Before breaking ground on any commercial construction project, there's one document that shapes every major design decision: the geotechnical report. This technical document provides critical information about subsurface conditions at your project site, information that directly impacts foundation design, construction methods, project costs, and long-term building performance.
For developers, property owners, architects, and contractors, understanding what a geotechnical report contains and how to use it can mean the difference between a successful project and costly surprises during construction. NOVA's geotechnical engineering team has prepared thousands of these reports for commercial projects across Georgia, Florida, North Carolina, and South Carolina. Here's what you need to know.
What Is a Geotechnical Report?
A geotechnical report is a technical document prepared by a licensed geotechnical engineer that summarizes subsurface conditions at a specific project site. The report presents data collected through field investigation and laboratory testing, along with engineering analysis and recommendations for foundation design and site development.
Unlike generic soil maps or regional geology references, a geotechnical report is site-specific. It documents the actual conditions encountered at your property through direct investigation—soil borings, test pits, laboratory analysis, and groundwater observations. This site-specific data forms the basis for structural engineering decisions and helps identify potential challenges before construction begins.
The geotechnical investigation and resulting report serve multiple purposes: they inform foundation design, guide earthwork specifications, identify potential construction challenges, and provide documentation that supports building permit applications and lender requirements.
What Does a Geotechnical Report Tell You?
A comprehensive geotechnical report answers the fundamental questions that drive foundation design and site development planning.
Subsurface Soil and Rock Conditions
The report describes the soil and rock layers encountered beneath your site, including their depths, thicknesses, compositions, and engineering properties. This includes classification of soil types (clay, sand, silt, organic material), identification of rock formations, and documentation of any fill material from previous site development.
For commercial projects in the Southeast, understanding these conditions is particularly important. Georgia's Piedmont region presents residual soils derived from decomposed rock that can vary significantly across short distances. Florida's coastal areas often involve challenging conditions, including loose sands, organic soils, and limestone formations susceptible to dissolution. The Carolinas present diverse geology ranging from coastal plain sediments to mountain residual soils.
Groundwater Conditions
The report documents groundwater levels encountered during the investigation and estimates seasonal fluctuations that may affect construction and long-term performance. High groundwater can affect excavation methods, require dewatering during construction, influence the selection of foundation types, and affect below-grade waterproofing requirements.
In coastal areas of Florida and the Carolinas, groundwater conditions often drive major design decisions. The report helps project teams anticipate these challenges and plan accordingly.
Soil Bearing Capacity and Foundation Recommendations
Perhaps the most critical information for structural engineers, the geotechnical report provides allowable soil bearing pressures and foundation recommendations. This data tells the structural engineer how much load the soil can safely support, which directly determines foundation type and sizing.
The report typically recommends appropriate foundation systems based on site conditions, whether shallow spread footings are adequate, whether deep foundations (driven piles or drilled shafts) are required, or whether ground improvement techniques should be considered. These recommendations consider both the soil's capacity to support loads and its potential for settlement over time.
Settlement Estimates
Beyond bearing capacity, the report estimates how much the structure may settle under load and how long that settlement will take to occur. Excessive or differential settlement can cause structural damage, so understanding settlement behavior is essential for foundation design.
Settlement concerns are particularly relevant for sites with compressible soils, such as soft clays common in coastal areas or organic soils encountered in low-lying areas throughout the Southeast.
Seismic Considerations
For projects in seismically active areas, the report provides site class determination and seismic design parameters required by building codes. Charleston, South Carolina, and the surrounding areas have specific seismic design requirements based on historical earthquake activity. The geotechnical report provides the site-specific data needed for proper seismic design.
Earthwork and Excavation Guidance
The report includes recommendations for site grading, fill placement, and compaction requirements. This information guides earthwork contractors in preparing the site and ensures that fill materials and compaction meet engineering specifications.
For sites requiring significant cut or fill, the report may address slope stability, temporary excavation support requirements, and the suitability of on-site soils for reuse as structural fill.
Potential Problem Conditions
A thorough geotechnical report identifies conditions that could cause problems during construction or affect long-term building performance. This might include expansive clays that shrink and swell with changes in moisture, collapsible soils, corrosive soil conditions that affect concrete or steel, or sinkholes and karst features in limestone terrain.
Early identification of these conditions allows design teams to address them proactively rather than discovering problems during construction when options are limited and costs are higher.
