To ensure the stability of the wall during Quality Sample Drilling and the bottom of the hole, where necessary, a coil of coating pipes or a fluid generally consisting of a mixture of water and bentonite (in a percentage of 3-5%) is used. Bentonite is a very plastic volcanic clay. The bentonite mud is characterized by a volume weight slightly higher than that of water and by thixotropy, or by a very high viscosity in a state of rest and much less in the state of motion. These characteristics make the bentonitl mud particularly suitable not only for supporting the