Seismic earth pressures on flexible cantilever retaining walls with deformable inclusions

In this study, the results of 1-g shaking table tests performed on small-scale flexible cantilever wallmodels retaining composite backfill made of a deformable geofoam inclusion and granular cohesionlessmaterial were presented. Two different polystyrene materials were utilized as deformable inclusions.Lateral dynamic earth pressures and wall displacements at different elevations of the retaining wallmodel were monitored during the tests. The earth pressures and displacements of the retaining wallswith deformable inclusions were compared with those of the models without geofoam inclusions.Comparisons indicated that geofoam panels of low stiffness installed against the retaining wall modelaffect displacement and dynamic lateral pressure profile along the wall height. Depending on the inclusioncharacteristics and the wall flexibility, up to 50% reduction in dynamic earth pressures wasobserved. The efficiency of load and displacement reduction decreased as the flexibility ratio of the wallmodel increased. On the other hand, dynamic load reduction efficiency of the deformable inclusionincreased as the amplitude and frequency ratio of the seismic excitation increased. Relative flexibility ofthe deformable layer （the thickness and the elastic stiffness of the polystyrene material） played animportant role in the amount of load reduction. Dynamic earth pressure coefficients were compared withthose calculated with an analytical approach. Pressure coefficients calculated with this method werefound to be in good agreement with the results of the tests performed on the wall model having lowflexibility ratio. It was observed that deformable inclusions reduce residual wall stresses observed at theend of seismic excitation thus contributing to the post-earthquake stability of the retaining wall. Thegraphs presented within this paper regarding the dynamic earth pressure coefficients versus the wallflexibility and inclusion characteristics may serve for the seismic design of full-scale retaining walls withdeformable polystyrene inclusions. 2014 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

Protective effect of retaining wall on rock avalanche:A case study of Nayong rock avalanche in China

Rock avalanches are generally difficult to prevent and control due to their high velocities and the extensive destruction they cause.However,barrier structures constructed along the path of a rock avalanche can partially mitigate the magnitudes and consequences of such catastrophic events.We selected a rock avalanche in Nayong County,Guizhou Province,China as a case to study the effect of the location and height of a retaining wall on the dynamic characteristics of rock avalanche by using both actual terrain-based laboratory-model tests and coupled PFC3D-FLAC3D numerical simulations.Our findings demonstrate that a retaining wall can largely block a rock avalanche and its protective efficacy is significantly influenced by the integrity of the retaining wall.Coupled numerical simulation can serve as a powerful tool for analyzing the interaction between a rock avalanche and a retaining wall,facilitating precise observations of its deformation and destruction.The impact-curve characteristics of the retaining wall depend upon whether or not the rock avalanche-induced destruction is taken into account.The location of the retaining wall exerts a greater influence on the outcome compared to the height and materials of the retaining wall,while implementing a stepped retaining-wall pattern in accordance with the terrain demonstrates optimal efficacy in controlling rock avalanche.

Lateral earth pressure of granular backfills on retaining walls with expanded polystyrene geofoam inclusions under limited surcharge loading

Existing studies have focused on the behavior of the retaining wall equipped with expanded polystyrene(EPS)geofoam inclusions under semi-infinite surcharge loading rather than limited surcharge loading.In this paper,the failure mode and the earth pressure acting on the rigid retaining wall with EPS geofoam inclusions and granular backfills(henceforth referred to as EPS-wall),under limited surcharge loading are investigated through two-and three-dimensional model tests.The testing results show that different from the sliding of almost all the backfill in the EPS-wall under semi-infinite surcharge loading,only an approximately triangular backfill slides in the wall under limited surcharge loading.The distribution of the lateral earth pressure on the EPS-wall under limited surcharge loading is non-linear,and the distribution changes from the increase of the wall depth to the decrease with the increase of the limited surcharge loading.An approach based on the force equilibrium of a differential element is developed to predict the lateral earth pressure behind the EPS-wall subjected to limited surcharge loading,and its performance was fully validated by the three-dimensional model tests.

