Mechanical parameters estimation and tunnel deformation study for brittle rock under high overburden condition

The Overburden of tunnel construction is increasing recently.Rocks in the depths have high strength and high stress condition.With increasing confinement pressure,brittle rock will become more and more ductile and eventually behave like an ideally plastic medium.However,radial pressure of tunnel is rapidly reduced during excavation.The rock masses surrounding the tunnel are actually in low confinement condition.Tunnel deformation is mainly dominated by rock's brittle properties.Brittle rock exhibits a progressive loss of strength when they are compressed beyond failure.After reviews of various parameter estimation methods of post-peak strength,the strength loss experiment method,which combines Hoek-Brown failure criterion with rock core experiment,is proposed.According to an actual case analysis,the tunnel deformation at 600 m overburden is about the same whether the post-peak strength degradation occurred or not.Nevertheless,the tunnel deformation has an obvious difference when the overburden exceeds 2 000 m.The difference of deformation is expected 3-4 times.The strength degradation of brittle rock beyond failure;therefore,it plays an important role in deep tunnel deformation.