On a recent project off Capital Circle, the surface looked like standard sandy loam, but the excavation revealed buried organic silt at just four feet. That is Tallahassee geology. The city sits on a mix of Miocene Hawthorn Group sediments—clayey sands, silts, and occasional limestone stringers—making exploratory test pit investigations essential before any foundation design. A test pit lets the geotechnical engineer walk right up to the profile, measure strata thickness, and collect undisturbed bulk samples for index testing. Logging the sidewalls gives immediate insight into moisture conditions, root penetration, and the real depth of the Hawthorn clay cap. For shallow footings, retaining walls, or pavement subgrade, the test pit remains one of the most direct and cost-effective reconnaissance methods in Leon County.
A four-foot-deep test pit often reveals more about Tallahassee’s Hawthorn Group stratigraphy than a dozen SPT spoon samples.
Our approach and scope
Local ground factors
A notable hazard in Tallahassee is the presence of shallow, perched groundwater tables and soft Hawthorn Group clays that lose strength when wetted. Without a test pit excavation, a contractor can unknowingly place a footing on desiccated crust that sits above saturated, low-strength material. We have seen that pattern repeatedly in the Killearn Estates area, where surface clays look firm in dry weather but soften significantly after seasonal rains. A test pit exposes that transition zone. It also reveals undocumented fill—common on older lots near downtown—and allows the engineer to specify removal or stabilization before construction begins. The IBC requires that footings bear on undisturbed, competent soil; a visual inspection of the pit floor remains one of the simplest ways to confirm that requirement.
Reference standards
IBC Chapter 18 (Soils and Foundations), ASTM D2487 (Unified Soil Classification System), ASCE 7 (Minimum Design Loads), OSHA 29 CFR 1926 Subpart P (Excavation safety)
Additional services
Shallow Foundation Assessment
We log test pit sidewalls to identify the bearing stratum, measure its consistency, and carry out presumptive bearing values per IBC Table 1806.2.
Pavement Subgrade Evaluation
Bulk samples from the pit are tested for grain-size distribution and plasticity, then correlated with CBR road design parameters for flexible or rigid pavement sections.
Retaining Wall Site Reconnaissance
Test pits excavated behind proposed wall alignments reveal the retained soil profile, drainage characteristics, and any slickensided Hawthorn clay that demands special design attention.
Typical parameters
Questions and answers
How deep can you excavate a test pit in Tallahassee?
With a compact excavator, we routinely reach 10 to 14 feet in stable soils. In sandy Hawthorn Group formations near the Cody Scarp, OSHA shoring requirements may limit depth to about 8 feet unless a stepped excavation is used.
What does an exploratory test pit cost in Tallahassee?
For a standard 8-foot-deep pit with logging, sampling, and backfill, expect a range from US$520 to US$850 depending on access constraints and the number of pits on the same site.
Do you need a permit to dig a test pit in Leon County?
A site disturbance permit is generally not required for temporary exploratory excavations. However, we always contact Sunshine 811 for utility locating at least two business days before breaking ground.
Can you collect undisturbed samples from the pit floor?
Yes—block samples, thin-walled Shelby tubes pushed into the floor, or carefully trimmed bulk bags all work well. The method depends on soil type and the lab testing program specified by the design engineer.
How do you backfill the test pit after logging?
We backfill in lifts not exceeding 12 inches, compacting each lift with a vibratory plate or rammer. In landscaped areas, we restore topsoil and sod to match existing grade. More info.