岩溶坝区透水参数的随机模型

岩溶坝区的渗透特性受高应力场的作用,使其固有的非均质各向异性更趋复杂,采用确定性的方法不能准确的描述其本质特性。本文在对岩溶坝区透水性随机场进行分析的基础上,提出了渗透随机性的数学描述。考察岩溶坝区主要的两场作用,即渗流与应力场的耦合。基于Taylor随机有限元建立了渗流应力耦合的随机微分方程格式,并对耦合随机模型反演求解渗透参数提出了思路。     

地下洞室超欠挖问题非线性有限元分析

运用数值分析的方法,采用ANSYS10.0版有限元分析程序对洞室超欠挖进行三维模拟计算,分析了不同超挖位置、超挖深度、超挖数量等对洞室围岩稳定性的影响,得出了超欠挖部位应力集中数值解及塑性区产生的影响范围,为地下工程掘进施工和初期支护设计提供重要的参考依据。     

某边坡变形破坏机理的数值分析

某花岗岩矿岩土体主要有填土、粉质粘土、淤泥及淤泥质土、含泥中粗砂、粘土、残积砂质粘土,其下为花岗岩基岩。边坡最大高度75m,其中残积土层以上的土质边坡高度约50m。本文运用有限元强度折减法对该边坡的稳定性进行了研究,得出了潜在的破坏模式及各个滑动部分的安全系数。分析结果表明,本边坡存在3个潜在滑动面,其中两个为浅层滑动面,另一个为深层滑动面。两个浅层滑动面的稳定系数在1.13～1.17,处于临界状态。深层滑动面稳定性系数在1.29,目前尚处在相对稳定状态。根据分析结果,提出了如下加固措施:（1）对滑坡体进行削坡处理;（2）在其滑动面下方设置抗滑台阶;（3）采用预应力锚索框架梁结合肋柱进行加固处理。     

Performance of mixed and enhanced finite elements for strain localization in hypoplasticity

Displacement and mixed finite element formulations of shear localization in materials are presented. The formulations are based on hypoplastic constitutive laws for soils and the mixed enhanced treatment involving displacement, strain and stress rates as independently varied fields. Included in these formulations are the standard displacement method, the three‐field mixed formulation, the enhanced assumed strain method and the mixed enhanced strain method. Several numerical examples demonstrating the capability and performance of the different finite element formulations are presented. The numerical results are compared with available experimental data for Hostun RF sand and numerical results for Karlsruhe sand on biaxial tests. Copyright © 2011 John Wiley & Sons, Ltd.     

Elasto‐plastic analysis of block structures through a homogenization method

The paper describes the development and numerical implementation of a constitutive relationship for modeling the elasto‐plastic behavior of block structures with periodic texture, regarded at a macroscopic scale as homogenized anisotropic media. The macroscopic model is shown to retain memory of the mechanical characteristics of the joints and of the shape of the blocks. The overall mechanical properties display anisotropy and singularities in the yield surface, arising from the discrete nature of the block structure and the geometrical arrangement of the units. The model is formulated in the framework of multi‐surface plasticity. It is implemented in an finite element (FE) code by means of two different algorithms: an implicit return mapping scheme and a minimization algorithm directly derived from the Haar–Karman principle. The model is validated against analytical and experimental results: the comparison between the homogenized continuum and the original block assembly shows a good agreement in terms of ultimate inelastic behavior, when the size of the block is small as compared with that of the whole assembly. Copyright © 2009 John Wiley & Sons, Ltd.     

A nonlinear PDE formulation for offshore vessel pipeline installation

In this paper a nonlinear dynamic PDE formulation for a pipe string suspended from a pipelay vessel to the seabed in a pipelay operation is developed. This model extends a three-dimensional beam model capable of undergoing finite extension, shearing, twist and bending, to apply for marine applications by adding the effects of restoring forces, hydrodynamic drag and seabed interaction. The model is validated against the natural catenary equation and the FEM code RIFLEX. The model is extended to include the pipelay vessel dynamics by applying a potential theory formulation of a surface vessel, suited for dynamic positioning and low speed maneuvering, as a boundary condition for the PDE. This system is found to be input-output passive and stable. Pipeline installation applications where the presented model is suited are e.g., analysis and simulation of the installation operation, operability analysis, hardware-in-the-loop (HIL) testing for vessel control systems, and automation of the pipelay operation.     

Slope stability FEM analysis and retaining wall design: a case study of clinker in Benxi of Liaoning

Stability is always the most important problem after high slope was excavated. The study analyzed the stress and strain inside the slope by Finite Element Method (FEM) and carried through stress distribution and failure zone, then analyzed the stability of the slope using three different methods and came to the conclusion that it is in unstable condition, so the designed retaining wall was put forward which makes the slope stable.     

基于FME的土地管理数据共享途径的探讨

对空间数据共享的实现方法及土地管理数据进行了简单介绍，在分析FME体系结构的基础上给出了在土地管理中利用FME解决问题的实例，同时探讨了利用FME Objects及FME Server实现土地管理数据共享的具体开发方案。     

地震作用下边坡稳定性分析

考虑了边坡岩土体材料的动力特性以及地震特性,利用动力有限元时程分析方法对边坡在地震荷载作用下的动力特性进行了分析,采用最小平均安全系数对边坡稳定性进行了评价,并与拟静力法的结果进行了对比分析,对某具体工程实例计算结果表明该分析方法的可行性,可为地震作用下边坡工程设计工作提供一些有益的参考。     

Numerical analysis and centrifuge modeling of shallow foundations

The influence of non-coaxial constitutive model on predictions of dense sand behavior is investigated in this paper. The non-coaxial model with strain softening plasticity is applied into finite-element program ABAQUS, which is first used to predict the stress-strain behavior and the non-coaxial characteristic between the orientations of the principal stress and principal plastic strain rate in simple shear tests. The model is also used to predict load settlement responses and bearing capacity factors of shallow foundations. A series of centrifuge tests for shallow foundations on saturated dense sand are performed under drained conditions and the test results are compared with the corresponding numerical results. Various footing dimensions, depths of embedment, and footing shapes are considered in these tests. In view of the load settlement relationships, the stiffness of the load-displacement curves is significantly affected by the non-coaxial model compared with those predicted by the coaxial model, and a lower value of non-coaxial modulus gives a softer response. Considering the soil behavior at failure, the coaxial model predictions of bearing capacity factors are more advanced than those of centrifuge test results and the non-coaxial model results;besides, the non-coaxial model gives better predictions. The non-coaxial model predictions are closer to those of the centrifuge results when a proper non-coaxial plastic modulus is chosen.