互锚式薄壁挡土墙影响因素分析

针对日益增多的高填方路堤,提出了一种新型的挡土墙结构--互锚式薄壁挡土墙,它具有成本低廉、结构合理、施工方便的特点,有利于保护环境,具有广泛地应用前景。在现场测试的基础上进行有限元分析,总结出拉筋应力、侧向土压力、侧向位移等指标的可能影响因素,为这种新结构的设计及优化提供了理论依据。     

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。     

Prediction of stresses and strains around model tunnels with adjacent embedded walls in overconsolidated clay

This paper presents the results of finite element analyses carried out using different constitutive models for overconsolidated clay: the Modified Cam clay model and the Three-Surface Kinematic Hardening (3-SKH) model. These analyses are evaluated against data from an extensive series of physical model tests examining the influence of an embedded wall placed near a tunnel on ground movements and tunnel stability. It is shown that for heavily overconsolidated soils reasonable predictions of both deformations and failure can be obtained from kinematic hardening models such as the 3-SKH model, which allow plastic deformation inside a Modified Cam clay state boundary surface.     

Finite element reliability analysis of reinforced retaining walls

This paper presents the reliability analysis of reinforced retaining wall using finite element method. Response surface approach is used to approximate the performance function and a first-order reliability method (FORM) is used to evaluate the reliability index. In the analysis, displacement response of the reinforced retaining wall is considered as performance function and the corresponding reliability index is evaluated with the aid of a spreadsheet. Uncertainties associated with the soil and reinforcement properties are explicitly taken into account in the analysis. A parametric sensitivity analysis has been performed to bring out the effect of important uncertain parameters by evaluating the sensitivity of the reliability index with respect to each of the uncertain parameters. Results of the response surface method coupled with finite element analysis show the ease and successful implementation of the reliability analysis procedure for the reinforced retaining walls.     

Application of a Cam–Clay model to overconsolidated clay

The yield locus governing the stress–strain response of a soil may degrade during rebound at high overconsolidation ratios. The cause can be attributed to a breakdown in bonding. A Cam–Clay model is applied to account for the degrading yield locus, and the influence of this degradation is assessed using a theoretical approach for friction pile capacity. Stress changes in the soil continuum due to pile installation and setup are simulated by cylindrical cavity expansion and radial consolidation, anda segment loading model is used to determine the effective stress change in the soil at peak load transfer under undrained conditions. The results indicate that plastic rebound affects peak load transfer to at least the same extent as shear strength.     

Finite element analysis of consolidation of layered clay soils using an elastic visco-plastic model

This paper presents a general one-dimensional (1-D) finite element (FE) procedure for a highly non-linear 1-D elastic visco-plastic (1-D EVP) model proposed by Yin and Graham for consolidation analysis of layered clay soils. In formulating the 1-D FE procedure, a trapezoidal formula is used to avoid the unsymmetry of the stiffness matrix for a Newton (modified Newton) iteration scheme. Unlike many other 1-D FE approaches in which the initial in situ stresses (or stress/strain states) are considered indirectly or even not considered, the initial in situ stress/strain states are taken into account directly in this paper. The proposed FE procedure is used for analysis of 1-D consolidation of a clay with published test results in the literature. The FE modelling results are in good agreement with the measured results. The FE model and procedure is then used to analyse the consolidation of a multi-layered clay soils with a parametric study on the effects of the variations of creep parameters in Yin and Graham's 1-D EVP model. It is found that the creep parameters ψ/V and t₀ have significant influence on the compression and porewater pressure dissipation. For some boundary conditions, changes of parameters in one layer will have some effects on the consolidation behaviour of another layer due to the different consolidation rates. Finally, the importance of initial stress/strain states is illustrated and discussed. Copyright © 1999 John Wiley & Sons, Ltd.     

土钉墙开挖性状的有限元分析

土钉墙是粉砂土、黏性土等地区基坑开挖围护的主要形式之一。采用ABAQUS有限元软件建立土钉-面层-土体的相互作用模型,土体应用Mohr-Coulomb本构模型,土体与土钉间的接触性质为摩擦小滑移,在此基础上,得到了土体深层水平位移、面层位移、面层土压力和土钉轴力的分布形式和基本规律。计算结果表明：深层土体水平位移的最大值发生在墙顶靠下或者墙顶的位置;坑底水平位移从坡脚向坑中逐渐变小,在基坑开挖深度范围内,减小的速率较大,以后趋于某一稳定值;土钉轴力两头较小,中间较大,作用在面层上的作用力值远小于土钉轴力,该力与作用在面层上的作用力之和等于土钉轴力;土钉墙的面层土压力随着深度的增加,先增加到最大值后,再逐渐减小,每开挖一步面层土压力就会增加,且最大值向下移动。     

Finite element analysis of crack initiation in a block model experiment

SummaryFinite Element Analysis of Crack Initiation in a Block Model Experiment A Sand-plaster plate with two perpendicular joint sets loaded biaxially was studied by Rosenblad. A finite element simulation was achieved using two levels of iteration. Iteration with varying joint properties produced a convergent stress state (a solution) everywhere respecting the non-linear joint deformability and strength laws. But since this solution depends upon the biaxial loading of the model, the external load to initiate cracking of any block is itself the object of iterations. Close agreement was achieved between the physical and numerical models in many details.

