Numerical simulation of the response of a reinforced wall to a high speed train passage

The dynamic response of a mechanically stabilized earth wall to the passing of a high‐speed train is modelled using the finite element method. A three‐dimensional analysis is carried out, using a specific framework that allows performing the analysis with a moderate computational effort. In the first place, a so‐called multiphase approach is used to take into account the reinforcing strips. The moving load is taken into account by performing the calculation in a mobile referential using the properties of symmetry of the train cars and a simplifying assumption of periodicity for the whole train. We also assume a steady state. A partial validation of the approach is obtained by means of a comparison with an analytical solution. The quick increase in displacements induced by the train passing when the speed comes close to the celerity of Rayleigh waves clearly appears in the results. The vertical displacements, vertical stresses in the backfill, tensile forces in the strips and the influence of the stiffness of the soil are discussed. Copyright © 2017 John Wiley & Sons, Ltd.     

Analysis and Design of Retaining Wall having Reinforced Cohesive Frictional Backfill

The case of a rigid wall with inclined back face retaining reinforced cohesive-frictional backfill subjected to uniformly distributed surcharge load has been analyzed using limit equilibrium approach. The analysis considers the stability of an element of the failure wedge, which is assumed to develop in the reinforced earth mass adjoining the back face of wall. The non-dimensional charts have been developed for computing the lateral earth pressure on wall and the height of its point of application above the base of wall. The theoretical findings have been verified by model tests on a rigid wall retaining a dry cohesive-frictional soil reinforced by geogrid strips. Experimental results are in good agreement with the theoretical predictions. A design example has been included to illustrate the design procedure.     

Experimental and numerical study of the behavior of a reinforced-earth wall subjected to a local load

The mechanical response of earth structures reinforced with steel strips to loads associated with rail traffic is not well known. In order to better understand the deformations induced by train loads, and to improve design methods, a full-scale structure was built, instrumented, and tested near Rouen, France. Finite-element analyses were performed both in plane-strain and three-dimensional conditions, using different approaches to account for the interaction between the strips and the backfill material. After calibration of the soil-strip interface parameters for a load of 90 kN, simulations of the wall response to a load of 850 kN provided results in good agreement with measurements. Numerical models showed that the soil-strip interface parameters have a major influence on the predicted behavior. The proposed approach could be used for further studies of the influence of geometric and mechanical parameters.     

加筋土挡土墙边坡的稳定性分析

加筋挡土墙边坡是一种新型的复合边坡加固技术,用传统的方法很难设计这种复杂的结构。以一工程实例叙述了采用弹塑性有限元法预测加筋土边坡的稳定性的方法;给出了不同设计方案下的位移;分析了土体力学参数对边坡最大水平位移的影响。结果表明,土体的弹性模量、内摩擦角与粘聚力是影响边坡位移的重要因素。这些土力学参数与边坡最大水平位移是非线性关系,且有呈现临界点的趋势。因此,适当控制填土的力学性能参数有助于达到安全节省的设计目标。      

有限填土加筋土挡墙的稳定性及破坏模式分析

有限填土加筋土挡墙是短加筋土挡墙的一种特殊情况,其工作性状还没有被清晰地认识。文章在离心模型试验成果的基础上,采用FLAC软件建立有限填土加筋土挡墙的二维数值模型,讨论了加筋间距、加筋长度以及墙面与竖直平面的夹角对挡墙稳定性和破坏模式的影响。结果表明:（1）墙后有限填土情况下主动土压力约为库伦主动土压力的1/2~1/3;（2）在稳定地基工况下,挡墙均为复合破坏模式,滑动面呈折线型,在挡墙中下部,滑动面同时穿过了加筋区和填土区,从墙趾处滑出;在挡墙上部,滑动面基本沿着填土与稳定墙面的接触面向上发展;（3）潜在滑动面是自下向上逐渐形成的,体现为下部剪切、上部拉张的特征;（4）在墙后有限填土情况下,加筋长度减小到0.4H时,挡墙仍能保持稳定,加筋间距在控制挡墙稳定性方面具有重要作用。     

