Rocks and tunnels

Abstract

This chapter discusses engineering problems related to rock mass during underground constructions. Rock bursting or squeezing can occur in hard or soft rocks under high stresses, compromising the stability of underground structures. The principal factors that are generally considered in tunnel design are the in situ stresses and the mechanical properties of the rock mass. At greater depths, the rock mass can be overstressed, resulting in either brittle fracture of the intact rock or shear failure along pre-existing discontinuities such as joints or shear zones. Extremely hard and massive rock mass is preferable environment for tunnel construction; however, some engineering problems may occur at greater depths where the rock mass is under very high stresses. When tunnels are excavated in jointed rock mass at relatively shallow depths, the most common type of failure is wedge and/or slide of rock blocks. The problem of raveling ground can occur in disintegrated rock mass under relatively high stress conditions.