Types of retaining walls

A retaining wall is a structure built to hold back earth (or water) on one side where the ground level changes abruptly, to carry the road on the hill side or to protect the valley-side fill. Types used in road construction are:

1. Gravity walls

Resist the earth pressure by their own weight.

• Dry stone masonry: stone placed without mortar. Cheap, flexible and drains freely, for low heights (up to about 3 m).
• Stone masonry in cement/lime mortar: for heights up to about 6 m, with weep holes.
• Plain concrete: where stone is not available.

2. Semi-gravity walls

Plain concrete with a little reinforcement, thinner than a gravity wall.

3. Cantilever RCC walls

An inverted T or L shaped RCC wall; the stem acts as a cantilever, and the weight of the soil on the heel provides stability. Economic up to about 6 to 8 m.

4. Counterfort and buttress walls

RCC walls with vertical ribs (counterforts, behind the stem; buttresses, in front) at regular spacing, which support the stem. For heights above about 8 m.

5. Gabion walls

Rectangular wire-mesh boxes filled with stones, stacked in steps. They are flexible, permeable, easy to build with local labour and tolerate settlement; very popular in Nepal on hill roads.

6. Crib walls

Interlocking precast concrete or timber members filled with soil or gravel; are flexible.

7. Reinforced earth (MSE) walls

Layers of compacted fill with strips, grids or geotextiles tied to facing panels. They are economical for high walls and perform well in earthquakes.

8. Anchored / soil-nailed walls and sheet piles

For steep unstable cut slopes; use ground anchors or nails.

9. Breast walls

Built on the hill side to support a cut face, and prevent rock fall (as opposed to retaining walls on the valley side).

  Gravity wall     Cantilever RCC       Gabion
     /|              |  stem               ___
    / |              |                    |___|__
   /  |   soil    ___|__ heel             |_____|__
  /___|          |toe  |                  steps

Basis of selection

• Height of the wall and the type and strength of the backfill.
• Bearing capacity and depth of the foundation soil, and settlement.
• Availability of local materials (stone, sand, cement) and skilled labour.
• Cost and construction time.
• Drainage conditions (provide weep holes, filter) and ground water.
• Seismic conditions and flexibility.
• Space available and aesthetics.
• Ease of maintenance and repair.