3D simulation for tunnelling effects on existing piles

Abstract Numerical simulation was performed to analyse the effects of two advancing open face tunnel excavations on existing piled foundations into London Clay stratum. As excavation advances, it is necessary to cut and remove piles in the tunnel face (‘cut’ piles). Piles outside the tunnel face remain in-situ and are referred to as ‘adjacent’ piles. A suitable end-bearing capacity had to be selected for the piles in order to guarantee an accurate distribution of the axial pile load. Negative skin friction increases with higher end-bearing capacities of the piles. Additionally, the stiffness of the building has a significant impact on the settlement of the piles. The stiffer the building, the lesser the settlement of the piles. The results of the model indicated a considerable zone of influence due to the tunnel: one tunnel diameter in advance of the excavation face; one tunnel diameter behind the excavation face; and transversally, five times the tunnel diameter either side from the centre point between the two tunnels. Due to the negative skin friction, the factor of safety for adjacent piles was 1.1 and for cut piles 1.0.