Geotechnical Report
The engineer's report on what lies underground and how to build on it.
Quick Answer
A geotechnical report is a document prepared by a geotechnical engineer that describes subsurface soil, rock, and groundwater conditions at a site based on borings, sampling, and lab testing. It gives recommendations for foundations, earthwork, and pavements. Designers and contractors use it to select foundation systems and anticipate excavation and site preparation costs.
The Full Picture
Every building sits on the ground, and the ground varies. A geotechnical investigation tells the project team what is there. Engineers drill borings or dig test pits, collect samples, perform field and laboratory tests, and record groundwater depth. The resulting report documents the soil profile and explains how those conditions affect the design and construction of the project.
A typical report includes a site and project description, the exploration methods and boring logs, a summary of subsurface conditions, lab test results, and engineering recommendations. Those recommendations commonly address foundation type and allowable bearing pressure, expected settlement, slab-on-grade support, retaining walls, seismic site classification, excavation and dewatering, fill placement and compaction, and pavement sections. Reports often contain limitations, since borings sample only a small portion of the site.
The report matters contractually and financially. Many contracts reference it, and disputes over differing site conditions often turn on what the report disclosed and how the contract treats it, for example whether it is included for information or as a contract document. Unexpected rock, soft soils, contaminated fill, or high groundwater are common drivers of cost and schedule change.
For preconstruction teams, the geotechnical report is an input to estimating and planning. Estimators read it to price excavation, shoring, dewatering, import or export of soil, and foundations, and they check whether the assumptions match the drawings. If the report is missing, outdated, or inconsistent with the structural design, the team typically raises it with the design team before bid.
Real Examples
Common Misconceptions
People assume: A geotechnical report guarantees the conditions across the whole site.
Actually: Borings sample only discrete locations, so conditions between them are interpreted. Reports include limitations, and conditions can differ from what the exploration found.
People assume: The geotechnical report is the same as an environmental report.
Actually: A geotechnical report addresses engineering properties of soil and rock for design. Environmental site assessments address contamination and liability, and are prepared separately.
Frequently Asked Questions
Who prepares a geotechnical report?
A licensed geotechnical engineer or an engineering firm that performs soil exploration, laboratory testing, and analysis for the project.
When is a geotechnical report needed?
Generally before foundation design is finalized, and often before purchasing a site or bidding. Building codes and local jurisdictions may also require a report for certain projects.
What is in a geotechnical report?
Boring logs, soil and groundwater conditions, test results, and recommendations for foundations, earthwork, retaining structures, and pavements.
How does a geotechnical report affect construction cost?
It informs foundation type, excavation difficulty, dewatering, soil improvement, and fill requirements, all of which can significantly change project cost and schedule.
What is a differing site condition?
A subsurface condition materially different from what the contract documents indicated or from what is ordinarily encountered. Contracts address how such conditions are handled and who bears the cost.