Study on the escaping condition of backfill grouting based on two-phases flow for shield tunnelling during whole section rock

Abstract

During the process of full section surrounding rock shield tunneling, the occurrence of synchronous grout escaping can seriously affect the assembly quality of the detached shield tail segment ring. The segment is prone to quality accidents such as floating, misalignment of the tunnel pipes, and even cracking, and even a large number of rock fractures in the shield tail gap mix with water flow towards the excavation face and pressure chamber, leading to frequent fissure water gushing out of the screw conveyor. Taking the shield tunnelling section of Nanjing Metro Line 6 as the engineering background, this paper uses the finite element software Ansys Fluent to establish the two-phases flow shield tail escaping grout model, and analyzes the influence laws of the grout properties, grouting pressure difference, grouting escaping thickness and other factors in the process of grout escaping behind the shield tail wall based on Bingham fluid. The results show that the amount of synchronized grout escaping increases linearly with the increase of grouting pressure difference and grouting escaping thickness, and decreases with the increase of grout shear yield stress. The paper also discusses the three-dimensional curved surface of grout escaping volume, grouting pressure difference and grouting fluid properties behind shield tunnel tail in a full section surrounding rock shield project of Nanjing Line 6, and gives the measures to prevent grout escaping when the allowable grout escaping volume is not more than 1m3: when the grouting escaping thickness is 20mm, the grouting pressure difference should be controlled within 0.20∼0.25MPa, and the shear yield stress of the grouting fluid should be controlled within 300∼350Pa.