Blast Resistant Analysis of Rock Tunnel Using Abaqus: Effect of Weathering

Tunnels have become an essential part of metro cities, therefore, always been under threat of destruction due to explosive used for causing blasts. To understand the behaviour and blast resistance of underground rock tunnel under internal blast loading a 3D model of rock tunnel of 5 m diameter has been developed in Abaqus using finite element technique. Nonlinear elastoplastic material models are adopted through different constitutive material models, for rock, concrete, reinforcement, inside-air of tunnel and trinitrotoluene (TNT). The focus is placed on the effect of weathering in rock tunnel. Four different stages of weathering of rock Granite has been considered. Trinitrotoluene has been used to simulate in-situ event of internal blast loading. The TNT sphere and air surrounding it, have been modelled using coupled Eulerian-Lagrangian technique. Further, the steel reinforced cement concrete lining behaviour has been analyzed in terms of tension-compression damage. The behaviour of surrounding rock along with weathering has been studied in conjunction with blast effect. The results extracted in terms of deformation, particle velocity, vibration, energy, pressure and damage has been used to understand response of weathered rocks. The rocks in general and granites in particular can show sudden variation in their strength due to different stages of weathering. Along, linear directions varying degrees of weathering can creep in due to presence of shear zones or very closely spaced joints. It has been observed that weathering of rock causes significant reduction in blast-resistance of tunnel. A progressive deformation in case of blasting has been observed from fresh granite to highly weathered granites through slightly and medium weathered ones. However, highly weathered rock has shown unique behaviour and has failed miserably.