Bentonite suspension is used to protect the working face and to transport the excavated material during tunnel construction. The bentonite suspension needs to be cleaned after it has fulfilled its task. The separated sandy material is reused at the construction site (noise barriers, sand fillings). By optimizing the separation plant for the treatment of the soil material and for the recycling, resources are saved. By minimizing the consumption of bentonite and flocculances, the cost effectiveness of the project is increased and the environment is less polluted.