Shaking table tests on a cantilever retaining wall with reinforced and unreinforced backfill

Physical modelling of cantilever retaining walls with and without backfill reinforcement was conducted on a 1g shaking table to evaluate the mitigation effect of reinforcement on system dynamics(g denotes the acceleration of gravity).The model wall has a height of 1.5 m with a scale ratio of 1/4 and retains dry sand throughout.The input motions are amplified to three levels of input peak base acceleration,0.11g,0.24g,and 0.39g,corresponding to minor,moderate,and major earthquakes,respectively.Investigation of the seismic response of the retaining walls focuses on acceleration and lateral displacement of the wall and backfill,dynamic earth pressures,and tensile load in the reinforcements(modeled by phosphor-bronze strips welded into a mesh).The inclusion of reinforcement has been observed to improve the integrity of the wall-soil system,mitigate vibration-related damage,and reduce the fundamental frequency of a reinforced system.Propagation of acceleration from the base to the upper portion is accompanied by time delay and nonlinear amplification.A reinforced system with a lower acceleration amplification factor than the unreinforced one indicates that reinforcement can reduce the amplification effect of input motion.Under minor and moderate earthquake loadings,reinforcement allows the inertia force and seismic earth pressure to be asynchronous and decreases the seismic earth pressure when inertia forces peak.During major earthquake loading,the wall is displaced horizontally less than the backfill,with soil pushing the wall substantially;the effect of backfill reinforcement has not been fully mobilized.The dynamic earth pressure is large at the top and diminishes toward the bottom.

Model Test and Numerical Analysis on Long-Term Mechanical Properties of Stepped Reinforced Retaining Wall

Model tests and numerical analyses of stepped reinforced retaining wall were performed to investigate the effects of rheology of backfill and creep of geogrids on the long-term performance of the structure.The geogrid tensions,soil pressures,wall deformations and foundation pressure were measured during model construction and loading.A visco-elasto-plastic model and an empirical nonlinear visco-elastic model were utilized to simulate the stresses and deformations of geogrid-reinforced earth-retaining wall under long-term loads.By comparing test data with numerical results,it is shown that the foundation pressure distribution is nonlinear,and the lateral constraint of geogrids for backfill can cause a redistribution of foundation pressure.The curve of soil pressure is outside convex at each step initially,and it is close to the distribution for the case of vertical wall subsequently.The variation trend of geogrid tensions at different heights is obtained.Moreover,the failure mechanism and development mode of potential slip surface in retaining wall are proposed.

Mechanical performance of a double-face reinforced retaining wall in an area disturbed by mining

The application of a double-face reinforced retaining wall during road construction can reduce engineering costs, speed road paving and have a good influence on environment. An ABAQUS numerical model of a double-face reinforced retaining wall was built. The influence of surface subsidence induced by mining was considered. A physical model test was also performed in the laboratory on a reinforced retaining wall. The influence of subsidence induced by mining was observed. The numerical results match measurements in the laboratory very well. The vertical pressure on the base of the retaining wall, the horizontal displacement of the wall and the horizontal soil pressure acting on the wall were analyzed. The differential settlement of the reinforced belt and axial forces in the wall were also studied.

Study on Ultimate Pullout Force of Grouting Anchors of the Anchor-Pull Retaining Wall

Determination of the grouting anchor pullout force is a key step during the design of anchor-pull retaining wall, but it is mostly determined relied on empirical formula at present, and the rationality and the safety cannot be effectively guaranteed. Based on the engineering case of the gravity retaining wall of Qinglin Freeway, the model test was designed, and combined with the results of the ABAQUS finite element numerical analysis, it was analyzed that how the anchor axial pulling force distributes. The results showed that the force of the anchor near the wall bolt was large and which far from the wall was small and the ultimate pullout force was proportional to the length, diameter and shear strength. When the end tension of the anchor was small, the top load played a leading role on the anchor tension. This conclusion confirmed the calculation formula of ultimate pullout force was and provided a theoretical basis for anchor-pull retaining wall design and calculation.

