Crib walls are formed from interlocking precast units (parallel to and at right angles to the line of the wall) that are built up to form a series of hollow boxes. The boxes are filled with selected granular material to form a retaining wall. The individual units are generally small enough to be installed manually on site.

Because the maximum length of a unit is in the region of 1 m, walls can be readily curved in plan and can be of varying height.