The effects of undercrossing tunnelling on the settlement of footings subjected to cyclic loading

Abstract

In urban areas, due to the expansion of underground systems and space limitation, many tunnels will be constructed beneath existing tunnels, roads or railways which may be subjected to traffic loading. Undercrossing tunnelling disturbs the stress state in soils and may affect the long-term settlement behaviour of existing structures under cyclic loading. A series of physical model tests were performed to investigate the effects of undercrossing tunnelling on the settlement behaviour of existing footings subjected to cyclic loading. The undercrossing tunnelling induced volume loss is simulated using a self-designed device in steps between loading cycles. The variation of footing settlement and soil stresses in the ground are presented and discussed under different cyclic loading amplitudes, volume losses and footing positions relative to the new tunnel. The results indicate that including volume loss between loading cycles enlarges the footing settlement during the subsequent cyclic loading, even if the footing is out of tunnelling induced settlement profile, and the greater the volume loss, the greater the enlargement. The enlargement decreases as the footing gets farther away from the new tunnel. The enlargement is attributed to the change of relative density and/or the change of stress state in the soil induced by tunnelling.