Face pressure calculation is a critical factor when tunneling using Slurry Shield TBMs. Especially in case of low overburden, there is a very narrow band of lower and upper margins of suitable Face Pressure, as using a too high one might be as critical as using a too low one.
The face pressure calculations are always done assuming that the quality of the slurry during operation can guaranty proper rheological, physical & chemical properties able to fit the expected geological and hydro-geological conditions.
Therefore, using slurry having inadequate properties can compromise the effectiveness of a correct applied face pressure and result in increasing the risks of high volume loss, high settlements and face instability.
This paper will discuss the principles of Slurry Quality Control during operation with reference to Singapore contest and in particular to tunneling in mix face conditions along the Bukit Timah Granite formation.
Keywords: Tunneling, TBM, Slurry, Bukit timah granite.