Muck Improvement Experiment of Earth Pressure Balance Shield Tunnel in Water-rich Sand Layer Based on Pressure Transfer Characteristic

Objective Due to the characteristics of strong permeability and high water content in water-rich sand layer, the poor muck improvement can easily cause accidents such as spout spilling of screw conveyor and mud cake formation on the cutter plate during shield tunneling, thus affecting shield construction efficiency. So it is necessary to study the muck improvement of earth pressure balance shied tunnel in water-rich sand layer. Method Based on the typical water-rich sand layer working conditions in Qili Station-Minyuan Road West Station interval on Nanchang Metro Line 4, an indoor muck improvement experiment is carried out. The self-made shield soil chamber model device is used to implement soil chamber model experiments on different improved mucks. Based on muck pressure transfer characteristics, the correlations among slump, permeability coefficient and earth pressure transfer coefficient K0 of different improved mucks are established, and the improvement effect of muck under different K0 is studied. Result & Conclusion When foam is used alone to improve the muck, the transfer coefficient K0 of muck is positively correlated with slump, but negatively correlated with permeability coefficient of the muck. When the slump of the muck exceeds 200 mm, K0 decreases gradually. In order to achieve the ideal requirements of muck improvement for earth pressure balance shield in water-rich sand layer, the matched ratio of conditioners is suggested as follows: 25% of foam injection, or 10% injection rate of added bentonite mud. Laboratory and soil chamber model experiments show that the greater K0 is, the better the improvement effect of muck will be. In actual projects, the ideal K0 value of improved muck by using foam alone is 0.60-0.65. While foam and bentonite slurry are combined to improve the muck, the ideal K0 of improved muck is about 0.85.