It is fundamental not to underestimate the need for an adequate design of the drainage system, especially considering its importance for subsequent works. The design and choice of the drainage system are linked to a correct identification of the hydraulic model of the subsoil that can be reconstructed with the prior knowledge of the following characteristics:
1) stratigraphic conditions of the affected soils, measured up to a depth at least double that of the excavation;
2) conditions of permeability of the affected soils detected by in situ tests;
3) interdependency between the aquifer and the surrounding hydrological conditions, ex. the presence of water courses, pipes or canals, permanent drainage, discontinuity of the subsoil and everything that may affect the normal outflow of groundwater;
4) logistical conditions of the construction site.
From the knowledge of the stratigraphic data of soils, it is possible to obtain:
– the type of plant to be used;
– the methods of installation of the system;
– the installation depth of the wellpoints;
– the installation distance of the system from the excavation.
From the knowledge of soil permeability data, it is possible to obtain:
– the center distance between the filter tips;
– the number and size of the suction groups;
– consumption of motive power.
From the knowledge of the logistical conditions of the construction site it is possible to obtain:
– the layout of the plant;
– the means necessary for the installation of the system;
– possible need for special works;
– execution time.