What Must a Geotechnical Report Include for Permitting?

A complete geotechnical report contains the exploration program (boring locations, depths, and logs), soil and rock descriptions with classification, groundwater observations, laboratory test results (strength, compressibility, expansiveness, corrosivity), and engineering analysis with recommendations: allowable bearing pressures for shallow foundations, deep foundation capacities and installation criteria, estimated total and differential settlement, lateral earth pressures for walls, subgrade preparation and fill requirements, pavement design parameters, and seismic site class with liquefaction assessment. The report's value is in the recommendations, not the raw data. Boring logs tell you what is down there; the engineer's analysis tells you what to build on it. A good report states the foundation options explicitly — shallow versus deep — with the settlement and cost implications of each, so the structural engineer and owner can make an informed choice rather than guessing.

The structural engineer cannot size a footing without the allowable bearing pressure, cannot check serviceability without the settlement estimate, and cannot run the seismic analysis without the site class. The geotechnical report is not background reading — it is input data, and missing or vague parameters stall the structural design. We review every report against a simple test: does it give us every number the foundation design needs, stated unambiguously? Liquefaction deserves special attention in seismic regions. If loose saturated soils can lose strength during an earthquake, the report must assess the hazard and recommend mitigation — ground improvement, deep foundations bearing below the liquefiable layer, or structural accommodation of the resulting settlement. Expansive soils get similar focus where they occur: the report should quantify swell potential and recommend slab and foundation details that tolerate it. These are the findings that change projects, and they are exactly why the investigation happens before the structural design, not during it.

A useful geotechnical report starts with a well-scoped investigation. Under-scoped investigations produce vague reports; vague reports produce conservative, expensive foundations. Confirm these when scoping and reviewing the work.

• Scope matches the structure: boring depth and spacing suited to the building loads and soil variability
• All design parameters present: bearing capacity, settlement, lateral pressures, and site class stated clearly
• Groundwater addressed: observed levels, seasonal variation, and dewatering or waterproofing implications
• Seismic hazards assessed: site class, liquefaction potential, and mitigation recommendations where needed
• Foundation options compared: shallow vs deep with settlement and cost implications, not just one answer