M.E. Structural Engineer
One of the biggest problems that arrive in construction is dealing with steep slopes and difficult grades. There is a huge concern for erosion and even planning difficulties. A retaining wall is one solution for construction at such places. This type of wall or system of walls holds back the earth and water. Coupled with drainage systems, retaining walls can also reduce and manage storm water. They create a strong barrier to increase the landscape making it more functional.
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Retaining walls are generally built to hold back soil mass. Tough, retaining walls can also be constructed for aesthetic landscaping purposes. Different types of retaining walls are constructed at different places depending on various factor i.e. type of material to be used, type of soil, slope of hill side, local building codes, topography of site.
So, here we have discussed various types of retaining walls.
Types of Retaining Wall
01. Gravity Retaining Walls
Gravity retaining wall depends on its own weight only to resist lateral earth pressure. Generally, gravity retaining wall is massive because it requires significant gravity load to counter act horizontal soil pressure. While designing gravity retaining wall, sliding, overturning, and bearing forces shall be taken into consideration. It can be constructed from different materials such as stone, concrete and masonry units. Crib retaining wall and gabion retaining wall are type of gravity retaining walls, being used more frequently nowadays.
02. Cantilever Retaining Walls
Cantilever retaining walls are constructed of reinforced concrete. Cantilever retaining wall consists of a relatively thin stem and a base slab. The base is divided into two parts, namely the heel and toe. The heel is the part of the base under the backfill and the toe is the other part of the base. It uses much less concrete than monolithic gravity walls, but requires more design and careful construction. It can be formed on site or precast in a factory.
03. Counterfort Retaining Walls
Counterfort retaining walls are same as cantilever walls except they have thin vertical concrete webs at regular intervals along the backside of the wall and these webs are known as counterforts. The counterforts tie the slab and base together, and the purpose of them is to reduce the bending moments and shear forces imposed on the wall by the soil. The secondary effect of these webs is to increase the weight of the wall from the added concrete. It can be precast or formed on site.
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04. Semi-Gravity Retaining Walls
Semi-gravity retaining walls are the specialized form of gravity walls. These types of retaining walls have some tension reinforcing steel included so as to minimize the thickness of the wall without requiring extensive reinforcement. They are a blend of the cantilever wall and gravity wall designs. These walls are often constructed of reinforced concrete, un-reinforced concrete, or stone masonry. The rigid gravity walls develop their soil retaining capacity from their dead weights. The semi-gravity walls, such as cast-in place concrete cantilever walls, develop resistance to overturning and sliding from self-weight and weight of soil above the wall footing.
05. Prefabricated Modular Gravity Walls
These walls include crib walls, bin walls, and gabion walls. A crib wall, concrete or timber, is a gravity retaining structure that consists of interlocking concrete or timber elements. Each crib unit is filled with compacted granular soil. A bin wall, concrete or metal, is constructed of adjoining closed-face or open-face bins. Each bin unit is filled with compacted granular soil. Gabion walls consist of baskets made of galvanized steel mesh or PVC coated wire mesh. The baskets are filled with durable rock ranging in size from 4 to 8 inches.
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06. Non-Gravity Cantilevered Walls
These types of retaining walls develop lateral resistance through the embedment of vertical wall elements and support retained soil with wall-facing elements. Vertical wall elements are normally extended deep in the ground to provide lateral and vertical support. The vertical wall elements can be piles, drilled shafts, steel sheet piles, etc. Wall faces can be reinforced concrete, metal, or timber.
07. Anchored Walls
For the construction of high retaining walls, deep cable rods or wires are driven deep sideways into the earth, then the ends are filled with concrete to provide an “anchor”. These are also known as tiebacks. These types of retaining walls typically consist of the same elements as the non-gravity cantilevered walls but derive additional lateral resistance from one or more tiers of anchors. The anchored walls are typically used in the cut situation, in which the construction proceeds from the top to the base of the wall.
08. Mechanically Stabilized Earth (MSE) Walls
These types of retaining walls normally include a facing element and a reinforcement element embedded in the backfill behind the facing. The facing element can be concrete, segmental block or panel, or steel wire mesh. The reinforcement element can be either geo synthetic (geo textile, geo grid) or metallic (strip, grid, wire mesh). These types of retaining walls are often used to support fills and when substantial total and differential settlement are anticipated. Most of the MSE walls are proprietary, and a list of pre-approved MSE walls for use can be obtained from the geotechnical engineer.
09. Hybrid Systems
Retaining walls that use both mass and reinforcement for stability are termed as Composite retaining wall or Hybrid systems.
10. Piled Retaining Wall
Pile retaining walls are constructed by driving reinforced concrete piles near to each other.
Piles are forced into a depth that is satisfactory to counter the force which tries to push over the wall. It is employed in both permanent and temporary works. These types of retaining walls give high stiffness retaining component which are capable to hold lateral pressure in large excavation depths with nearly no disturbance to surrounding structures or properties. Sheet pile walls are built using steel sheets into a slope or excavations up to a required depth, but it cannot resist very high pressure. Sheet pile retaining walls are economical up to height of 6m.
11. Gabion Retaining Walls
These types of retaining walls are multi-celled, rectangular wire mesh boxes, which are filled with rocks or other suitable materials. It is constructed for construction of erosion control structures. Gabion retaining walls are also used to stabilize steep slopes.
12. Crib Retaining Wall
These types of retaining walls are also one form of gravity wall. They are constructed of interlocking individual boxes made from pre-cast concrete or timber. The boxes are filled with crushed stone or other coarse granular materials to form a free draining structure. Basic types of crib retaining walls include timber retaining walls and reinforced precast. It is suitable for supporting planter areas, but it is not recommended for support of slopes or structures.
Retaining walls are constructed not only for creating a beautiful landscape, but also serve major functionality. The advantages of retaining walls include erosion control, flood prevention, and adding value to your residence. A short retaining wall can also be turned into a seating area, making these walls a truly versatile addition to your yard.