The influence of out‐of‐plane stress on a plane strain problem in rock mechanics

This paper considers the excavation of a cylindrical cavity in a uniformly prestressed mass of brittle Mohr‐Coulomb rock. Previous plane strain displacement solutions have assumed that the out‐of‐plane stress remains the intermediate principal stress at all points. It is here shown that when this assumption breaks down, an inner plastic zone is created in which σr < σz = σθ. A displacement solution is given for this case, using a variable‐dilation plastic flow rule, and results are compared with the previous solution for specific problems. A significant difference is observed only for problems involving a large drop in strength upon yield.