Soil conditions
Identification and characterization of the soil layers encountered during the investigation.
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You Can See the Land. A Geotechnical Investigation Helps You Understand What’s Beneath It.
Before designing a foundation, it is important to understand the soil and subsurface conditions that will support the structure. A geotechnical investigation gives engineers and builders information for better decisions about foundations, earthwork, drainage, and construction.
Understand Your PropertyUnderstanding What’s Below the Surface
A property can look perfectly suitable for construction from the surface while very different conditions exist underground. Soils can vary considerably—even across the same property.
Depending on the site, subsurface conditions may include clay, sand, silt, gravel, rock, fill material, expansive soils, compressible soils, variable soil layers, shallow groundwater, or other moisture conditions.
A geotechnical investigation evaluates subsurface conditions at selected locations so a qualified geotechnical professional can develop recommendations for the proposed construction. The findings are typically documented in a geotechnical report.
What you build above ground depends heavily on what is supporting it below ground.
It Starts in the Field.
The exact investigation depends on the project, site, and geotechnical professional. Borings or test locations are selected based on the proposed project, and testing represents the conditions encountered at those locations and depths—not every condition across an entire property.
Soil borings
Test pits
Soil sampling
Rock evaluation
Laboratory testing
Field testing
Groundwater observations
Review of existing site conditions
The Ground Has a Story.
Depending on the scope of the investigation, a geotechnical report may provide information or recommendations concerning:
Soil strength & bearing
Information engineers can use when evaluating how the proposed structure will transfer loads into the ground.
Expansive soils
Some clay soils can change volume as moisture conditions change, which can be important for foundation and site recommendations.
Settlement
Certain soil conditions may be more susceptible to compression or settlement under structural loads.
Groundwater & moisture
Observed conditions can affect excavation, foundations, drainage, and construction methods; they can also vary seasonally.
Site preparation
Recommendations may address stripping, unsuitable materials, fill placement, compaction, moisture conditioning, and building-area preparation.
Earthwork
Recommendations may address excavation, fill materials, compaction, slopes, and other earthwork considerations.
Foundation recommendations
The geotechnical engineer may provide parameters the structural engineer or other design professional can use for an appropriate system.
Don’t Choose the Foundation Before Understanding the Ground.
Foundation decisions should not be based solely on preference. Depending on the structure and site conditions, a project might ultimately use slab-on-grade, pier-and-beam, drilled piers, grade beams, deep foundations, or other engineered systems. The appropriate solution depends on structural loads, building design, site conditions, soil behavior, drainage, local requirements, and engineering recommendations.
Foundation design should respond to the site—not assumptions about the site.
What Is Underground Can Affect What the Project Costs Above Ground.
Subsurface conditions can materially affect construction costs. Discovering them during planning gives the team an opportunity to incorporate them into design and budgeting. Discovering them after excavation begins can result in changes, delays, and unexpected costs.
The goal isn’t to eliminate every unknown. It’s to reduce avoidable surprises.
Additional excavation
Removal of unsuitable material
Imported structural fill
Soil stabilization
Compaction and moisture conditioning
Rock excavation
More substantial foundation systems
Additional piers
Drainage improvements
Construction dewatering
Site grading requirements
These Are Not Necessarily the Same Investigation.
Property owners sometimes use the phrase “soil test” to describe several different evaluations. A geotechnical investigation generally focuses on subsurface conditions relevant to structures, foundations, earthwork, and related construction. A septic or onsite wastewater evaluation is performed for a different purpose and may evaluate soil and site characteristics relevant to wastewater treatment and disposal. Requirements, testing methods, professionals, and terminology vary by jurisdiction; one should not automatically be assumed to replace the other.
A Survey Tells Us Where. Geotechnical Information Helps Tell Us What Is Below.
A land survey can establish property boundaries, easements, improvements, elevations, or other survey information depending on its type and scope. A geotechnical investigation evaluates subsurface conditions at specific locations. They answer different questions and can both play important roles during development.
Survey
Where are the boundaries, features, and relevant physical locations?
Site plan
How should the property be organized?
Geotechnical investigation
What subsurface conditions should the project team understand?
Engineering
How should proposed structures and site improvements respond to those conditions?
Earlier Information Can Lead to Better Decisions.
The appropriate timing depends on the project. Ideally, the team understands significant subsurface conditions early enough for the findings to inform foundation design, site preparation, engineering, budgeting, and construction planning. Where possible, proposed building locations should be sufficiently developed so testing can be targeted appropriately.
Each Step Gives the Next Professional Better Information.
01 — Understand the property
Boundaries, access, topography, drainage, existing conditions, and development goals.
02 — Develop the site plan
Determine where structures, roads, infrastructure, and future development may belong.
03 — Develop the concept
Establish approximate structures, layouts, sizes, and project requirements.
04 — Investigate site conditions
Coordinate appropriate surveys, geotechnical investigation, wastewater evaluations, and other required studies.
05 — Engineer & document
Appropriate licensed professionals use available project and site information to develop technical documents.
06 — Price & build
Contractors have better information for establishing scope, pricing, and construction methods.
Good development is a sequence of informed decisions.
What a Geotechnical Report Does Not Do
A geotechnical investigation does not eliminate all construction risk. Subsurface conditions can vary between test locations, groundwater and moisture conditions can change, and unexpected conditions can still be encountered during construction. A geotechnical report should be interpreted and used by the appropriate design and construction professionals within the scope for which it was prepared; it is not a guarantee of site conditions.
Know More About the Property Before You Build on It.
Developing rural property means understanding more than what can be seen from the surface. The site plan helps establish where development should occur. Conceptual design helps define what should be built. Geotechnical information helps appropriate professionals understand the ground that will support it. Together, these early planning steps provide better information for engineering, budgeting, contractor bidding, and construction.
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