What Is Retaining Wall?
It is a structure constructed to retain materials such as soil and maintain the surface of the ground at diﬀerent elevations on either side of it. A retaining wall is constructed to retain earth and other such materials that tend to slide and repose at a specific inclination angle. The retaining wall provides lateral support to the backfill, embankment, or to hold them vertically.
Backfill is a material which is retained or supported by the retaining wall. The backfill may have its top surface in a horizontal or an inclined position. The amount of backfill lying above the horizontal plane at the top of a wall elevation is known as the surcharge. The inclination of the surcharge to the horizontal is known as the surcharge angle. The surcharge angle is denoted by “β”.
During the rainy season, the pore water pressure is developed in the backfill material. To release this pore water pressure, weep holes are provided in the retaining walls.
Longitudinal drains are provided at the top of the backfill and in front of the retaining wall. Backfilling near the retaining wall is done with broken stones, gravels, or coarse sand so that drainage in longitudinal direction is improved and water pressure on the wall is released.
A retaining wall consists of the following components:
- Toe slab
- Heel slab
- Counter forts (in case of counterfort retaining walls)
- Shear key
Types Of Retaining Wall
There are various types of retaining walls which are classified according to the shape and mode of resisting the pressure. The diﬀerent types of retaining walls are as follows:
- Gravity retaining wall
- Cantilever retaining wall
- Counter-fort retaining wall
- Buttress wall
- Bridge abutment
- Box culvert
Let us discuss each one of them in detail below.
1. Gravity Retaining Wall
A gravity retaining wall is constructed using plain concrete or brick masonry. The stability of the gravity retaining wall is maintained by its weight. A gravity retaining wall is generally constructed up to a height of 3 m.
2. Cantilever Retaining Wall
Cantilever retaining wall is the most common type of retaining wall. It consists of components like stem, heel slab, and toe slab which act as a cantilever beam. The stability of cantilever retaining wall is maintained by the weight of the retaining wall and the weight of the earth on the heel slab of the retaining wall.
A cantilever retaining wall is used when the height of the wall is up to 6 m. The cantilever wall resists the horizontal earth pressure as well as other vertical pressures by way of bending of diﬀerent components acting as a cantilever.
There are 3 different types of cantilever retaining walls.
- T – shaped cantilever retaining wall.
- L – shaped cantilever retaining wall.
- T – shaped cantilever retaining wall with shear key.
3. Counterfort Retaining Wall
Counter-fort retaining walls are constructed in such a way that the stem and the base slab of the wall are tied together by the means of counter-forts. Due to the provision of counter-forts, the vertical stem, and the heel slab act as a uniform and continuous slab, in contrast to the cantilevers of the retaining wall. However, the toe slab acts as a cantilever bending upwards.
The counter-forts provided in the retaining wall acts as a tension member which supports the stem and eventually reduces the bending moment in it. It also supports the heel slab and minimizes the bending moment in it. The counter-forts are generally spaced at a distance of approximately one-third the height of the retaining wall.
The stability of the counterfort retaining wall is maintained by the weight of the earth at its base slab and the self-weight of the retaining wall. The counter-fort retaining walls are economical for heights of approximately 6 m and above.
4. Buttress wall
A buttress wall is the modified version of the counter-fort retaining wall in which the counter-forts, known as the buttresses, are provided at the other side of the backfill.
A buttress wall is more economical when compared to a counter-fort retaining wall. Buttress walls are not much preferred due to the provision of buttresses in the wall. These buttresses reduce the clearance on the front side of the wall.
The buttresses act as a compression member, supporting the stem and reduces the bending moment in it. It provides support to the toe slab and reduces bending moment in it. Buttresses are provided at a spacing equal to approximately one-third of the height of the wall.
5. Bridge Abutment
A wall type bridge abutment is similar to the cantilever type retaining wall. In this, the top of stem of the retaining wall is braced by the deck slab of the bridge. The stem can be designed as fixed at the base and simply supported at the top.
6. Box Culvert
A box culvert acts as a closed frame. It consists of single or multiple cells. In addition to the lateral earth pressure, a box culvert also resists the vertical load from the soil above it and is also resistant to the vehicle loads.
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