土体干缩裂隙发育过程及断裂力学机制研究进展

Review on Soil Desiccation Cracking Behavior and the Mechanism Related to Fracture Mechanics

土体干缩开裂是一种常见的自然现象,能极大弱化土体的工程性质,是许多岩土、水利和地质工程问题的直接诱因。然而,目前学界关于干缩裂隙的发育机理尤其是裂隙现象中蕴含的力学机制尚缺乏深入认识,重视程度严重不够。基于国内外近些年来围绕土体干缩开裂所开展的研究,着重对裂隙发育机理和断裂力学理论的应用进行了系统的归纳和总结,并基于当前的研究不足,提出了今后的研究重点和方向。结果表明:(1)蒸发为土体干缩开裂的前提,对于初始饱和的土体而言,土体开裂发生时仍处于饱和状态,水分蒸发处于常速率阶段,此时对应的含水率为临界含水率;(2)土体发育干缩裂隙是内部应力作用的结果,在干燥过程中,基质吸力引起的张拉应力达到或超过抗拉强度时,土体发生开裂,因此,基质吸力和抗拉强度是影响土体开裂的两个关键力学参数;(3)土体开裂与体积收缩密切相关,收缩是土颗粒在张拉作用下发生移动的宏观表现,可以分为正常收缩、残余收缩和零收缩阶段,且大多数裂隙发生在正常收缩阶段,少部分发生在残余收缩阶段,体积收缩为开裂提供了空间,因此,收缩是裂隙形成和发育的必要条件;(4)断裂力学是研究土体开裂破坏的主要工具之一,运用断裂力学对土体裂隙发育过程进行解释一般有两种途径,即从应力的角度和从能量的角度,涉及的土体断裂力学参数包括应力强度因子、断裂韧度和能量释放率,是用来判断土体是否开裂以及什么时候开裂的有力依据;(5)用于测定土体断裂参数的方法主要有三点弯曲断裂试验和直接拉伸试验,以及基于这两种方法改进的试验方法。

Soil shrinkage cracking,which is a common natural phenomenon,can greatly weaken the engineering properties of soil and is a direct inducement for many geotechnical,water conservancy and geological engineering problems.However,at present,there is a lack of in-depth understanding of the mechanism of shrinkage crack development,especially the mechanism of cracking.Based on the research carried out around soil shrinkage cracking in recent years at home and abroad,the application of cracking development mechanism and fracture mechanics theory in this subject were systematically summarized;the research focus and direction of this subject based on the shortcomings of the current research were put forward.The results show that①evaporation is the premise of soil shrinkage cracking;for the initially saturated soil,the soil is still at saturation stage when the soil cracking occurs,and the water evaporation is at a constant velocity stage;at this moment,the corresponding water content is the critical;②the soil shrinkage cracking is the result of internal stress;during the drying process,the soil cracks when the tensile stress caused by the matrix suction reaches or exceeds the tensile strength;therefore,the matrix suction and tensile strength are the two key mechanical parameters affecting soil cracking;③the soil cracking is closely related to the volume shrinkage;shrinkage is the macroscopic manifestation of the movement of soil particles under tension;shrinkage can be divided into three stages(normal,residual and zero shrinkages),and most fractures occur in the normal shrinkage stage,and a small part occurs in the residual shrinkage stage;volume shrinkage provides the space for cracking,so shrinkage is a necessary condition for fracture formation and development;④fracture mechanics is one of the main tools to study the destruction of soil cracking;there are two ways(stress and energy)to explain the process of fracture development by using fracture mechanics;the involved fracture mechanics parameters are stress intensity factor,fracture toughness and energy release rate;there are all strong evidences for judging whether the soil cracks and when cracks;⑤the main methods to measure soil fracture parameters are three-point bend fracture test and direct tensile test,as well as the two improved tests.