Flow through fissures in rock mass applies simultaneously the normal hydrostatic seepage pressure and the tangent hauling pressure (the dynamic seepage pressure) on fissure walls. The cubic law of single fissure flow, the seepage theory and the basic equation of fluid mechanics are utilized to deduce the equations for the hydrostatic seepage pressure and the hauling pressure under three cases of single fissure without fillings. single fissure with fillings and water-filling flow. A computation example is also given to analyze quantitatively the double mechanical effects of flow through fracture network in rock mass. It can be shown that both the hydrostatic seepage pressure and the hauling pressure make the stress components in rock mass bigger, and especially the hauling pressure makes the shear stress component obviously much bigger.
Analysis of coupled seepage and stress fields in fractured rock mass is extensively concerned with by the researchers and engineers in the field of geotechnical engineering in the recent years (Louis, 1974: Oda, 1986: Tsang, 1987: Wu Yanqing, et al, 1995). The key for couple analysis is the interaction mechanism between stress and the fluid flow. The principle of effective stress is extensively applied in the recent research for couple analysis, in which only the hydrostatic seepage pressure is considered and the effect of hydrodynamic seepage pressure on the deformation of fractures is neglected. In fact, when the hydraulic gradient is large (such as between upstream and downstream of high dams, near pumping or pressuring wells, etc.], the hydrodynamic seepage pressure is too big to be neglected. The fluid flow through fractures exerts simultaneously the hydrostatic seepage pressure and the hydrodynamic seepage pressure on the fissure walls. The hydrostatic seepage pressure makes the fracture aperture larger, and the hydrodynamic seepage pressure (i.e. the hauling pressure) exerts the tangent pressure on the fissure walls. Wu Yanqing (1998) proposed the effect of the hauling pressure by lowering the shear strength of rock and soil mass. The purpose of this paper is to deduce the equations for determining the hauling pressure and hydrostatic seepage pressure by means of the momentum law of fluid mechanics and the cubic law of the single fissure flow. The equations are designated for the cases of no-filled fissure, filled fissure and the combined flow of fluid and the fillings, respectively, which are the foundation of the interaction mechanism between stress and fluid flow in fractured rock mass. A computation example is also given to analyze quantitatively the double mechanical effects of flow through fracture network in rock mass.
The basic assumptions applied in this paper are the same as those for deducing the cubic law of the single fissure flow (Bear, 1979). That is, a single fissure distributes in the rock mass, the aperture of which is constant, the extending length of which is infinite and the walls of which are straight, smooth and stationary.
