Study on seismic stability and performance of reinforced soil walls using shaking table tests

The paper reports a 1 g shaking table test that was carried out on a reinforced soil wall with an objective to study the acceleration amplification in the backfill, and phase differences between dynamic responses of the reinforced and retained zones. Results of the study show that including the observed larger acceleration amplification in the upper half of the wall, and the phase difference between maximum lateral earth pressure and inertial load in the backfill in the analysis would lead to more accurate predictions of: (1) the wall response relative to predicted reinforcement load, (2) elevations of line of action for both the inertial and lateral earth forces in the backfill, and (3) wall deformations, as compared to pseudo-static methods of analysis.     

强地震荷载作用下临水挡土墙的拟动力法稳定性分析

 假设墙后填土破坏面为曲面,用正弦波模拟地震加速度时程曲线,采用拟动力法对临水挡土墙进行稳定性分析,确定了挡土墙和墙后填土所受的阻尼力和惯性力,获得地震荷载作用下挡土墙的被动土压力、抗滑和抗倾覆稳定性系数的封闭形式解析解。定量分析地震加速度、放大系数、墙后填土的物理力学参数和动水压力对挡土墙的滑动位移、挡土墙的抗滑和抗倾覆稳定性系数的影响,得出当地震加速度、放大系数越大,水位越高,内摩擦角越小,临水挡土墙的稳定性越差。     

某河道护岸工程加筋土挡墙的原型观测

通过对某河道护岸工程加筋土挡墙的筋带拉力、面板土压力、基底压力、填土分层沉降、面板水平位移以及潮位变化等进行施工期间的原型观测 ,分析并研究了筋带拉力、面板土压力和基底压力随填土厚度变化的规律 ,以及填土分层沉降、面板水平位移以及潮位变化的分布规律及其影响因素     

回填EPS混合土的防滑悬臂式挡墙地震稳定性分析

以一种带防滑齿的"T"型悬臂式挡土墙为对象,采用振动台模型试验揭示了分别回填EPS混合土和天然南京细砂时的挡墙地震稳定性特征。分析并比较了墙–土体系的地震反应以及墙背动土压力分布,重点讨论了试验的防滑悬臂式挡墙位移模式以及回填土性质对墙背动土推力的影响。试验结果表明,回填EPS混合土时,填土地表加速度反应相对更小。回填土的动土推力对墙体转动位移的贡献随激励峰值的增大而增大;墙–土惯性相互作用效应与回填土的动力变形模式密切相关。两种回填料下的墙背动土压力分布形态具有显著差异;砂土–挡墙体系的动土推力与地表峰值加速度间趋向非线性关系,作用点接近2/3墙高。回填EPS混合土时两者更接近线性关系,且动土推力作用点接近1/3墙高。两种体系的动土推力作用点随地表峰值加速度增大均略有下移。基于试验结果与几种经典的解析方法预测结果比较,给出了EPS混合土柔性挡墙抗震分析的几点建议。     

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。     

Study of the behavior of mechanically stabilized earth (MSE) walls subjected to differential settlements

The limit equilibrium (LE) analysis has been used to design MSE walls. Presumably, the deflection of MSE walls can be limited to an acceptable range by ensuring sufficient factors of safety (FOSs) for both external and internal stabilities. However, unexpected ground movements, such as movements induced by excavations, volume changes of expansive soils, collapse of sinkholes, and consolidations of underlying soils, can induce excessive differential settlements that may influence both the stability and the serviceability of MSE walls. In this study, a numerical model, which was calibrated by triaxial tests and further by a specially-designed MSE wall tests, investigated the behavior of an MSE wall as well as the influence of various factors on the performance of the MSE wall when the wall facing settled relatively to the reinforced zone. The numerical results showed that the differential settlement would cause substantial vertical and horizontal movements for the MSE wall, as well as an increase in lateral earth pressure and geosynthetic reinforcement strain. The maximum horizontal movement and increase of the lateral earth pressure occurred at about 1.0 m above the toe. The differential settlement resulted in a critical plane that coincided with the plane of 45°+?/2. The maximum increase of the strain for each geogrid layer occurred in that plane, and the bottom layer had the greatest strain increase among all layers of reinforcement. The study further indicated that the surcharge, backfill friction angle, tensile stiffness of geogrid, reinforcement length and MSE wall height had noticeable influences on horizontal and vertical movements, and strain in geosynthetics. According to the results, the MSE wall that had a higher factor of safety would have less movements and geosynthetic strain increase. In contrast, only the friction angle, tensile stiffness and MSE wall height showed some degree of influence on the lateral earth pressure due to differential settlements.     