高速公路加筋陡坡路基长期工作特性研究

为研究高速公路环境与边坡填筑一体化设计关键技术,在对某高速公路段12 m高加筋边坡进行长期工作特性的现场试验研究基础上,建立考虑格栅黏弹性和土体黏弹塑性流变模型的高速公路加筋边坡数值分析模型,采用增量-初应变迭代法对各种工况进行了分析计算。通过与试验测试数据的对比,验证数值的可靠性,进而进行大量变动参数的数值分析,详细地探讨加筋边坡填筑过程中加筋结构的力学特性。在将试验数据和数值分析结果的对比分析的基础上,得到边坡加筋体内土压力、地基应力和格栅拉力分布规律及其成因,随后与类似加筋直墙和单级加筋路堤的研究结果对比,得到多级加筋陡坡的一般规律及其破坏模式。     

地震作用下挡土墙主动土压力及转动位移分析

分析地震引起的挡土墙位移及墙后土压力,对于评估挡土墙可靠性具有重要意义。基于拟动力法,考虑时效、地震波传播的相位差、超载、墙背摩擦角、填土黏聚力以及填土开裂等影响,建立地震作用下挡土墙主动土压力计算模型,获得挡土墙绕墙趾转动模式下主动土压力大小、分布形式及作用点高度。同时,考虑挡土墙本身受地震荷载作用的影响,求出挡土墙绕墙趾的转动位移。通过与Mononobe-Okabe法对比可知,文中获得的主动土压力值与Mononobe-Okabe法接近,但Mononobe-Okabe法低估了主动土压力作用点高度,表明采用Mononobe-Okabe法设计存在风险。通过算例分析了地震系数、墙背摩擦系数、超载大小、时间、填土黏聚力和内摩擦角对挡土墙转动位移的影响。     

The Effect of the Modular Block Type on Segmental Walls in Soil Reinforced by Geogrid

The behavior of retaining walls in geosynthetic reinforced soil is complex and requires studies and research to understand the mechanisms of rupture, the behavior of the reinforcements in the soil and the behavior of the main elements of the system: reinforcement-wall-soil. Several researches have been done on the use of geosynthetics as backfill massive reinforcement material (experimental studies, numerical analysis, reduced models …). This parametric study was conducted to investigate the influence of modular blocks type on the behavior of reinforced soil segmental walls. A 3.6 m high wall is composed of modular blocks of earth sand reinforced with four geogrid layers was modeled. The properties of materials, the wall geometry, and the boundary conditions will be explained later. The finite difference computer program FLAC3D was used in this study. The results of this numerical study allowed deducing the importance of this parameter. The type of modular blocks has significant effect to decrease the values of lateral displacements of the wall and decreased tensile stress values in the layers of geogrid.

     

Slipping strip analysis of reinforced earth

Reinforced earth in plane strain is idealized as a homogeneous material with the strips attached to the elastic soil matirx by a conceptual shear zone. A ‘no-slip’ finite element model is derived by assigning a large shear modulus to the shear zone. Relaxation of this modulus using a tangential stiffness algorithm in conjunction with a Mohr–Coulomb strip-slip criterion allows slipping to be simulated. The finite element formulation is validated and the finite element discretization assessed by comparisons against exact solutions for a simple test problem. An idealized reinforced earth wall example is used to demonstrate the feasibility of the method and to answer the question: ‘is slipping significant?’ The method is shown to be potentially useful, and slipping is shown to be significant.     

基于颗粒抗转动模型的刚性挡墙被动土压力临界状态离散元分析

简要介绍了颗粒抗转动模型,并将其引入离散元程序中,通过建立挡墙地基模型和合理选取模型参数,分别考虑了地基填土不同密实度和挡墙不同位移模式（被动T模式、RB模式、RT模式）情况下,刚性挡墙被动土压力随挡墙位移增长发展到达临界状态时,土压力系数 随位移发展的变化规律及墙后填土剪切带的形成规律,并与其他学者的研究成果进行对比分析。研究结果表明,土压力系数 随着挡墙位移增长的变化规律与填土的孔隙比（或相对密实度）和挡墙的位移模式紧密相关。随着孔隙比的减小或相对密实度的增大,土压力系数 会逐渐由位移硬化特性过渡为位移软化特性。尽管中密试样在双轴压缩试验中呈现出应变软化特性,而中密样的土压力系数 随着挡墙平动位移的增长可能呈现出位移软化特性,也可能呈现位移硬化特性。随着刚性挡墙向墙后土体推移,试样中的剪应变随之增大,并会在墙后形成应变局部化,即剪切带的出现。与室内试验剪应变云图相似,离散元较好地模拟了土压力临界状态时剪切带分布规律。同时,墙后土体表面不再是光滑的平面,而是逐渐隆起的凹凸面;随着挡墙位移增长,土体表面隆起量越来越大,直至土体破坏。     

