交通荷载下台阶式加筋土挡墙动力响应的试验研究

台阶式加筋土挡墙在山区道路边坡支挡结构中应用广泛,针对总高相同的二级台阶式加筋土挡墙开展1∶3大型缩尺模型试验,首先分析交通循环荷载作用下台阶宽度D对加筋土挡墙顶部基础沉降比的影响,进而选取D=0.4H2(H2为下级挡墙高度)的台阶式加筋土挡墙,研究交通荷载幅值及频率变化时,挡墙位移、土压力、筋材应变和潜在滑动面的动力响应规律。结果表明:加载初期挡墙顶部沉降和面板水平位移增加明显,但随循环次数增加呈收敛趋势;面板最大水平位移出现在上级墙高约0.85H(H为总墙高)处,且分布模式几乎不受幅值及频率变化影响;荷载幅值和频率对上级挡墙筋材应变的影响明显,下级挡墙筋材在上级墙趾下方处应变较大;二级挡墙水平土压力值沿墙高均呈顶部与底部小而中部较大的分布形式;上级挡墙潜在破裂面随荷载幅值增大而下移,由局部破坏逐渐向深层整体破坏演变;填筑过程将使下墙近面板处垂直应力增至约为1.5倍自重。研究结果将为台阶式加筋土挡墙设计与施工提供有益指导。     

土工格栅加筋土柔性桥台结构性能的试验研究

基于静载作用下加筋土柔性桥台结构工作性能的试验研究,综合对比分析桥台基础距下部挡墙面板的距离D对柔性桥台结构极限承载力、下部挡墙变形特点、筋材应变和土压力的影响。试验结果表明：当下部加筋挡墙中筋材长度为整体桥台高度时,桥台结构极限承载力随偏移距离D增加呈现先增加后减小趋势,且在D为0.4H_L(H_L为下部挡墙高度)时达到最大值;加筋柔性桥台整体结构加载至破坏前一级载荷时,桥台基础沉降与台背加筋土顶部沉降均呈近似线性变化,且D/H_L为0.4时二者差异沉降最小;挡墙面板顶部的水平位移明显大于中、底部,且挡墙水平位移与挡墙高度比值均小于1%;挡墙中各层筋材应变最大值随D增加而逐渐向远离面板方向发展,且D为0.4H_L时台背加筋土和下部挡墙加筋中筋材的应变相差不大,整体柔性桥台结构工作性能达到最佳状态。     

循环荷载下台阶式加筋土挡墙力学与变形性能的试验研究

台阶宽度是影响台阶式加筋土挡墙力学与变形性能的重要因素之一。首先开展室内单级加筋土挡墙极限承载力试验,基于此确定循环荷载幅值,进而研究循环荷载作用下台阶宽度D对二级台阶式加筋土挡墙位移、土压力、筋材应变规律和可能的潜在滑动面影响。试验结果表明:面板位移最大值及附加水平土压力峰值出现在墙高约0.85H(H为总墙高)处;台阶越宽,下级墙面板位移、附加水平压力和墙底靠近面板处垂直压力减小,底层筋材应变也呈减少趋势;承载板基础沉降和挡墙面板水平位移在试验初期加载时增加明显,当循环次数N大于5000次后增幅减缓并呈收敛趋势;上级挡墙可能的潜在滑动面以贯穿加载板近面板端和0.6H_1(H_1为上级墙高)面板处或者贯穿加载板远面板端和(0.3～0.4)H_1面板处为主。该成果将丰富试验研究并为实践应用提供借鉴和参考。     

静动载下筋材变化对加筋土挡墙性能影响分析

为了研究动静荷载下,加筋长度及筋材类型变化对加筋土挡墙工作性能的影响,进行了7种工况下的加筋土挡墙模型试验,对比分析了加筋土挡墙的水平土压力、水平土压力系数、墙面水平位移和加载板竖向沉降及筋材应变等参数的发展规律。试验结果表明:动载下加筋土挡墙筋材应变随着加载时间的增长、加筋长度的减小、位置高度的增加而增大,且顶层筋材应变远远大于其他层;加筋长度及筋材横肋的减少明显降低挡墙的承载性能,格栅横肋减少导致挡墙极限承载力降低18% ,加筋长度减少使面板水平位移最大增大了2.2倍;与静载作用下相比,动载下土工格栅的侧向约束作用及网兜效应能够得到更好地发挥。     

顶部条形荷载作用下加筋土挡墙水平变形分析

基于有限元数值方法,综合研究了顶部条形荷载宽度、偏移距离、荷载大小、筋材长度和填土性质等对挡墙水平变形的影响,研究结果表明：增加基础偏移距离,导致墙面水平变形逐渐减小,而最大变形出现位置逐渐降低;当增加基础宽度或荷载等级,可显著增加加筋土挡墙水平变形前者使最大水平变形出现的位置逐步下移,后者使最大水平变形出现位置逐步上移,最终趋于稳定;增加填土抗剪强度,可显著提高挡墙抗变形能力,从而显著减少加筋土挡墙面板水平变形;增加筋材长度可有效减小墙面水平变形,当筋材长度增至0.7倍墙高后,继续增加筋材长度对墙面板水平变形的控制作用减弱。     