含建筑桩基的顺层岩质边坡桩锚支护体系振动台模型试验研究

基于Bockinghamπ定理,对具有建筑桩基的顺层岩质边坡桩锚支护体系开展振动台模型试验,通过分析预应力锚索、建筑桩基的应变以及边坡坡顶加速度,研究支护体系的动力响应规律。结果表明,预应力锚索的应变在地震波加速度达到峰值时达到最大值,且上排锚索受力大于下排锚索,随着地震幅值的增大,最上排锚索锚固段率先发生滑移破坏失去锚固作用;建筑桩基应变最大值点位于滑动面以下一定深度,且远离边坡坡面的建筑桩基受力大于邻近边坡坡面的建筑桩基;坡顶各点峰值加速度随地震波幅值增大整体表现为线性增大,但在Wenchuan-Wolong波(0.55g)和Sin波(0.4g)工况时,各点峰值加速度相对有所下降,随着地震波幅值增大,各点峰值加速度放大系数在汶川波和正弦波作用下并非单调变化,而是表现为先减小后增大波动变化特点。

强夯作用下回填砂土挡墙墙后土压力分布研究

挡土墙墙后土压力分布是墙体形状及配筋设计的重要依据,为研究强夯作用下挡墙墙后土压力分布规律,开展了自重、堆载及强夯荷载下的挡土墙物理模型试验,通过不同深度的土压力监测,分析了夯击落距和夯击次数对墙后土压力分布的影响,重点分析了强夯冲击松动区的影响,并基于等效静力法修正了强夯作用下墙后土压力理论计算公式。结果表明:单次夯击作用下墙后土压力瞬间增大至极值后逐渐衰减至稳定,随着夯击次数的增多,土体逐渐密实,相应的墙后土压力会逐次增加;浅部土体在强夯作用下会形成冲击松动区,松动区内土体变得松散从而土压力值较小,而松动区下部土压力随深度迅速增大后再减小,呈“鼓肚”状非线性分布;松动区土体重度、松动区厚度尤其是后者对于墙后土压力理论分布曲线影响较大,考虑松动区影响的墙后土压力等效静力法修正理论公式更符合实际情况。

航道开挖对护岸结构影响的离心模型试验研究

为了研究航道开挖对新老护岸结构的影响,依托东宗线航道四改三工程,利用大型土工离心模型试验平台研究航道开挖对老挡墙护岸结构、新施工钢板桩的受力和变形特征的影响,得出航道开挖过程中板桩两侧土压力的分布规律。结果表明,随开挖深度增加,靠岸侧(主动侧)土压力逐渐减小;受板桩位移、变形及离心模型试验重液影响,临水侧(被动侧)土压力部分减小,底部土压力增大。开挖卸载导致老挡墙呈现向水侧移动且向后翻转的趋势。设计工况的极限开挖深度约为3.6 m,此时钢板桩顶部帽梁的水平位移达到0.069 m;对于6、8和10 m 3种长度的板桩,其极限开挖深度约为0.5~0.6倍桩长,且随着桩长增加极限开挖深度逐渐降低。研究得出不同板桩长度下开挖深度的阈值,可为工程建设提供技术参数。

挡墙平动墙后被动土压力研究

墙后土压力分布形式是挡土墙设计与施工的重要参考依据。本研究开展了单一硬土、硬土-软土-硬土、软土-硬土-软土和单一软土4组挡墙平动室内模型试验,分析了墙后实测侧向水平土压力分布规律。结果表明,挡墙平动,对于成层土,被动土压力均在土层交界处土应力发生突变,墙后被动土压力图呈锯齿梯形台阶分布;在侧向水平荷载作用下,水平分层地基软硬土层界面处,无应力集中与应力扩散,与竖向荷载作用下分层地基应力集中和应力扩散存在显著区别。

多级加筋土挡墙在工程中应用及模型试验分析

多级边坡在实际工程中普遍存在滑坡、边坡稳定性低等问题,为研究多级加筋土挡墙在工程实践中的应用。本文基于已有研究成果,通过实地考察和模型试验,进行了深入研究。通过模型试验并运用slide软件进行边坡稳定性及滑动面模拟计算,研究了不同加筋条件下多级加筋土挡墙的工作性能,分析了加筋材料、加筋层数、加筋间距等因素对挡墙稳定性和变形特性的影响。结果表明,加筋材料和层数间距可以改变边坡的摩擦角,提升土体的整体稳定性,在锚杆支护条件下安全系数总体可以提高111%。