Estimation of static earth pressures for a sloping cohesive backfill using extended Rankine theory with a composite log-spiral failure surface

The Rankine earth pressure theory is extended herein to an inclined c–? backfill. An analytical approach is then proposed to compute the static passive and active lateral earth pressures for a sloping cohesive backfill retained by a vertical wall, with the presence of wall–soil interface adhesion. The proposed method is based on a limit equilibrium analysis coupled with the method of slices wherein the assumed profile of the backfill failure surface is a composite of log-spiral and linear segments. The geometry of the failure surface is determined using the stress states of the soil at the two boundaries of the mobilized soil mass. The resultant lateral earth thrust, the point of application, and the induced moment on the wall are computed considering global and local equilibrium of forces and moments. Results of the proposed approach are compared with those predicted by a number of analytical models currently adopted in the design practice for various combinations of soil’s frictional angles, wall–soil interface frictional angles, inclined angles of backfill and soil cohesions. The predicted results are also verified against those obtained from finite element analyses for several scenarios under the passive condition. It is found that the magnitude of earth thrust increases with the backfill inclination angle under both the passive and active conditions.

     

台阶式加筋土挡墙的原型试验研究

对一座台阶式钢筋混凝土串联拉筋加筋土挡墙的筋带应力、土侧向压力、土竖向压力及挡墙变形进行了实测和分析, 所得结论可供设计类似支挡结构时参考。     

离心模型挡土墙试验设备的研制

土压力问题是土力学和岩土工程领域的基本研究课题。土压力离心模型试验是验证土压力计算方法和研究土压力形成物理机制的有力工具。笔者研制开发的土压力离心模型试验设备,可用于刚性挡墙的静止土压力和平动模式下主动侧土压力的研究。该设备采用电机作为驱动系统,使得挡墙能够缓慢均匀地位移;配备有控制挡墙位移的自动控制系统,使得挡墙在离心加速度增大的过程能够保持静止状态。针对填土面水平、墙后填土为砂土的情况进行了离心模型试验,测量了墙背土压力及填土位移场随挡墙位移量的变化。试验结果规律好,验证了设备的有效性。     

Vulnerability assessment of reinforced concrete buildings subjected to seismically triggered slow-moving earth slides

The objective of this paper is to develop an efficient analytical method for assessing the vulnerability of low-rise reinforced concrete buildings subjected to seismically induced slow-moving earth slides. Vulnerability is defined in terms of probabilistic fragility curves, which describe the probability of exceeding a certain limit state of the building, on a given slope, versus the Peak Horizontal Ground Acceleration (PHGA) at the assumed “seismic bedrock”, allowing for the quantification of various sources of uncertainty. The proposed method is based on a two-step, uncoupled approach. In the first step, the differential permanent landslide displacements at the building’s foundation level are estimated using a dynamic non-linear finite difference slope model. In the second step, the calculated differential permanent displacements are statically imposed at the foundation level to assess the building’s response to differing permanent seismic ground displacements using a finite element code. Structural limit states are defined in terms of threshold values of strains for the reinforced concrete structural components. The method is applied to typical low-rise reinforced concrete frame buildings on shallow foundations with varying strength and stiffness characteristics (isolated footings and continuous slab foundation), standing near the crest of a relatively slow-moving earth slide. Two different slope models are selected representing a cohesive and a purely frictional soil material. The paper describes the method and the derived fragility curves for the selected building and slope typologies that could be used in quantitative risk assessment studies at site-specific and local scales.     

考虑分层填筑及地应力平衡的挡土墙数值仿真

针对重力式挡土墙墙后分层填土对墙身受力影响的问题,深入研究分析墙背土压力动态变化值及规律性,利用大型通用有限元分析软件ADINA,建立了平面应变单元及墙、土接触单元的有限元计算模型,并且综合考虑墙后回填土Mo-hr-Coulomb材料本构模型,初始地应力场平衡、墙后回填土分层碾压填筑,设置墙、土之间的接触受力进行有限元...     

