These systems can serve a structural function, a drainage function, or both. The draining elements are microdrains, perforated and positioned sub-horizontally and fanned out, oriented uphill to favour water discharge by gravity. The size of the wells is chosen with the aim of allowing the insertion and functioning of the perforation equipment for the microdrains. Generally, the minimum internal diameter is greater than 3.5 m for drains with a length of 20 to 30 m. Longer drains require wells with a diameter of up to 8–10 m. To determine the network of microdrains planners take into consideration the makeup of the subsoil and the hydraulic regime of the slope.