Experimental Investigation of Face Stability of a Slurry Shield Tunnel Based on a Newly Developed Model Test System

A new small-scale slurry shield machine including a complete slurry-circulation system was designed to simulate the advancing process of slurry-shield tunneling. A series of model tests were thereby carried out to evaluate the performance of this slurry-shield machine. The test results show that the face stability is significantly related to the slurry pressure in chamber at relative depth C/D = 1 or 1.5. However, the rotation speed of cutterhead should be paid more attention than the slurry pressure in the case C/D = 0.7. This indicates that the rotation speed of the cutterhead and the slurry volume should be tightly controlled when the P-s increased by 100 kPa in the chamber when the case C/D was less than 1.0 in the prototype project. With respect to this cohesive-frictional soil, the ground movement ahead of the face is very sensitive to slurry pressure fluctuation and the arching effect in soil is rather weaker in all cases. A comparison with quantitative predictions by theoretical method shows that the minimal admissible slurry pressures calculated by the designed method are close to the measured values, while the designed method overestimates the maximum allowable slurry pressure. The results yield from theoretical model show good agreement with the measurement of critical P-s at the relative depth C/D < 1 while the theoretical could not precisely predict either the measured P-sl or the measured P-su for deeply-buried tunnels. A larger admissible range of P-s is thereby available for deep-burial tunneling project than for shallow tunnel.