 Drainage galleries can be associated with a series of radial drains which augment their efficiency.The positioning of this type of work is certainly connected to the local morphological, geological and structural conditions.This type of measure is used in those cases in which, below the material to be removed, the rock face is sound and stable (for example unstable material at the top of the hillside, rock blocks thrusting out from the hillside profile, vegetation that can widen the rock joints, rock blocks isolated from the joints).