Tunnel Shotcrete Performance due to Varying Thickness and Bond to Hard Rock
The structural behaviour of fibre reinforced shotcrete (sprayed concrete) as support in hard rock tunnels are complex and depends on the interaction between shotcrete, bolts and rock. It is here studied how variations in shotcrete thickness and bond strength affect the behaviour of this type of rock support system. Numerical models are used to simulate bond failure, shotcrete cracking and pull-out of grouted rock bolts. It is shown that local variations in shotcrete thickness affects possible shrinkage crack patterns and when subjected to the load from a loose block, the force is transferred to the surrounding rock through bond stresses distributed over a narrow band in the shotcrete. Moreover, it is shown how the structural capacity with respect to bond failure depends on the shotcrete thickness.