Foundation Engineering / module 9
Immediate settlement of shallow foundations
The calculation is easy. Knowing E is the hard part.
What you will understand
- Compute immediate settlement of a shallow foundation on an elastic half-space
- Distinguish rigid and flexible foundation behaviour and say which to compare against
- Explain why the modulus, not the equation, dominates the uncertainty
- Select an appropriate stiffness for the stress and strain range a foundation actually imposes
Lessons
The elastic calculation
Rigid, flexible, and which number you are comparing.
Which stiffness?
The number that decides the answer, and how to choose it.
Module summary
- Immediate settlement is proportional to net pressure, to width, and to 1/E
- A rigid foundation settles uniformly; its influence factor differs from the centre factor of a uniformly loaded flexible foundation
- Soil stiffness is not a constant — it falls sharply with strain
- Using a laboratory modulus from a triaxial test typically overpredicts settlement
- Halving E doubles the settlement, so an uncertain modulus dominates everything else
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 notesCheck your understanding
Practice
A rigid square foundation is 3 m wide and carries 120 kPa on an elastic half-space with E = 20,000 kPa and ν = 0.3. Using the tabulated influence factor 0.99, estimate settlement in mm.
Check yourself
Which input dominates the uncertainty in an immediate settlement prediction?