Mesh-free analysis applied in reinforced soil slopes

One of the most applicable geotechnical structures whose analysis is carried out through iterative procedures is the reinforced soil slope. In this regard, the most successful method for the reinforced slope analysis through numerical methods is the finite element method whose updating mesh may result in some difficulties. In this study, the Natural Element Method (NEM), which is a mesh-free method, in conjunction with conventional limit equilibrium is implemented to find the slip surface in the reinforced slopes. Results demonstrate the convergence and preciseness of the present method in comparison with the other numerical methods and conventional limit equilibrium method.     

挡墙加固非饱和土边坡整体稳定性分析

在对挡墙加固边坡进行设计和评价时应综合考虑基质吸力和挡墙对边坡整体稳定性的影响。应用可以考虑基质吸力的弹塑性强度折减有限元程序,分析了挡墙加固非饱和土边坡的整体稳定性,揭示了基质吸力对加固边坡整体稳定性的影响程度,同时亦分析了整体潜在滑动面位置的变化情况,并进行了关于吸力摩擦角的敏感性分析。     

Computer aided design of geosynthetic reinforced soil walls

Summary The computer aided design of geosynthetic reinforced soil walls is reported. The magnitude of tensile forces in the geosynthetic reinforcement has also been studied under external vertical and horizontal strip loads.     

Analysis of geosynthetic reinforced soil structures with orthogonal anisotropy

Reinforced soil with geosynthetics as a composite material represents significant orthogonally anisotropic properties. However, current analytical methods usually treat the soil and reinforcement separately, which is not true of practical situations. Therefore, it is difficult to use these methods to study the real effects of the reinforcement. This paper presents an analytical model based on the theory of elasticity for orthogonally anisotropic materials that can be used in analyzing reinforced soil structures with geosynthetics. The stresses and deformations at any point within the reinforced soil structure can be determined by the proposed model. The capabilities of the model have been illustrated by application to an example problem involving a physical model test of a geosynthetic reinforced soil structure. The results of the model prediction are compared with those obtained from the model tests as well as finite element analysis. It is shown that the results of the analytical solution are in good agreement with those of the physical model tests and the finite element analysis.     

Probabilistic analysis of reinforced slopes using RFEM and considering spatial variability of frictional soil properties due to compaction

Probabilistic stability analyses of constructed wrapped-face reinforced slopes (or embankments) using frictional soils were carried out using the random finite element method (RFEM). Soil properties reported in the literature for unsaturated frictional fills compacted to different densities were used in the simulations. Bar elements were added to the RFEM code to simulate extensible geosynthetic reinforcement layers and the Davis approach was used to improve numerical stability for purely frictional soil slopes at collapse. The influence of isotropic and anisotropic spatially variable soil strength was investigated and shown to have a large influence on the variation of maximum mobilised tensile forces in reinforcement layers for the steep 5 m-high slopes in the study. The influence of fill placed at different layer thickness and compacted to different levels was simulated by adjusting the soil strength and unit weight, and the vertical strength correlation length in the anisotropic spatially variable strength field used in each slope realisation. Numerical results showed that vertical strength correlation lengths approaching the magnitude of fill lift heights can control the probability of failure for reinforced slopes constructed with weak fills placed in lift heights close to but less than the wrapped reinforcement spacing used in the study.     

活树桩固坡对边坡稳定性影响的数值分析

作为一种经济、环保的植物固坡方法,活树桩在发达国家得到了较为广泛的应用.笔者介绍了活树桩固坡方法的应用和施工方法,讨论了其加固机理.采用弹塑性有限元分析活树桩固坡对边坡稳定性的影响,研究了活树桩的入土长度、加固位置、数量、角度及其根系发展等因素对边坡安全系数影响的规律.     

加筋土挡墙设计方法对比与实例分析

在工程实践中,国内外土工合成材料加筋土挡墙的设计方法存在差异。基于对国内外加筋土设计方法和工程实践的分析和认识,分别以我国相关设计规范和北欧加筋土结构设计指南为准则,以湖北省某高边坡加固工程为案例,完成了土工合成材料加筋土挡墙的详细设计方案。根据设计计算结果,对比两种设计体系在加筋土挡墙设计理论、设计参数的取值、验算方法等方面的差异。并对产生这些差异的原因进行了分析,为我国土工合成材料加筋土设计规范修订和工程实践提供借鉴。     

