面板和筋材刚度对加筋土挡墙工作性状的影响

利用有限元法研究了面板和筋材刚度对不同坡度下加筋土挡墙应力变形特性的影响。结果表明:斜坡加筋土挡墙的面板侧向位移和侧向土压力比修筑在水平场地上的挡土墙更高,同时,侧向土压力随面板刚度的增大以及筋材刚度的减小而增大,面板侧向位移随筋材刚度的增大而减小,但随着面板刚度的增大,面板侧向位移呈现先减小、后增大的趋势,面板最大侧向位移所处的位置由面板中部上移至顶部,并产生了类似悬臂结构的绕墙趾转动趋势,同时,面板的挠曲也逐渐减小。研究结论可为加筋土挡墙在山区公路修筑中的应用提供一定指导。     

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。     

地震作用下模块式面板土工合成材料加筋土挡墙的内部稳定分析

由于造价低廉,性能优良且外表美观,模块式面板土工合成材料加筋土挡墙在我国交通及城建等领域有着广泛的应用前景。大量的工程实践证明,土工合成材料加筋土挡墙的抗震性能良好,但仍有必要进行合理的抗震设计,而内部稳定校核是加筋土挡墙抗震设计的一个重要环节,它一定程度上决定了高烈度地震区加筋土挡墙的配筋方式及配筋密度。应用非线性动力有限元法分析不同加筋长度、加筋间距及不同地震作用下模块式土工合成材料加筋土挡墙在地震作用下的内部稳定,研究了筋材蠕变对加筋土挡墙动力内部稳定的影响,并将有限元分析的结果与国外规范建议的内部稳定校核结果进行比较。研究结果表明,在正常配筋密度条件下,各层筋材最大内力的位置与规范建议的位置有一定的区别,墙体下部更加远离面板;且筋材的最大内力沿高度的分布与该规范计算结果差别较大;而筋材蠕变使筋材的内力出现重分布。     

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...     

多级加筋土复合式挡墙的现场试验

在现场对由L型挡土墙与加筋土挡墙形成的多级加筋土复合式挡墙进行了原位试验。试验表明:土压力和拉筋应变随上覆填土厚度增加而增大,但增速却减小;L型挡土墙的加筋土体底部竖向土压力沿筋长方向在加筋土施工期间呈非残性分布,在其上的中且上级模块式加筋土挡墙的竖向土压力施工期呈明显的非线性分布,但最大值均靠近拉筋尾部;L型加筋土挡墙的拉筋应变非常小,且曲线只有一个峰值;模块式加筋土挡墙的加筋土体底部竖向土压力沿筋长方向起初呈线性分布且大小基本相同,但随着填土厚度的增大而呈明显的非线性分布,且出现双峰值;中、上级挡墙的墙面板基底竖向应力随填土厚度的变化形式基本一样,且随填土厚度的增大先是内侧大于外侧,而后是外侧大于内侧;模块式加筋土挡墙的墙背侧向土压力沿墙高、拉筋应变沿筋长方向均呈非线性分布,且实测值均较小。     

多级加筋土复合式挡墙的现场试验

在现场对由L型挡土墙与加筋土挡墙形成的多级加筋土复合式挡墙进行了原位试验。试验表明:土压力和拉筋应变随上覆填土厚度增加而增大,但增速却减小;L型挡土墙的加筋土体底部竖向土压力沿筋长方向在加筋土施工期间呈非残性分布,在其上的中且上级模块式加筋土挡墙的竖向土压力施工期呈明显的非线性分布,但最大值均靠近拉筋尾部;L型加筋土挡墙的拉筋应变非常小,且曲线只有一个峰值;模块式加筋土挡墙的加筋土体底部竖向土压力沿筋长方向起初呈线性分布且大小基本相同,但随着填土厚度的增大而呈明显的非线性分布,且出现双峰值;中、上级挡墙的墙面板基底竖向应力随填土厚度的变化形式基本一样,且随填土厚度的增大先是内侧大于外侧,而后是外侧大于内侧;模块式加筋土挡墙的墙背侧向土压力沿墙高、拉筋应变沿筋长方向均呈非线性分布,且实测值均较小。     

