Abstract: During earth pressure balance (EPB) shield tunneling in water-rich gravel stratum, the ground is difficult to condition and the water is easy to spew out from the screw conveyor. Hence, the bentonite slurry, carboxymethyl cellulose (CMC) and polyacrylamide solution (PAM) are used as main conditioning materials, and the foam is used as auxiliary conditioning material for the laboratory slump test and constant head permeability test on gravel of Kunming Metro Line No. 4. The test results show that: (1) When the bentonite slurry or the mixture of bentonite slurry and CMC is used, the flow plasticity of conditioned gravel is overlarge; while the flow plasticity of the gravel conditioned by bentonite slurry and PAM can be improved, and the foam has no effect on flow plasticity of gravel conditioned by bentonite slurry and PAM. (2) The CMC, bentonite slurry and PAM can improve the ground permeability, and the permeability coefficient of the gravel increases with the increase of conditioning materials; while the foam has no effect on the permeability of gravel conditioned by bentonite slurry and PAM. According to the test results, the bentonite slurry ratio, the bentonite injection ratio (BIR), the PAM injection ratio (PIR) and the foam injection ratio (FIR) are determined as 1 ∶ 4 (with 1% CMC), 25%, 12. 5% and 20% or 1 ∶ 3, 25%, 7. 5% and 20%, respectively to condition the gravel in Kunming Metro Line No. 4 when the water head height is about 25 m.

Key words: earth pressure balance(EPB) shield, water-rich gravel stratum, spewing, ground conditioning