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ZusammenfassungFinite Elemente Analysis der Rieinleitung in einem Block-Modellversuch Eine biaxial belastete Sand-Gips-Platte mit zwei vertikalen Kluftscharen wurde von Rosenblad untersucht. Durch die Anwendung von zwei Iterationsstufen wurde eine Simulation des Problems mit der Methode der finiten Elemente erreicht. Iterationen mit variierten Klufteigenschaften konvergierten und führten zu Spannungszuständen, welche den Gesetzen der nicht-linearen Kluftdeformation und den Festigheitsgesetzen entsprachen. Da diese Lösung von der biaxialen Belastung des Modells abhängt, ist die äußere Belastung, welche zur Rißeinleitung jedes Blocks führt, daher selbst Gegenstand von Iterationen. Man fand gute Übereinstimmung zwischen dem physikalischen und numerischen Modell, auch im Detail.

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RésuméEtude par éléments finis du début de la fracturation, dans un assemblage de blocs en contrainte biaxiale Une plaque d'un mélange sable—plâtre, avec deux systèmes de discontinuités orthogonales, a été etudiée en contrainte biaxiale par Rosenblad. On a etudié le problème avec un modèle d'éléments finis qui itère à deux niveaux. Une série d'itérations sur les propriétés des discontinuités produit une solution, en termes de contraintes, qui respecte les lois non-linéaires de déformabilité et de résistance. Cependant, cette solution dépend du chargement du modèle; donc, la charge nécessaire au commencement de la fracturation fait elle-même l'objet d'itérations. On a obtenu un très bon accord entre les résultats des modèles plysiques et ceux du calcul par éléments finis.

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With 15 Figures     

Discrete element analysis for active and passive pressure distribution on retaining wall

Analysis based on Discrete Element Method (DEM) is presented for active and passive earth pressure distribution behind a retaining wall under different modes of wall movement. Soil mass in the present model is treated as comprising of blocks which are connected by elasto-plastic Winkler-springs. The solution of this method satisfies all equilibrium and compatibility conditions. Formulation of the method is briefly reviewed. Examples are shown to demonstrate the applicability of the method for analyses of earth pressure behind a gravity retaining wall. The DEM can be used to study the sliding patterns of backfill blocks which effect the earth pressure distribution behind the wall. Advantages of this method over the conventional limit equilibrium method are also discussed.     

超固结粘土的剪切带数值模拟

基于中井的子负荷面本构关系模型,采用高精度的隐式应力积分算法,研究了平面应变试验中超固结粘土试样的变形局部化问题。模拟了不同的加载速度和边界约束条件,得到了超固结比为8的藤森粘土土体内部明显可见的X型剪切带和单一型剪切带。结果表明：土体的剪胀特性、孔隙水在土体内的移动规律以及边界约束条件对剪切带的形成和发展起着控制作用。     

考虑流变性状的软土地基固结有限元分析

对具有流变性状的软土地基固结特性进行了研究,编制了相应的有限元程序。利用该程序对某高速公路软土地基固结问题进行了计算和分析。通过计算结果与实测结果的对比可得到以下结论：在软土地基的固结变形计算中,考虑流变性状的影响是必要的,其计算值与实测值比较吻合。     

Ground disturbance caused by shield tunnelling in a stiff, overconsolidated clay

Attewell, P.B. and Farmer, I.W., 1974. Ground disturbance caused by shield tunnelling in a stiff, overconsolidated clay. Eng. Geol., 8: 361–381.

Some of the factors affecting ground deformation around shield tunnelling excavations in stiff clays are considered. There is particular reference throughout the paper to an analysis and interpretation of measured ground deformation around a 4.146-m diameter, hand-excavated, shield-driven tunnel at a nominal axis depth of 29.3 m in the overconsolidated London Clay. The maximum surface settlement was found, by precise levelling, to be 6.1 mm but the shape of the transverse surface settlement profile conformed to a normal probability curve only up to the time of shield passage. Of the contributory ground losses at the tunnel, yield of the clay at the tunnel face appears to dominate to the extent of generating up to 50% of the eventual surface settlement. Measurement evidence suggests a rate of yield at the face that is 2 to 3 times the radial yield over the shield and implies that up to about one-fifth of the surface settlement could be attributed to radial yield into the grouted sections of the erected tunnel lining.     

