Water flow in fractured rock mass due to surface infiltration is a saturated-unsaturated seepage process. Aimed at rock mass with large fracture density, which can be equivalent to a continuum, a mathematical model for saturated-unsaturated seepage flow in fractured rock mass due to surface infiltration is established in this paper. Galerkin finite element method is used as numerical simulation means and a finite element program used to a calculate saturated-unsaturated seepage now due to surface infiltration is worked out. A model experiment is used to examine the reasonableness of the program. The examined result shows that the mathematical model and the program in this paper are reasonable. The application of the simulation method presented here in a practical engineering problem shows that the method is reliable and feasible.
The pan from water table to ground surface of fractured rock mass is an unsaturated region which isn't full of water. Therefore, water flow in fractured rock mass due to surface infiltration is a saturated-unsaturated seepage process. During rainfall (or flood discharging atomized rain), perched water will form in the unsaturated region due to precipitation infiltration from ground surface, thus raising harmful factors which can't be considered using the previous saturated seepage models to the stability of rock slope and drainage. That is, the formation of perched water not only reduces mechanical strength index or rock mass but also increases temporary water load, which will cause landslide of rock slope(Zhang & Liu 1997).In addition, the drain holes which were designed on the basis of the calculated results of saturated seepage models are no function to the above mentioned perched water. Moreover, nuclear waste disposal(Peters & Klavetter 1988) and migration of ground surface pollutant with infiltration water(Kueper et al. 1992) will involve the matter of saturated- unsaturated seepage flow in fractured rock mass due to surface infiltration. Therefore, it has great engineering significance to study the saturated-unsaturated seepage now in fractured rock mass due to surface infiltration. Four kinds of mathematical models which can be selected to study water now in fractured rock mass are as follows: equivalent continuum model, discrete fracture network model, double-porosity model and discrete media-continuum coupled model(Hu et al 2000). Although it is possible to produce equivalent fracture network based on statistical parameters of measured data of fracture, it is difficult to conduct hydraulic analysis of three-dimensional fracture network owing to the complex nature of fracture network. Moreover, to unsaturated seepage flow, the unsaturated permeability of rock matrix can't be omitted as compared with that of fracture(Salam & Chrysikopoulos 1996). Therefore, it is inappropriate to use discrete fracture network model to study saturated-unsaturated seepage flow in fractured rock mass. It is difficult to determine the water exchange term of dual-porosity model and discrete media-continuum coupled model exactly(Gerke & Genuchten 1993). However, the accuracy of the water exchange term affects the simulation precision of model directly. In addition, the amount of analysis work of the above mentioned models is large.
