engleski

The inverse estimate for the excavation stability around a tunnel

Design of tunnels in rock mass require thought procedures in many ways different from other design projects, because the principal construction material is the rock mass itself rather than other engineered material. Resolving of problems related to the primary support carrying capacity usually follows the stress and strain analysis of the underground rock mass by the tunnel opening. Such problem could also be resolved by using an inverse method which means by assuming the ultimate limit state of the support elements and checking whether such reactive pressures of the support elements will retain the underground rock mass in stable state, namely does the underground rock mass meet the failure criteria. This would prove possible ultimate equilibrium in the primary support system - underground rock mass interaction. This is the principal advantage of the inverse method since an input material constant on which the results depend is reduced to a very small number. On the case of road tunnel driving, the method of boundary elements with the Hoek-Brown's failure criteria was used in computations. Computations have to be performed by choosing the mechanical rock characteristics in accordance with the categories of rocks and the assumed limit bearing capacities of appropriate support types. The problem is to determine the stresses and displacements around a tunnel excavation of specified cross-section, given the primary support systems pressure and assumed fracture propagation in rock mass surrounding a tunnel opening. The upgraded boundary element program for two-dimensional stress, displacement and failure analysis conducts the stress and strain analysis for the area by the tunnel opening. This paper shows the results of an analysis for the tunnel "Pod Vugleš" in the part from Zagreb to Rijeka motorway as a part of European Vb traffic corridor. The excavation of tunnel was performed by using the multi-phase New Austrian Tunnel Method.

tunnel; GEO ultimate limit state-failure; primary support systems; boundary elements; stress analyses

Safety in the Underground Space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and 32^nd ITA General Assembly