Numerical Modelling of Hydraulic Fracturing in Rock Mass by Xfem

Abstract

A numerical model based on the extended finite element method (XFEM) is developed to serve this purpose. The present approach involves several features of an effective numerical tool in modelling hydraulic fracturing: the generalized shape functions are used in a cluster of nodes around the cracks, whereas the conventional finite element shape functionsare applied outside the cracks; the ramp function is introduced to remove the blending elements in the XFEM setting; and the contact conditions between crack faces are considered by combining the mortar method with the augmented Lagrange's method. This study assumes uniform water pressures at the crack faces. The effect of the water pressure on the fracture behaviours of cracks and the interaction between the hydraulic and natural fractures are analyzed. Numerical examples are presented and discussed to show that the water pressure acting on the crack faces has a significant influence on the stress and the deformation in the vicinity of the cracks, and the crack propagation path depends on the mechanical properties of rock mass and natural fracture faces, water pressure, insitu stresses, and relative positions of natural and hydraulic fractures.