Laboratory model test of slurry shield tunnelling in saturated sandy soil

Experimental tests were carried out using a laboratory-scale model of a slurry shield machine to investigate the mechanical behaviours of soil in response to excavation in saturated sandy ground. The experimental model includes a miniature slurry shield machine that can approximate real tunnel construction, replicating the in situ methods of cutterhead excavation, temporary support with pressurised slurry at the face, advancement of the shield machine and a slurry circulation system. The effects of slurry characteristics, soil permeability and advance rate of the shield machine on the ground displacement, slurry infiltration and excess pore water pressure were analysed and these data were compared with predictions in previous studies. The results confirm that the model tests can effectively simulate the principal operations of a real slurry shield machine. Compared to the test results presented, previously proposed models tend to overestimate the increase rate of pore water pressure in front of the tunnel face, especially in cases of soil with lower permeability, higher concentrations of bentonite mixed slurry and lower advance rates. The slurry-infiltrated zone in front of the shield machine is non-uniform across the tunnel face and extends radially to a larger area than the tunnel diameter. The shape of the slurry-infiltrated zone can be categorised as one of two typical types: (a) cone; (b) bulb.