Under what condition is a soil investigation required?

A soil investigation is required when the soil bearing capacity is under 1500 psf. This threshold is crucial because it helps determine whether the soil can adequately support structures without risk of settlement or failure. When the soil bearing capacity is below this limit, a detailed investigation is necessary to assess the soil's characteristics and ensure that appropriate foundation design measures are taken.

If the bearing capacity is higher than this value, it is generally considered sufficient to support typical residential loads without needing extensive investigation, thereby saving time and resources. Therefore, the requirement for a soil investigation aligns with the necessity to ensure safety and structural integrity when the bearing capacity is on the lower end of the spectrum.