tags: #publish links: [[Engineering]] created: 2021-12-11 Sat --- # Retaining walls https://practical.engineering/blog/2021/12/5/why-retaining-walls-collapse Retaining walls have to hold back large *lateral* forces from soil. There are a few main techniques, which may be combined: - Cantilever: L-shaped base or lever extending *under the base of the wall* so that the wall's own weight helps resist outward pressure. - Pile or sheet: really a variant on cantilever: the vertical piles act as levers, the outward force at the top being resisted by soil around the sub-ground base of the pile. - Soil layering: to reduce soil movement and therefore outward pressure, e.g. via layers of geotechnical fabric. - Soil nails: drilled and surround-filled with grout, to reduce soil movement. - Soil anchors: tensioned partially-sleeved rods, which pull the wall face back into the bank, compacting and reducing movement. - Surface cover: to prevent erosion, e.g. shotcrete or concrete panels. Shotcrete is not usually the main load bearer on its own - there would be underpinning structure or rebar. Weight on top of the wall, soil type and water content all contribute to forces. Walls more than a metre and a half, or close to heavy surface load, typically need careful engineering. Freezing causes large forces from ice expansion, so drainage is important.