The suitable slurry pressure in a slurry type shield should satisfy the following conditions: 1) to keep stability in the cutting face. 2) to minimize the deformation of ground around the cutting face. 3) never to generate the hydrofracturing around the cutting face by the slurry pressure. This paper investigates the suitable slurry pressure in sandy as well as cohesive ground using a model slurry type shield machine. As a result, it is clarified that the pressure acting on the cutting face is the sum of the slurry pressure and the pushing pressure on the cutting face by the cutter and that the suitable slurry pressure is given by Eq. (1).
P_ms=σ_h-P_c…(1)
P_ms: the suitable slurry pressure, σ_h: the earth pressure at rest around the cutting face, P_c: the pushing pressure on the cutting face by the cutter