Assessment of excavation intersections’ stability in jointed rock masses using the discontinuum approach

Abstract

During ore deposit development, vast networks of excavations are designed, and the volume of their intersections reaches 10%. At excavation intersections, the prediction of stress-strain state changes is complicated due to spatial geometry, the cross-coupling effect, construction sequence, etc. Mechanical properties of rocks, joint set parameters and the initial stress field also have a significant impact on stress redistribution. According to studies, up to 40% of the total number of failures in excavations occur during their intersections’ construction or reinforcing. Loads on the intersection support in accordance with existing methods are determined as for single excavations with an equivalent span and defined as the width of the larger excavation. The trend towards the intensification of mining, an increase in depth and the complexity of mining and geological conditions also complicate stress state assessment. Existing approaches need to be revised and updated for a more accurate prediction of the stress-strain state at intersections, and should consider spatial geometry, joint sets and initial stress field parameters. In this research, discrete element numerical modelling in 3DEC is done and the results are compared with existing empirical methods. Numerical models are created in a spatial setting and contain explicit representations of joints in the rock mass. Models are verified based on in-situ data, and the obtained results show a difference of up to 2 times in comparison with empirical results. This indicates that the reliability of the existing empirical methods is low, which may lead to stability loss on an intersection. Therefore, empirical methods should be updated. This can be done on the basis of numerical modelling, which shows sufficient convergence with in-situ data.