Drilling muds are necessary to prevent collapse of excavation walls in unstable soil. Muds are prepared by mixing bentonite poder with water in different ratios. Bentonite mud has excellent tixotropic properties, forming the cake short time after mixing water+bentonite and releasing heat. Bentonitic muds are suspensions of very fine grain clay poder, mixing must be done in certain way in order to achieve a colloidal suspension. There are also available polymeric muds, made by mixing water + chemical products, however so far bentonite mud is still of higher quality for all types of soil, and also polymeric muds cannot be pumped with common centrifugal pumps, since this would brake the polymer chain.