Optimizing borehole location for stress state assessment by geomechanical method of core discing

Abstract

The article addresses the reliability of the stress–strain analysis and rockburst hazard assessment in rock mass using the geomechanical method of core discing. The theoretical experimentation used CAE Fidesys system. This system performs the strength and other-type computations using the finite element method—a numerical method of problem solution in applied physics. The experiments have two stages. At the first stage, the model of rock mass with core drilling for the stress state assessment by core discing is constructed; the computation aims to determine vertical stresses such that the tensile stresses along the core axis exceed the ultimate tension strength (discing condition). At the second stage, the rock mass with the destress boreholes is modeled; the aim of the modeling is to determine the influence zones of the destress boreholes. The applied experimentation was carried out in underground openings of Taimyrsky Mine. The research has found the influence exerted by some destress boreholes on the stress state assessment by core discing. The theoretical experiments and practical testing results show a good agreement, which proves their reliability. The final conclusions are: inside the protected zones formed by destress drilling, the stresses effectively reduce down to safe values; to avoid errors inrockburst hazard assessment by core discing, core drilling should be performed at a distance from the destressing surface not less than 5 diameters of the destress boreholes; interpretation of the stress state assessment results should take into account the nonuniform stress distribution in the plane of destressing. The authors appreciate participation of D. Kh. Gilyazev, Head of the Rockburst Prediction and Prevention Department, Taimyrsky Mine (till 2021) in this study.