公路路堤边坡条带式加筋土挡墙模型试验及优化设计研究

土工合成材料加筋土技术广泛应用在公路路堤边坡挡墙结构中.公路路堤边坡加筋土挡墙既受到车辆的竖向荷载,也受到来自车辆撞击防护栏、风荷载作用在隔音墙的水平荷载.模型试验以公路填方路堤边坡工程为研究背景,设计加筋土挡墙模型试验及加载装置,模拟施加路堤边坡挡墙上的竖向静荷载、水平瞬时荷载和水平静荷载,研究加筋土挡墙优化设计方法.试验研究以0.2mm厚的白卡纸为面板,采用100g规格的无纹信封用牛皮纸为筋材,中粗砂作为填料.采用理论分析计算方法得出筋带所需面积,通过加筋土挡墙模型试验确定极限荷载大小,应用FLAC3D进行数值模拟和优化分析得到路堤边坡加筋土挡墙优化设计方案.     

土工格栅返包土工袋加筋土挡墙的地震响应分析及设计建议

为了研究土工袋加筋土挡墙在地震作用下的抗震性能,开展了大型的振动台模型试验。结果表明：随着加载的持续进行,挡墙模型的自振频率降低,阻尼比增加;PGA放大系数随输入地震动峰值加速度的增大而减小,墙高对PGA放大系数的影响反倒不大。土工袋加筋土挡墙的峰值动土压力呈现“中间小,两头大”的分布规律,且墙高越高,输入地震动峰值加速度越大,峰值动土压力越大,而不同地震波形的频谱差异对土压力量值和分布的影响较小。通过数值模拟研究了坡度对土工袋加筋土挡墙力学特性的影响,认为土工袋加筋土挡墙墙后侧向土压力和筋材的拉应力随着墙体坡度的增大而增大,当墙体坡度小于1∶0.75时,侧向土压力较小;当墙体坡度大于1∶0.75时,墙后土压力迅速增加,土压力的分布图式类似呈三角形分布。筋材的拉应力沿长度方向呈单峰型分布,各层筋材的拉应力随上覆填土厚度的增加而增大,但增加的幅度逐渐减小。另外,土工袋加筋土挡墙的剪应变增量、活动区范围以及位移均随墙体坡度的增大而增大。     

墙面倾角对模块式加筋土挡土墙结构影响的分析

基于FLAC3D建立了加筋土挡土墙数值模型，在验证模型有效性的基础上，通过调整墙面倾角，分析墙面倾角对模块式加筋土挡土墙的侧向变形、土压力和筋材拉力的影响。结果表明：当墙面倾角由90°逐渐减小至65°时，模块式加筋土挡墙的侧向变形、面墙后的土压力和筋材拉力均出现减小；侧向变形模式由外倾-平移式转为平移、平移-鼓胀式；面板后水平土压力沿墙高的分布规律由线性分布转变为非线性分布；墙内筋材的拉力峰值与墙面倾角间呈线性关系，筋材与模块连接处的拉力与墙面倾角间呈指数关系；75°是模块式加筋土挡土墙的合理倾角，不仅便于墙面绿化，而且可减少挡土墙变形，提高挡土墙的稳定性。     

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...     

Analyzing the influence of facing batter on reinforcement loads of reinforced soil walls under working stress conditions

The level of reinforcement loads in a reinforced soil retaining wall is important to its satisfactory operation under working stress conditions since it basically determines the wall deformation. Consequently, proper estimation of the reinforcement load is a necessary step in the service limit-state design of this type of earth retaining structures. In this study, a force equilibrium approach is proposed to quantify the influence of facing batter on the reinforcement loads of reinforced soil walls under working stress conditions. The approach is then combined with a nonlinear elastic approach for GRS walls without batter to estimate the reinforcement loads neglecting toe restraint. The approximate average mobilized soil strength in the retaining wall is employed in the force equilibrium analysis. The predictions of reinforcement loads by the proposed method were compared to the experimental results from four large-scale tests. It is shown that the proposed semianalytical approach has the capacity to reproduce the reinforcement loads with acceptable accuracy. Some remaining issues are also pinpointed.     

