Deterioration laws of Hoek-Brown parameters in freeze–thaw multi-fractured rock mass

Abstract

The Hoek-Brown criterion can better depict the nonlinear failure characteristics of rock mass, which has been widely used in the fields of large-scaled slopes, deep-buried tunnels, foundations in complex geological conditions, hydropower dams, and energy mining. In view of the previous studies mostly focused on the property reduction of freeze–thaw rock, the deterioration study of Hoek-Brown parameters for freeze–thaw multi-fractured rock mass was investigated in this study. Firstly, Monte-Carlo method was used to generate two-dimensional discrete fracture network, according to which the multi-fractured rock-like samples were prepared. Freeze-thaw cycle experiments were subsequently designed and executed to observe the apparent damage of freeze–thaw effect on the samples. Then, laboratory direct shear tests on freeze–thaw samples under multistage normal loading were carried out. The shear performances of freeze–thaw rock mass were analyzed based on the shear stress-shear displacement curves of samples with different freeze-thawed cycles. Besides, considering the deficiencies of the existing Hoek-Brown parameter estimation methods such as complicated sample preparation and strong subjectivity, a new estimation method based on shear test was proposed by deducing the shear expression of Hoek-Brown criterion, which was programmed in MATLAB and verified by direct shear test results. On this basis, the values of Hoek-Brown parameter of those samples under different freeze–thaw cycles were determined, and the variation law with freeze–thaw cycles was summarized. It turned out that the values of GSI and mi both decrease with the increase of freeze–thaw cycles, and the decreasing rate is also lowering, according with the negative exponential function model.