The Inverse Estimate for the Excavation Stability Around a Tunnel

摘要

Design of tunnels in rock mass require thought procedures in many ways different from other designrnprojects, because the principal construction material is the rock mass itself rather than otherrnengineered material. Resolving of problems related to the primary support carrying capacity usuallyrnfollows the stress and strain analysis of the underground rock mass by the tunnel opening. Suchrnproblem could also be resolved by using an inverse method which means by assuming the ultimaternlimit state of the support elements and checking whether such reactive pressures of the supportrnelements will retain the underground rock mass in stable state, namely does the underground rockrnmass meet the failure criteria. This would prove possible ultimate equilibrium in the primary supportrnsystem - underground rock mass interaction. This is the principal advantage of the inverse methodrnsince an input material constant on which the results depend is reduced to a very small number. On therncase of road tunnel driving, the method of boundary elements with the Hoek-Brown’s failure criteriarnwas used in computations. Computations have to be performed by choosing the mechanical rockrncharacteristics in accordance with the categories of rocks and the assumed limit bearing capacities ofrnappropriate support types. The problem is to determine the stresses and displacements around a tunnelrnexcavation of specified cross-section, given the primary support systems pressure and assumedrnfracture propagation in rock mass surrounding a tunnel opening. The upgraded boundary elementrnprogram for two-dimensional stress, displacement and failure analysis conducts the stress and strainrnanalysis for the area by the tunnel opening. This paper shows the results of an analysis for the tunnelrn“Pod Vugle?” in the part from Zagreb to Rijeka motorway as a part of European Vb traffic corridor.rnThe excavation of tunnel was performed by using the multi-phase New Austrian Tunnel Method.