On the effective stress coefficient of saturated fractured rocks

Abstract

The applicability of the classic Terzaghi or Biot effective stress laws to fractured rocks is not clear. Based on discrete element models, bulk modulus method and equivalent strain method are presented to determine the effective stress coefficient of saturated fractured rocks, and were examined with the regular fracture network I. Two types of discrete fracture networks, including regular and random network models, were built, and a total of over 300 numerical simulations were performed using the equivalent strain method for sensitivity analysis of the effective stress coefficient of fractured rocks to the fracture geometries characteristics, and the mechanical properties of both the intact rock and the fracture. The classic effective stress laws for porous media cannot be extended to fractured rocks, mainly due to the different volumetric deformation behaviors between porous and fractured materials. The effective stress coefficient is the largest in the regular fracture network I and the smallest in the random fracture network. As the normal and shear stiffness of the fracture increase, the effective stress coefficient decreases, while it increases with the increasing elastic modulus and Poisson’s ratio of the intact rock. An empirical model was proposed to predict the effective stress coefficient of saturated fractured rocks.