Retaining wall
Retaining walls are relatively rigid walls used for supporting the soil mass laterally so that the soil can be retained at different levels on the two sides. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to (typically a steep, near-vertical or vertical slope). They are used to bound soils between two different elevations often in areas of terrain possessing undesirable slopes or in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses.
Definition
A retaining wall is a structure designed and constructed to resist the lateral pressure of soil, when there is a desired change in ground elevation that exceeds the angle of repose of the soil.
The most important consideration in proper design and installation of retaining walls is to recognize and counteract the tendency of the retained material to move down slope due to gravity.
Unless the wall is designed to retain water, It is important to have proper drainage behind the wall in order to limit the pressure to the wall's design value. Drainage materials will reduce or eliminate the hydrostatic pressure and improve the stability of the material behind the wall.Drystone retaining walls are normally self-draining.
Types of retaining wall
Gravity walls depend on their mass (stone, concrete or other heavy material) to resist pressure from behind and may have a 'batter' setback to improve stability by leaning back toward the retained soil.
For short landscaping walls, they are often made from mortarless stone or segmental concrete units (masonry units).Dry-stacked gravity walls are somewhat flexible and do not require a rigid footing.
Earlier in the 20th century, taller retaining walls were often gravity walls made from large masses of concrete or stone. Today, taller retaining walls are increasingly built as composite gravity walls such as: geosynthetics such as geocell cellular
confinement earth retention or with precast facing; gabions(stacked steel wire baskets filled with rocks); crib walls (cells built up log cabin style from precast concrete or timber and filled with granular material); or soil-nailed walls (soil reinforced in place with steel and concrete rods).
Cantilevered
Counterfort /Buttress on Cantilevered Wall
Cantilevered retaining walls are made from an internal stem of steel-reinforced, cast-in-place concrete or mortared masonry (often in the shape of an inverted T). These walls cantilever loads (like abeam) to a large, structural footing, converting horizontal pressures from behind the wall to vertical pressures on the ground below. Sometimes cantilevered walls are buttressed on the front, or include acounterfort on the back, to improve their strength resisting high loads. Buttresses are short wing walls at right angles to the main trend of the wall. These walls require rigid concrete footings below seasonal frost depth. This type of wall uses much less material than a traditional gravity wall.
This type of soil strengthening, often also used without an outside wall, consists of wire mesh "boxes", which are filled with roughly cut stone or other material. The mesh cages reduce some internal movement and forces, and also reduce erosive forces. Gabion walls are free-draining retaining structures and as such are often built in locations where ground water is present. However, management and control of the ground water in and around all retaining walls is important.