Effects of facing,reinforcement stiffness,toe resistance,and height on reinforced walls

This study numerically investigated the combined effect of reinforcement and facing stiffness, wall height, and toe resistance on the behavior of reinforced soil (RS) walls under working stress conditions. For RS walls with vertical segmental block facing, parametric analyses showed that the combined effect of the facing stiffness, wall height, and toe resistance on the distribution of the maximum reinforcement load with depth may be limited to approximately 4 m above the base of the wall. Furthermore, the shape of the distribution of the reinforcement load may be a function of the combined effect of the wall height, reinforcement stiffness, toe resistance, and facing stiffness. For a given facing stiffness and fixed-base conditions, increasing the height of the wall and reinforcement stiffness may change the distribution shape of the reinforcement load from trapezoidal to the triangular. Additionally, the maximum reinforcement loads calculated using finite element analyses were compared to the values predicted by design methods found in the literature. Some limitations of those design procedures are presented and discussed.     

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。     

Behaviour of geogrid reinforced soil retaining wall with concrete-rigid facing

Monitoring was carried out during construction of a cast-in-situ concrete-rigid facing geogrid reinforced soil retaining wall in the Gan (Zhou)-Long (Yan) railway main line of China. The monitoring included the vertical foundation pressure and lateral earth pressure of the reinforced soil wall facing, the tensile strain in the reinforcement and the horizontal deformation of the facing. The vertical foundation pressure of reinforced soil retaining wall is non-linear along the reinforcement length, and the maximum value is at the middle of the reinforcement length, moreover the value reduces gradually at top and bottom. The measured lateral earth pressure within the reinforced soil wall is non-linear along the height and the value is less than the active lateral earth pressure. The distribution of tensile strain in the geogrid reinforcements within the upper portion of the wall is single-peak value, but the distribution of tensile strain in the reinforcements within the lower portion of the wall has double-peak values. The potential failure plane within the upper portion of the wall is similar to “0.3H method”, whereas the potential failure plane within portion of the lower wall is closer to the active Rankine earth pressure theory. The position of the maximum lateral displacement of the wall face during construction is within portion of the lower wall, moreover the position of the maximum lateral displacement of the wall face post-construction is within the portion of the top wall. These monitoring results of the behaviour of the wall can be used as a reference for future study and design of geogrid reinforced soil retaining wall systems.     

不同墙趾约束条件下模块式加筋土挡墙离心模型试验

开展了墙趾正常约束、仅对模块–基座界面作光滑处理、仅对基座–地基界面作光滑处理,以及对基座–地基界面作光滑处理且将基座前方土体挖除这4组不同墙趾约束条件的模块式加筋土挡墙离心模型试验,以研究工作应力下墙趾约束条件对挡墙内部稳定性的影响。研究结果表明,墙趾约束条件对模块式加筋土挡墙内部稳定性影响显著;对模块–基座界面作光滑处理的挡墙,其底层模块沿该界面滑移,挡墙中下部的墙面水平位移和筋材应变明显增大,筋材连接力沿墙高呈三角形分布;对基座–地基界面作光滑处理的挡墙,基座前方地基土仍可给基座提供足够的墙趾约束作用,挡墙内部稳定性同墙趾正常约束情况;对于基座–地基界面作光滑处理后又将基座前方土体挖除这种模拟墙趾受到冲刷的挡墙,其基座沿该界面滑移,挡墙中下部的墙面水平位移和筋材应变显著增大,筋材连接力接近极限状态AASHTO法计算的筋材最大拉力,但挡墙仍能保持稳定;在墙趾可能受到冲刷的极端情况下,挡墙在设计上不应考虑墙趾的约束作用,而对于正常服役状态的挡墙,可采用考虑墙趾约束作用的K-刚度法进行挡墙内部稳定性的计算。     

