Geotechnical · 6 min read
Settlement, subsidence and underpinning in Brisbane
Settlement is the ground under your footings compressing or losing support. Unlike seasonal clay movement it does not come back, and differential settlement — one part of the building dropping more than another — is what damages structures.
Total versus differential settlement
A building can settle uniformly by quite a lot with little damage. Differential settlement of a few tens of millimetres across a slab will crack walls, rack door frames and tilt floors.
That is why we take floor levels. A level survey across the slab shows the shape and magnitude of movement, which separates settlement from reactive soil heave and shrinkage.
Common causes on Queensland sites
Uncontrolled or poorly compacted fill, footings founded above the intended bearing stratum, soft alluvial and estuarine soils, leaking sewer and stormwater eroding support, excavation next to existing footings, and consolidation under new fill or slabs.
The remedial options
Not every case needs underpinning. Fixing drainage, removing the source of moisture change or grouting a void is often enough.
- Mass concrete underpinning — deepening footings to a competent stratum
- Screw piles and helical piles — fast, low vibration, immediate load capacity
- Bored piers and micropiles — where high capacity or restricted access is involved
- Resin injection and grouting — to fill voids and re-level slabs
- Ground improvement and load transfer beams — for larger structures
Fees
Settlement inspection with floor levels: $400. Written assessment report: add $300. Settlement control, underpinning and pile design is quoted on the findings — send us photos and the site details for a free quote.
Frequently asked questions
- How do I know if my house is settling or just moving with the clay?
- Seasonal clay movement is cyclic — cracks open in dry months and close after rain. Settlement is progressive and one-directional. Floor level surveys and crack monitoring over time distinguish the two.
- Is underpinning always needed?
- No. In many cases correcting drainage and removing the cause stabilises the building. Underpinning is for genuine loss of support.
Book a $400 settlement inspection including floor levels.
Request a quote