脆性岩石破裂过程损伤与渗流耦合数值模型研究

大量的实验结果表明，脆性岩石的渗透性不是一个常量，而是应力和应力诱发损伤破裂的函数．建立了一个描述非均匀岩石渗流-应力-损伤耦合数学模型(FSD Model)，开发出岩石破裂过程渗流-应力-损伤耦合分析计算系统(F-RFPA^2D)．在该系统中，单元的力学、水力学性质根据统计分布而变化，以体现材料的随机不均质性，材料在开裂破坏过程中流体压力传递通过单元渗流-损伤耦合迭代来实现．该系统能够对岩石试件在孔隙水压力和双轴荷载作用下裂纹的萌生、扩展过程中渗透率演化规律及其渗流-应力耦合机制进行模拟分析．最后，给出两个算例：算例1模拟载荷作用下岩石应力应变-渗透率全过程．模拟结果表明，非均匀性对岩石的应力峰值强度、峰值前后其渗透性演化规律及其破裂机制影响十分明显，模拟结果和实验结果较为一致；算例2模拟孔隙水压力作用下岩石拉伸断裂过程，通过和物理实验对比验证，验证了模型计算结果的可靠性。

STUDY ON MODEL OF DAMAGE AND FLOW COUPLING IN BRITTLE ROCK FAILURE PROCESS

Experimental results provide strong evidence that rock permeability cannot be a constant but a function of stresses and stress-induced damage. In this paper, a numerical code Rock Failure Process Analysis (F-RFPA2D) is implemented by introducing a flow-stress-damage (FSD Model) coupling model for heterogeneous rocks and taking into account the growth of the existing cracks and the formation of new fractures. In this FSD model, material is discribed by many elements with the same size and different mechanical and permeability parameters in order to reflect the heterogeneity of rock. The water fluid pressure during failure process is obtained by flow and stress coupling iteration. A coupling analysis of flow and damage under hydraulic fracturing on rock is attained to simulate the fracture process of rock, and this model has been used to investigate the behavior of fluid flow, damage evolution and their coupling action in samples subjected to both hydraulic and biaxial compressive loading. Two numerical simulations are given. The results of the first simulation suggest that the nature of fluid flow in rocks varies from material to material and the peak strength of the rock samples and the change of rock permeability during progressive failure process depend strongly upon the heterogeneity of the rocks, and the numerical results compare well with the corresponding experimental results. Another simulation result presents a failure process subjected to tensile stress caused by pore pressure. It shows that the FSD model is valid by comparing with the experimental results.