Earth pressure coefficients for reinforcement loads of vertical geosynthetic-reinforced soil retaining walls under working stress conditions

Based on the nonlinear elastic theory and stress-dilatancy theory, two earth pressure coefficients were proposed to analyze the reinforcement loads at the potential failure surface of vertical geosynthetic-reinforced soil retaining walls under working stress conditions. The earth pressure coefficients take into account the force equilibrium and compatible deformations between soil and reinforcement, and can be obtained by solving two implicit functions by an iterative or graphic method. The effects of backfill compaction and facing restriction are taken into account in the earth pressure coefficients by two additional stress factors, which have been derived analytically using straightforward approaches. To validate the effectiveness of the proposed methods, comparisons were made with the results from large scale tests and numerical simulations. It was demonstrated that the reinforcement loads predicted by the proposed methods were in good agreement with the experimental or numerical results.     

Experimental evaluation of the effect of compaction near facing on the behavior of GRS walls

Experimental studies have been carried out to evaluate the effect of the compaction condition at the back of block facing on the behavior of geosynthetic reinforced soil (GRS) walls. Three GRS walls with 1.2?m high were constructed at the COPPE/UFRJ Geotechnical Laboratory. The walls were well-instrumented in order to monitor the values of the reinforcement load, toe horizontal load, horizontal facing displacement, horizontal stress at the back of the block facing, and vertical displacement on the top of the walls. The behavior of the walls has been investigated at the end of construction and during the surcharge application (post-construction). At the end of the loading, the toes of the walls were gradually released to also verify the influence of the different toe restraints. The results clearly show the effect and call attention to the importance of the compaction conditions near the facing on the behavior of GRS walls.     

失稳加筋土挡土墙加固方案及技术评价

 加筋土挡土墙是国内外广泛采用的挡土墙建设技术。由于交通荷载的急剧增加和该类挡土墙的固有缺陷,国内有多处加筋土挡土墙产生变形甚至倒塌。以山东省荷泽市人民路立交桥加筋土挡土墙失稳为例,对其失稳的内在根源和力学机制进行分析。通过多种加固方案对比,确定以压力注浆、双向斜拉预应力锚固、挂网喷射混凝土等技术为主的综合加固治理方案;运用数值模拟层次分析方法,分别对实施不同技术措施所产生的加固效果进行分析。研究结果表明,斜拉预应力锚杆抑制失稳加筋土挡土墙上部的纵向开裂和墙趾剪切破坏带的塑性滑移,并提供较高的抗拉强度、刚度和较快的增阻速度;混凝土喷层使墙面弧形外鼓得到约束。经现场实施综合加固方案,监测结果显示加固工程取得预期效果,表明该技术方案对类似问题具有推广应用价值。     

格宾加筋土挡墙抗震性能及数值分析

基于有限差分程序FLAC3D动力分析模块,建立水平地震作用下格宾加筋土挡墙足尺数值模型,通过抗震模型试验结果验证数值模型的可靠性,分析不同强度地震波作用、不同竖向加筋间距时,格宾加筋土挡墙的水平位移响应、震陷、加速度响应及破坏模式,在此基础上,提出格宾加筋土挡墙抗震设计相关措施与建议。结果表明:在不同峰值加速度作用下,格宾加筋土挡墙没有出现倒塌破坏,在较大的水平位移及沉降发生后仍能继续承载,表现出良好的抗震性能;在地震波频率特性基本不变的情况下增长加速度峰值,墙面加速度放大系数有减小的趋势;格宾加筋土挡墙建造于7度及以下、8度、9度及以上抗震设防区时,格宾网竖向间距分别不宜大于1.0m、0.75m、0.5m;水平地震作用下挡墙潜在破裂面为双线段组合形式;提出格宾加筋土挡墙抗震设计位移控制标准。