采用环剪仪对超固结黏土抗剪强度特性的研究

利用大型高速环剪仪,对不同超固结比、法向应力和剪切速率下的超固结饱和黏土的峰值强度和残余强度特性进行了研究,并对循环荷载作用前后残余强度的变化进行了初步探讨。试验结果表明,（1）超固结比对超固结黏土的峰值强度和残余强度有着明显的影响;（2）在剪切速率相同的条件下,土体达到残余强度时的位移取决于现存的应力状态,而与应力历史无关;（3）剪切速率越大,峰值强度随之增大,达到稳定残余强度时的剪切位移也随之增加,但剪切速率的变化对残余强度值几乎没有影响;（4）在循环荷载作用下残余强度不同程度的降低,最大降低幅度达12.2 %;当土体剪切面为不规则剪切带时,施加循环荷载后出现残余强度上升的现象。     

软黏土中伞式吸力锚基础水平承载有限元分析

伞式吸力锚基础(USAF)是传统吸力锚基础的改进型,其独特的结构型式在海洋岩土工程中具有更大的发展潜力。预先通过室内小尺度模型确定了USAF水平承载的位移控制标准,继而对软黏土中不同加载高度下USAF承载规律及地基土变形特性进行有限元分析,并对波浪循环荷载作用下的海床土应力折减效应进行了阐述。结果表明:随水平荷载加载高度升高,USAF的转动中心上移,海床土的应力扩散深度加深。"锚枝"和"筒裙"的增加使主筒侧壁土抗力发生应力重分布,锚前上部和锚后底端土体为USAF承载力的核心控制区。黏质海床超静孔隙水压力的累积对USAF土抗力的发挥影响显著,进而降低整个结构的水平承载能力。上述研究成果对完善USAF在海洋岩土工程中的应用具有重要意义。     

止水帷幕对基坑环境效应影响的有限元分析

采用Biot固结理论分析了止水帷幕对基坑工程环境效应的影响,包括止水帷幕不同打设深度的效果,以及两种封闭式止水帷幕发生漏水意外时对地下水位和坑外土体位移的影响等。在有限元编程中,将开挖土体置为空气单元可以简化处理过程。算例分析结果表明,深厚透水地基中增加竖向止水帷幕的深度并不能有效减小对周围环境的影响;漏水部位周围土体的渗流等势线较为密集,渗流速度较大,容易诱发扩大破坏;竖向封闭式止水帷幕漏水引起的坑边土体的沉降和地表土体的侧移相对较大,水位下降迅速等。其结果可供基坑工程漏水事故环境效应的评价和对策研究时参考。     

Finite element analyses of bridge abutments on firm clay

In finite element analysis of soil-structure interaction problems involving firm to stiff overconsolidated clay, there have been difficulties in modelling the stress-strain response of the soil. Non-linearity and anisotropy of the soil depend on the inherent anisotropy of its particle structure and the induced anisotropy of its stress history and current stress path. In CRISP modelling of the centrifuge test of an abutment wall and its backfill of sand on the surface of a firm to stiff overconsolidated kaolin, the clay foundation was divided into 6 broad zones in accordance with the stress history and stress path. Undrained movements of the abutment and its subsoil were closely modelled in two analyses; one with a non-linear elastic model and the other with the Schofield model with shear modulus G assigned to the foundation zone in accordance with the estimated strain level as well as stress history and stress path. In the prediction of consolidation movement, there is a difficulty in the current critical state soil model in CRISP. The fe solution incorrectly predicted that substantial horizontal movement would accompany settlement due to consolidation, whereas the centrifuge test showed mainly vertical movement. This is attributable to the pronounced anisotropy separately observed in element tests.     

Seismic analysis of cantilever earth retaining walls embedded in dry sand by simplified approaches and finite element method

In engineering practice simplified methods are essential to the seismic design of embedded earth retaining walls, as fullydynamic numerical analyses are costly, time-consuming and require specific expertise. Recently developed pseudostatic methods provide earth stresses and internal forces, even in those cases in which the strength of the soil surrounding the structure is not entirely mobilised. Semiempirical correlations or Newmark sliding block method provide an estimate of earthquake-induced ...     

黑龙江省荣华立井壁后空洞破坏及注浆有限元分析

井壁溃沙、壁后空洞对立井的影响一直威胁着煤矿安全生产,对破坏的立井稳定性规律研究分析及处理方法备受关注。本文应用大型有限元分析软件ADINA,采用莫尔-库仑准则和拉伸破坏准则的组合并结合现场仪器原位检测模拟井壁后空洞破坏以及注浆,对荣华立井壁溃沙、壁后空洞对立井稳定性的影响和壁后注浆治理时不同注浆压力对井壁稳定性影响的基本规律进行研究,并依据分析结果制定了注浆方案。数值仿真分析表明:溃沙、空洞对井筒稳定有不利影响,并造成地表沉降;注浆压力对井筒稳定性有直接影响,当注浆压力达到一定值时,井壁竖向应力可出现拉压力,水平应力增大易导致井壁破裂。     

System reliability-based analysis of cantilever retaining walls embedded in granular soils

Reliability-based analysis of cantilever retaining walls requires consideration of different failure mechanisms. In this paper, the reliability of soil-wall system is assessed considering two failure modes: rotational and structural stability, and the system reliability is assumed as a series system. The methodology is based on Monte Carlo Simulation (MCS), and it deals with the variability of the design parameters in the limit equilibrium analysis of a wall embedded in granular soil. Results of the MCS indicate that the reliability of the failure components increases exponentially by increasing the variability of design parameters. The results of the system reliability indicate how the system reliability is different from the component reliabilities. The strength of the weakest component influences the reliability of the system. The system reliability index increases with the wall section gradually. However it remains constant for the rotational failure mode.