Mechanical response and failure pattern of a modified mixed compression-shear experiments based on acoustic emission and numerical simulation.

There is potential danger of conical shear failure surface in karst cave roof under pile foundation load. To understand the mechanical and failure characteristics of rocks under such conditions. In this study, an auxiliary device consisting of an indenter and a hollow support combined with a servo-controlled mechanical equipment was used to perform mixed compression-shear tests. The laboratory tests were studied numerically by finite difference methods. This study set up 4 groups of height variables 20, 30, 40, 50 mm and 3 groups of aperture variables 20, 30, 40 mm. AE (acoustic emission) tests are adopted to study the failure characteristics of specimen. The experimental results show that the peak load increases with the sample height while decreases with the aperture of support. This paper defines an apparent elastic modulus in terms of displacements and loads, which increases with height by 42.12, 51.7, and 49.00 KN/mm for apertures from 20 to 40 mm. The AE data show that the ratio of RA (ratio of rise time to maximum amplitude) to AF (average frequency of AE count) gradually increases as the support aperture increases, indicating that the aperture is approximately close to the radius of the indenter and that shear damage is approximately significant. The numerical simulation results show that the shear stress is the largest at the position where the upper surface of the specimen contacts with the indenter, and the displacement is the largest at the position where the lower surface of the specimen overlaps with the support hole. The extrusion phenomenon caused by dilatation is the main reason for the tensile failure detected during the experiment. [ABSTRACT FROM AUTHOR]