The Chartership Forum

Reinforced Concrete Design / module 12

Retaining walls

How wall restraint, ground movement and drainage affect earth pressure and retaining-wall behaviour.

What you will understand

  • Derive the active earth pressure coefficient, and say what it assumes about movement
  • Choose between active, at-rest and passive pressure from how the wall is restrained
  • Carry out the three stability checks, and say which normally governs
  • Explain why water is so much more severe than soil
  • Design the stem as a cantilever, using the right height
  • State plainly which quantities are geotechnical inputs rather than structural ones

Lessons

  1. Earth pressure

    Why the load on a retaining wall depends on the wall, and why water is the thing that actually breaks them.

  2. Stability, and designing the wall

    Three checks before any reinforcement, and the one that usually governs.

Module summary
  • The pressure depends on how far the wall can move — active needs it to yield
  • A propped wall attracts AT-REST pressure, half as much again as active
  • Water uses no coefficient at all: K = 1, because it has no shear strength
  • Overturning moment goes with the CUBE of the retained height
  • Sliding usually governs a cantilever wall, not overturning
  • Blocked drainage can increase water pressure and cause retaining-wall failure.
  • Stability comes before strength — reinforcement cannot stop a wall sliding
Teaching basis and review status

These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.

Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.

Read the lesson register and outstanding review notes

Check your understanding

Practice

A soil has φ = 25°. What is Ka?

Check yourself

A basement wall is propped by the ground floor and the basement slab. Which pressure applies?

Practice

A 4 m wall retains soil with Ka = 0.33 and γ = 18 kN/m³. What is the overturning moment about the base, in kNm/m?

Practice

If that wall were 6 m instead of 4 m, by what factor does the overturning moment increase?

Check yourself

A cantilever retaining wall fails its sliding check. Which change does NOT help?

Practice

Water stands 3 m deep behind a wall. What is the horizontal force from the water alone, in kN/m? Take γw = 9.81 kN/m³.