Stress–dilatancy based modelling of granular materials and extensions to soils with crushable grains

Stress–dilatancy relations have played a crucial role in the understanding of the mechanical behaviour of soils and in the development of realistic constitutive models for their response. Recent investigations on the mechanical behaviour of materials with crushable grains have called into question the validity of classical relations such as those used in critical state soil mechanics. In this paper, a method to construct thermodynamically consistent (isotropic, three‐invariant) elasto‐plastic models based on a given stress–dilatancy relation is discussed. Extensions to cover the case of granular materials with crushable grains are also presented, based on the interpretation of some classical model parameters (e.g. the stress ratio at critical state) as internal variables that evolve according to suitable hardening laws. Copyright © 2004 John Wiley & Sons, Ltd.     

A non‐coaxial critical state soil model and its application to simple shear simulations

The yield vertex non‐coaxial theory is implemented into a critical state soil model, CASM (Int. J. Numer. Anal. Meth. Geomech. 1998; 22 :621–653) to investigate the non‐coaxial influences on the stress–strain simulations of real soil behaviour in the presence of principal stress rotations. The CASM is a unified clay and sand model, developed based on the soil critical state concept and the state parameter concept. Without loss of simplicity, it is capable of simulating the behaviour of sands and clays within a wide range of densities. The non‐coaxial CASM is employed to simulate the simple shear responses of Erksak sand and Weald clay under different densities and initial stress states. Dependence of the soil behaviour on the Lode angle and different plastic flow rules in the deviatoric plane are also considered in the study of non‐coaxial influences. All the predictions indicate that the use of the non‐coaxial model makes the orientations of the principal stress and the principal strain rate different during the early stage of shearing, and they approach the same ultimate values with an increase in loading. These ultimate orientations are dependent on the density of soils, and independent of their initial stress states. The use of the non‐coaxial model also softens the shear stress evolutions, compared with the coaxial model. It is also found that the ultimate shear strengths by using the coaxial and non‐coaxial models are dependent on the plastic flow rules in the deviatoric plane. Copyright © 2006 John Wiley & Sons, Ltd.     

Finite deformation analysis of geomaterials

The mathematical structure and numerical analysis of classical small deformation elasto–plasticity is generally well established. However, development of large deformation elastic–plastic numerical formulation for dilatant, pressure sensitive material models is still a research area. In this paper we present development of the finite element formulation and implementation for large deformation, elastic–plastic analysis of geomaterials. Our developments are based on the multiplicative decomposition of the deformation gradient into elastic and plastic parts. A consistent linearization of the right deformation tensor together with the Newton method at the constitutive and global levels leads toward an efficient and robust numerical algorithm. The presented numerical formulation is capable of accurately modelling dilatant, pressure sensitive isotropic and anisotropic geomaterials subjected to large deformations. In particular, the formulation is capable of simulating the behaviour of geomaterials in which eigentriads of stress and strain do not coincide during the loading process. The algorithm is tested in conjunction with the novel hyperelasto–plastic model termed the B material model, which is a single surface (single yield surface, affine single ultimate surface and affine single potential surface) model for dilatant, pressure sensitive, hardening and softening geomaterials. It is specifically developed to model large deformation hyperelasto–plastic problems in geomechanics. We present an application of this formulation to numerical analysis of low confinement tests on cohesionless granular soil specimens recently performed in a SPACEHAB module aboard the Space Shuttle during the STS‐89 mission. We compare numerical modelling with test results and show the significance of added confinement by the thin hyperelastic latex membrane undergoing large stretching. Copyright © 2001 John Wiley & Sons, Ltd.     

Microplane constitutive model for porous isotropic rocks

The paper deals with constitutive modelling of contiguous rock located between rock joints. A fully explicit kinematically constrained microplane‐type constitutive model for hardening and softening non‐linear triaxial behaviour of isotropic porous rock is developed. The microplane framework, in which the constitutive relation is expressed in terms of stress and strain vectors rather than tensors, makes it possible to model various microstructural physical mechanisms associated with oriented internal surfaces, such as cracking, slip, friction and splitting of a particular orientation. Formulation of the constitutive relation is facilitated by the fact that it is decoupled from the tensorial invariance restrictions, which are satisfied automatically. In its basic features, the present model is similar to the recently developed microplane model M4 for concrete, but there are significant improvements and modifications. They include a realistic simulation of (1) the effects of pore collapse on the volume changes during triaxial loading and on the reduction of frictional strength, (2) recovery of frictional strength during shearing, and (3) the shear‐enhanced compaction in triaxial tests, manifested by a deviation from the hydrostatic stress–strain curve. The model is calibrated by optimal fitting of extensive triaxial test data for Salem limestone, and good fits are demonstrated. Although these data do not cover the entire range of behaviour, credence in broad capabilities of the model is lend by its similarity to model M4 for concrete—an artificial rock. The model is intended for large explicit finite‐element programs. Copyright © 2002 John Wiley & Sons, Ltd.     

任意空间剖面图打印的实用程序

本文介绍了一个根据测站的经度(或纬度)打印任意空间剖面图的实用程序,通过自定义坐标,可打印在国家气象局制的6300号底图上。本程序采用BASIC语言,已在 Apple-Ⅱ上实现,对其中的部分语句修改后,也可以用于IBM-PC等其它微机上,用本程序制图,速度快,准确性高,可作为日常性的天气分析预报工具。     

应用塑性图对陕西特殊土的判别

塑性图是由卡萨格兰德（Ａ·Ｃａｓａｇｒａｎｄｅ）于１９４２年首次提出的，该图将阿太量（Ａ·Ａｅｔｅｒｂｅｒｇ）界限（液限、塑限）应用于土质分类．本文根据塑性图判别理论并应用塑性图，对陕西省特殊土（黄土、三趾马红土、膨胀土等）进行了判别，结果为黄土位于ＣＬＹ区，三趾马红土和膨胀土位于ＣＨＥ区，其效果较好，达到了分类的目的．     

基于星座图改进的QAM盲均衡算法

针对多模辅助算法均方误差高的缺点,提出了两种基于星座图改进的盲均衡算法.首先利用16QAM星座图信息,增加多模辅助算法代价函数中信号点的均衡数目,得到改进的多模辅助算法,与多模辅助算法相比,改进后的算法稳态均方误差更低,而且收敛速度略有提高;其次将改进的多模辅助算法和判决引导算法相结合,根据均方误差调整两种算法的比例,得到的混合算法进一步降低了稳态均方误差.水声信道仿真结果表明:提出的两种算法都可以有效地降低均方误差,适用于对精度要求较高的场合.     

在数字化地形图中图摘纵横断图形

对传统纸质图摘纵横断数据采集的一般流程进行分析,从相关步骤环节入手,分析缺点。编写的图摘纵横断软件对步骤环节进行改进,作业人员完成对数字化电子地形图中图摘纵横断的数据采集过程,从而完成了传统纸质图摘纵横断数据采集的成果要求,同时进一步提供了为检验人员对数据的完整性、正确性加以核对的便利性。通过作业人员的实践,取得了良好的效果。