Model test on sand retaining wall reinforced with denti-strip inclusions

In conventional reinforced soil structures,the reinforcements are often laid hori-zontally in the soil.In this paper,a new concept of soil reinforced with denti-strip inclusions was proposed and a series of laboratory model tests were carried out on sand retaining wall reinforced with denti-strip inclusions.Besides the horizontal displacements of the facing,the lateral earth pressures acting on vertical elements were measured.A microscopic measurement was performed to investigate the deformation and progressive failure of the sand within model retaining wall.Based on the image analytical technique,the bearing capability and interaction mechanism of reinforced sand retaining wall were analyzed.The model of the initial shear failure and potential failure surface were also put forward.From the experimental results,it is shown that denti-strip inclusions can increase the bearing capability of retaining wall significantly and restrict the facing displacements efficiently,as compared with conventional horizontal reinforcement.

Deformation and localisation behaviours of reinforced gravelly backfill using shaking table tests

To understand the deformational behaviours of geosynthetics-reinforced soil retaining walls(GRS RWs),a series of plane-strain shaking table tests was conducted on retaining wall models.The backfill of the models was made of poorly graded gravel.Deformations and strains in the gravelly backfill induced by seismic loading are recorded in real time,which are of importance to understand the seismic strength and stability of the GRS RW systems,as strain localisation development in the backfill and foundation is related to the degree of strength degradation of the system.In the present study,we aimed at quantifying the induced deformations of the GRS RW models due to shaking.Digital image correlation(DIC)technique was then employed to analyse and provide full-field deformation and motion images with the models.It is demonstrated that,unlike conventional contact devices that are yet limited to provide quantities of a singular and fixed location,DIC provides deformation and motion of the area of interests to reveal the evolution of localisation.

直立式废旧轮胎胎面挡土墙(无加筋/加筋)抗震性能试验对比研究

为了解废旧轮胎胎面挡土墙的抗震性能,促进模块式废旧轮胎胎面挡土墙在高烈度地震区域的推广应用,针对直立式废旧轮胎胎面挡土墙(无加筋/加筋)开展抗震性能试验对比研究。基于相同的测试条件,分别建立了直立式废旧轮胎胎面挡土墙和土工格栅加筋废旧轮胎胎面挡土墙的两种振动台试验模型,考虑近场什邡地震波和远场松潘地震波的作用,研究不同地震强度下的墙体加速度、侧向位移、残余变形、墙后填料加速度、竖向沉降和墙背动土压力的响应特征,并与传统悬臂式刚性挡土墙的动力响应特征进行对比,综合评价以塞土轮胎为墙体面板的废旧轮胎挡土墙的整体抗震性能。得出直立式废旧轮胎胎面挡土墙(无加筋)挡土墙抗震性能较弱,而直立式废旧轮胎胎面挡土墙(加筋)整体抗震性能显著提高。

土工格室加筋土挡墙静载模型试验研究

土工格室加筋土挡墙因其结构轻巧、稳定性高而具有广阔的工程应用前景,均匀长加筋面板式格室挡墙性能尤为良好,但目前相关的试验研究尚少。以拟建的长加筋面板式土工格室挡墙为对象,开展了竖向分级静载作用下的室内模型试验,对挡墙的变形、墙内竖向应力以及格室加筋层应变进行了测试和分析,探讨了均匀长格室层的加筋作用机制。结果表明:竖向荷载作用下,挡墙上部填土沿水平方向产生了中间大、墙面处小的不均匀沉降,埋于其中的格室加筋层因受弯而产生“网兜”效应,合并格室较强的侧限作用,致使部分竖向应力转化为格室的水平应力,多层格室的水平向转化作用使得挡墙底部的竖向应力明显减小,沉降沿水平方向亦趋于均匀分布。挡墙上部的翘起变形使得加筋层对墙面产生向下的拉力,故墙面竖向位移随荷载的增加而迅速增长;且对墙面产生向内收缩的作用,有效限制了上部墙面的水平位移,0.375H~0.75H(H为总墙高)范围内格室墙面水平位移较大,最大值出现在0.375H高处。加筋层应变沿水平方向的分布形式受填筑高度和荷载的影响较小,竖向荷载作用下均匀长加筋面板式格室挡墙的潜在破裂面的剖面线形为距墙踵一定距离的竖向缓变曲线。该成果可为此类土工格室加筋土挡墙的实践应用提供有价值的设计、施工参考。

