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Parapet wall, gravity and counterfort retaining walls

Short answer

A parapet wall is a 0.6-1.0 m high wall on roof edges for safety, fire barrier, and aesthetics, with coping and DPC. A gravity retaining wall resists earth pressure by its own weight, trapezoidal with battered front face, used up to 3-4 m height. An RCC counterfort wall uses vertical triangular ribs (counterforts) at 2.5-3.5 m spacing to strengthen stem and base slab, economical for heights above 6 m.

Describe parapet wall, gravity retaining wall and reinforced cement concrete counterfort wall with suitable sketch.

Parapet wall

A parapet is a low wall (0.6-1.0 m high) built along the edges of a roof or terrace. It protects people from falling, hides the roof (and tanks) from view, carries the coping, and acts as a barrier against fire spreading between adjoining roofs. It is built of brick, stone or RCC, 115-230 mm thick, with a coping (RCC or stone, projecting about 40 mm with a drip groove) on top and a DPC at the base to stop water seeping into the roof.

    ===========  coping (drip)
    |         |
    |parapet  | 0.9 m
 ===|=========|==== roof slab

Gravity retaining wall

A wall of stone, brick or plain concrete which resists the earth pressure by its own weight. It is trapezoidal in section with a wide base, and the front face is battered. It is used up to about 3-4 m height. Weep holes drain the backfill.

          ______
         /      |
        /       |<-- P_a  backfill
       /   W    |    (earth pressure)
      /         |
     /__________|_______
         base
  front face battered, back face vertical

RCC counterfort retaining wall

For high walls (above about 6 m), a thin RCC stem and base slab are strengthened by vertical triangular ribs (counterforts) placed behind the wall at about 2.5-3.5 m c/c. The stem acts as a continuous slab spanning between the counterforts, and the counterforts act as T-beams cantilevering from the base slab. The weight of the backfill over the heel helps stability. It is economical for greater heights because it saves material compared with cantilever walls.

 PLAN                                 SECTION
    backfill side                        stem
  ---+-----+-----+-----+---              |\
     |     |     |     |  counterforts   | \  counterfort
  =======================  stem          |  \     backfill
    front (exposed) face               __|___\__________
                                       toe    heel slab

✓ Answer checked by Claude Opus 5.5 (high effort)

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