Shape Optimization of Tunnel by Finite Element Method

The stresses around the periphery of tunnel openings are in general independent of factors such as size of the opening and elastic modulus of surrounding geotechnical material. The stresses however depend upon the shape of the opening and the residual stresses. At any point over the periphery the significant stresses are the normal stresses in the direction tangential to the opening periphery. By trials involving appropriate modifications to the finite element idealization, the shape of the opening could be derived such that the tangential tensile stresses are minimized and simultaneously the compressive tangential stresses are below the permissible limits. Though, pure theoretical analysis involving a trial process is available through the texts on structural optimization, the problem in case of tunnels has limitations. Here, selection has been made from few practically feasible shapes of the openings. This concept has been demonstrated in detail through nine different investigations for the case of a railway tunnel