非饱和土边坡稳定分析方法探讨

在对非饱和土边坡进行稳定分析时,应该全面地考虑基质吸力对边坡稳定的贡献。首先,分别探讨了基于Fredlund非饱和土强度表达式和Bishop非饱和土有效应力强度公式将强度折减有限元法推广到非饱和土边坡稳定分析中的具体方法;然后,开发了可以考虑基质吸力两种处理方法的强度折减有限元计算程序;最后,给出了一个非饱和土边坡稳定分析的对比算例,说明了二者的不同特点。     

土坡稳定极限分析上限法中的多解性分析

土坡稳定极限分析上限法中采用了完全塑性区假定,即假定土坡内存在一个处处位于屈服面上的滑动体。将滑动体内部条块界面上的强度发挥系数视为优化变量,利用功能平衡方程得到了对于给定滑动面的多个安全系数,基于和声算法和潘家铮极值原理选择其中最大的安全系数作为该滑动面的抗滑稳定安全系数,利用该方法对于两个典型土坡算例进行了分析,将其结果与常规极限分析上限法结果进行了比较,给出了完全塑性区假定对计算结果的影响。     

Limit analysis of the stability of slopes reinforced with anchors

An approach based on the category of upper bound theorem of limit analysis is proposed in this article to consider the reinforcing effect of one row of anchors on slope stabilization. The shear strength reduction technique is used in the determination of the safety factor of the slope. The effect of anchor reinforcement is assumed to be an external axial force applied on the slope, and in the formulas of kinematic limit analysis, the work rate done by the anchor can be calculated. So, the stability analysis can be conducted without any assumptions on the acting position and decomposition of the axial force of anchors. Results were compared with those obtained using both the limit equilibrium method and numerical method. A parametric study was carried out to illustrate the effect of anchor orientation and position on slope stabilization. Copyright © 2011 John Wiley & Sons, Ltd.     

土钉加固黏性土坡加载的离心模型试验研究

进行了不同坡度土钉加固边坡坡顶加载的离心模型试验,观测了土坡的破坏过程并测量土坡的位移场,研究了土钉加固黏性土坡的承载力、变形和破坏规律以及坡角对其破坏规律的影响。试验结果表明,坡顶荷载的增加引起土坡变形的增加,变形的集中产生和发展导致滑裂面的形成并使土坡发生破坏。土钉变形规律受加载阶段和加载底板的综合影响,坡顶荷载越大,接近坡顶的土钉弯曲挠度越大,钉土间的相互作用越强。土坡的坡角越大,承载力越低,土体呈现出更显著的向坡面位移的趋势。     

加筋土挡墙在填方高边坡中的应用

文章以一个具体工程为例，介绍了加筋土挡墙在填方高边坡工程中的设计与施工，得出了一些有参考价值的结论。     

A new model for geosynthetic reinforced soil

It is common to use geosynthetics to reinforce soft-soils or peat with a view to improve their load — settlement response. A new foundation model element — the rough membrane, is proposed to represent the response of the geofabric. Combining this element with Winkler springs and Pasternak shear layers to model respectively the soft soil and the granular fills, a new foundation model is presented for the geosynthetic — granular fill — soft soil system. Analysis of results at small displacement indicates the effect of granular fill to be more and significant than that of the membrane thus confirming large scale model test results of Jarrett and results based on F.E.M. (Boutrup and Holtz). The effect of the membrane increases with the load or decreasing soil stiffness.     

加筋土挡墙地震稳定性的拟动力分析

为研究不同筋材条件下加筋土挡墙地震稳定性,采用两种简化破裂面形式;由于拟静力法的局限和加筋土挡墙的成层特性,对水平和竖向地震力同时作用下的加筋土挡墙,运用拟动力法和水平条分法推导出其筋材拉力总和与临界破裂角的计算公式。算例分析结果表明,筋材拉力总和随着地震加速系数、回填土重度或者滑动体上部超载的增大而增大;随着土体内摩擦角或者填土黏聚力的增大而减小;当条件相同时,可延展性筋材所承受的筋材拉力总和大于不可延展性筋材所承受的。与拟静力法和规范中的方法比较,基于拟动力法的加筋土挡墙的设计也更加经济。     

