Counterfort Retaining Wall
The counterfort retaining wall is a type of retaining wall with counterforts attached to the inside face of the wall to further resist lateral thrust and materials used for retaining walls are treated lumber, concrete block systems, stone, brick, and poured concrete.
The stem and the base and also base slab are tied together by counterforts at suitable intervals in the counterfort retaining wall and the vertical stem, as well as the hell slab, acts as a continuous slab because of the provision of counterforts.
To counterforts, the stem and heel slabs are effectively fixed so due to lateral earth pressure, the stem bends horizontally between the counterforts. Thus due to the reduction of the moment, the thickness of the stem and the heel slab is considerably reduced.
To reduce the shear forces and bending moments imposed on the wall by the soil the counterforts tie the slab and base together. For height over about 6m counterfort retaining wall is economical and is adopted for larger heights.
These walls can be precast or formed on-site and for heights above 25 ft more economical than cantilever walls.
Parts of Counterfort Retaining Wall:
There are the following parts of counterfort retaining wall as given below;
- Toe Slab
- Heel Slab &
Design of Stem:
- As a continuous slab, the stem acts, and on the slab, soil pressure acts as the load.
- Over the height, earth pressure varies linearly and between the counterforts, the slab deflects away from the earth’s face.
- At the base, the bending moment in the stem is maximum & reduces towards the top.
Bending Moment for Stem:
- Maximum Bending Moment occurring mid-way between counterforts = pl2/16
- Maximum Bending Moment occurring at the inner face of counterforts = pl2/12
l = The clear distance between the counterforts.
p = The intensity of soil.
Design of Toe Slab:
- The base width as b = 0.6 H to 0.7 H and the projection of base width is 1/3 to 1/4.
- To an upward soil reaction, the toe slab is subjected and designed as a cantilever slab fixed at the front face of the stem.
- Along the length of the toe slab, reinforcement is provided on earth face and front counterforts are provided above the toe slab if the toe slab projection is large.
Design of Heel Slab:
As a continuous slab spanning over the counterforts, the heel slab is designed and due to the weight of soil and self-weight of the slab, it is subjected to downward forces.
- Maximum positive bending moment = pl2/16 &
- Maximum negative bending moment occurring at counterforts = pl2/12
Design of Counterforts:
From the stem, counterforts are subjected to outward reactions and produce tension along the outer sloping face of the counterforts.
The counterforts are designed as a T-beam of varying depth due to the inner face supporting the stem is in compression and at both ends, the main steel provided along the sloping face shall be anchored properly.
As perpendicular to the sloping side, the depth of the counterfort is measured.
Advantages of Counterfort Retaining Wall:
There are the following advantages of these walls such as;
- These walls are more economical to tie the vertical wall with the heel slab by counterforts.
- To support vertical walls this wall acts as a tension member.
- This wall reduces the bending moment and supports the hell slab.
- By weight of the earth and by self-weight stability is maintained.
- From 6m to 8m this wall height ranges.
- These walls are more widely used because it is hidden beneath the retained materials.
- For more efficient space in front of the wall, these walls have a clean and uncluttered face.