Abstract: The development of cities often involves the construction of new tunnels underneath densely distributed existing structures. When the tunnels experience complicated and difficult conditions, failure may occur at the tunnel face and pose great threat to the existing structures. The results of three centrifuge tests to simulate existing structures in a uniform silt and in the silt with a 4 m thick clay layer are introduced. A technique is developed to simulate the instability of the excavation face and reproduce the failure mode. The tests show that when the displacement of the excavation face is controlled (0.48H, where H is the excavation height) or there is a clay interlayer near the excavation surface, soil arching is formed to confine the failure and reduce the deformation and strain of the existing tunnel. When the displacement of the excavation face increases to 0.83H, an overall collapse is trigged and induce significant deformation and strain on the existing tunnel.