Study on Flow Plasticity and Permeability of Mixture Conditioned Muck for Metro Shield Tunnel in Water-rich Sand Stratum

Abstract

[Objective] When tunnel boring machine advancing in the water-rich sand layer, problems such as high cutter torque, serious wear and spout of the screw conveyer can be easily generated. In order to ensure the safety of construction, it is necessary to improve the muck. [Method] Based on a shield tunnel section project of Xi’an Metro Line 16, the muck modifier is selected according to the characteristics of poor self-stability, high friction and high permeability of sandy soil stratum. By combining slump test, permeability test and on-site test, two schemes of foam alone conditioning and mixed foam-bentonite slurry conditioning are used to carry out the experimental research on muck conditioning in water-rich sand layer. [Result & Conclusion] In the actual shield tunneling construction, on the premise of safety, efficiency and economy and based on the data obtained in laboratory tests, the conditioning scheme of mixed foam-bentonite slurry is adopted. The performance of the modifier meets the requirements of shield tunneling construction when the ratio of bentonite to water is 1/8 and the foam mass fraction is 3%. The muck conditioning by foam alone is greatly affected by water content. The higher the water content is, the smaller the optimal foam injection rate (FIR) becomes. The best muck conditioning option for medium sand is 10% of the bentonite slurry injection ratio (BIR) and 20%~25% of FIR. The best muck conditioning option for gravel sand is 10% of BIR and 35%~40% of FIR. Engineering practice shows that the muck conditioning has good effect and the parameters of shield tunneling are stable.

Keywords

• metro
• shield tunnel
• muck conditioning
• flow plasticity
• permeability
• water-rich sand stratum