采用K–刚度法设计的模块式加筋土挡墙数值模拟

基于一采用K–刚度法设计的模块式加筋土挡墙建立有限差分数值模型,并采用界面双曲线模型真实模拟底层模块–水平基座界面及水平基座–地基界面,研究实际模块式加筋土挡墙在工作应力下的性状,并进一步分析墙趾界面剪切特性。结果表明:数值计算的挡墙筋材应变分布、填土中各层筋材最大拉力、墙面筋材连接力和墙面最大位移值与实测值比较吻合;K–刚度法计算的填土中筋材最大拉力值与数值模拟和实测值吻合较好,但墙面连接处筋材因受地基沉降和填土压实产生的下拉力影响而大于填土中筋材最大拉力,故K–刚度法不能用于墙面筋材连接力的验算;相较于刚性地基,压缩性地基上模块式加筋土挡墙的墙趾正应力系数较大,而墙趾承担荷载比例较小;尽管基座–地基界面剪切刚度较模块–基座界面小很多,由于其承受的剪应力也很小,墙趾并不会沿着基座–地基界面发生滑移破坏,模块–基座界面对挡墙墙趾起到主要的约束作用。     

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。     

软土地基加筋土挡墙现场试验研究

 结合一软土地基反包式土工格栅加筋黏性土挡墙现场测试,对挡墙填筑过程中原地表沉降、墙趾水平和垂直位移、墙面水平位移、挡墙内部垂直土压力和墙背水平土压力,以及筋材应变分布等进行分析,探讨其工作性状及其稳定性。分析结果表明：软土地基加筋土挡墙的破坏形式表现为外部失稳;挡墙墙面出现“鼓肚”现象,其最大水平位移位于挡墙中部墙高位置;格栅应变在距墙面0.8 H(H为挡墙的高度)处最大,设计上的0.3H法不能适用于深厚软土地基加筋土挡墙。研究成果可为今后类似工程的研究、设计与施工提供参考。     

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。     

软弱地基刚/柔性组合墙面加筋土挡墙数值模拟

 基于软弱地基刚/柔性组合墙面加筋土挡墙离心模型试验,建立原型挡墙三维精细化有限差分数值模型,探讨挡墙在上覆荷载作用下的性状及受力机制。研究结果表明,数值模型计算结果与离心模型试验结果吻合较好,显示该型挡墙具有很好的承载性能,能适应软弱地基的大变形;挡墙在上覆荷载下产生的变形增量和结构受力与填土内部潜在滑移面位置密切相关,当潜在滑移面位置超过连接件埋深范围时,连接件作用降低,使得挡墙变形和筋材拉力增量明显增大,不均匀沉降显著,而刚性墙面墙背水平土压力和连接件拉力减小;由于“张力膜效应”,下面布置有连接件的筋材较下面无连接件的筋材,其拉力要大一些;上覆荷载引起的作用在组合墙面上的水平荷载可采用朗肯主动土压力计算,设计上,宜按连接件多承担水平荷载考虑。     

加筋土挡墙相似比例模型试验研究

本文对一软土地基上土工格栅反包直立墙面加筋土挡墙进行了相似比例模型试验,以土工格栅为筋材,以砂土为填料,分析其在顶部条形荷载作用下,墙顶沉降、墙面水平位移、墙底地基垂直应力、地基中孔隙水压力、加筋应变的变化规律。对其工作性状及其稳定性作了探讨。     

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...     

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。     

软土地基加筋土挡墙数值模拟及稳定性探讨

 对一软土地基加筋土挡墙建立二维数值模型,模拟其在分级堆载情况下挡墙和地基内的沉降、水平位移、土压力,以及土工格栅轴向应变的变化规律,模拟结果与现场实测结果基本吻合。采用有限元强度折减法计算的挡墙稳定性和滑裂面位置与实测情况一致,表现为深层滑动失稳。模拟和实测的各层筋材最大应变出现在距墙面4～6 m的位置,与目前土工合成材料加筋挡墙设计理论的朗肯破坏面位置不同,其原因是目前的挡墙设计理论基于刚性地基假定,未考虑地基变形对筋材应变分布及稳定性的影响。采用该数值模型探讨加长挡墙底部筋材对其稳定性的影响,得出挡墙稳定性与底部筋材加长长度和层数关系密切。得到的挡墙稳定性与筋材加长长度和层数的关系曲线,对于软土地基加筋土挡墙设计有指导意义。     

不同筋材界面剪切试验研究

为了研究废旧轮胎、土工格室和土工格栅3种不同土工合成材料的筋-土界面抗剪特性,对试样开展了一系列大型直剪试验。对比了3种筋材的加筋效果,并研究了竖向荷载对筋-土界面抗剪强度和剪应力-剪切位移曲线特征的影响。试验结果表明:筋-土界面的剪切应力与剪切位移关系为非线性;几种不同筋材加筋效果较为显著,其中废旧轮胎的加筋效果最为明显;筋-土界面的黏聚力提高较大,内摩擦角变化相对较小,表明筋-土界面主要依靠提高黏聚力增大其抗剪强度。确定了各筋材加筋界面抗剪强度指标,并分析了3种筋材的加筋机理。     

