Observation of Ground Movement with Existing Pile Groups Due to Tunneling in Sand Using Centrifuge Modelling

In developing urban areas, there are unavoidable interactions between existing structures and new construction such as tunnelling through preexisting pile foundations. An accurate prediction of the ground deformation due to tunnelling is necessary to assess potential damage to those existing structures. Two dimensional tunnelling model tests were carried out to study the movement of both soil surface and subsurface layers of dry Toyoura sand with two pile groups of different length at both sides of the tunnel. The model pile group has four piles with spacing and diameter ratio of 5. The tunnelling process was simulated by reducing the diameter of the model tunnel with initial diameter of 70 mm for various ground loss values at 100g centrifugal acceleration. The induced soil movement and displacement of pile foundation were observed using the particle image velocity technique and displacement transducers. The test cases were conducted at two different tunnel cover depth and diameter ratios (C/D = 1.5 and 2.5) and three different horizontal distances between the pile groups and the tunnel. Tunnel machine showed good agreement of soil movements with the results from real site construction at small ground loss ratios. The cases with the pile group induced larger maximum settlement in the vertical direction than the cases without piles. There was an effect of the pile groups on the ground movement at the location more than five times pile diameter away from the piles in the longitudinal direction.