土体龟裂力学机理及理论模型研究进展

REVIEW ON THE MECHANISM AND THEORETICAL MODEL OF DESICCATION CRACKING IN CLAY SOIL

土体龟裂是一种常见的自然现象,它对土体的物理力学性质有重要影响,是许多工程地质及环境地质问题的重要诱因。开展土体龟裂研究,探讨其形成机理并构建相应的理论模型,一直是本课题的研究重点和难点。根据近年来国内外围绕土体龟裂所取得的研究成果,着重对土体龟裂的力学机理及相关理论模型研究进展进行了归纳和总结,并依据各模型的理论基础及其特点进行了分类和评价,得到如下主要认识:学界关于龟裂的形成机理尚未有统一认识,主流观点认为龟裂是土体张拉破坏的一种表现形式,张拉应力和抗拉强度是控制龟裂形成的两个关键力学指标,但上述力学机理不能解释所有的土体龟裂现象。与土体龟裂相关的理论模型总体上可以分为4大类:(1)以断裂力学为理论基础的模型:代表性的有线弹性断裂力学模型、弹塑性断裂力学模型和基于线弹性断裂力学的有限元模型;(2)以张拉破坏为理论基础的模型:代表性的有线弹性力学模型、剪切破坏模型、弹性力学模型和黏性开裂模型;(3)以土体干缩变形过程为基础的含水率-体积变化模型;(4)以土体固结理论为基础的应力路径分析模型。在此基础上,进一步对各模型的适用条件及不足之处进行了评价。最后,笔者对该课题今后的研究重点和方向提出了建议,包括:蒸发过程中土体微观结构变化及微观力学分析;蒸发过程中孔隙水的迁移过程、分布特征及赋存状态研究;土体收缩研究;土体抗拉强度研究;裂隙发育宽度及深度预测理论模型研究;龟裂发育几何形态特征预测理论模型研究。

Desiccation cracking is a common phenomenon in clay soils,which have an important influence on the properties of soils,leading to all kinds of engineering and environmental problems.Therefore,studying the soils cracking phenomenon,finding out its mechanical mechanism and build theoretical model is of great importance.This paper introduces the mechanical mechanism and related theoretical models of soil cracking by collecting relevant data,analyzing the characteristics of each model,and introducing its classification based on the theoretical basis of the models.In general,the following main conclusions are obtained.Researchers think that the mechanism of the crack haven t been unified.The mainstream view thinks that cracks are a form of damage of soil.Tension stress and tensile strength are the two key mechanical indexes,but it can t explain all the cracking phenomenon.In general,the theoretical models related to soil cracking can be divided into four categories.(1)Based on the theory of fracture mechanics,representatives are the linear elastic fracture mechanics model,elastic-plastic fracture mechanics model and the finite element model based on linear elastic fracture mechanics.(2)Based on the theory of tension stress failure,representatives are the linear elastic model,the shear failure model,elastic mechanics model and the cohesive crack model.(3)Water content-volume change model based on the process of shrinkage deformation of soil.(4)The analysis of stress path model on the basis of the soil consolidation theory.On this basis,the shortcomings and applicable conditions of each model are evaluated.Finally,this paper also puts forward the key directions of the studies about the issues.They include soil microstructure change and micromechanics analysis during the process of evaporation,the migration process,distribution and occurrence of pore water in the process of evaporation,research on soil shrinkage,research on tensile strength of soil,prediction model about fracture width,depth and growth geometry characteristics of crack soil.