Numerical evaluation of the effect of foundation on the behaviour of reinforced soil walls

This study numerically investigates the influence of foundation conditions, in combination with other factors such as wall height and reinforcement and facing stiffness, on the behaviour of reinforced soil walls (RSWs) under working stress conditions. The foundation was simulated using different stiffnesses and geometries (with and without slope). The results highlight the importance of the combined effect of foundation conditions and the abovementioned factors on the performance of RSWs. The results of these analyses indicate that the shape of the distribution of the maximum reinforcement loads (T_max) with respect to wall height depends on the combined effect of the foundation condition, facing and reinforcement stiffness, and wall height, and varies from trapezoidal to triangular. Additionally, the results indicate that the effect of variations in foundation stiffness on reinforcement tension mobilisation decreases with wall height. Furthermore, the T_max prediction accuracy of three design methods were evaluated and some limitations of each method are presented and discussed.     

Numerical modeling of geosynthetic reinforced soil retaining walls with different toe restraint conditions

This paper reports numerical modeling of the prototype geosynthetic reinforced soil (GRS) walls corresponding to four centrifuge models that have different toe restraint conditions. The development of the interface stresses and displacements at wall toe during wall construction is investigated to understand how the toe carries load in the GRS walls with a practical toe structure. The numerical results show good agreement with the data from the centrifuge modeling. For the GRS walls with a leveling pad embedded in foundation soil, the shear resistance at the facing block-leveling pad interface acts as the toe resistance to counterbalance a portion of horizontal earth load, while the leveling pad-foundation soil interface play no role in wall performance because the soil passive resistance in front of the leveling pad inhibits the development of the shear stress and displacement on this interface. For the GRS walls with an exposed leveling pad, it is the leveling pad-foundation soil interface that works for carrying the earth load because the wall is more likely to slide along this weaker interface. The contribution of the toe to load capacity depends on the shear strength of the effective toe interface that contributes to the resistance against the earth load.     

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.     

Influence of toe restraint conditions on performance of geosynthetic-reinforced soil retaining walls using centrifuge model tests

Current design regulations most often require use of limit equilibrium methods for the internal stability analyses of geosynthetic-reinforced soil (GRS) walls. However, the limit-equilibrium based approaches generally over-predict reinforcement loads for GRS walls when comparing with measured data from full-scale instrumented walls under working stress conditions. Wall toe resistance has an important influence on the performance of GRS walls but is ignored in limit equilibrium-based methods of design. This paper reports centrifuge modelling of GRS walls which have different toe restraint conditions but are otherwise identical. The GRS wall models prepared in this study isolate the influence of wall toe resistance on the performance of walls. Based on measured data from four centrifuge wall model tests, a reduction in wall toe resistance (by reducing the interface shear resistance at the base of the wall facing or removing the soil passive resistance in front of the wall toe or both) induces larger maximum facing deformation and reinforcement strain and load. The results also demonstrate that the wall models with typical toe restraint conditions are most likely operated under working stress conditions while those with poor toe restraint conditions may experience (or be close to reach) a state of limit equilibrium.     

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.     

Field monitoring and analyses of the response of a block-faced geogrid wall using fine-grained tropical soils

This paper presents the results of a 4.2 m high instrumented section of block-faced geogrid wall built using fine-grained tropical soils as backfill. Laboratory tests were used to assess the soil resistance and the stress–strain behavior is reported. Monitoring was performed over two months, including the construction period, and indicated good performance. Reinforcement tension was measured at different locations in four different layers. A specific device was designed and used to monitor vertical and horizontal internal loads on blocks that comprised the wall face. Topography, inclinometers, and magnetic settlement plates were used to measure internal and external movements. Total pressure cells at five different locations near the foundation level measured vertical stresses. Analytical and finite element method analyses were carried out and the predicted and measured tension in the reinforcements and lateral movements are compared. In addition, the significance of soil matrix suction, induced stress due to backfill soil compaction, shear resistance parameters, on the wall block facing is discussed.     

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.     

钢筋混凝土剪力墙剪切刚度计算的斜向腹筋桁架-拱模型

钢筋混凝土剪力墙构件腹板为双向配筋,其剪切刚度的传统计算方法忽略竖向钢筋的作用,低估了剪力墙构件的剪切刚度和受剪承载力。为考虑双向配筋对剪力墙剪切刚度的影响,提出等效斜向腹筋桁架-拱模型,与传统桁架-拱模型不同,模型中桁架作用的腹杆由斜向等效受拉钢筋及斜裂缝间的混凝土斜压杆构成,斜向等效钢筋的方向与裂缝处两个方向钢筋的合力方向一致。采用最小能量原理推导了斜向压杆倾角的理论算式,在已有试验数据的基础上,对压杆角度理论算式进行简化,提出了便于工程应用的简化算式。斜向开裂后剪力墙的有效剪切刚度为斜向腹筋桁架模型剪切刚度与拱模型剪切刚度的叠加,采用该模型分别对现有的剪力墙试件进行计算,并将计算值与实测值进行了比较,结果表明,提出的斜向腹筋桁架-拱模型可以较为准确地计算钢筋混凝土剪力墙构件斜向开裂后的有效剪切刚度。