A multiphase approach to the stability analysis of reinforced earth structures accounting for a soil–strip failure condition

A multiphase model, developed in the context of elastoplasticity, is applied to the simulation and design of reinforced earth retaining structures. The main feature of this model is to combine the advantage of a homogenization approach, as regards its computational efficiency, with the ability to account for a specific failure condition at the interface between the soil and the reinforcing strips, which may have a decisive influence on the behavior of the structure. A particular emphasis is put on the stability analysis of this kind of reinforced soil structures, formulated within the framework of the yield design theory. Making use of a generalized rigid block failure mechanism, the stability of a reinforced earth retaining wall is investigated by means of the kinematic approach, leading to upper bound estimates for the stability factor of the structure, which are then favorably compared with the results of an elastoplastic analysis. Special attention is paid to assessing in a quantitative way how a specific soil–strip failure condition affects the stability of the reinforced earth structure as a whole.     

Soil reinforcing technique in mine backfilling

Summary Current methods of stabilizing mine backfill involve the introduction of cementing agents, rock fragments or timber into the fill mass. The aim of this study is to examine the applicability of reinforced earth principles in mine backfilling. Consideration is given to the identification of the functions and requirements of backfill. Various factors affecting the fill strength behaviour are examined, and the limitations of current fill practice are discussed. Part of the report is concerned with the development of, and advantages to be gained from employing reinforced earth techniques in mine backfill. Different mechanisms and performance of reinforced earth are also reviewed.     

Computation of sliding displacements of seawalls under earthquake conditions

To understand the serviceability aspects of seawalls, it is essential to study the permanent displacements of seawalls that occur during the earthquakes. Studies in the existing literature have concentrated on displacements of retaining walls with dry backfills; to the authors’ observation there is no specific analytical investigation devoted to the earthquake-induced displacements of retaining walls with submerged backfills. This paper focuses on sliding displacements of gravity type seawall retaining a submerged backfill under active earth pressure condition during the earthquakes. The threshold seismic acceleration coefficients required for initiation of sliding and the amount of sliding displacement due to seismic loading are calculated by adopting Newmark’s sliding block method. One of the prime features of the study is the estimation of seismic inertia forces in the submerged soil and wall applying the modified pseudo-dynamic method. The comparison of the results obtained using the proposed analytical formulation with the existing literature found to be in good agreement. A comprehensive parametric study has been conducted to understand the effects of different parameters such as seismic horizontal and vertical acceleration coefficients, soil and wall friction angles, width of the wall, wall inclination and excess pore water pressure ratio.

     

Modelling of earth and water pressure development during diaphragm wall construction in soft clay

The influence of a diaphragm wall construction on the stress field in a soft clayey soil is investigated by the use of a three‐dimensional FE‐model of seven adjacent wall panels. The installation procedure comprises the excavation and the subsequent pouring of each panel taking into account the increasing stiffness of the placed fresh concrete. The soft clay deposit is described by a visco‐hypoplastic constitutive model considering the rheological properties and the small‐strain stiffness of the soil. The construction process considerably affects the effective earth and pore water pressures adjacent to the wall. Due to concreting, a high excess pore water pressure arises, which dissipates during the following construction steps. The earth pressure finally shows an oscillating, distinct three‐dimensional distribution along the retaining wall which depends on the installation sequence of the panels and the difference between the fresh concrete pressure and the total horizontal earth pressure at rest. In comparison to FE‐calculations adopting the earth pressure at rest as initial condition, greater wall deflections and surface ground settlements during the subsequent pit excavation can be expected, as the average stress level especially in the upper half of the wall is increased by the construction procedure of the retaining structure. Copyright © 2004 John Wiley & Sons, Ltd.     

Analytical solution for the response of a flexible retaining structure with an elastic backfill

An extension of an existing analytical solution for the response of a flexible retaining wall subjected to seismic loading is presented. The solution is based on the assumption that the wall and the soil remain elastic and that there are no shear stresses at the wall–soil interface while the contact remains tied. In addition to the wall displacements due to bending, the wall can experience rigid‐body motions due to rotation and horizontal and vertical movements. The solution is verified by comparing its results with those of a finite element method. Results from the analytical solution together with those of the (FEM) are used to identify and quantify the relative importance of key parameters on the seismic response of a wall. The study shows that wall flexibility and horizontal rigid‐body motions of the wall and frequency content of the seismic input have a significant effect on the wall loads. The pressures behind a rigid wall decrease as the wall rotates about its base, whereas for a flexible wall, the soil pressures decrease as the friction between the backfill and the wall increases. The rigid‐body vertical movements of a wall have little impact on the dynamic pressures induced in the wall, except for a flexible wall where, when prevented, the dynamic loads may be reduced. Copyright © 2009 John Wiley & Sons, Ltd.