ABSTRACT
The cutting wheel of a TBM is in most cases a bit larger than the TBM itself. There is only a small difference (a few centimeters on a TBM with a diameter of 10 meters or more), but this difference is significant. It means that for a slurry shield bentonite can flow from the tunnel face back to the grout used to fill up the tail void. However, it is also possible that grout can flow from the tail void to the tunnel face. It is important to quantify the flow of both the bentonite and the grout because these flows determine the quality of the tail void grouting and in non-cohesive soils these flows have to be controlled to avoid erosion of the soil around the TBM. Furthermore these flows determine the pressure distribution on the TBM shield that is important in both the design of the TBM and to calculate the soil settlement that is caused by the TBM tunnelling. Lack of knowledge on the pressure distribution on the TBM led to deformations of the TBM during tunnelling (Barends, 2005).
