【作者】 曹林卫；

【导师】 彭向和；

【作者基本信息】 重庆大学 ， 工程力学， 2010， 博士

【摘要】 准脆性岩石材料的微缺陷主要有微裂纹和微孔洞,在岩石材料中,微裂纹形核和扩展是材料损伤、失效的主要机制。损伤在影响材料力学特性的同时,会对材料的渗透性产生影响。当压力水(流体)渗透到微裂纹中时,可在微裂纹上产生附加张开应力而加剧微裂纹的扩展,加速材料的损伤演化。在许多岩石工程问题中,渗流-应力耦合作用下材料的损伤及其发展已成为必须考虑的重要因素。基于微缺陷的变形及演化的细观损伤-渗流耦合模型,能够较真实地描述材料的损伤和渗透行为,受到了人们的普遍关注。一般地,材料内部的微裂纹可采用椭圆形微裂纹进行描述,以较真实地反映微裂纹系统的细观特性。本文基于细观损伤力学和统计学方法,考虑材料内部椭圆形微裂纹的变形、扩展、摩擦滑移及偏折扩展对材料变形和渗透性的影响,采用Taylor方法建立了计及微裂纹内水压力的准脆性岩石材料三维细观损伤-渗流耦合模型。文中采用深埋椭圆形微裂纹的代表性单元(RVE),在远场应力作用下,根据微裂纹变形和扩展规律的不同,将微裂纹受力状态分为拉剪和压剪,分别研究具有任意空间取向的单个微裂纹在裂隙水压力和远场应力下的附加柔度张量,考虑微裂纹的稳定扩展以及围压对微裂纹偏折扩展的影响,采用Taylor方法并引入概率密度函数,分别建立准脆性岩石在三轴拉应力和三轴压应力下的三维细观损伤本构模型。文中假设准脆性岩石的渗透性由岩石基体材料(多孔介质)的渗透率和微裂纹系统的附加渗透率两部分组成。拉-剪应力作用下,微裂纹处于张开状态,认为裂纹系统的附加渗透性变化取决于微裂纹法向开度的变化;压-剪应力作用下,认为裂纹系统的附加渗透性变化取决于偏折裂纹法向开度的变化。引入修正的立方定理,展开微裂纹变形、扩展过程中渗透通道和连通度的讨论,得到准脆性岩石的渗透张量表达式。在前面建立的三轴拉应力与三轴压应力下的细观损伤-渗流耦合模型基础上,建立任意载荷下的三维细观损伤-渗流耦合模型,将本文模型与商用有限元软件ABAQUS相结合,编写了用户自定义材料子程序UMAT。以湖北云应盐矿拟建天然气储备库为例,对建腔后腔体在不同内压下的变形特征及其对泥岩夹层渗透性的影响进行了初步研究。基于混合物理论和所建的细观损伤本构模型,建立了适合于描述层状盐岩复合体在加载过程中损伤演化特性的细观损伤本构模型,并运用所建模型对湖北云应盐矿纯盐岩和含夹层盐岩在不同围压下的三轴压缩试验进行计算,分析了围压对盐岩所受等效附加侧向应力的影响,计算结果表明所建模型能较好的描述试验现象。更多还原

【Abstract】 Microcracks and microvoids are the main microdefects in quasi-brittle rocks. Damage develops with the nucleation and growth of microcracks during deformation processes. The permeability of materials may change with the development of damage. When water (fluid) infiltrates into a microcrack, an additional opening stress is applied to the surface of microcracks, which may accelerate the growth of microcracks and the evolution of the damage of materials. In many rock engineering applications, damage and its evolution play a significant role in the constitutive behavior and permeability of materials subjected to coupled stress and seepage. Much effort has been made in constitutive modeling of coupled damage and permeability in quasi-brittle rocks, which is based on the deformation and growth of microdefects and could realistically describe the development of damage and permeability. In order to describe the properties of a microcracks system more exactly, the microcracks in materials should generally be assumed to be elliptic. In this dissertation, based on a micro-mechanics damage model and a statistical method, the influence of the deformation, growth, frictional sliding, and kinked growth of microcracks on the compliance and permeability of quasi-brittle rock materials is studied. These microcracks are assumed to be embedded in infinite isotropic elastic matrix subjected to different states of stress. A unified constitutive model for the damage and permeability of quasi-brittle rock materials is obtained with the Taylor’s scheme, taking into account the hydraulic pressure on the surfaces of microcracks. The compliance and its changes of a representative volume element (RVE) containing an embedded elliptic crack is analyzed, taking into account different patterns of deformation and growth of the crack under different states of stress, for example, the deformation and growth under tensile stress, and the frictional sliding and kinked growth under compressive stress. The steady growth of the mirocrack and the influence of confined pressure on the kinked growth of the microcrack are considered. The additional compliance tensor induced by a randomly oriented embedded elliptic microcrack is then derived.The deformation and growth of the elliptic microcrack under general states of stress are considered. The additional compliance induced by a single closed elliptic microcrack is derived. A simplified method to analyze the kinked deformation of the closed elliptic microcrack is suggested. The permeability of quasi-brittle rocks may consist of two parts: the permeability of the matrix, and the additional permeability induced by microcracks. Microcracks may open under some states of stress and hydraulic pressure, and form numerous additional seepage channels, which significantly increase the permeability of the rocks. The variation of permeability is closely related to the growth of microcracks. Based on these concepts and making use of the Darcy’s law and the modified cubic law of laminar flow, the additional permeability of a single crack is deduced. The seepage channels and crack connectivity coefficient during the deformation and growth of microcracks are discussed, and the effect of a randomly oriented microcracks system on the permeability of a rock material is then derived.A three dimensional unified micro-mechanical constitutive model for coupled damage and permeability is constructed by combining the model obtained under triaxially tensile stress with that under triaxially compressive stress. A user subroutine UMAT for the materials with randomly oriented elliptic microcracks is developed and embedded in commercially available finite element code ABAQUS. Taking the underground gas reservoir Yunying Salt Mine as an example, the deformation at different internal pressures is studied, and its influence on the permeability is predicted.A micromechanical damage model is built for laminated salt rocks with a mixture theory. The triaxial compressive testing result of Yunying laminated salt rock is analyzed. The influence of confined pressure on the equivalent additional stress is discussed. The numerical results agree well with experimental results, demonstrating the validity of the developed approach.更多还原