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 build of retaining walls consists of materials like masonry, stone, brick, concrete, vinyl, steel or timber. Certain areas have topography that varies from slightly rolling to mountainous. For such areas, retaining walls allow the construction of steps or level areas.
Every retaining wall supports a “wedge” of soil. The wedge is defined as the soil which extends beyond the failure plane of the soil type present at the wall site, and can be calculated once the soil friction angle is known. As the setback of the wall increases, the size of the sliding wedge is reduced. This reduction lowers the pressure on the retaining wall.
A retailing wall must satisfy the following conditions
- Must not be slippery
- Resist Overturning
- Must be build on a good bearing capacity soil.
TYPES OF RETAINING WALLS
To prevent downslope soil erosion, different retaining walls are built. These walls hold back soil from buildings, structure or a particular area.
 GRAVITY RETAINING WALL
Gravity Retaining walls use their mass or weight to resist the pressure exerted by the earth behind them. These walls usually have an average height of three to four feet. They are made from mortar-less stone or masonry units.
Gravity is able to hold back the earth or soil, due to its construction. These walls consist of a volume of materials. These materials are stacked together in the making of the walls. The weight or force of friction that is created by these materials is greater than the force exerted by the soil. The thickness of the wall at the base exceeds that at the top. A process known as ‘battering‘ helps the walls to improve stability by leaning back into the retained soil. In this process, as the walls get taller they slant backwards. Battering is done to prolong the lifespan of gravity walls, which otherwise would tilt outward. Construction of gravity walls demands a high quantity of building materials. That is the reason these walls are difficult to build, and get more cumbersome as they get gravity
 SHEET PILLING RETAINING WALL
Sheet pile retaining walls are usually used in soft soil and tight spaces. Sheet pile walls are made out of steel, vinyl or wood planks which are driven into the ground. For a quick estimate the material is usually driven one third above ground, two third below ground, but this may be altered depending on the environment.
A cable or a rod is used as a tie-back anchor to the walls. The rods are placed at a distance and tied to the back of the walls. Hydrostatic pressure is one of the main causes of the instability of the walls. So to eliminate this drawback, proper drainage has to be ensured during construction.
 CANTILEVERED RETAINING WALL
Cantilever retaining walls are manufactured in the form of an inverted ‘T’. The word ‘cantilever’ means ‘projecting horizontal beam fixed at one end only’. Here, it means that the walls transform horizontal pressure from behind the wall into vertical pressure on the ground below. The footer of cantilever walls should be wide enough to prevent the wall from tipping. The thickness of not only the footer but also that of the wall is important. The walls are built with steel reinforcement in both the footing and wall structures. Cantilever retaining walls are and should be designed only by structural engineers. They are not meant for self-building purposes.
Cantilever walls are among the taller retaining walls, and are single layer walls. Here, the walls have uniform thickness and are tied to a footing. Properly engineered cantilever walls hold back sufficient amount of soil. Typical basements in a house are an example of these retaining walls.
 ANCHORED RETAINING WALL
An anchored retaining wall can be constructed in any of the aforementioned styles but also includes additional strength using cables or other stays anchored in the rock or soil behind it. Usually driven into the material with boring, anchors are then expanded at the end of the cable, either by mechanical means or often by injecting pressurized concrete, which expands to form a bulb in the soil. Technically complex, this method is very useful where high loads are expected, or where the wall itself has to be slender and would otherwise be too weak.
 CONCRETE RETAINING WALL
Concrete retaining walls are high built and have deeper and heavier soil underneath them. These properties make them offer better resilience and solidity. These walls require greater base depth so as to create a better foundation. Properly installed concrete retaining walls do not face problems like tilting, bowling or cracking. They are also not susceptible to climate induced degradation.
 BLOCK RETAINING WALL
For enclosing an area in a garden, block retaining walls are the most suitable. These walls are of two types. Modular retaining walls, and segmental retaining walls. They have interlocking concrete units to hold back the load of the soil. Similar to gravity walls, they use the force of gravity to resist overturn and sliding. The nature of the walls prevents hydrostatic pressure as well.
 ROCK RETAINING WALL
The rocks and stones that are used in the construction of these walls must suit the landscape. When rocks are stacked together, spaces are left between the rocks. These spaces or gaps are filled with the soil mix. If plants are allowed to grow in between the rocks, it will strengthen the walls. Growing roots will prevent soil from becoming loose, and help prevent soil erosion.
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