Non-linear analysis of rock masses in underground openings and determination of support pressure

In attempting to develop a comprehensive non-linear analytical solution, applicable to various excavation shapes under different loading conditions, an elasto-viscoplastic model has been adopted. The advantage of this model is that it reflects the rock mass behaviour much more better than the elastoplastic models and it is capable of evaluating the time-dependent characteristics of the rock mass around underground openings. The Hoek-Brown and Mohr-Coulomb yield criteria were used to define the yield condition for the rock, and a "no-tension criterion" was used to determine the likely tension areas around the excavation. A computer program was prepared for determining elasto-viscoplastic stresses and displacements around the underground opening and the finite element method was used as the numerical solution. A horse-shoe tunnel and a circular tunnel were analyzed and the results obtained were compared with the elastic solution. The results reveal the significance of the elasto-viscoplastic model as a very relevant method for these type of problems.