考虑摩擦损耗的加筋挡土墙临界高度研究

目前加筋挡土墙临界高度研究忽略了土-筋间的摩擦损耗这一客观因素。为进一步完善加筋挡土墙临界高度计算公式,基于极限分析上限法,充分考虑加筋挡土墙发生内部破坏时,速度间断面上筋材和土体的能量损耗率以及两者之间的摩擦损耗率,建立分析方程并推导出加筋挡土墙临界高度计算公式,然后采用离心试验数据应用该文推导公式进行求解验算。结果表明：将摩擦损耗计入内部能量损耗求得的加筋挡土墙临界高度更加接近离心试验结果与筋材实际破坏情况,验证了筋-土间的摩擦作用是影响加筋挡土墙稳定性及其临界高度的重要因素。实际工程中,可增加筋材-土体间的摩擦系数来提高挡墙的稳定性,使设计更加优化。     

横向地震作用下土工合成材料加筋土挡墙筋材拉力分析

土工合成材料加筋土挡墙具备优良的抗震性能,但是,国内外现行的加筋土挡墙筋材动拉力计算方法存在地震动参数选用不尽合理的问题,一方面可能带来结构安全隐患,另一方面也造成了工程界的疑虑.基于此,在前期工作的基础上应用非线性动力有限元法分析了高加筋土挡墙在不同地震激励作用下的地震响应,重点讨论了强震作用下筋材拉力的影响因素.分...     

土工格栅加筋石灰土挡墙工程特性试验研究

以河北省保（定）沧（州）高速公路模块式土工格栅加筋石灰土挡墙为工程依托,以现场原型试验为手段,系统研究了该结构工作状态下的基底竖向土压力、墙面板背部侧向土压力和土工格栅拉筋应变分布规律。试验结果表明：基底竖向土压力沿筋长近似呈梯形分布,其大小一般小于理论值,最大值发生在墙背附近,且随竣工后时间的延续有下降的趋势;实测墙背侧向土压力沿墙高呈非线性增长分布,数值小于主动土压力;实测拉筋应变沿筋长呈单峰值分布,且数值均小于0.6%。试验结果可以为类似工程的设计、研究提供参考。     

Earth pressure coefficients for design of geosynthetic reinforced soil structures

There are several methods proposed in the last two decades that can be used to design geosynthetic reinforced soil retaining walls and slopes. The majority of them are based on limit equilibrium considerations, assuming bi-linear or logarithmic spiral failure surfaces. Based on these failure mechanisms, design charts have been presented by several authors. However, the use of design charts is less and less frequent. The paper presents results from a computer program, based on limit equilibrium analyses, able to quantify earth pressure coefficients for the internal design of geosynthetic reinforced soil structures under static and seismic loading conditions. Failure mechanisms are briefly presented. Earth pressure coefficients calculated by the developed program are compared with values published in the bibliography. The effect of seismic loading on the reinforcement required force is also presented. To avoid the use of design charts and based on the obtained results, approximate equations for earth pressure coefficients estimation are proposed. The performed analyses show that the failure mechanism and the assumptions made have influence on the reinforcement required strength. The increase of reinforcement required strength induced by the seismic loading, when compared to the required strength in static conditions, grows with the backfill internal friction angle. The effects of the vertical component of seismic loading are not very significant.     

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.     

Influence of drainage condition on Coulomb-type active earth pressure

The present paper focuses on the computing of Coulomb-type active earth pressure acting on a retaining wall provided with a drainage system or without and supporting a soil mass subject to steady water seepage. The influence of drainage conditions on the critical inclination of the failure surface and the coefficient of active earth pressure is investigated by discussing their variations with increasing effective internal friction angle of the soil mass. The results indicate that when the soil effective internal friction angle is increased, the critical inclination increases, but the coefficient of active earth pressure decreases. It is better to provide the drainage at the base of the backfill as well as at the bottom of the wall base rather than providing the drainage along the vertical face of the wall. Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 5–8, September–October, 2008.     

Soil-reinforcement interaction: Stress regime evolution in geosynthetic-reinforced soils

Understanding the stress regime that develops in the vicinity of reinforcements in reinforced soil masses may prove crucial to understanding, quantifying, and modeling the behavior of a reinforced soil structures. This paper presents analyses conducted to describe the evolution of stress and strain fields in a reinforced soil unit cell, which occur as shear stresses are induced at the soil-reinforcement interface. The analyses were carried out based on thorough measurements obtained when conducting soil-reinforcement interaction tests using a new large-scale device developed to specifically assess geosynthetic-reinforced soil behavior considering varying reinforcement vertical spacings. These experiments involved testing a geosynthetic-reinforced mass with three reinforcement layers: an actively tensioned layer and two passively tensioned neighboring layers. Shear stresses from the actively tensioned reinforcement were conveyed to the passively tensioned reinforcement layers through the intermediate soil medium. The experimental measurements considered in the analyses presented herein include tensile strains developed in the reinforcement layers and the displacement field of soil particles adjacent to the reinforcement layers. The analyses provided insights into the lateral confining effect of geosynthetic reinforcements on reinforced soils. It was concluded that the change in the lateral earth pressure increases with increasing reinforcement tensile strain and reinforcement vertical spacing, and it decreases with increasing vertical stress.     

