Experimental study of surface failure induced by tunnel construction in sand

An experimental study was conducted to determine the effects of tunnel construction on ground movements in sand. In this regard, a small-scale three-dimensional model test was developed, and several laboratory model tests were carried out under single gravity in a sand sample with three different relative densities of 30, 50, and 75% and a cover-to-diameter ratio of 3. To simulate the volume loss induced by the tunnel boring machine, the casing method was utilized. In the model tests, an elastic aluminium liner was used as a tunnel supporting system and a pipe casing was utilized to model a tunnel shield. By pulling out the tunnel shield progressively and replacing it with tunnel liner, the soil was allowed to move toward the tunnel and the surface settlements were measured by using linear variable differential transformers. The results show that increasing the value of the relative density of sand reduces the ground movements induced by tunneling. The settlement trough width increased almost linearly with increment of the overburden. Also, the results reveal that in dense sand the ground settlement trough is slightly less than the volume loss. For loose sand, the volume of settlement trough is nearly twice the volume loss. In shallow tunneling and loose sand produces remarkable movement on the ground surface.