R.C. retaining wall

A cantilever reinforced-concrete retaining wall: a vertical stem and a footing that together hold back a difference in ground level. The earth bearing on the heel of the footing «ballasts» the wall and keeps it steady against overturning and sliding, while a drain with weep holes behind the stem releases the water, removing the most dangerous thrust. It is the structure that holds slopes, embankments and excavations.

A retaining wall holds back an embankment or a slope, resisting the horizontal thrust of the earth. The commonest form is the reinforced-concrete cantilever: a vertical stem built into a footing, working together as a single inverted L.

The secret of the cantilever is the footing: its inner part, the heel, reaches under the embankment, so the weight of the earth bearing on it stabilises the wall against overturning. The outer part, the toe, widens the bearing. The fundamental checks are three: overturning, sliding on the founding plane and the bearing capacity of the soil.

The real enemy is water: if it builds up behind the wall it doubles the thrust. This is why a drain — gravel and a perforated pipe — is placed behind the stem, and weep holes are left, through-holes that let the water out. The earth-side face is waterproofed to protect the concrete. Without drainage even a well-sized wall can fail.

The cantilever bends under the thrust: the main reinforcement sits on the tension side — towards the earth in the stem, at the bottom in the heel — and must be placed with the right cover so it does not corrode. Concrete of a suitable class, generous cover on the earth side and waterproofing ensure the durability of the structure, often buried and no longer inspectable.