加筋格宾挡墙在重复荷载作用下动变形特性试验研究

 为研究加筋格宾挡墙变形特性,对加筋格宾挡墙进行重复荷载作用下的模型试验,得出5种频率(2,4,6,8,10 Hz)、3种振幅(40～80,50～100,60～120 kPa)的动载作用下加筋格宾挡墙面墙累计侧向变形和竖向变形(沉降)的变化规律,以及影响面墙动变形特性的主要因素及其显著性;并对分级卸载时面墙的变形特性也进行分析研究。结果表明：挡墙动变形特性受振动次数、动荷载幅值以及格宾笼填充率等因素的影响,振动频率影响不显著;挡墙较大侧向变形发生在第3～5层;随着动荷载幅值的增大,达到变形稳定所需的振动次数增加,变形值亦增大;动变形的发展随振动历时的增长而增大,初期增长较快,随后逐渐变缓;分级卸载过程中,面墙侧向变形几乎没有弹性恢复。     

台阶式加筋土挡墙面板水平位移与稳定性关系研究

为研究台阶式加筋土挡墙面板水平位移特征及其最大水平位移与稳定性的量化关系，采用验证的有限差分数值方法确定挡墙面板水平位移和每层筋材最大拉力，并借助强度折减方法确定相应挡墙的稳定系数，进而参数化分析填土及地基土性质、筋材性质和分级模式对面板水平位移及挡墙稳定性的影响，结果表明：(1)针对两级加筋土挡墙，保持其他参数不变：增加填土内摩擦角φ或黏聚力c，挡墙自稳能力增强，最大水平位移和实际筋材最大拉力均明显减少；增加上级或下级挡墙筋材长度，面板最大水平位移呈减少趋势，挡墙稳定系数相应增加，当上级筋材长度为0.7H(H为总墙高)和下级筋材长度为0.6H时，挡墙变形和稳定系数趋于稳定；减少筋材层间距或增加筋材刚度，挡墙最大水平位移减小，而稳定系数相应增加。(2)针对各级挡墙均分总墙高的台阶式加筋土挡墙，增加台阶宽度，面板最大水平位移先减小后渐趋稳定，对于规范推荐的填土(φ=34°)，确定相邻两级挡墙互不影响的临界台阶宽度为1.2倍分级墙高。(3)当台阶式加筋土挡墙总墙高和相对台阶宽度不变时，增加分级数导致最大水平位移和稳定系数均呈先减少后增加的趋势；两级加筋土挡墙上、下级墙高比不大于1时，墙高比...     

循环荷载作用下格栅防护柔性埋地管道的性能分析

交通循环荷载下埋地管道性能与防护是当前研究的重点问题,首先针对格栅加筋柔性管道开展试验研究,分析管道埋深H为3D(D为管道外径)时循环荷载水平和频率、首层格栅埋深、长度、层间距和筋材层数对管道力学与变形性能的影响,试验结果表明:首层格栅最佳埋深u为0.4B(B为加载板宽度),最佳层间距ug为0.5B,最佳铺设长度L为5D;增加格栅层数能显著增强土体,从而有效减少管道变形和加载板沉降;提高荷载水平或降低荷载频率使管道变形、加载板沉降和格栅应变整体显著增加;格栅应变随其与加载板中心的距离增加而减小,格栅中心点应变随循环次数增加呈现先增加后减少的趋势。进而,基于有限元数值模拟分析管道埋深H、加载板宽度B和管径D对管道力学性能的影响,数值结果表明增加管道埋深或减小加载板宽度,管道径向变形减小;同等荷载作用下,减小管径时管道径向变形增大,筋材加筋效果减弱,适当增加管道直径,有利于筋材加筋作用的充分发挥,从而减小管道径向变形。     

水平静–动荷载作用下加筋土挡墙变形破坏机制研究

实际工程中加筋土挡墙除承受竖向荷载作用,还承受着水平向的静荷载和冲击荷载作用。鉴于此,对水平静–动荷载作用下的加筋土挡墙进行室内模型试验,分别对挡墙变形、水平土压力、筋材应变及潜在破裂面进行归纳和总结,探究其变形破坏机制。结果表明:减小加筋间距、增大筋材长度可增强加筋土挡墙的稳定性,并有利于控制变形,对于抵抗冲击荷载作用,增加筋材长度更为有效;加筋土挡墙在水平静荷载作用下变形和土压力均呈渐进式发展,但在各级冲击荷载作用下,其变形和土压力均发生明显的"阶梯式"突变;静、动荷载作用下筋材应变均呈现单峰值状态,总体上部大、下部小,与挡墙变形一致;与竖向荷载破坏模式不同,当筋长为0.75H(H为墙高)时,静、动荷载作用下加筋土挡墙均表现为加筋区末端破坏,但筋长增加至1.5H时,静、动荷载下挡墙破坏模式不同。研究成果不但为水平荷载作用下加筋土挡墙的设计研究提供依据和参考,同时还可丰富加筋土理论。     

