Compaction and materials testing during construction
Why fill, subgrade and concrete are tested on site, what a field technician checks, when to book the visits and which reports to keep for the building inspector.
A soils report gives recommendations; construction testing checks that the work in the field actually meets them. Geotechnical and materials testing firms send technicians to the site at key stages, under the supervision of an engineer, and issue a report for each visit.
What is tested
- Subgrade inspection: before footings are poured, the technician or engineer checks that the soil at the bottom of the excavation matches what the report expected and is not soft, frozen or disturbed.
- Compaction of fill: under slabs, driveways, foundations or behind walls, engineered fill is placed in layers and each layer is tested for density, usually with a nuclear densometer, against a laboratory reference.
- Granular materials: samples of gravel or crushed stone are tested to confirm they meet the specified gradation.
- Concrete: slump, air content and temperature are checked on delivery, and cylinders are cast and broken in the lab to confirm strength. Canadian concrete practice follows CSA standards.
- Other checks, depending on the project: asphalt, piles, anchors or backfill around services.
When to book
- Before construction, ask the firm which visits the soils report or the specifications require and agree on the notice they need.
- Call before each stage: excavation complete, each lift of fill, each concrete pour. A missed test can mean digging up work already done.
- Keep the excavation open and dry until the subgrade has been reviewed.
Reports to keep
Each visit produces a field report, and lab results follow for samples. Keep them with the soils report: the building inspector, the designer, a lender or a future buyer may ask for them. A failing result is not a disaster if it is caught early; it usually means more compaction, replacing a material or adjusting the design.
Who needs it
Commercial and multi-unit projects almost always include testing. For a house, it is often required when the foundation sits on engineered fill, when the soils report asks for it, or when the municipality requires an engineer's sign-off.
Describe your project and its stages in the form: local testing firms get back to you. See also what a soils report contains.