Approximation of Stress near Tunnel Intersections in Deep Burst-Prone Mines for Support Selection and Rockburst Hazard Assessment

Assessing the depth of rock fracturing around tunnels is of critical importance for the design of ground support systems in strainbursting ground. Considering the heterogeneity of the rock, explicit modelling of stress-fracturing around tunnels at such a massive scale is a numerically demanding task. Previously, a semi-empirical approach to evaluate the extreme depth of failure based on elastic modelling has been suggested. It can be adopted at a mine scale by performing explicit modelling of large excavations (stopes, caves, chambers, etc) and then approximating anticipated conditions at tunnel locations using elastic approximations to obtain the local stress level. This implicit approach to incorporating tunnels into the stress model ignores interactions between tunnels, which can result in the underestimation of stress when tunnels are in close proximity, such as near intersections. To investigate this, we have explicitly modelled the stress distribution around tunnels near intersections with various configurations and loading conditions. Using these results, we present an approach to estimating stress magnifications near intersections that does not require explicit numerical modelling. A mine-scale example of an extraction level at a schematic block-caving mined is used to demonstrate the implications in the context of deformation-based support design and rockburst hazard assesment. 1 INTRODUCTION The design and selection of support in stress-fractured and strainbursting ground is informed by the displacement demand anticipated prior to a strainburst and both the displacement and energy demand during a strainburst (Kaiser and Moss, 2022). The pre-burst displacement demand depends on the depth of damage dpre that has accumulated since support installation and the rockmass bulking factor (BF). Similarly, the displacement and energy demands imposed during a strainburst can be related to the depth of strainbursting dSB. For rockburst hazard assessment (RBHA; Kaiser and Moss, 2022; Malovichko, 2023) in strainbursting ground, it is essential to obtain these demands and to asses their variability, which allows for estimation of the probability of exceedance of design thresholds.