Experimental study on clogging of cutterhead for panel earth-pressure-balance shield tunneling in cohesive strata

The panel EPB shield machine is prone to mud cake problems when excavating in clay ground. The cutters will be gradually covered by the mud cake, and the opening of the cutterhead will be clogged. The tunneling efficiency will be reduced and even the shield machine will completely lose its tunneling capacity. Thus, the mud cake poses great influences to shield tunnel construction. The adhesion mechanism between the cutterhead and the soil particles is introduced. The indoor tests are conducted by using the self-made panel cutterhead excavating simulation devices. Changes of cutterhead-driving speed and torque are studied, and the relationship between these parameters and the clogging of cutterhead is revealed. The research results demonstrate that the cutterhead clogging is a gradual process. The soil particles adhere to the cutters first and then gradually expand to form mud cake. The mud cake will cover the cutters and reduce the penetration and block the opening, reducing the efficiency of discharging. The influences of mud cake is mainly reflected in the increase of cutter head torque, the slower tunneling speed and the lowering of the smoothness of discharging. When the mud cake begins to form, the increase of cutter torque accords with the cubic polynomial function, and the tunneling speed is exponentially reduced. The water content of soil has a significant effect on the formation of mud cake and clogging of the cutter head. If the water content approaches the plastic limit, the mud cake will form easily, the shield tunneling efficiency will be minimized, and the risk of clogging is the highest. The research results are of great significance in assessing the risks of mud cake and clogging of cutterhead of panel EPB shield tunneling in clay ground.