What is Retaining Walls and Why It is Constructed ?
What is a Retaining Wall?
A retaining wall is a wall of increasing thickness, built to hold out against the pressure of earth filling. It is a structure that is designed & constructed to face lateral pressure of soil & hold back soil materials. The lateral pressure might also be liquid, sand & other granular materials behind the retaining wall structure. Retaining walls is commonly required in the construction of wing walls, hill roads, and masonry dams. It can be built in plain cement concrete, reinforced cement concrete, and dry stone masonry.
p = total horizontal pressure per meter length of retaining wall
w = weight of filling in kN per cubic meter
h = depth in meter
Φ = angle of repose of the soil
Note:- Total horizontal pressure at the retaining wall act at h/3 from the base.
==> Types of Retaining Wall →
- Piled Retaining Wall
- Cantilever Retaining Wall
- Gravity Retaining Wall
- Gabion Retaining Wall
- Anchored Retaining Wall
- Crib Retaining Wall
- Counter-fort/ Buttressed Retaining Wall
- Hybrid Systems
- Mechanically Stabilized Earth (MSE) Retaining Wall
1. Piled Retaining Wall →
- Piled retaining walls are constructed by driving reinforced concrete piles close to each other.
- Piles are forced into deep that is sufficient to oppose the force which tries to push over the wall.
- It can be enlisted in both permanent and temporary works.
- Piles walls offer high rigidity retaining elements that can hold lateral pressure in huge excavation depths with almost no disturbance to surrounding properties or structures.
- Sheet pile walls are built using steel sheets into a slope or excavation up to a required depth but it cannot face very high pressure.
- Sheet pile retaining wall is economical up to the height of 6 meters.
2. Cantilever Retaining Wall →
- A cantilever retaining wall is the most common type of retaining wall.
- A cantilever retaining wall is a collection of base slabs and stems.
- It is constructed from reinforced concrete and precast concrete or prestressed concrete.
- It is constructed both on-site or precast.
- The cantilever retaining wall is economical up to the height of 10 meters.
- The portion of the base slab underneath stocked material is termed Heel, and the other part is termed toe.
3. Gravity Retaining Wall →
- Gravity wall depends on dead load only to resist lateral earth pressure.
- Generally, a gravity retaining wall is massive because it requires a significant gravity load to prevent soil pressure.
- It can be constructed with different materials such as stone, concrete, and masonry units.
- Gravity retaining wall is economical up to the height of 3 meters.
- While gravity wall is designed, sliding, overturning, and bearing forces shall be taken into consideration.
- Gabion, Bin, and Crib retaining walls are also types of gravity retaining walls.
4. Gabion Retaining Wall →
- Gabion retaining wall is multi-celled, rectangular wire mesh boxes that are filled with stones or other appropriate material.
- Galvanized wire is most common but stainless steel and PVC coated wires are also used.
- It is also used to balance steep slopes.
- Gabion retaining wall costs between 700 and 1000 per square foot.
5. Anchored Retaining Wall →
- An anchored retaining wall is nailed at the top and the bottom using cables that are attached to the rock or soil behind it.
- This type of wall is suitable for loose soil or rock.
- Anchored retaining wall is applied where the space is limited or thin retaining wall is required.
- Anchors are operated into the material and then expanded at the end of the cable and then holes are filled by injecting pressurized concrete.
- Anchors function against sliding pressure and overturning.
6. Crib Retaining Wall →
- The crib retaining wall is consists of cells made of concrete, timber, and plastic/fibre.
- The interlock areas are filled with earth back-fill or free-draining materials, enabling a free escape of water and eliminating the hydro-static pressure.
- The most common materials used for crib wall construction are timber and reinforced precast.
- It is suited to support planter areas.
- A crib retaining wall is also a type of gravity retaining wall.
- The crib retaining wall is ok up to a height of 5-6 meters and is mostly used for landscape walls.
7. Counter-fort/Buttressed Retaining Wall →
- Counter-fort/Buttressed retaining wall is a cantilever retaining wall but strengthened with counter-fort inflexible with the back of the wall slab and base slab.
- Counter-fort wall height ranges from 8-12 meters.
- Counter-fort spacing is equal to or slightly larger than half of the height of counter-fort.
8. Hybrid/Composite Retaining Wall →
- A hybrid or Composite retaining wall is a wall that uses both factors, their mass and reinforcement for stability.
9. Mechanically Stabilized Earth (MSE) Retaining Wall →
- MSE retaining wall is a composite structure consisting of alternating layers of compacted backfill and soil reinforcement elements fixed to a wall facing.
- It is the most economical and commonly constructed retaining wall.
- Extreme wall heights can be achieved and extreme loads can be carried in MSE retaining wall.
- In MSE retaining wall bearing pressure is distributed over a wide foundation area.