SPT Testing in St. Johns: Get Real N-Values for Your Foundation

For a standard single-family residential site in the St. Johns area, a two-borehole SPT program with lab classification typically runs between CA$840 and CA$1,160 total. The final number depends on access conditions—sites on steep slopes like those in the Battery or Southside Hills may require a smaller rig or additional setup time—and on how deep we need to go before hitting refusal. If we encounter bedrock at 3 meters, that’s a quicker job than drilling through 15 meters of glacial till. We provide a firm quote after a site walk, never a surprise invoice.

The short answer: at least two for any structure larger than a detached garage. NBCC 2020 doesn’t prescribe a fixed number, but our standard for a single-family home in St. Johns is two boreholes placed at opposite corners of the footprint. For a commercial building or multi-unit residential on a lot wider than 20 meters, we recommend three or more. The reason is the glacial geology here—we’ve seen boreholes 10 meters apart hit completely different stratigraphy, and a single hole gives you a false sense of uniformity that no engineer should rely on.

SPT gives you a physical soil sample every 1.5 meters that we can take to the lab for grain size, plasticity, and visual classification. CPT pushes an electronic cone into the ground and gives you a continuous profile of tip resistance and sleeve friction—great data, but no sample to hold in your hand. In St. Johns, we typically start with SPT because the glacial soils here often contain cobbles and boulders that can damage a CPT cone, and because most structural engineers want lab-classified samples for foundation design. We use CPT as a supplement when we need to detect thin silt layers between SPT intervals, especially on soft-ground sites near the harbour.

We send a preliminary borehole log with raw N-values and soil descriptions within 4 business days of completing field work—most contractors use this to keep the excavation and formwork schedule moving. The full geotechnical report with lab results (grain size curves, Atterberg limits, moisture content) and foundation recommendations follows within 10 to 12 business days. If you’re on a tight timeline, tell us before we mobilize and we’ll prioritize your lab queue. Rush turnaround is available for an additional fee, and we’ve delivered final reports in 5 business days for urgent projects.