Classification optimization of tunnel surrounding rock based on geometric parameter effect of joints

Abstract

Abstract This research aims to study the relationship between the mechanical properties and failure modes of jointed rock mass and the geometrical parameters of the joint and to optimize the grading of the tunnel surrounding rock according to the test results. The numerical model of the jointed rock mass is established using the discrete element particle flow program PFC2D. An uniaxial compression test simulation is conducted for the joint rock mass, considering that the joint dip angle and joint spacing exist simultaneously. Test results show that when the joint dip angle is 45°, the mechanical properties of the jointed rock mass are the worst, the UCS and elastic modulus are the smallest, and the Poisson’s ratio reaches the maximum. When the joint spacing is large, the joint dip angle leads to failure. With the increase in the joint dip angle from 0° to 45°, the failure mode changes from intact rock mass failure to plane and block failure. The change rule is the opposite when the joint dip angle ranges from 45° to 90°. When the spacing is small, the joint spacing dominates the failure mode. With an increase in spacing, the failure mode changes from an intact rock mass to a plane and block failure mode. Based on the influence of joint geometric parameters on the mechanical properties of the rock mass, the surrounding rock classification method was optimized using the basic quality index of the rock mass (BQ).