地震动土压力水平层分析法

Mononobe-Okabe公式是挡土结构设计中关于侧向动土压力计算的常用方法。但Mononobe-Okabe公式的诸多假设使得其公式适用范围受限,而且无法给出地震动土压力合力作用点位置及地震动土压力强度沿墙背分布情况。为弥补以上不足,基于Mononobe-Okabe平面破裂面假设,采用水平层分析法推导地震条件下主动和被动土压力合力及其作用点位置、土压力强度分布公式,并采用图解法得到临界破裂角的显式解答。公式考虑水平和垂直地震加速度、墙背倾角、挡墙墙背与填料黏结力和外摩擦角、均布超载等诸多因素,可以适用于黏性土和无黏性土的主动和被动土压力计算。分析结果表明,地震条件下土压力强度沿墙高为非线性分布,在相应简化假设条件下公式与Mononobe-Okabe公式完全一致。     

地震作用下挡土墙抗倾覆稳定安全系数研究

基于拟动力法,考虑墙背面和填土面倾斜的工况,推导出挡土墙在地震作用下的抗倾覆稳定安全系数的计算表达式。数值算例结果表明,稳定安全系数随着填土内摩擦角、墙土外摩擦角和墙背面倾角的增大而增大,随地震放大系数、水平加速度影响系数和填土面倾角的增大而减小。其中,只有在地震作用较大时,放大系数的影响才逐渐显现,同时,摩擦角的影响却相对减弱;墙背面倾角和填土面倾角不同时,稳定系数随地震作用的变化趋势基本一致。通过对比2种计算方法的结果可知,拟动力法由于考虑了地震周期和地震波效应的影响,计算得到的稳定安全系数比拟静力法大。     

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.     

SV波作用下刚性挡土墙地震主动土压力时频域计算方法

 基于弹性波动理论,概化刚性挡土墙的动力分析模型,利用水平分层法,建立单元体的受力平衡微分方程,借助Hilbert-Huang变换,提出地震作用下刚性挡土墙地震主动土压力的时频域计算方法,并通过与振动台试验结果的对比验证该方法的合理性。分析输入波频率对刚性挡土墙墙后填土的临界破裂角、地震主动土压力合力以及作用点的影响,结果表明：随着地震烈度的增大,临界破裂角逐渐减小,地震主动土压力合力逐渐增大,合力作用点位置略有上移;随着输入波频率的增大,临界破裂角和地震主动土压力合力分别呈“倒马鞍型”和“正马鞍形”分布,并且均在输入波频率与刚性挡土墙系统自振频率相近时达到最大,而地震主动土压力合力的作用点则基本上不变;按照现有规范不考虑输入波频率进行刚性挡土墙地震稳定性设计,可能会降低挡墙的地震安全储备。刚性挡土墙地震主动土压力的时频域计算方法不仅能够考虑地震波三要素(峰值、频率以及持时)对挡墙土压力的影响,同时也能够为其他类型支挡结构的抗震时频设计提供一定的参考。     

A new generation of soil-geosynthetic interaction experimentation

A new device was developed to comprehensively assess the interaction between soil and reinforcement as well as the interaction between neighboring reinforcement layers in a reinforced soil mass, under both working and ultimate interface shear stress conditions. An understanding of these two interactions is required to assess the mechanical behavior of a geosynthetic-reinforced soil mass considering varying vertical reinforcement spacings. Specifically, the new device allows direct visualization of the kinematic response of soil particles adjacent to the geosynthetic reinforcement layers, which facilitates evaluation of the soil displacement field via digital image analysis. Evaluation of the soil displacement field allows quantification of the extent of the shear influence zone around a tensioned reinforcement layer. Ultimately, the device facilitates investigating the load transfer mechanisms that occur not only at the soil-reinforcement interface, but also at distances farther from the interface, thereby providing additional insight into the effect of vertical reinforcement spacing on a reinforced soil mass. Finally, the device allows monitoring of dilatancy within the reinforced soil mass upon shear stress generation at the interface between soil and reinforcement. Overall, the device was found to provide the measurements needed to adequately predict the strains developing both in reinforcement layers tensioned by direct application of external loads as well as in reinforcement layers tensioned by the shear transfer induced by adjacent geosynthetic reinforcements. Ultimately, the proposed experimentation technique allows generation of data required to evaluate the load transfer mechanisms amongst soil and reinforcement layers in reinforced soil structures. The strain magnitude in the neighboring reinforcements was found to exceed a magnitude of 10% of the strain magnitude obtained in the active reinforcement. The zone of shear stress transfer from the soil-reinforcement interface was found to exceed 0.2 m on each side of the active reinforcement.     

