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How much geotechnical testing is enough before foundation design?
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A basic soil report may be enough for a straightforward site, but I’m unsure where the point is that more site-specific investigation becomes worthwhile. The report needs to give the foundation designer useful information about bearing capacity, groundwater, and any expansive or compressible soils, not just a general description of what was sampled.
How do you decide whether the initial scope is adequate, or whether known conditions such as slope, fill, or nearby excavation call for additional testing? I’d also want the geotechnical findings reviewed with the foundation designer before settling on the foundation approach or site budget. Who usually coordinates that review, and what gaps in a report are worth clarifying early?
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Rather than judging the scope by the number of borings alone, ask the geotechnical engineer to spell out what the initial investigation assumes and which design questions it can’t answer. Then the foundation designer can say whether more borings or lab tests are likely to change the foundation choice or just add detail. That’s especially useful when slope, fill, or nearby excavation might make conditions vary across the site.
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