Development and application of simulation test system for slurry balance shield

To study the excavation control and the balance mechanism on the cutting face during underwater excavation of slurry balance shield (SBS), the basic parameters and working modes of SBS are determined after investigation of model shield machines worldwide, and then a simulation test system for SBS is developed. The system mainly consists of model box, shield machine assembly, thrusting system, hydraulic power system, operation system and cryogenic unit. It can simulate the main procedure of SBS excavation under the maximum water head of 100 m, and can really reproduce the dynamic formation process of the slurry membrane during excavation, which is critical for illustrating the mechanism of water-earth pressure balance and may provide important parameters for the design and control of SBS. The similar stratum and slurry are prepared based on the sandy gravel strata, and an excavation test is then carried out to verify the function of the simulation system. The space-time variation laws of the ground surface settlements as well as the slurry membrane morphology during shield excavation are also analyzed. The results show that because the cutter head has no over-excavation and the stratum is directly supported by the shield shell, the soil movement is restricted, and the stratum deformation is mainly caused by the stress release caused by the excavation. As the mud discharge device is long, which enhances the temporary storage capacity of mud, the ground surface settlements before shield passing through increase with trust force, cutter head speed and speed of mud discharge device. After the shield passing through, the ground surface settlements decrease due to shield-soil friction. The slurry permeation region in front of the cutter head is approximately symmetric about the shield axis, and the slurry membrane morphology is a flip "pot" shape, whose dimensions are about 20% to 43% of the external diameter of the cutter head.