Ground reaction curve for tunnels using pre-injection in consideration of rockburst potential

Pre-injection is a technique that involves injecting grout materials into the ground prior to excavation, with the aim of stabilizing the surrounding rock mass. This paper introduces an analytical closed-form model for determining the ground reaction curve of tunnels in rock masses exhibiting elastic-brittle-plastic behavior and adhering to the Mohr-Coulomb failure criterion. The model incorporates the reinforced region created by the pre-injection method. When the rock mass is reinforced through pre-injection, plastic regions can form independently in both the natural and injected rock masses. This leads to six distinct modes of the problem. The analytical model presented in this paper considers three possible scenarios for the development of plastic regions. Each scenario comprises four stages, with each stage representing a different mode of the problem. While injecting the rock mass can enhance its strength and stiffness, it may also increase the brittleness of the injected rock mass and create stress concentrations within it, particularly when brittle grouts are used. As a result, this can elevate the risk of rockburst due to unstable failure. The results obtained from the model demonstrate that ductile grout performs exceptionally well in controlling tunnel convergence in rock masses, as it accommodates deformation without sudden failure, even in squeezing rock mass conditions. Conversely, the use of brittle grouts should be approached with caution, particularly in squeezing rock masses, due to their susceptibility to rockburst incidents.