What water does to a wall
Dry soil pushes on a wall with a predictable, designed-for pressure. Add water and two things happen: the soil gets heavier, and the water itself pushes with a pressure that increases with depth. A wall designed for dry earth can see its load double when the backfill saturates. That is why walls fail after rain, years after they were built.
The drainage system
Behind the face, a zone of clean crushed rock lets water fall freely to the base. A slotted pipe wrapped in filter sock collects it and carries it to a stormwater connection or an outlet on the low side. Filter fabric between the rock and the native soil keeps clay fines from washing in and choking the drain. Where the wall face allows, weep holes give water a second way out.
Systems that drain themselves
An open crib face, a gabion basket and the rock-filled cores of an Allan Block wall all let water straight through. They still get a base drain, but they are forgiving. A concrete sleeper wall or a reinforced block wall is a solid panel; everything depends on the drainage behind it, and we treat it accordingly.
