Elastoplastic Solutions for Deep Tunnel Excavation in Weak Rocks with High Geostress Considering Different Stress Release Measures

Abstract

The Deformation Reserved (DR) method and the Pilot Heading (PH) method are two commonly used stress release methods in the construction of weak rock tunnel under high geostress. The ground pressure exerted on the support would be reduced to a certain extent with the stress release measures according to the Convergence–Confinement principle. The elastoplastic solutions of tunneling with DR method and PH method are derived, respectively, considering the support delay. By introducing the concept of stress release ratio, the equivalent relationship between two methods is studied. The effects of these two methods on reducing the contact pressure between surrounding rock and support are compared. Furthermore, the stress release effects of DR method and PH method under different conditions are explored. The results show that DR method is much more suitable when the geostress is not very high and surrounding rock is intact with high strength. Contrarily, if the geostress is quite high and the surrounding rock is very weak, PH method is suggested. For DR method, the stress release effect abates gradually with the increase of initial geostress, but the effect of stress release by PH method is much better under high geostress. Though both DR method and PH method are effective in reducing the contact pressure between surrounding rock and lining, the reserved deformation and the radius of the pilot tunnel are not suggested to be as large as possible.