土工泡沫减压膨胀土挡墙侧向压力及影响因素分析

墙后膨胀性填土在吸水膨胀后,将对挡墙产生较大的侧向压力,严重时可能引起挡墙失稳。在墙背与膨胀性填土之间铺设可发性聚苯乙烯土工泡沫(expanded polystyrene geofoam,简称EPS)缓冲层,利用EPS的高压缩特性,为填土的侧向变形提供空间,可有效减小作用于挡墙的侧向压力。为了探明墙后铺设EPS的膨胀土挡墙在膨胀土浸润至饱和状态时,侧向压力沿墙高的分布规律及影响因素,开展了EPS减压膨胀土挡墙模型试验和相应的理论分析。结果表明:(1)当膨胀土浸润至饱和时,铺设密度为12 kg/m3的EPS可减小膨胀土挡墙约50%的总侧向压力;(2)无EPS的膨胀土挡墙的侧向压力沿墙深逐渐增大,而含EPS的膨胀土挡墙的侧向压力沿墙深基本相同;(3)EPS厚度越大,密度越小,对挡墙侧向压力的减压效果越好。

新型挡土墙砌块剪切性能试验与数值分析

新型装配式挡土墙由榫卯型砌块干垒而成,通过模型试验,并结合有限元模拟,从局部的角度出发,对不同榫卯数量砌块的剪切性能进行了对比研究,结果表明:竖向压力和榫卯数量对砌块的抗剪性能有一定的影响,竖向压力越大,砌块的抗剪强度越高;榫卯数量的增多,砌块之间契合性变差,砌块的抗剪强度会降低;砌块损伤主要发生在榫卯部分,生产时应采取措施进行局部加强。该榫卯型砌块挡土墙的优化设计和加固提供了参考。

粉细砂填料柔性挡墙受力变形特性模型试验

本文以孟加拉达卡绕城高速公路为依托,通过模型试验研究了以粉细砂为填料的土工格室柔性挡墙在静载作用下的受力变形机理。试验过程对挡墙土压力、结构层的水平位移和土工格室壁应变进行了监测。试验结果表明:墙踵处水平土压力最大,最大值为24.8 kPa,墙中心位置的土压力最小,最小值为15.8 kPa;挡墙同一高度处,墙背的土压力要大于挡墙中部土压力,土压力分布曲线均为内凹曲线;挡墙墙身最大水平位移位于墙高H/2处,水平位移最大值为66 mm,为墙宽的2.2%,墙身水平位移分布呈外凸曲线,墙身变形模式为鼓型;土工格室应变在墙趾处最大,柔性挡墙墙身内土工格室的最大应变连线在墙高H/2以下区域从墙趾到墙背线性发展,最大应变连线与水平面的夹角为34°,在墙高H/2以上区域,格室最大应变连线沿墙背向挡墙顶面发展。柔性挡墙破坏模式为内部破坏,破裂面为折线型。试验结果为柔性挡墙设计提供了参考。

榫卯型装配式挡土墙模型超载变形试验研究

提出了新型榫卯装配式重力挡土墙,并对3种不同的墙背形式(直立式、俯斜式、仰斜式)进行了受力变形模型加载试验,结果表明,3种形式的挡土墙位移模式一致,基本由先是发生墙身绕墙趾转动(RB模式),然后墙身整体离开土体方向发生平移(T模式)两种模式组成,3种形式挡土墙极限横向位移在距墙底0.4H~0.67H范围内较为突出,且砌块挡土墙后土压力曲线和挡土墙位移曲线高度一致,其计算需结合砌块位移,为砌块挡土墙的设计提供了参考。