Structural Principles of Retaining Walls

Definition

• A retaining wall is built to hold back soil.
• Required for sloping sites needing excavation where room is insufficient or impractical to batter the soil.
• Walls over 1 meter high must be designed by a qualified structural engineer.

Purpose of Design

• Retaining wall designs must resist soil pressure and ensure structural stability.

Types of Retaining Walls

1. Incline Retaining Wall

• Leans into excavated soil.
• Constructed at an angle between 45 and 80 degrees.
• Materials: brickwork, pre-cast interlocking concrete units.

2. Gravity Retaining Wall

• Relies on its own weight to resist overturning forces from soil.
• Typically made from heavy materials like stone, brickwork, or concrete.

3. Cantilever Retaining Wall

• Most complex type; requires careful engineering design.
• Utilizes steel reinforcement and varying concrete thickness to counteract soil forces.

Hydrostatic Pressure Management

• All retaining wall systems aim to minimize hydrostatic pressure, which is the pressure of water contained in soil.
• Strategies include:
  • Controlling backfill material to be coarse and well-draining (e.g., scoria).
  • Installing an agricultural drain behind the wall to direct water to stormwater drains.
  • Using weep holes at the base of the wall to relieve hydrostatic pressure.

Additional Considerations

• Retaining walls may serve as external walls of buildings and require waterproofing to prevent moisture ingress.
• Waterproofing is achieved through tanking, which includes waterproof membranes.