An experimental study on the nonuniform tunnel lining

The elliptic and the horseshoe-shaped tunnels are considered to be more economical than the conventional circular tunnel because an amount of the excavated soil and the unnecessary space can be reduced. In this research, the model tests are carried out for investigating the effects of the tunnel shape, and the variation of the lining thickness on the tunnel stability. The tests are carried out on three types of the tunnel shape: circle, ellipse and horseshoe. For the elliptic and the horseshoe-shaped tunnel, the variations of the lining thickness are taken into consideration. The Styrofoam and silica sand are used to model tunnel lining and underground material respectively. The circumferential strains, generated at the surface of the lining, are measured after loading the tunnel by earth pressure. The axial force and the bending moment are calculated and demonstrated. The stability of each lining-thickness pattern is compared and the efficiency of increasing the tunnel stability by varying the lining thickness is discussed.