Numerical Study of the Failure Response and Fracture Propagation for Rock Specimens with Preexisting Flaws under Compression

Abstract

This study incorporated an elastic brittle damage constitutive model into a program for modeling and analysis through a user subroutine interface to define a material’s mechanical behavior and considered nonlinear geometric effects. The Weibull distribution function was adopted to consider the heterogeneity-related uncertainty of the strength and stiffness. The 2D models used were discretized using plain strain reduced integration elements with the option of element removal after being fully damaged. We verified the accuracy of the user subroutine code by reproducing the observed failure behavior of an intact sandstone specimen with using previously suggested material parameters. The reliability of the numerical model was supported by an agreement between pre-existing experimental results and the numerical simulation results for specimens containing a single fissure with different inclination angles. Two parametric studies were conducted on the failure behavior of a specimen with a single fissure to investigate the effect of (1) the heterogeneity level and (2) the confining pressure. Stiffness and strength were shown to decrease with increases in the level of heterogeneity. Tensile cracks that appeared in the more homogeneous models were replaced by scattered damaged elements with increasing heterogeneity. Increasing the confining pressure increased the load capacity of the specimen, regardless of the inclination of the fissure angle. This trend was related to the amount of damage occurring before reaching the peak load. The maximum load was typically lower when the route length of the cracks formed before the peak load was larger. To investigate fracture coalescence behavior, specimens with two parallel fissures were modelled for four different ligament angles. The numerical simulations agree with the available experimental results, indicating that coalescence changed from shear to a tensile mode as the ligament angle increased.