Module 14
Pile capacity in clay — the α-method
One coefficient, quoted between 0.3 and 1.0, multiplying the term that matters most.
What this module covers
- Apply the α-method layer by layer to compute shaft resistance in clay
- Explain physically why α is less than one, and why it falls as the clay stiffens
- Compute base resistance in clay and say why Nc = 9 rather than 5.14
- Quantify how much the disagreement over α moves the answer, and respond to it properly
Lessons
Why the pile never gets the strength the laboratory measured.
Start lesson →A factor of three, sitting on the term that carries the pile.
Start lesson →
Module checkpoint
Check what you have taken in
2 questions
Question 1
A 0.6 m diameter bored pile has its base in clay with su = 90 kPa. Using Nc = 9, what is the base resistance, in kN?
Question 2
Over the same shaft, α = 0.3 gives 916 kN and α = 1.0 gives 3054 kN. By what factor does the shaft resistance vary?