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。     

平动模式下考虑剪应力作用的刚性挡土墙主动土压力计算

以墙后为无黏性填土的刚性挡土墙为研究对象,假定破裂面为通过墙踵的平面,且墙后土体中形成圆弧形土拱,考虑滑动土楔内水平土层间的平均剪应力,修正水平层分析法,得到平动模式下主动土压力的表达式。通过与文献中模型试验结果和现有理论成果的对比分析证明了修正方法的合理性。参数分析表明,水平土层间的平均剪应力和主动土压力一样,沿墙高为非线性分布,主要受墙背倾角、墙土摩擦角、填土内摩擦角等因素的影响。对于墙背竖直或墙背较陡且比较粗糙的挡土墙,考虑水平土层间平均剪应力作用算得的主动土压力合力作用点位置高于库仑解且低于不考虑剪应力作用的理论解答,而对墙背较缓且比较光滑的挡土墙,情况则正好相反。而且,不论是否考虑水平土层间的平均剪应力,主动土压力合力作用点位置都会随墙背变缓而降低。     

考虑变形影响的重力式挡墙地震土压力分布

利用汶川地震丰富的近场实震资料,分析总结了地震作用下挡墙的变形破坏模式,指出挡墙的变形模式与地基基础关系最为密切。位于岩质地基上的挡墙主要发生倾斜变形,位于土质地基上的挡墙则主要发生推移变形。在此基础上,基于温克勒地基模型,将土体看做是一系列弹簧和理想刚塑性体的组合体,分析得到了不同变形模式下挡墙地震土压力及其合力作用点的计算方法。结果表明：不同变形模式下挡墙的地震土压力分布特征各异,除平移模式外,其余变形模式下挡墙地震土压力随深度都呈非线性分布;位于岩质地基上的挡墙发生变形后地震土压力的合力作用点要比土质地基上的挡墙高。通过开展位于岩质地基和土质地基上挡墙的振动台模型试验,对文中提出的挡墙地震土压力计算方法进行了验证,发现试验结果和理论分析结果较相吻合。     

加筋土挡墙拉筋轴向应力分布规律研究

基于剪力滞模型基本原理对加筋土挡墙筋土作用机理进行了研究。根据拉筋轴向应力是由拉筋周围土体发生剪切位移而产生,紧邻拉筋周围土体仅受剪应力作用的假定,将加筋体单元中土体分为内、外两层,建立了拉筋轴向受力平衡方程,推导出了加筋土挡墙拉筋轴向应力特解。理论分析表明,加筋土挡墙中拉筋轴向应力沿拉筋长度L呈非线性分布,且在x≤L/2时出现一个峰值;当水平拉筋沿筋长方向出现凹陷或凸起时,在该位置将产生拉力峰值。该研究成果合理解释了加筋土挡墙中拉筋轴向应力出现多个峰值以及越靠近墙底部潜在破裂面位置越接近墙面板的原因。     

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。     

挡土墙地震主动土压力的库仑解

传统的Mononobe-Okabe法在实际工程中有着广泛应用,但它仅适用于无黏性土的极限土压力计算,且不能给出土压力分布。基于极限平衡理论,视墙后填土为服从Mohr-Coulomb屈服准则的理想弹塑性材料,假定墙后塑性区的一簇滑移线为直线即平面滑裂面,考虑墙背倾角、地面倾角、土黏聚力和内摩擦角、墙土之间黏结力和外摩擦角、地面均布超载、塑性临界深度以及水平和竖向地震系数等因素的影响,建立较为完善的塑性滑楔分析模型,进而采用极限平衡法求解挡土墙地震主动土压力、滑裂面土反力及其分布,并且通过量纲一化的分析首次提出几何力学相似原理。研究结果表明,总地震主动土压力随水平地震系数代数值的增大而增大;但随竖向地震系数代数值的增大并非总是减小,当水平地震系数较大时,可能出现先减后增的情况。     

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 。     

考虑土拱效应的挡土墙地震主动土压力静力研究

 在Mononobe-Okabe拟静力学理论的基础上,对挡土墙后填土进行应力分析,根据静力平衡求得滑裂面水平倾角。再结合土拱效应原理采用水平层分析法,对处于正常受力状态的填土微元体进行应力分析,并根据静力平衡和力矩平衡建立方程组,从而求得适用范围更广的地震作用下墙后土体的主动土压力、土压力系数、土压力合力作用点位置等的计算公式。利用数值方法分析土内摩擦角、墙土面摩擦角以及水平和竖向地震系数对滑裂角、主动土压力、土压力系数、土压力合力作用点位置的影响,并将计算结果与其他计算方法所得结果以及试验结果进行对比分析。