Foam used during EPB tunnelling in saturated sand, parameters determining foam consumption

The amount of foam injected during drilling with an EPB-shield in saturated sand is quite often based on experience and/or empiric relations. A method is presented in to calculate the amount of foam needed to create a muck with limited or no grain stress. The results show that, as expected, the volume of the foam to be injected is much larger in dry soil compared to saturated soil. In saturated soil the amount of foam to be injected depends on various parameters. The permeability of the soil in front of the EPB-shield appears very important. This paper describes the dependencies and shows that recommended foam injection ratio’s from literature may be too small when used in permeable sandy soil. The FIR of the foam in a mixture may be much smaller than of the original foam