脆性岩石各向异性损伤和渗透性演化规律研究

 在压应力作用下，脆性岩石的渗透性随着裂纹的扩展而演化。通过试验观察和微观机制分析，提出渗透系数计算方法。在已建立的细观损伤力学模型的基础上，对摩擦准则和加载函数进行改进，采用改进模型模拟Lac du Bonnet花岗岩三轴压缩试验。根据力学模型中得到的损伤变量和裂纹的法向、切向位移，引入连通系数描述裂纹扩展过程中，裂纹逐渐贯通形成渗流通道，采用立方定律作为单个裂纹中渗流方程，利用细观力学定义裂纹半径和等效开度，对各方向裂纹上的渗流速度进行平均化，得到渗透系数张量计算方法。采用此方法对Lac du Bonnet花岗岩现场试验结果进行模拟，比较轴向和侧向渗透系数的不同演化规律，预测不同围压条件下轴向渗透系数的演化规律。分析结果表明，模型的计算值与试验值非常吻合，验证了模型的适用性。

RESEARCH ON ANISOTROPIC DAMAGE AND PERMEABILITY EVOLUTIONARY LAW FOR BRITTLE ROCKS

Permeability in brittle rocks under compressive stress changes with crack growth. A method to calculate permeability evolution is presented，in which both experimental phenomenon and inherent mechanism of permeability evolution are taken into account. The mechanical model is based on the research of ZHU Qizhi et al，two modifications are applied to frictional criterion and potential function；and the modified anisotropic damage model is used to simulate triaxial compression test of Lac du Bonnet granite. According to damage variable and crack normal and tangential deformation obtained in mechanical model，a function of connectivity coefficient is used to describe the ratio of the crack involved in hydraulic flow to total number of crack，more and more cracks are involved in hydraulic flow when microcracks grow；the cubic law is used for seepage flow in a single crack，crack radius and equivalent aperture are defined by micromechanical result；a method is proposed to analyze permeability evolution in brittle rocks under deviatoric stress. The proposed method is employed to simulate in-situ permeability test of Lac du Bonnet granite. Comparison between axial and lateral permeability evolutions under increasing deviatoric stress is carried out；axial permeability evolution under different confining stresses is also predicted. It is shown that the numerical simulation results and experimental data are in good agreement.