The Chartership Forum

Foundation Engineering / module 10

Consolidation settlement and differential movement

The slow half of the problem — and the half that actually cracks buildings.

What you will understand

  • Compute primary consolidation settlement honouring the stress history
  • Explain why the preconsolidation stress changes the answer by a factor of two or more
  • Use the time factor to predict how settlement develops, and the effect of drainage path
  • Distinguish total from differential settlement and say which governs damage

Lessons

  1. How much, and how fast

    Stress history sets the magnitude; the drainage path sets the clock.

  2. Differential movement

    What actually damages buildings.

Module summary
  • Consolidation settlement depends on where the loading sits relative to the preconsolidation stress
  • The same layer settled 99 mm overconsolidated and 260 mm normally consolidated — a factor of 2.6
  • Time scales with the square of the drainage path, so halving it quarters the time
  • Damage is caused by differential settlement and angular distortion, not by uniform movement
  • A settlement calculation without a differential estimate has not answered the design question
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

Two columns 8 m apart settle 35 mm and 15 mm. What is the angular distortion, expressed as 1/N — give N.

Practice

A 4 m clay layer drains both ways with cv = 2 m²/year, so the drainage path is 2 m. Given that 90% consolidation needs Tv = 0.848, how long does it take, in years?

Check yourself

Why does the preconsolidation stress have such a large effect on the calculated settlement?