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Abstract 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.
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Received: 09 January 2014
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2015, Vol. 34 
