Understanding Retaining Walls and Their Design

Structural Principles Retaining Walls A retaining wall is a wall built to hold back soil. It is required to support soil where a sloping site requires excavation and either there is insufficient room or it is impractical to batter the soil. Retaining walls over 1 metre high must be designed by a qualified structural engineer. The engineer designs the retaining wall so that it is able to resist soil pressure and is a stable structure. Incline Retaining Wall An incline retaining wall leans into the excavated soil and is constructed at an angle between 45 and 80 degrees. It may be constructed from brickwork or pre-cast interlocking concrete units. Gravity Retaining Wall A gravity retaining wall relies on its own weight to resist overturning forces from the soil. It is typically constructed of heavy materials such as stone, brickwork or concrete. Cantilever Retaining Wall A cantilever retaining wall is the most complex of the three types and must be carefully designed by an engineer. It relies upon the correct placement of steel reinforcement and varying thickness of concrete to resist the compressive and tensile forces exerted on the wall by soil pressures. All types of retaining wall systems aim to minimise the build-up of water pressure exerted upon the wall by the water contained within the soil. This pressure is called hydrostatic pressure. Minimising hydrostatic pressure can be achieved by carefully controlling the backfill that is placed behind the retaining wall. It must be coarse, well-draining material, such as scoria. An agricultural drain placed behind the wall within the free-draining backfill will help drain the water away to the stormwater drainage system. A series of weepoles in the base of the wall will also minimize the effects of hydrostatic pressure exerted upon the wall. In some cases retaining walls form the external wall of a building and therefore must be adequately sealed to prevent moisture entering the building. This is achieved by applying tanking, which is a waterproofing system that incorporates waterproof membranes.

The engineer designs the retaining wall so that it is able to resist soil pressure and is a stable structure. Incline Retaining Wall An incline retaining wall leans into the excavated soil and is constructed at an angle between 45 and 80 degrees. It may be constructed from brickwork or pre-cast interlocking concrete units.

Gravity Retaining Wall A gravity retaining wall relies on its own weight to resist overturning forces from the soil. It is typically constructed of heavy materials such as stone, brickwork or concrete. Cantilever Retaining Wall A cantilever retaining wall is the most complex of the three types and must be carefully designed by an engineer.

It relies upon the correct placement of steel reinforcement and varying thickness of concrete to resist the compressive and tensile forces exerted on the wall by soil pressures. All types of retaining wall systems aim to minimise the build-up of water pressure exerted upon the wall by the water contained within the soil. This pressure is called hydrostatic pressure.

Minimising hydrostatic pressure can be achieved by carefully controlling the backfill that is placed behind the retaining wall. It must be coarse, well-draining material, such as scoria. An agricultural drain placed behind the wall within the free-draining backfill will help drain the water away to the stormwater drainage system.

A series of weepoles in the base of the wall will also minimize the effects of hydrostatic pressure exerted upon the wall. In some cases retaining walls form the external wall of a building and therefore must be adequately sealed to prevent moisture entering the building. This is achieved by applying tanking, which is a waterproofing system that incorporates waterproof membranes.

Transcript for:Understanding Retaining Walls and Their Design

Transcript for:
Understanding Retaining Walls and Their Design