Stability of a long unsupported circular tunnel in soils with seismic forces

Research paper by Debarghya Chakraborty, Jyant Kumar

Indexed on: 18 Mar '13Published on: 18 Mar '13Published in: Natural hazards (Dordrecht, Netherlands)


By using the lower-bound finite element limit analysis, the stability of a long unsupported circular tunnel has been examined with an inclusion of seismic body forces. The numerical results have been presented in terms of a non-dimensional stability number (γH/c) which is plotted as a function of horizontal seismic earth pressure coefficient (kh) for different combinations of H/D and ϕ; where (1) H is the depth of the crest of the tunnel from ground surface, (2) D is the diameter of the tunnel, (3) kh is the earthquake acceleration coefficient and (4) γ, c and ϕ define unit weight, cohesion and internal friction angle of soil mass, respectively. The stability numbers have been found to decrease continuously with an increase in kh. With an inclusion of kh, the plastic zone around the periphery of the tunnel becomes asymmetric. As compared to the results reported in the literature, the present analysis provides a little lower estimate of the stability numbers. The numerical results obtained would be useful for examining the stability of unsupported tunnel under seismic forces.