Seismic stability of a long unsupported circular tunnel

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.

[1]  A. S. Osman,et al.  2D and 3D upper bound solutions for tunnel excavation using ‘elastic’ flow fields , 2007 .

[2]  S. Sloan,et al.  Upper bound limit analysis using discontinuous velocity fields , 1995 .

[3]  J. Pastor,et al.  Finite element method and limit analysis theory for soil mechanics problems , 1980 .

[4]  David M. Potts,et al.  Stability of a shallow circular tunnel in cohesionless soil , 1977 .

[5]  Scott W. Sloan,et al.  Stability of dual square tunnels in cohesive-frictional soil subjected to surcharge loading , 2011 .

[6]  A. S. Osman,et al.  On the kinematics of 2D tunnel collapse in undrained clay , 2006 .

[7]  F. Yang,et al.  Stability of Shallow Tunnel Using Rigid Blocks and Finite-Element Upper Bound Solutions , 2010 .

[8]  E. Leca,et al.  Upper and lower bound solutions for the face stability of shallow circular tunnels in frictional material , 1990 .

[9]  E. Davis,et al.  The stability of shallow tunnels and underground openings in cohesive material , 1980 .

[10]  W. WilsonDaniel,et al.  Undrained stability of a circular tunnel where the shear strength increases linearly with depth , 2011 .

[11]  Scott W. Sloan,et al.  Stability of a circular tunnel in cohesive-frictional soil subjected to surcharge loading , 2011 .

[12]  Chung-Jung Lee,et al.  Ground movements and collapse mechanisms induced by tunneling in clayey soil , 2003 .

[13]  Scott W. Sloan,et al.  UNDRAINED STABILITY OF A SQUARE TUNNEL IN A SOIL WHOSE STRENGTH INCREASES LINEARLY WITH DEPTH , 1991 .

[14]  Jyant Kumar,et al.  Effect of Footing Roughness on Bearing Capacity Factor Nγ , 2007 .