Retaining walls may be defined as a wall built to resist the pressure of liquid, earth filling, sand, or other granular material filled behind it after it is built. It is commonly required in the construction of hill roads, masonry dams, abutments and wingwalls of bridges and so on. Depending upon the site conditions, type of material to be retained and the height of the wall to be constructed, retaining wall may be built in dry Stone masonry, stone masonry, brick masonry, plain cement concrete and reinforced cement concrete.
Types of Retaining Walls:
Some of the types of Retaining Walls are,
- Gravity Retaining walls
- Cantilever Walls
- Counterfort walls
- Buttress Walls
Dry Stone Retaining Walls:
This is the simplest form of retaining wall. The stability of such walls depends upon the arrangement of stones in the wall and the friction between the individual stones. The stones used in the wall should be of large size and roughly hammer-dressed so as to ensure maximum bedding area. The wall should have a minimum top width of 60 cm. and the front face should have a batter varying from 1 in 4 to 1 in 3. The batter of I in 4 is adopted for walls lesser than 4.5 m in height. In principle, the height of dry stone masonry wall should be restricted to 6 m. For walls above 4.5 m in height, the upper 4.5 m of the walls is usually built of dry rubble stone masonry and the portion below this height is built with mortar.
The stones used in the wall construction are laid at right angle to the face baller. A proper bond is maintained and the front and the rear faces of the wall are nicely bonded with the hearting. The filling immediately behind the wall should consist of stone chips gravel or similar granular material and not earth. 75 to 100 mm. square weep-holes should be provided in the wall at 2m c/c vertically and horizontally to drain off the water from the filling behind. The wall has been shown in figure 943 on page (252).
Dry Stone Pitching or Revetment:
It is generally provided to protect the slopping face of an earthen cutting or embankment from erosion. Stones used, should be perfectly sound and roughly cut to fit in the shape of the pitching. In case of channels and dams, pitching should be carried at least 90 cm. above the high flood level and to ensure its stability, the toe should be prevented from slipping by suitable construction. The slopes of embankment should not be steeper than 1:1, a slope of 1½ : 1 being usually adopted. The thickness of pitching varies from 30 cm. to 75 cm. Selected stones are tightly hand packed and all the interstices are filled up with smaller pieces of stone and wedged up tight. Every stone in pitching is laid flat and no projecting stones are allowed.