考虑筋材蠕变-温度耦合效应的加筋土挡墙变形分析

基于既有土工合成材料筋材蠕变试验结果及蠕变特性分析，构建一种考虑蠕变-温度耦合效应的筋材本构模型，并利用二维瞬态热传导方程，建立计算加筋土挡墙温度的有限差分公式，进而确定加筋土挡墙温度并结合筋材本构模型计算面板水平位移和筋材最大应变，综合分析了初始温度、温度幅值、筋材层间距、墙顶超载、填土内摩擦角和导热率等因素对挡墙水平位移和筋材应变的影响。计算结果表明：挡墙竣工后初次环境温度升温过程使面板水平位移和筋材最大应变增加明显，后续温度周期性变化时挡墙变形增长缓慢；挡墙初始温度越高，其初期变形增加明显，而增加温度幅值导致面板长期变形量增加明显；增加墙顶超载、筋材层间距或减小填土摩擦角，导致相同时间内面板水平变形增加明显；填土导热率对面板水平位移和筋材最大应变的影响较小；环境温度周期性变化下，3 a内挡墙最大水平位移δ_max与墙高H比值δ_max/H变化范围在0.9%～1.5%；筋材最大应变靠近面板且最大值接近10%的限值，实践中应重点关注靠近面板的筋材长期性能变化对加筋土挡墙变形和稳定性影响。     

Cyclic response of footing on geogrid-reinforced sand with void

This paper describes laboratory tests on footing constructed on unreinforced and geogrid-reinforced sand with circular a void subjected to a combination of static and repeated loads. The settlement of the footing was measured for up to 5000 cycles of loading and unloading. The variables examined in the testing program include the number of geogrid layers, the location of the void within the soil, the amplitude of cyclic load, and the number of load cycles. The results show that the footing performance due to cyclic loading is better for thicker geogrid reinforced sand with a void than for unreinforced sand with no void. In addition, a critical region was found to exist under the footing, under which a void results in increased footing settlement. Overall, the results indicate that the reinforced soil-footing systems with sufficient geogrid-reinforcement and sufficient void embedment depth behave much more stiffly and are thus capable of handling greater loads with lower settlement than those in unreinforced soil without a void. The undesirable effect of the void on the footing behavior can be eliminated. In addition, the results show that the values of footing settlement increase rapidly during the initial loading cycles; thereafter the rate of settlement is reduced significantly as the number of loading cycles increases.     

格栅加筋挡土墙加载速率相关的变形强度特性分析及有限元模拟

根据土工格栅加筋挡土墙的模型试验,分析研究了加筋挡土墙在加载速率变化条件下的变形和强度特征.试验中通过墙背填土顶面的条形基础在垂直方向施加荷载,加载过程中基础沉降速率不断发生变化,期间还包含蠕变加载和循环加载.试验发现土工格栅加筋挡土墙存在非常显著的速率相关的行为特性,即沉降速率发生变化时,基底压力-沉降曲线也发生相应...     

格栅条带式加筋胎面挡土墙变形性能数值计算

采用土工格栅加筋的方法提高废旧轮胎挡墙的承载性能,促进废旧轮胎挡墙的推广应用,通过数值计算方法分析了不同墙顶荷载下有无土工格栅加筋的废旧轮胎挡墙的水平变形与竖向沉降反应特征,得出铺设土工格栅加筋的方法可显著减小墙体的水平变形和竖向沉降,提高废旧轮胎挡墙结构的承载能力,随着外荷载的增加,墙体变形模式依次呈凹凸微小变化型、“弯弓”型、“似弯弓”型和“鼓腮”型和直线型。考虑土工格栅的加筋长度、竖向加筋间距以及格栅加筋刚度3种因素对废旧轮胎+土工格栅加筋土挡墙的水平变形的影响,得出在废旧轮胎加筋土挡墙设计中,建议土工格栅的加筋长度选取范围为0.5H～0.7H,土工格栅竖向间距的选取范围为0.4 m~0.7 m,格栅刚度不宜大于5 000 kN/m。     

Modeling of the cyclic behavior of shallow foundations resting on geomesh and grid-anchor reinforced sand

