Stability Analysis of Different shapes of Tunnel in Cohensionless Soils

One of the crucial factors that has gained widespread popularity during the tunnelling construction process is the face stability of tunnel that mainly depends upon the support pressure to be applied at the face of tunnel against the overburden pressure and surcharge loading acting on the earth surface. In this study, stability of different cross sections of tunnels has been investigated in cohesionless soil (loose and medium dense sand) using the Finite Element Analysis software Plaxis 2D V20. Tunnel having cross sectional dimension B as width, D as height positioned at a depth H from the surface of ground. Due to the overburden pressure acting on the face of the tunnel, a suitable uniform compressive pressure is applied at the tunnel periphery in form of lining or anchorage system against the collapse. Variation of deflection at periphery of tunnel is presented for different combinations of H/D and Ф (angle of internal friction of soil), and lining thickness. It is observed that at a particular lining thickness with the increase in H/D, the displacement at the crown in tunnel increases and this could be resisted by increasing the lining thickness. The crown deflection of circular tunnel at particular H/D, lining thickness and Ф was less as compared to semi-circular and square tunnel.