加筋土边坡地震稳定性动点安全系数分析方法

对于地震作用下的土工合成材料加筋土边坡,边坡内部结构的动力响应十分复杂,按照已有的安全系数的方法评价比较困难。结合安全储备系数的原理,并考虑到水平方向和竖直方向地震荷载的共同作用,提出求解加筋土边坡地震稳定性的动点安全系数时程分析方法。在理论分析的基础上,分别定义加筋土边坡土体、土工合成材料和筋-土界面的动点安全系数,并建立数值模型。根据所定义的动点安全系数,在计算过程中使用开发的计算工具对动力响应过程中的动力特性数据进行记录、计算和存储,得到加筋土边坡数值模型在地震荷载作用下的动点安全系数。分析结果表明：动点安全系数时程分析方法具有良好的工程适用性;动点安全系数时程分析方法对复杂的加筋土边坡工程进行的地震稳定性分析考虑了加筋土边坡不同结构的综合稳定性,比现有的分析方法更明确地反应出加筋土边坡工程中相对薄弱的结构,对加筋土边坡工程的抗震设计提供一定参考价值;相比水平方向的地震,竖直方向的地震作用对加筋土边坡中筋材和筋-土界面的稳定性影响较大,但对加筋土边坡土体稳定性影响较小。     

Design method for local load on a geosynthetic reinforced soil structure

This paper presents a method for the design of geosynthetic reinforced soil structures, adapted for the case of a local surcharge load. The load has an important influence on the mechanical behaviour of the reinforcement. The basic calculation method is described and a design calculation method is proposed for the case of a locally loaded structure. This new approach is validated on the basis of experimental results obtained on several full-scale embankments, locally loaded to failure. These experimental results are compared to the results of calculation with partial safety factors from Eurocode 7.     

岩质高边坡的锚固设计及其稳定性分析

通过分析岩质高边坡的稳定性,采用格构式加固设计,确定了详细的设计方案;采用有限差分方法来模拟加固方案的数值解法,建立了实际的差分模型,经过计算得出加固后的边坡滑动面消失,支护后岩质边坡的稳定性系数满足要求,边坡处于稳定,为以后实际的边坡加固工程设计和计算依据提供借鉴。     

A generalized procedure for the optimum design of nailed soil slopes

A new method is proposed for the optimum design of nailed soil slopes. A rigorous method of stability analysis, namely the Janbu's method, is modified in the limit equilibrium formulation, considering the effect of reinforcement. Only the tensile resistance of the reinforcement is included and the effects of shear and bending neglected. The total reinforcement force required to raise the factor of safety to a desired value has been minimized with the inclinations of the reinforcement and the distribution of the reinforcement forces as decision variables. In order to illustrate the efficacy of the proposed method, the results are compared with the available solutions. The effect of the number and relative locations of the reinforcements on the amount of reinforcement required, is studied. The lengths of reinforcement required to raise the factor of safety to various desired values and the corresponding optimum designs are presented. The acceptability of the critical surface is verified, by ensuring that the shear and normal stresses are positive along the critical surface.     

加筋土计算中等效附加应力法的改进

等效附加应力法的基本思路是把加筋土中筋的作用等效成外力加在土骨架上,取加筋土中的土体进行计算。这种方法能够适用于纤维加筋、分层加筋和土钉墙等不同情况,且能够克服一般复合材料方法中复合材料本构模型难以建立,和把筋土分开考虑的方法中接触面单元过多的弊病。但以前的等效附加应力法需要迭代计算,这给有限元编程带来困难,而且不利于已有程序的改编。对等效附加应力法进行改进,只要在原有土的弹性矩阵或弹塑性矩阵中加上一个附加矩阵就可以直接求解。这就使得不需要迭代就可以直接应用等效附加应力法进行加筋土计算,大大简化了编程难度,改进方法的提出有助于等效附加应力法的推广应用。     

边坡稳定性分析的条块稳定系数法

鉴于传统条分法对边坡安全系数定义和使用的局限性,引入了条块稳定系数的概念。分析了条间力推力线高度的影响因素,假定条间力传递时都具有相同的条间力稳定系数 ,并考虑了条块重力偏心矩的影响。根据条块的力和力矩平衡关系以及条间力假定,建立了求解条块稳定系数的四元方程组。在此基础上,求得条块稳定系数随滑动面的分布状况。根据条块稳定系数随滑动面的分布规律划分了滑体的主滑段、抗滑段和牵引段,大致判断滑坡的滑动模式。根据滑面上抗滑力和下滑力之比的定义,求解边坡整体稳定系数。采用传统条分法和所建立的条块分析法分别以圆弧滑动和折线形滑动的两个实例进行了验算,说明了条块分析法的优越性和可靠性。