Lanzhou metro line 1 passes mainly through ②-10 and ③-11 sandy pebble strata

most of the line is under the groundwater level and the strata have high permeability. EPB (earth pressure balance) shield tunneling in such strata will not only easily lead to high torque and serious wear of cutterhead and screw convey

but also cause screw conveyor spewing

which lead to an engineering accident. Therefore

the properties of sandy pebble strata need to be improved to make the tunneling safe. Bentonite slurry and foam are selected to condition sandy pebbles. Slump

permeability coefficient and friction coefficient between the soil and steel tube are obtained by different conditioning schemes. When the slump is in the range of 15 to 20 cm

the optimal conditioning scheme which can meet the workability requirement

and can make the screw conveyor keep soil pressure balance

prevent spewing is determined by the theoretical calculation. Engineering practice shows that the effect of conditioning scheme with injection ratio of foam and slurry 7% and 8% respectively is remarkable

which can provides some guidelines for soil conditioning and screw convey anti-spewing during EPB shield tunneling in sandy pebble stratum with rich water in Lanzhou city.