A retaining wall is defined as a structure whose primary purpose is to provide lateral support for soil or rock. In some cases, such as basement walls and certain types of bridge abutments, it may also support vertical loads. The more common types of retaining walls are shown in below Fig. and include gravity walls, cantilevered walls, counterfort walls, and crib walls. Gravity retaining walls are routinely built of plain concrete or stone, and the wall depends primarily on its massive weight to resist failure from overturning and sliding. Counterfort walls consist of a footing, a wall stem, and intermittent vertical ribs (called counterforts) that tie the footing and wall stem together. Crib walls consist of interlocking concrete members that form cells which are then filled with compacted soil.
Granular soils (sands or gravels) are the standard recommendation for backfill material. There are several reasons for this recommendation
- Predictable Behavior. Import granular backfill generally has a more predictable behavior in terms of earth pressure exerted on the wall. If silts or clays are used as backfill material, expansive soil-related forces could be generated by these soil types.
- Drainage System. To prevent the build-up of hydrostatic water pressure on the retaining wall, a drainage system is often constructed at the heel of the wall. This system will be more effective if highly permeable granular soil is used as backfill.
- Frost Action. In cold climates, the formation of ice lenses in the backfill soil can cause so much lateral movement that the retaining wall will become unusable. Backfill soil consisting of granular soil and the installation of a drainage system at the heel of the wall will help to protect the wall from frost action.
Retaining Wall Analyses
below Figure shows various types of retaining walls and the soil pressures acting on the walls. Three types of soil pressures act on a retaining wall: (1) active earth pressure, which is exerted on the back side of the wall, (2) passive earth pressure, which acts on the front of the retaining wall footing, and (3) bearing pressure, which acts on the bottom of the retaining walls footing.
References:
- BUILDING DESIGN AND CONSTRUCTION HANDBOOK for Frederick S. Merritt & Jonathan T. Ricketts