Design, Construction and Types of Retaining Walls
A retaining wall is a structure that retains (holds back) any material (usually earth) and prevents it from sliding or eroding away. It is designed so that to resist the material pressure of the material that it is holding back.
Types of Retaining Walls
An earth retaining structure can be considered to have the following types:
Gravity Retaining Walls
It is that type of retaining wall that relies on their huge weight to retain the material behind it and achieve stability against failures. Gravity Retaining Wall can be constructed from concrete, stone or even brick masonry. Gravity retaining walls are much thicker in section. Geometry of these walls also help them to maintain the stability. Mass concrete walls are suitable for retained heights of up to 3 m. The cross section shape of the wall is affected by stability, the use of space in front of the wall, the required wall appearance and the method of construction.
Reinforced Retaining Walls
Reinforced concrete and reinforced masonry walls on spread foundations are gravity structures in which the stability against overturning is provided by the weight of the wall and reinforcement bars in the wall. The following are the main types of wall:
Concrete Cantilever retaining wall
A cantilever retaining wall is one that consists of a wall which is connected to foundation. A cantilever wall holds back a significant amount of soil, so it must be well engineered. They are the most common type used as retaining walls. Cantilever wall rest on a slab foundation. This slab foundation is also loaded by back-fill and thus the weight of the back-fill and surcharge also stabilizes the wall against overturning and sliding.
Counter-fort / Buttressed retaining wall
Counterfort walls are cantilever walls strengthened with counter forts monolithic with the back of the wall slab and base slab. The counter-forts act as tension stiffeners and connect the wall slab and the base to reduce the bending and shearing stresses. To reduce the bending moments in vertical walls of great height, counterforts are used, spaced at distances from each other equal to or slightly larger than one-half of the height Counter forts are used for high walls with heights greater than 8 to 12 m.
Precast concrete retaining wall
Prestressed retaining wall
Reinforced Soil Retaining Walls
Mechanically stabilized earth walls are those structures which are made using steel or GeoTextiles soil reinforcements which are placed in layers within a controlled granular fill. Reinforced soils can also be used as retaining walls, if they are built as:
This category covers walls which use soil, reinforced with reinforcing bars, to provide a stable earth retaining system and includes reinforced soil and soil nailing.
Constructing a soil nailed wall involves reinforcing the soil as work progresses in the area being excavated by the introduction of bars which essentially work in tension, called Passive Bars. These are usually parallel to one another and slightly inclined downward. These bars can also work partially in bending and in shear. The skin friction between the soil and the nails puts the nails in tension.
The type of retaining walls that use both factors that is their mass and reinforcement for stability are called Hybrid or Composite retaining wall systems.
Anchored Earth walls
Any wall which uses facing units tied to rods or strips which have their ends anchored into the ground is an anchored earth wall. The anchors are like abutments. The cables used for tieing are commonly high strength, prestressed steel tendons. To aid anchorage, the ends of the strips are formed into a shape designed to bind the strip at the point into the soil.
Gabions are cages, cylinders, or boxes filled with earth or sand that are used in civil engineering, road-building, and military application and many others. OR Gabion elements fitted to geogrid 'tails' extending into supported soil. For erosion control caged rip-rap are used. For dams or foundation building, metal structures are used.
Sheet Pile Walls
Steel sheet pile walls are constructed by driving steel sheets into a slope or excavation upto the required depth. Their most common use is within temporary deep excavations. They are considered to be most economical where retention of higher earth pressures of soft soils is required. It cannot resist very high pressure.