Shape of underground openings and rock bolt length

The boundary stresses around an underground opening govern its stability. It has been studied by Hoek & Brown (1982) that the shape of underground opening does affect the boundary stresses around an underground opening. Parametric study using FLAC 3D code has been carried out for two shapes of underground opening and considering various other parameters like the tunnel depth, the in situ stress, the uniaxial crushing strength (UCS) of intact rock material and the Bieniawski’s rock mass rating (RMR). The results of the study covering induced boundary stresses, minimum safety factor and the required rock bolt length for these two shapes are presented in the paper.