Foundations and Groundwork
What the domain tests
Foundations and Groundwork tests soil identification, bearing capacity, foundation types, trench excavation, concrete, damp-proof courses, stepping and settlement.
Core rules
- Foundations transfer load to the ground without excessive settlement. Found on firm soil below topsoil and the zone of seasonal movement.
- Strip foundations suit loadbearing walls; pad foundations suit columns; rafts suit weak or variable ground; piles reach stronger deep strata.
- Concrete blinding is normally about 50 mm thick. Footing width and thickness come from design.
- Step strip foundations on sloping ground to keep the required depth.
- A DPC should be at least 150 mm above external ground level; lap DPC and DPM correctly and keep mortar off the DPC.
- Backfill in layers and compact; protect concrete while curing.
Worked example
A wall carries 30 kN per metre and the allowable bearing pressure is 150 kN/m². Required footing area per metre = 30/150 = 0.2 m², so calculated width = 0.2 m. The practical minimum for a 230 mm wall is 600 mm, so use 600 mm. Check pressure: 30/0.6 = 50 kN/m², which is below 150 kN/m². Reasoning: use the greater of calculated and practical minimum width.
Traps
- Dividing load by pressure with inconsistent units.
- Founding on topsoil or uncontrolled fill.
- Placing the DPC below ground level.
- Forgetting termite protection where required.
- Leaving trenches open to rain without protection.