Study on Fracture Criterion for Hydraulically Induced Crack Initiation in Granite

Laboratory hydraulic fracturing experiments were conducted on uniaxially loaded cubic specimens of anisotropic granite to investigate the effect of anisotropy on the hydraulic fracture, and to exploit a method for predicting the breakdown pressure based on uniaxial tensile strength. Based on uniaxial tensile strength data, the results of the hydraulic fracturing experiments were analyzed with respect to the fracture angle and breakdown pressure. It was shown that the concept of a critical tensile stress at a characteristic distance, modified to account for the anisotropy of tensile strength, was able to explain the observed extension behaviours of hydraulic fractures.