与高程的关系,采用MIDAS/GTS软件对模型试验进行振型分析,分析了模型边坡的自振频率与覆土厚度的变化关系.试验结果表明：①模型破坏时最先出现的裂缝在边坡的中上部,且6 cm覆土厚度的模型对振动的响应最大,对应到实际工程中时12m厚度土层覆盖的边坡是最应该注意防护的.②不同厚度的土层破坏的形式不同：当土层厚度较薄时模型破坏较迅速,基本沿结构面发生整体滑动破坏,且滑动呈现一定的流体特性;当覆土较厚时裂缝先在模型中上部出现,随着振动的持续裂缝继续发展,最后发生整体性崩塌.③随着高程的增加峰值加速度总体呈放大趋势,但最大值出现在边坡中上部而非坡顶,说明不仅均质边坡有加速度的高程放大效应,层状边坡也具有加速度的高程放大效应.     

STUDY ON DYNAMIC RESPONSE AND INSTABILITY OF SOIL-ROCK MIXTURE DEPOSIT WITH DIFFERENT STONE CONTENTS AND SLOPE GRADIENTS

Soil-rock mixture deposit is an extremely heterogeneous loose rock-soil deposit formed since Quaternary, which is composed of blocks, fine-grained soil and pore with a certain engineering scale and high strength and has a certain stone content. These soil-rock mixtures accumulated on slopes have been completely destroyed and their mechanical strength is very low. They are widely distributed in the mountainous areas of Southwest China, which poses a great threat to the engineering. Earthquakes occur frequently in Southwest China, and the instability of soil-rock mixture deposit under seismic load is one of the important factors causing the damage to this type of deposit. The dynamic response of soil-rock mixture deposit under seismic load is an important index to study its instability mechanism under seismic load. Based on indoor shaking table model test, the influence of rock content and slope gradient on dynamic response characteristics of soil-rock mixture deposit was studied. In model tests, rock content is 30%, 40% and 50%respectively, and slope gradient varies from 20°, 30° and 40°. Two different seismic loading frequencies and three different excitation strengths were given. The peak acceleration(PGA)amplification coefficients in horizontal and vertical directions of soil-rock mixture deposit were analyzed under the change of rock content and slope gradient. The permanent displacement and deformation law of the top and foot of the slope of soil-rock mixture deposit were analyzed by model test. The experimental results show that the dynamic acceleration response characteristics of the soil-rock mixture deposits at the top and foot of the slope are different under different slope gradients and rock content conditions, and the horizontal PGA amplification coefficients of the soil-rock mixture deposits are also different. With the same seismic frequency and excitation intensity, the horizontal PGA amplification coefficient increases with increased slope gradient, and the rate gets faster. With the increase of stone content, the magnification coefficient of horizontal PGA decreases, and the higher the stone content, the slower the decrease rate of horizontal PGA magnification coefficient. When the slope gradient of soil-rock mixture deposit increases, the corresponding horizontal and vertical PGA amplification coefficients increase with the same seismic frequency and excitation intensity. The amplification coefficients of PGA in the vertical direction are different, but the overall magnification is weaker than that in the horizontal direction. The vertical PGA amplification coefficients of the foot, middle and lower parts of the slope are larger, while the vertical PGA amplification coefficients of the upper and middle parts of the slope tend to decrease. The higher the frequency of seismic wave is, the smaller the vertical PGA amplification coefficient corresponding to the same elevation will be, which indicates that the vertical PGA amplification coefficient is negatively correlated with the elevation. The variation trend of PGA magnification coefficient of soil-rock mixed deposit in vertical direction is different with the change of stone content. Under the same excitation intensity, the larger the slope gradient is, the larger the permanent displacement at the top of the slope will be, and the larger the rock content, the smaller the corresponding displacement at the top of the slope. The permanent displacement of the top of the slope is obviously larger than that of the foot of the slope, which indicates that the magnification effect of the top of the slope is obvious. After the vibration process and sliding of the landslide, the large-sized particles in the soil-rock mixture deposit move downward faster and slip on the surface of the deposit body. There was a very obvious phenomenon of particle sorting in the pile-up at the foot of the landslide body. The results of this study are of practical significance for the analysis of the dynamic response law of soil-rock mixture deposit under seismic load due to the change of rock content and slope gradient.     

