Retaining walls are vertical or near-vertical structures designed to retain material on one side, preventing it from collapsing or slipping or preventing erosion. They provide support to terrain where the soil’s angle of repose is exceeded and it would otherwise collapse into a more natural form. The principal characteristic of a retaining wall is being able to withstand the pressure exerted by the retained material, which is usually soil.
Retaining walls may include a parapet that extends above the height of the retained material, often for safety reasons.
The main uses of retaining walls are to help prevent soil erosion, create usable beds out of steep terrain and to provide decorative or functional landscaping features. They may be independent structures, or may be part of a wider construction works, such as a building.
The wall is normally constructed by first excavating a soil bank, followed by laying a mass concrete to form a reinforced footing. Blocks in the first course are then laid whilst the concrete is still green, with blocks lightly tapped in place. Higher slump concrete should be worked into and around in order to haunch to the first course.
Behind the blocks of the first course, a 100 – 150 mm subsoil drainage pipe lined with a non-woven geotextile shall be laid. Either or one end of the pipe shall be diverted to nearest main drain, so that water could be discharged.
Thereafter, blocks are laid one by one in stretcher bond without mortared joints, as the blocks slot into each other. As construction proceeds, suitable infill material (e.g. fine friable topsoil or sand) shall be placed in the pockets of each successive course, and backfill material (e.g. sand or graded stone) shall be compacted.
For difficult soil condition and extra surcharge from the upper slope ~ a need of heavy duty wall design ~ it may be necessary to incorporate the blocks with geotextile and increase the wall angle to achieve the safety factor.