Analytical and Numerical Study of the Mechanics of Rockbolt Reinforcement around Tunnels in Rock Masses |
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| Authors: | C Carranza-Torres |
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| Institution: | (1) Department of Civil Engineering, University of Minnesota, Duluth Campus, USA |
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| Abstract: | Summary This paper addresses the problem of quantifying the mechanical contribution of rockbolts installed systematically around tunnels
excavated in rock masses. The mechanical contribution referred to here is that of increased stress confinement and decreased
tunnel convergences as compared with corresponding stresses and displacements obtained for non-reinforced tunnels. The problem
is treated analytically first by presenting a closed-form solution for stress and displacement distributions around a circular
tunnel excavated in elastic material and reinforced by grouted or anchored rockbolts. The analytical solution assumes that
rockbolts are regularly spaced around the tunnel and that axi-symmetry conditions of geometry and loading apply. The results
obtained with the closed-form solution are shown to be equivalent to the results of the same problem solved with traditional
numerical methods. Based on the analytical and numerical results and by introducing dimensionless ratios that allow to quantify
the increase of radial stresses and the decrease of radial displacements in the reinforced region of the tunnel, the paper
shows that reinforcement can have a significant mechanical effect (i.e., increasing the confinement and decreasing the convergences)
in tunnels excavated in rock masses of poor to very poor quality. The paper analyzes then the mechanical contribution of rockbolt
reinforcement when the rock mass is assumed to behave elasto-plastically. For this case, it is shown that rockbolt reinforcement
can also have a critical effect in controlling the extent of the plastic failure zone and the convergences of the tunnel.
Correspondence: C. Carranza-Torres, Department of Civil Engineering, University of Minnesota, Duluth Campus, 1305 Ordean Court,
Duluth, USA |
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| Keywords: | : Tunnel reinforcement rockbolt convergence-confinement elasticity elasto-plasticity numerical modelling rock mass Hoek– Brown failure criterion Geological Strength Index |
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