Abstract
The stability of a long unsupported circular tunnel (opening) in a cohesive frictional soil has been assessed with the inclusion of pseudo-static horizontal earthquake body forces. The analysis has been performed under plane strain conditions by using upper bound finite element limit analysis in combination with a linear optimization procedure. The results have been presented in the form of a non-dimensional stability number (γmaxH/c); where H=tunnel cover, c refers to soil cohesion and γmax is the maximum unit weight of soil mass which the tunnel can support without collapse. The results have been obtained for various values of H/D (D=diameter of the tunnel), internal friction angle (ϕ) of soil, and the horizontal earthquake acceleration coefficient (αh). The computations reveal that the values of the stability numbers (i) decrease quite significantly with an increase in αh, and (ii) become continuously higher for greater values of H/D and ϕ. As expected, the failure zones around the periphery of the tunnel becomes always asymmetrical with an inclusion of horizontal seismic body forces.
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