Types of Geotechnical Reports
Depending on the project stage and scope, NOVA's geotechnical engineers may prepare different types of reports to meet specific needs.
Preliminary Geotechnical Assessment
A preliminary assessment provides early-stage information for site evaluation, feasibility studies, or due diligence during property acquisition. This report may rely on limited field investigation combined with review of available geologic maps, aerial photographs, and historical records. It identifies potential geotechnical concerns and estimates the scope of investigation needed for design.
Geotechnical Investigation Report
The full geotechnical investigation report supports detailed design. It documents a comprehensive field investigation (soil borings, sampling, in-situ testing), laboratory testing results, engineering analysis, and specific recommendations for foundation design, earthwork, and construction. This is the primary geotechnical document used by structural engineers for foundation design.
Geotechnical Data Report
A data report presents factual information from the field investigation and laboratory testing without interpretive analysis. This format is sometimes used for design-build projects where the design-build team performs its own engineering interpretation, or for projects where the owner wants to separate factual data from engineering opinions.
Who Uses the Geotechnical Report?
Multiple project stakeholders rely on the geotechnical report, each with different interests and needs.
- Property owners and developers use the report to understand site conditions, anticipate foundation costs, and identify potential challenges that could affect project feasibility or budget.
- Structural engineers use bearing capacity values, settlement estimates, and foundation recommendations to design foundations that safely support the structure. The geotechnical report is an essential input for structural design.
- Architects use the report to understand how site conditions may influence building layout, below-grade space design, and coordination with civil engineering.
- Civil engineers use earthwork recommendations, pavement subgrade information, and drainage considerations for site design.
- Contractors use the report to understand excavation conditions, plan construction methods, select appropriate equipment, and accurately price earthwork.
- Building officials review the report as part of the permit application to verify that the foundation design is supported by an adequate geotechnical investigation.
- Lenders may require geotechnical reports as part of their due diligence before financing construction projects.
Important Limitations to Understand
While geotechnical reports provide essential information, they have inherent limitations that all stakeholders should understand.
The report documents conditions at specific investigation locations (boring or test pit locations) at a specific point in time. Subsurface conditions between investigation points are inferred based on the geotechnical engineer's interpretation and professional judgment. Actual conditions may vary from those encountered during the investigation.
If the project scope changes significantly after the geotechnical investigation, a taller building, deeper basement, or different structural system, the original report may no longer be adequate. Changes in project scope should be reviewed with the geotechnical engineer to determine whether additional investigation is needed.
The report is prepared for a specific client and project. It should not be used for other purposes or by parties not involved in the original project without the geotechnical engineer's written consent.
Regional Considerations in the Southeast
Geotechnical conditions vary significantly across NOVA's service area, and our geotechnical professionals understand the specific challenges each region presents.
- Georgia's Piedmont Region: Residual soils derived from decomposed granite and gneiss can have highly variable properties. Partially weathered rock (PWR) zones require careful evaluation for foundation bearing and excavation planning.
- Florida: Coastal plain geology includes loose sands, soft organic soils, and limestone formations. Karst features (sinkholes, solution cavities) require specialized investigation techniques. High groundwater tables affect virtually every project.
- Coastal Carolinas: Soft coastal plain soils, high groundwater, and hurricane-driven flood considerations influence foundation design. Charleston area projects must address seismic design requirements.
- North Carolina Piedmont and Mountains: Variable residual soils over rock, potential for expansive clays, and complex geology in mountain terrain require experienced local knowledge.
Getting Started with Your Geotechnical Investigation
The geotechnical investigation should begin early in project planning, ideally during the feasibility or schematic design phase. Early investigation allows time for the results to inform design decisions and helps avoid surprises that could delay the project or increase costs.
To scope an appropriate investigation, your geotechnical engineer needs to understand the proposed development: building size and height, structural system, anticipated foundation loads, below-grade construction, and any site constraints. This information allows the engineer to design an investigation that provides the data needed for your specific project.
NOVA's geotechnical engineering services include investigation planning, field exploration, laboratory testing in our AASHTO-accredited laboratories, engineering analysis, and detailed reporting. Our team works closely with project stakeholders to ensure the investigation scope matches project needs and the resulting report provides actionable information for design and construction.
For questions about geotechnical reports or to discuss investigation needs for your commercial project, contact NOVA's geotechnical team. With 20 offices across Georgia, Florida, North Carolina, and South Carolina, we provide local expertise backed by regional resources.
