Soil conditioning tests on sandy soil for earth pressure balance shield tunneling and field applications

Abstract

When performing earth pressure balance (EPB) shield tunneling in a sandy stratum, spewing and incomplete soil discharge often occur. Soil conditioning agents are needed to modify the excavated soil so that it has flow plasticity. Conditioned sandy soil and conditioning agents from Nanchang Metro Line 4 were evaluated using laboratory and performance tests. The results show that the foam expansion rate (FER) and half-life time (H-T) increase with increasing foam agent concentration (cf) up to a critical concentration of 5%. A high molecular weight polymer inhibits the FER and H-T of the foam. However, when the VR (the volume ratio of the polymer and foam agent) exceeds 0.3, the polymer increases the viscosity of the foam agent solution, which reduces the foam drainage rate and increases the foam stability. The reduction of the soil permeability by the polymer is the most obvious effect. When FIR = 40%, VR = 0.1 and SIR = 30%, the conditioned sand undergoes an appropriate state with good flow plasticity, with relatively low rotational torque and SD because the agglomeration effect of the polymer improves the homogeneity of the sandy soil. The engineering application of this soil conditioning scheme, which was based on laboratory test results, ensured the smooth completion of the tunnel.