Soil pressures at the cutting wheel and the pressure bulkhead of an EPB-shield

Soil pressureswere measured on both sides of the cutterwheel of an EPB-shield during tunnelling in saturated sand, using foam for soil conditioning. The measured pressures are compared with the pressures at the pressure bulkhead. The pressures are not purely hydrostatic but the results are also influenced by the yield strength of the foam mixture and the effective stresses. At the lowest positions, the sensors sometimes measured effective stresses. This led to peaks in the pressures measured. It is shown that for the soil conditions present, the pressures measured at the pressure bulkhead are comparable to the pressures measured at the rotor, but the pressure gradients can differ significantly (around 30% difference in gradients is possible). The measurements show that the pressure distribution is asymmetric due to the rotation of the cutter head.Soil pressureswere measured on both sides of the cutterwheel of an EPB-shield during tunnelling in saturated sand, using foam for soil conditioning. The measured pressures are compared with the pressures at the pressure bulkhead. The pressures are not purely hydrostatic but the results are also influenced by the yield strength of the foam mixture and the effective stresses. At the lowest positions, the sensors sometimes measured effective stresses. This led to peaks in the pressures measured. It is shown that for the soil conditions present, the pressures measured at the pressure bulkhead are comparable to the pressures measured at the rotor, but the pressure gradients can differ significantly (around 30% difference in gradients is possible). The measurements show that the pressure distribution is asymmetric due to the rotation of the cutter head.P