Shape ratio effects on the mechanical characteristics of rectangular prism rocks and isolated pillars under uniaxial compression

Abstract

Isolated pillars in underground mines are subjected to uniaxial stress, and the load bearing cross-section of pillars is commonly rectangularly shaped. In addition, the uniaxial compression test (UCT) is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress. The shape effects of rock mechanical properties under uniaxial compression are mainly quantitatively reflected in the specific shape ratios of rocks. Therefore, it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress. In this study, granite, marble and sandstone rectangular prism specimens with various height to width ratios (r) and width to thickness ratios (u) were prepared and tested. The study results show that r and u have a great influence on the bearing ability of rocks, and thin or high rocks have lower uniaxial compressive strength. Reducing the level of r can enhance the u effect on the strength of rocks, and increasing the level of u can enhance the r effect on the strength of rocks. The lateral strain on the thickness side of the rock specimen is larger than that on the width side, which implies that crack growth occurs easily on the thickness side. Considering r and u, a novel strength prediction model of isolated pillars was proposed based on the testing results, and the prediction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.