Storage tank foundations with frequent discharges and filling or road embankments under repeated traffic loads are examples of foundations subjected to the cyclic loading with the amplitude well below their allowable bearing capacity. The concern exists for the amount of uniform and non-uniform settlement of such structures. The soil under such foundations may be reinforced with geosynthetics to improve their engineering properties.This paper deals with the effects of using the new generation of reinforcement, grid-anchor, for the purpose of reducing the permanent settlement of these foundations under the influence of proportion of the ultimate load. Unloading-reloading field tests were performed to investigate the behavior of a square footing on the sand reinforced with this system under such loads. The effects of footing size and reinforcement types on the cyclic behavior of the reinforced sand were studied experimentally and numerically by the aid of computer code. The large-scale results show that by using the grid-anchors, the amount of permanent settlement decreases to 30%, as compared with the unreinforced condition. Furthermore, the number of loading cycles reaching the constant dimensionless settlement value decreases to 31%, compared with the unreinforced condition. Another goal of this paper is to present the equations for reinforced soil under cyclic loading to prevent such complicated calculation involved in deformation analysis. According to these equations, calculation of the permanent settlement and the number of load cycles to reach this amount for each foundation with a given size on the geomesh and grid-anchor reinforced sand, without further need to carry out the large-scale test, is supposed to perform easily.     

软土地基临江特大型相邻深基坑同期施工监测分析

 结合软土地基临江两相邻深基坑施工监测数据,分析两基坑同期开挖过程中邻近位置围护墙变形、支撑轴力和立柱沉降受到的影响,分析结果表明：相邻位置中部的围护墙变形呈增大趋势,角部及远离相邻位置的围护墙变形受邻近基坑影响较小;相邻基坑开挖对邻近位置的围护墙顶竖向位移影响较大,基坑距离越小,相邻位置围护墙顶水平位移越大;邻近基坑处支撑轴力达峰值后呈变小趋势,立柱竖向位移值呈加大趋势;与已有理论对比发现基坑相邻位置围护结构变形不同于独立基坑开挖的情况。     

Experimental investigation on the performance of multi-tiered geogrid mechanically stabilized earth (MSE) walls with wrap-around facing subjected to earthquake loading

Construction of mechanically stabilized earth (MSE) walls in multi-tiered configurations is a promising solution for increasing the height of such walls. The good performance of this type of walls after recent major earthquakes was reported in a number of technical studies. In the present study, an experimental approach was adopted to compare the seismic performance of single-tiered and multi-tiered MSE walls using physical modeling and through conducting a series of uniaxial shaking table tests. To do so, several geogrid-reinforced soil walls with wrap-around facing (i.e., three-, two-, and single-tiered) with a total height of 10 m were designed in the form of prototypes of 1-m-height wall models. The step-wise intensified sinusoidal waves were applied to the models in 14 typical forms. Comparing the shaking table test results confirmed the post-earthquake advantages of multi-tiered MSE walls. The results revealed that tiered walls exhibited better behaviors under earthquake loading in terms of the seismic stability of the wall, displacement of the wall crest, horizontal displacement of the wall facing, deformation mode and failure mechanism of the wall, settlement of backfill surface, and seismic acceleration responses.     

循环荷载作用下黏性土加筋挡墙有限元动力特性分析

在循环荷载作用下,对加筋土挡墙进行有限元模拟分析,研究黏性土加筋土挡墙的动力特性.重点研究挡墙回填土为黏性土条件下,不同加筋材料、动荷载峰值加速度对加筋土挡墙的影响.由计算结果认为在循环荷载作用下加筋土挡墙水平位移受动荷载峰值加速度影响较大,加筋土挡墙最大位置出现在挡墙下部,黏性回填土的加筋土挡墙变形量要小于砂土回填的加筋土挡墙.     

Self-centring segmental retaining walls—A new construction system for retaining walls

This paper reports on an experimental study on a new self-centring retaining wall system. Four post-tensioned segmental retaining walls (PSRWs) were experimentally tested. Each of the walls was constructed using seven T-shaped concrete segments with a dry stack. The walls were tested under incrementally increasing cyclic lateral load. The effect of the wall height, levels of post-tensioning (PT) force, and bonded versus unbonded condition of PT reinforcement on the structural behavior of the PSRWs was investigated. The results showed that such PSRWs are structurally adequate for water retaining structures. According to the results, increasing the wall height decreases initial strength but increases the deformation capacity of the wall. The larger deformation capacity and ductility of PSRW make it a suitable structural system for fluctuating loads or deformation, e.g., seawall. It was also found that increasing the PT force increases the wall’s stiffness; however, reduces its ductility. The residual drift and the extent of damage of the unbonded PSRWs were significantly smaller than those of the bonded ones. Results suggest that this newly developed self-centring retaining wall can be a suitable structural system to retain lateral loads. Due to its unique deformation capacity and self-centring behavior, it can potentially be used for seawall application.