有限土体刚性挡墙平动模式被动土压力试验研究

经典的库仑或朗肯土压力理论无法适用有限土体情况下的土压力问题。利用研制的土压力试验模型装置,进行了一组不同填土宽度的刚性挡墙平动模式室内模型试验,采用微型土压力盒量测从静止状态到被动极限状态的水平土压力分布的变化,利用颗粒图像测速技术研究土体内滑裂面发展规律。试验结果表明:半无限土体情况下的被动土压力大小、分布和合力作用点与库仑被动土压力较为接近。而有限宽度情况下移动挡墙上各深度的被动土压力值均大于库仑被动土压力,且土体宽度越窄,挡墙的被动极限位移有增大趋势,挡墙下部的被动土压力增大更明显,土压力分布的非线性程度愈高,被动土压力系数越大,被动土压力合力作用点明显往墙底移动。随着填土宽度的减小,填土表面的隆起愈明显,滑裂面的倾角略有增大。当移动挡墙达到或接近极限状态时,固定边界上的水平土压力随填土宽度的减小而逐渐增大,甚至接近库仑被动土压力。     

Negative Pore Air Pressure Generation in Backfill of Retaining Walls During Earthquakes and its Effect on Seismic Earth Pressure

In order to investigate the seismic behavior of conventional type and geosynthetic-reinforced soil retaining walls, 1-g model shaking tests were conducted. Model walls having a height of about 50 cm were placed on a subsoil layer and backfilled with a layer of dense dry Toyoura sand. They were subjected to several steps of horizontal irregular excitations. As a result, generation of negative pore air pressure in the backfill was observed. The maximum amplitude of the negative pore air pressure during each shaking step increased with the base acceleration. Based on analyses of the measured data, it was inferred that such negative pore air pressure was caused by outward wall displacement relative to the backfill and not by dilative behavior of the backfill. It would cause a reduction in the seismic earth pressures exerted from the backfill. This feature suggests an advantage of a rigid full-height facing for reinforced soil walls over the segmental types of facing. A simplified numerical procedure to evaluate earth pressure was applied while considering the effects of the negative pore air pressure, and it could qualitatively simulate the measured behavior in terms of the seismic earth pressure and the angle of failure plane in the backfill.     

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.     

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 polystyren     

Numerical simulation of geosynthetic-reinforced soil walls under seismic shaking

This paper presents the results of numerical simulation of three full-scale geosynthetic-reinforced soil walls that were seismically loaded by a shaking table. Material model parameters were determined from the available laboratory data. In particular, the backfill was simulated with a cap model with parameters dependent of stress level. Hardening parameters of cap model were determined from hyperbolic relation derived from the relevant hydrostatic compression tests. A discussion on the calibration of modeling parameters is presented. Responses compared include (a) maximum wall displacement, (b) maximum backfill settlement, (c) maximum lateral earth pressure, (d) maximum bearing pressure, (e) maximum reinforcement tensile load, (f) absolute maximum acceleration in reinforced soil zone, and (g) absolute maximum acceleration in retained soil zone. Qualities of simulations were evaluated and are discussed. It was found that not all the calculated results agree well with the measured data. However, strong inference or high confidence is anticipated for the closely matched responses such as lateral earth pressure and horizontal displacement utilizing the calibrated model described herein. As indicated by the calculated results, seismic wall displacement decreases with decreasing reinforcement spacing. Factors responsible for comparison discrepancy are discussed. Variability within the measured data is thought to have contributed to some of the comparison discrepancies.     

