An experimental and theoretical research on shield screw conveyor discharging efficiency in moderately weathered mudstone strata and its influence on clogging

When an earth pressure balance shield machine is tunneling in cohesive soils, a poorly effective soil conditioning scheme often leads to clogging in the cutterhead and the screw conveyor, which reduces tunneling efficiency and may even cause the shield machine to stop tunneling. Different from the conventional test method that use artificial clay soil, this study relies on the field shield engineering in mudstone strata and conducts soil conditioning tests using the field soil as the basic material. Using a shield soil migration model test, the whole process of clogging in a screw conveyor is reproduced, and the pattern of migration change of soil in the screw conveyor is obtained. The screw conveyor torque decreases with the increase of foam injection rate. When the slump of soil reaches 15 cm, the torque tends to be stable. Based on this, this study innovatively establishes a theoretical calculation model that can quantitatively describe the relationship between the soil discharge and the pressure gradient. Experimental verification shows that this model can not only quantitatively describe the variation laws of the soil discharge and the pressure gradient, but also qualitatively reveal the influence mechanism of the soil chamber pressure and soil fluidity on the discharge efficiency. Finally, using the Ziyang line of the Chengdu rail transit as a field test, it is found that under the recommended soil conditioning scheme, the clogging problem in the shield cutterhead and screw conveyor is greatly reduced and the efficiency of shield tunneling is significantly improved.