Study on the hydromechanical behavior of single fracture under normal stresses

Abstract

The coupling between hydraulic and mechanical behavior of the fractured rock mass is of great significance for various civil and environmental engineering projects. In order to study the hydro-mechanical behavior of single fracture, seepage tests under different confining pressures and fracture water pressures were conducted on single shear fractures produced by triaxial loading of diabase rock samples from Danjiangkou Water Reservoir, China. Test results show that fluid pressure acting on fracture surfaces has strong influences on the hydraulic behavior of the fracture. Based on the classic Biot poroelasticity theory and by taking the fracture as assembling of a set of voids in rock mass, a generalized Biot coefficient is introduced to describe the interaction effect between pore fluid pressure and fracture deformation. Then, a nonlinear constitutive equation for single fracture under both normal stress and fluid pressure is developed. Later, the mechanical deformation of the fracture is related to the fracture hydraulic conductivity through “cubic law”, so that a coupled mechanical-hydraulic model is proposed. All the four parameters involved in this model have their physical significances and can be determined through mechanical compression tests and seepage tests. A first validity of the model is made by predicting the variation of fracture flowrates versus normal stress under different fluid pressures.