裂隙岩体非稳定渗流的复合单元算法

 针对裂隙岩体渗流非连续、非均质和各向异性的特点，提出裂隙岩体非稳定渗流的复合单元算法，给出详细的计算格式和数值处理的关键技术，包括复合单元的前处理、求解自由面边界流量项的积分方法以及溢出边界的判断准则。该算法的特点是：(1) 可准确地离散岩体内任意分布的裂隙；(2) 可考虑岩块的渗透性及其与裂隙间的水量交换；(3) 可与传统有限单元计算程序无缝整合；(4) 复合单元的拓扑信息由裂隙面和常规有限单元的交切计算生成，由于事先未考虑裂隙的存在，极大地减轻了人工剖分网格的工作量；(5) 对裂隙岩体非稳定渗流过程中裂隙与岩块渗流不同步的现象具有较强的描述能力，并能提供近似于有限单元法的计算精度。通过典型砂槽试验验证了该算法的正确性和有效性。最后，对裂隙岩体进行非稳定渗流分析，计算结果很好地反映了岩体内水压力的传递过程，实现了对裂隙与岩块因水力特性不同而导致的不同于整体流向的局部流动的模拟。

COMPOSITE ELEMENT ALGORITHM FOR UNSTEADY SEEPAGE IN FRACTURED ROCK MASSES

An algorithm of composite element for calculating the unsteady seepage in fractured rock masses was established according to the hydraulic properties of fractured rock masses including the discontinuity，the heterogeneity and the anisotropy. The pre-process of composite element，the method to calculate the integral over free surface boundary and the judging criterion of overflow boundary，etc. were presented. The features of the algorithm are as follows：(1) It can simulate arbitrary distributed fractures exactly. (2) The permeability of intact rock and the flow exchange between rock blocks and fractures are considered. (3) It can be integrated into conventional finite element method easily. (4) The topological information of composite elements is obtained by the calculation of intersection and incision between fractures and the finite elements. In this way，the mesh generation is not restricted by fractures and is considerably simplified. (5) The phenomenon that seepage in rock blocks and in fractures are out of sync can be simulated by using the algorithm which provides the same precision of calculation as finite element method. The validity of the algorithm was verified by a typical seepage test. Finally，the algorithm was applied to calculate the unsteady seepage behaviours in fractured rock masses and to reveal the process of pressure transfer. The calculated results show that the direction of local flow is different from the general one，which is due to the different hydraulic properties of fractures and rock blocks.