The Slurry-shield technique
This tunnelling technique is based on the use of a drilling mud as indicated by its designation. The main function of this drilling fluid is to stabilize the excavation by insuring a liquid support during the tunnelling phase. It also fulfils other essential functions like the transport of the cuttings or secondary for lubrication, and the cooling of the cutting tools. This drilling fluid is generally a bentonite suspension: its composition and characteristics change while tunnelling.
The definition of the most appropriate drilling fluid and in particular its properties is obviously of main concern for challenging project: heterogeneity of the front face, low overburden, high permeable ground, water sensitive ground, etc. As a result, the choice of the drilling mud additives will have to comply with all the specificity of each drilling mud functions in accordance with environmental aspects.