Abstract: In earth pressure balance (EPB) shield tunnels in waterrich sandy gravel strata, water is easily spewed from screw conveyors. Hence, a soil conditioning test is conducted on waterrich sandy gravel strata based on the shield tunnel project of Kunming Metro Line 4. First, the soil permeability is evaluated by conducting a laboratory test. Second, a slump test is conducted on the site, and the effect of slump values on the tunneling parameters is analyzed. Finally, the surface subsidence is monitored to evaluate the effect of soil conditioning. Accordingly, guidance on soil conditioning of waterrich sandy gravel strata in Kunming is presented. The following results are obtained. (1) There is a positive relationship between the slump value of sandy gravel strata in Kunming and its water content, and the permeability parameter decreases with time, attaining a value of zero after 2 h. (2) The cutterhead torque and thrust are small, and the tunneling speed is high in soils with a good plastic flow. (3) According to the analysis of the tunneling parameters, the slump of soil between 5 and 10 cm can satisfy the construction requirements for waterrich sandy gravel strata.

Key words: metro tunnel, waterrich sandy gravel strata, earth pressure balance (EPB) shield, soil conditioning, field test