衡重式加筋土路肩挡墙土工离心模型试验研究

以某山区公路旧路拓宽改造工程中新建的衡重式加筋土路肩挡土墙为原型,设计了4组模拟墙体实际位移形态的土工离心模型试验,讨论了墙后土体压实度和土中加筋对墙背土压力和路基填土变形的影响规律。试验表明：①墙后土体加筋对减小墙背承受的土压力作用随填土压实度的提高而趋于明显,主要影响区域位于上墙背的下半部分,压实度由88%增至95%会引起上墙背土压力分布由近似线性增大演化为折线型变化;②衡重台对其上覆填土存在托举效应,致使下墙背的土压力大幅减小,其影响范围约为衡重台以下约1/3下墙高度;③墙后土体加筋能提高路基填土的抗变形能力,减小因墙体侧向位移引起的填土表面下沉,对降低新旧路基间的不均匀变形效果显著。     

各向异性砂土主动土压力的离心模型试验研究

 利用新研制的土压力离心模型试验设备,通过土压力盒测量作用在挡土墙上的土压力分布,利用非接触图像测量系统(GIPS)测量土体位移,对各向异性的南京云母砂分别进行沉积面铅直和水平两个方向的土压力离心模型试验。通过对比试验得到的土压力分布与理论公式计算得到的各向同性砂土土压力分布,以及两种沉积方向的砂土的滑裂面位置,对各向异性砂土的土压力及土体变形破坏问题进行初步研究。结果表明：随着挡土墙向远离墙后填土方向运动的位移不断增大,作用在挡土墙上的土压力逐渐减小,墙后填土中各点的位移不断增大,在墙后土体中逐渐形成滑裂面。当挡土墙的位移量达到10－3H(H为试样模型高度)时,墙后填土达到主动极限平衡状态。受到片状云母颗粒排列方向的影响,沉积面铅直的土体滑裂面比沉积面水平的滑裂面略显平缓。     

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.     

考虑邻近地下室外墙侧压力影响的平动模式挡土墙主动土压力研究

 对于挡土墙距既有地下室很近,墙后填土宽度有限的情形,采用经典的库仑、朗肯土压力理论计算挡墙主动土压力是不严格的。通过有限元数值分析发现,当挡墙平动、填土达到主动极限状态时,无黏性土滑动土楔与邻近地下室外墙并未脱开,地下室外墙上全深度承受侧压力;随着填土宽高比n的不同,挡墙与地下室外墙间土体内将形成一道或多道滑裂面,且最靠近地表的滑裂面与挡墙或地下室外墙交点以上的土压力近似为库仑主动土压力。由此建立新的土压力计算模型,给出了挡墙主动土压力系数 和第一道滑裂面倾角 的求解方法,采用水平薄层单元法,得到了挡土墙主动土压力的分布以及合力作用点相对高度 的理论公式,并通过典型算例,与经典土压力理论、前人理论方法及有限元数值解进行对比。研究发现,挡土墙土压力为非线性的鼓形分布,当土体内摩擦角 和墙土摩擦角 取定值且 0°时, 随着n的增大而增大,而 和 随着n的增大而减小,当 时, 和 值与库仑解一致;当 0°时,不论n取何值, 和 值恒等于朗肯理论解,且 。     

