Discussion of cutterhead opening design for earth pressure balance machines (EPBMs) in soft grounds

Among the various parts of the earth pressure balance (EPB) cutterheads, the opening distribution on the cutterhead face plays a crucial role in successful of the tunneling projects in soft grounds. However, the amount of published literature on this subject is very limited, as a result, tunnel boring machine (TBM) manufacturers have been developed different soft ground cutterheads with varied opening distributions through their experience. In this paper, at the first step, the field studies results for soft ground cutterheads opening design were expressed. Next, the paper mainly focused on the numerical studies using discrete element method (DEM) to evaluate the adaptability of the EPB system and cohesive and non-cohesive soils fluidity by changing the opening distribution on the cutterhead. Finally, the optimum opening ratio and its distribution for different soils by considering the value of the thrust force, cutterhead torque and soil fluidity condition as important parameters were proposed based on the analysis results from DEM accordingly. Furthermore, the flow characteristics of soil particles inside the EPB chamber was obtained through examination of velocity field, also the practical aspects with further application in TBM industry by considering field studies and a real example were discussed.