不同厚度饱和砂土中群桩P-Y滞回曲线规律研究

根据Buckingham π定理设计制作直群桩和斜群桩相似模型,通过电磁式振动台试验方法,分别考虑非液化砂土、300 mm和380 mm两种不同厚度饱和砂土,开展在规则正弦波输入下桩土相互作用P-Y滞回曲线规律研究.结果 表明:在非液化砂土中,P-Y滞回曲线的主斜率变化较小,说明在振动输入过程中,桩周土体刚度并未发生显...     

兰桥排土场边坡失稳模式及其稳定性数值分析

以兰桥矿区排土场边坡工程为例,在掌握排土场边坡工程地质条件的基础上,详细分析该多台阶排土场边坡失稳的破坏模式和主要影响因素,采用极限平衡法和有限元强度折减法对其稳定性进行分析。计算结果表明,该边坡可能沿着排土场下卧腐殖土层滑动,塑性区首先在腐殖土层贯通,接着主要向上产生2条塑性区变化带,其中沿着中部台阶边坡发展的塑性区较早贯通,而塑性区朝坡顶的贯通相对滞后;随着地下水位的升高,竖向拉应力区有扩展趋势,其产生的附加位移越大,对边坡的安全越不利;以竖向增量位移的变化趋势作为监测和分析边坡稳定性的依据时,应避开位移为零或变化很小的坡段;水平增量位移集中于坡脚,并且在边坡中部偏下的位置开始产生剧变,这种不连续的过渡,更加剧了边坡失稳的可能性。     

横向非一致地震激励下埋地管道的动力响应分析

为研究埋地管道在地震激励时管-土相互作用的动力响应问题,研发双向层状剪切连续体模型土箱,建立管G土相互作用有限元分析模型,对横向非一致地震激励下埋地管道地震响应进行数值模拟分析,并与试验结果进行对比.结果表明:数值模拟和振动台试验结果中的管道应变峰值均呈现出沿管道中间大两端小的现象,管道中间应变峰值最小达到两端的1．6倍左右;管道加速度、 土体加速度峰值均随着加载等级的提高而增大,涨幅愈加明显,多峰频率由0~10Hz逐渐向10~ 20Hz频域扩散,管道运动更为自由;土体位移随着加载等级的提高呈现逐级增大的现象,在加载等级增加到0．4g 时位移曲线斜率减小,土体非线性表现明显.数值模拟和振动台试验对比分析的结论表明数值模拟分析的合理性和试验结果的可靠性,为研究横向非一致激励对埋地管道地震响应的影响提供了依据.     

Mitigation measures for pile groups behind quay walls subjected to lateral flow of liquefied soil: Shake table model tests

This paper presents experimental results of a series of 1g shake table tests on mitigation measures for a model consisting of a 3×3 pile group and a sheet-pile quay wall in which the pile group was subjected to liquefaction-induced lateral spreading. First, general observations associated with the mechanism of lateral spreading and pile response are presented based on tests without remedial measures, followed by in depth discussions. Second, three remedial techniques were deployed to provide an adequate seismic performance of the pile group and the quay wall: (i) mitigating sheet pile of floating type, (ii) mitigating sheet pile of fixed end type, and (iii) anchoring the quay wall to a new pile row. The main objective of these mitigation methods was to restrict ground distortion behind the quay wall, enhancing seismic response of pile group and quay wall. This mitigation philosophy was decided based on the outcome of the first part, which consisted of a series of tests without mitigation measures. In addition, it should be noted that the proposed countermeasures were selected to be applicable for existing vulnerable pile groups, which are at risk of liquefaction and lateral spreading. Results of different mitigation tests are comparatively examined using a parameter called reduction factor, and the effectiveness of each countermeasure is discussed in detail. The results demonstrate that by applying the proposed mitigation measures the seismic performance of both pile group and quay wall can be improved, as a result of reduction in soil displacement and velocity of soil flow.