Abstract：The mixed mode fractures in quasi-rock materials under compression-shear loading are usually simulated using Griffith cracks with zero thickness. It leads to the result that the initiation angles of wing cracks are independent of the fracture orientation angles and the confining pressure. However，many previous experiments showed this conclusion was not valid necessarily. Therefore，a theoretical and also an experimental analyes are carried out to investigate the influence of geometric characteristic on the initiation angles of wing cracks，e.g. the thickness of pre-existing fractures and the radius of curvature near the fracture tip. The proposed method will provide a theoretical frame for the experimental analysis of mixed mode fractures of samples under compression-shear loading，and also for further stress analysis of the morphologically complex cracks.
