What is counterfort retaining wall and when is it used?

Short Answer:

A counterfort retaining wall is a type of reinforced concrete wall that includes triangular-shaped vertical supports called counterforts on the back side of the wall, spaced at regular intervals. These counterforts connect the vertical wall (stem) to the base slab, reducing bending and shear stress by acting like stiffeners.

Counterfort retaining walls are used when the height of the retained earth is large (typically more than 6 meters). They are suitable for heavy load conditions and are commonly seen in bridge approaches, basement walls, industrial sites, and areas with high embankments.

Detailed Explanation

Counterfort Retaining Wall and When It Is Used

A counterfort retaining wall is a specially designed structure used to retain large volumes of earth. It is a variation of a cantilever retaining wall but strengthened with additional inclined supports called counterforts. These counterforts are placed behind the wall at regular intervals and are connected to both the wall stem and the base slab. Their function is to reduce bending moments and shear forces by tying the stem and heel slab together.

Instead of acting as a flexible cantilever slab, the wall between two counterforts behaves more like a fixed-end slab. This makes the wall more economical for greater heights as the wall thickness can be reduced due to lower internal stress.

What Is Counterfort Retaining Wall

  1. Structure and Working
  • The main wall that retains the soil is called the stem.
  • The counterforts are triangular or trapezoidal slabs placed perpendicular to the stem on the earth-retaining side.
  • These counterforts are usually spaced 2 to 3 meters apart.
  • They tie the back of the wall to the base slab, making the entire structure work as a single unit.
  • As a result, the wall behaves like a continuous slab supported by beams, which greatly reduces bending stress and material requirement.
  1. Materials and Design
  • Made of reinforced cement concrete (RCC) for both stem and counterforts.
  • Proper anchorage and reinforcement detailing is important at the junctions.
  • Adequate cover and waterproofing are also applied due to exposure to moisture and backfill soil.

When Is It Used

  1. Large Retained Heights
  • Counterfort walls are most economical when the retained height exceeds 6 meters.
  • For lower heights, simple gravity or cantilever walls are more cost-effective.
  1. Heavy Load or Wide Backfill Areas
  • Used where high earth pressure, heavy surcharge, or large backfilled areas are present.
  • Suitable for bridge approaches, railway embankments, and highway cuttings.
  1. Industrial and Infrastructure Projects
  • Applied in large basement walls of factories, water treatment plants, or powerhouses.
  • Also used in retaining structures in harbor areas and large dock facilities.
  1. Where Space Behind the Wall Is Not Restricted
  • Since the counterforts project behind the stem, they require space at the rear side.
  • In tight spaces or urban areas, this type may not be suitable.
  1. Economical for Tall Walls
  • Though the construction is more complex, it becomes cost-effective for taller walls due to material savings in the stem and base slab.
Conclusion

A counterfort retaining wall is a reinforced wall strengthened with inclined supports called counterforts that reduce internal stresses. It is best suited for retaining large soil heights, especially where heavy loads or wide earth fills are expected. Its design ensures stability and strength for tall and demanding retaining applications in infrastructure and industrial projects.