Experimental study on seismic response of soilbags-built retaining wall

The seismic performance of soilbags-built retaining wall model was studied experimentally. A series of small-scale shaking table tests with the input of different amplitude sinusoidal waves and a large-scale shaking table test in a designed laminar shear box with the input of the Wenchuan earthquake wave were carried out on soilbags' retaining wall models. For comparison, the small-scale shaking table tests were also conducted on horizontally reinforced retaining wall models. The horizontal acceleration responses, the Fourier spectra, the dynamic earth pressure and the lateral displacements of soilbags' retaining wall models were investigated in shaking table tests. The results show that the seismic response of the soilbags' retaining wall is equivalent to or even slightly better than that of the horizontally reinforced retaining wall. The fundamental frequency and the Fourier spectral characteristics of the soilbags’ retaining wall are similar to those of backfill sands. The dynamic earth pressure of the wall model fluctuates almost synchronously with the input Wenchuan wave and no residual earth pressure is induced by the seismic loading. The permanent lateral displacements are small when subjected to multiple shakings, providing a proof that the retaining wall of soilbags has a good seismic performance.     

Performance of two-tiered reinforced-soil retaining walls under strip footing load

In the current study, an attempt was made to investigate the performance of two-tiered mechanically stabilized earth walls (T-TMSEWs) under static footing loading using reduced-scale model tests. For this purpose, twenty-four T-TMSEW models were constructed with three different types of reinforcement (metal strips, geogrid and geostraps) and were loaded using the rotatable and non-rotatable strip footings in different distances to the wall crest. Findings indicated that, although decreasing the reinforcement stiffness and the soil-reinforcement interaction reduces the ultimate bearing capacity of footings, the use of extensible reinforcements with low pull-out capacity and allowing the footing to tilt can be two effective solutions in T-TMSEWs to minimize deformations of backfill surface and connection loads as well as lateral pressures. It was observed that the use of a two-tiered configuration in MSE walls and also reducing tensile stiffness and soil-reinforcement interaction simultaneously, not only lead to change in the slip surface geometry but also prevent the development of deep slip surfaces in the lower tier. On the other hand, increasing the footing distance to the wall crest in the range of reinforced zone was found to be another influential solution to improve the bearing capacity, reduce wall deformations and also minimize lateral pressures.     

预应力返包式加筋土挡墙的动力响应分析

在地震作用下,返包式加筋土挡墙作为一种柔性结构常因侧向变形较大或局部产生破坏而影响其正常使用。为解决该问题,提出了预应力返包式加筋土挡墙结构。为完善预应力返包式加筋土挡墙的设计理论,运用拟动力法和附加应力法理论,以预应力返包式加筋土挡墙作为研究对象,结合现有的加筋土挡墙侧向动土压力和侧向位移计算理论,提出了一套用于计算预应力返包式加筋土挡墙侧向动土压力和侧向位移的理论公式。结合室内振动台模型试验验证了所提理论方法的可行性和合理性。该方法计算简洁,适用性广,能够较好地计算预应力返包式加筋土挡墙的侧向动土压力和侧向位移,对完善预应力返包式加筋土挡墙的设计理论具有一定的指导和借鉴意义。     

无黏性有限土体主动破坏及土压力离散元分析

建立在半无限土体假定上的朗肯土压力理论和库伦土压力理论,在挡土墙后填土有限的情况下不再适用。针对墙后无黏性填土,采用离散元方法分别对光滑、粗糙墙面平动模式下墙后有限宽度土体主动破坏的过程进行研究,分析了挡土墙运动过程中滑裂带发展、土体位移规律以及墙后水平土压力分布的情况。研究结果表明,墙体光滑情况下,滑裂带呈直线,墙后填土宽高比较小时,可以观察到滑裂带的反射,墙后土体呈多折线破坏模式,滑裂带倾角基本与库伦理论滑裂带倾角相等,且与土体宽高比无关,水平土压力合力受土体宽高比影响亦不大。墙体粗糙情况下,滑裂带呈曲线,反射现象随墙体粗糙程度增加而减弱,滑裂带倾角随土体宽高比增大而减小,最终落于库伦理论滑裂带内侧。此时,存在一临界宽高比,当墙后土体宽高比小于此值时,主动土压力随宽高比增大而增大,大于此值时,主动土压力不受宽高比影响。而无论墙体粗糙与否,墙后土体宽高比越小,达到极限状态所需墙体位移均越小。     

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。