Retaining Walls Flashcards
What is a retaining wall?
Retaining wall is a structure used to retain earth or other loose materials which would not be able to stand vertically by itself. In other words, a retaining wall is a structure designed and constructed to resist the lateral pressure of soil when there is a change in ground elevation that exceeds the angle of repose of the soil.
A retaining wall can also be defined as a wall that provides lateral support for a vertical or near-vertical slope of soil.
List the types of retaining walls.
1. Gravity retaining walls
2. Semi-gravity retaining walls
3. Cantilever retaining walls
4. Counterfort retaining walls
5. Buttress retaining walls
Explain gravity retaining walls.
Gravity retaining walls are constructed with plain concrete or stone masonry. They depend for stability on their own weight and any soil resting on the masonry. This type of construction is not economical for high walls.
Explain semi gravity retaining wall.
A semi gravity retaining wall is a type of gravity retaining wall constructed using a small amount of steel, thereby minimizing the size of wall sections.
What is the angle of repose of the soil?
This is the angle relative to the horizontal plane on which soil can be piled without slumping.
What is a cantilever retaining wall?
This type of retaining wall is used in situations where there is need to retain backfill of moderate height i.e between 4-7m. It is a reinforced concrete wall, having a thin stem and base slab, which utilizes cantilever action to retain the backfill. In cross section most cantilevered walls look like “L”s or inverted “T”s. To ensure stability, they are built on solid foundations with the base tied to the vertical portion of the wall, the stem, with reinforcement rods.
Explain a counterfort retaining wall.
Counterfort retaining walls are similar to cantilever walls. When the height of the cantilever retaining wall is more than about 7m, it is economical to provide vertical bracing system known as counter forts, which tie the wall and the base slab together. These counterforts are placed at regular intervals and their purpose is to reduce shear and bending moments. The counterforts are placed at the back of the wall and can be backfilled if need be.
What is a buttress retaining wall?
A buttress wall is similar to a counterfort wall except that the vertical bracing system is located on the side of the vertical wall opposite to the retained material i.e it can be seen and occupies more space in front of the wall, and act as compression struts. The buttress is a compression member as compared to the counterforts which are tension members.
Explain diaphragm walls.
A diaphragm wall is a continuous reinforced concrete wall constructed in the ground to support major construction activities like the construction of dams, tunnels, basements etc. The wall is designed to reach very great depth, sometimes up to 50m. They act as a retaining wall, support for the underground structure, or as a foundation.
Diaphragm walls are commonly used in congested areas and can be installed in close proximity to existing structures, with minimal loss of support to existing foundations.
What is the technique of constructing diaphragm walls?
Diaphragm walls are constructed by the slurry trench technique. The technique involves excavating a narrow trench that is kept full of an engineered fluid or slurry. The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse. Slurry trench excavations can be performed in all types of soil, even below the ground water table. The diaphragm walls are usually excavated under bentonite slurry and are constructed with panels.
Explain proportioning retaining walls.
In designing retaining walls, an engineer must assume some of their dimensions. This process is called proportioning, and such assumptions allow the engineer to check trial sections of the walls for stability. If the stability checks yield undesirable results, the sections can be changed and rechecked.
Explain drainage provisions in retaining walls.
Most failures of walls higher than 3m is caused by water pressure in a backfill that was assumed to remain dry by the designer. Ensuring good drainage in walls can follow two approaches which are:
- Remove water from backfill.
- Keep water out of backfill.
Explain drainage provisions in retaining walls.
Most failures of walls higher than 3m is caused by water pressure in a backfill that was assumed to remain dry by the designer. Ensuring good drainage in walls can follow two approaches which are:
- Remove water from backfill.
- Keep water out of backfill.
Explain drainage provisions in retaining walls.
Most failures of walls higher than 3m is caused by water pressure in a backfill that was assumed to remain dry by the designer. Ensuring good drainage in walls can follow two approaches which are:
- Remove water from backfill.
- Keep water out of backfill.
What are the construction problems of retaining walls?
1. Retention of soil while the wall is being built when excavation is necessary.
2. Control of water.
3. Control of the quality of materials and workmanship
4. Careful backfilling.
