Support to rock excavations provided by sprayed liners

Abstract

The support provided to mining excavations by sprayed liners is investigated. A long cylindrical excavation of circular cross-section is considered. Three models to analyse liner mechanisms are presented. In the first model the liner forms a thin cylindrical layer firmly bonded to the surface of the excavation. The rock surrounding the excavation may contain open joints and fractures due to the excavation process. In the second model the liner material penetrates into the fractures to their full extent. In the third model the liner material penetrates some distance into the fractures but the fractures extend well beyond this depth and are taken to extend to infinity. The excavation is subjected to a uniform shear stress at infinity which could represent a perturbation due to mining or a geological disturbance. Two cylindrical regions are considered, an inner region and an outer region which extends to infinity. The stress and displacement in each region are calculated, using plane strain theory of elasticity. In the first model the transfer of stress from the rock to the liner is investigated and the decrease in the stress concentration factor in the rock due to the liner is calculated. In the second and third models the change in the displacement, rotation and stress due to the penetration of the liner material into joints and fractures is investigated. Representative values for the changes in stress and displacement at the surface of the excavation predicted by the three models are presented.