 Moreover, these drainage systems must be installed on the stable part of the slope.Drainage systems made up of microdrains are placed inside galleries with lengths that can reach 50–60 m. The sizes of the galleries are conditioned by the need to insert the drain perforation equipment.For this reason the minimum transversal internal size of the galleries vary from a minimum of 2 m, when using special reduced size equipment, to at least 3.5 m, when using traditional equipment.