Three-dimensional centrifuge modelling of the effects of twin tunnelling on existing pile group in expansive clay

A three-dimensional centrifuge modelling is conducted to investigate the effects of twin tunnel construction on existing pile groups in expansive soil with volume loss of 2.0%. Surface settlement troughs, additional bending moments and axial forces are studied. As expected, the measured settlement troughs induced by each tunnel excavation fit the Gausian distributions well. It is found that the combined settlement trough caused by twin tunneling is similar to the superposition of two individual settlement troughs by each single tunneling. Consistently, the additional bending moments of piles induced by each of the two tunnels are similar, where the maximum induced occurs near the axis of tunnel. The additional axial forces induced in front and rear piles are different due to the the first and second tunnel advancements. The maximum induced axial force is 10% of work load of the piles.