Module 11
Rafts and mat foundations
One big foundation instead of many small ones — and why that is not automatically better.
What this module covers
- Say when a raft is the right answer and when it is an expensive reflex
- Compute the net pressure under a compensated raft and its degree of compensation
- Explain why a raft settles far more than a pad at the same bearing pressure
- Describe how raft stiffness controls differential settlement, and what a piled raft adds
Lessons
Three good reasons, and one very good one.
Start lesson →What a raft is actually good at.
Start lesson →
Module checkpoint
Check what you have taken in
2 questions
Question 1
A building applies a gross pressure of 150 kPa. In soil weighing 19 kN/m³, how deep must the excavation be for full compensation, in metres?
Question 2
A 12 m raft at 93 kPa settles 42 mm, while a 2.5 m pad at 150 kPa settles 14 mm. Why does the raft settle more at lower pressure?