A soil boring is a narrow hole drilled into the ground so an engineer can recover soil samples and measure how dense each layer is below the surface. It's the main field test behind foundation design in Florida, and it's how engineers see what is actually under a lot instead of guessing at the surface. A single soil boring test usually takes a few hours, and the information it produces shapes the foundation design and sometimes the decision to buy the property at all.
What A Soil Boring Tells An Engineer
Florida soil changes fast with depth. A lot can have clean sand on top, a layer of organic muck a few feet down, clay below that, and limestone deeper still. None of that shows at the surface.
Each boring gives a vertical profile of one spot on the site. As the hole is advanced, the crew collects samples at regular intervals and measures how much effort it takes to drive a sampler through each layer. Put several borings together, and the engineer can map how the layers run across the property and where the weak zones are.
A geotechnical boring shows how strong the soil is at the depth the foundation will bear on and how much it may settle under load. It also locates the water table and flags any soft, organic, or loosened zones that need to be removed or improved before construction.
Why Soil Borings Are Ordered
Most soil borings in Florida are tied to a specific decision. Common reasons include:
- New construction or a structural addition, where the building department or structural engineer needs a sealed report
- Settlement, cracking, or ground depressions, where borings show if the cause is poor fill, a leaking line, or sinkhole activity
- Stormwater permits, which depend on the seasonal high water table and soil permeability
- Environmental due diligence, when a Phase I finds a possible release and soil or groundwater has to be sampled
Bechtol's Florida geotechnical engineering work starts with borings for almost every one of these, and the same field data often supports several of them at once.
People sometimes ask if they can test soil themselves. A shovel or a hand probe can show surface sand, but it can't measure density at depth, and building departments and lenders look for a report sealed by a licensed engineer.
What Happens During A Soil Boring Test
The engineer sets the boring locations and depths before anyone mobilizes. Bechtol places borings on the site plan and records GPS positions so each log ties back to an exact spot.
On the day of drilling, the crew sets up a rig matched to the site. Bechtol runs five drilling rig types, so tight residential lots and wetlands can still be drilled, along with open water and building interiors. The hole is usually advanced with hollow stem auger or mud rotary drilling, depending on how well the ground holds open.
At set intervals, the crew drives a split-barrel sampler using the standard penetration test (ASTM D1586) and records the blow counts. In clay layers, the engineer may call for a thin-walled tube sample (ASTM D1587), which is pushed rather than driven so the soil keeps its natural structure for lab testing. For shallow checks or tight access, a hand auger or probe may be enough.
Groundwater is recorded when it's first encountered and again after the level stabilizes. On a typical commercial site, field work takes one to three days.
What Comes Out Of A Soil Boring
Soil Samples
Every sampled interval produces a jar or tube of soil that goes back to the lab, labeled by boring and depth. These samples are what the lab classifies and tests, so they matter as much as the hole itself.
The Boring Log
The soil boring log is the field record for one hole. A Bechtol boring log shows SPT N-values, soil descriptions using the Unified Soil Classification System (ASTM D2487), sample recovery, and groundwater levels, all plotted by depth. Structural engineers read these logs directly, so consistent classification matters.
A low N-value flags loose sand or soft soil. A sudden drop in blow counts, fluid loss, or rods sinking under their own weight can point to a raveled zone above a limestone cavity.
Laboratory Testing
Samples go to Bechtol's in-house laboratory in DeLand. Typical tests include moisture content, grain size, Atterberg limits for clays, and organic content. Thin-walled tube samples can be used for consolidation and strength testing, which tells the engineer how much a clay layer will compress under a new load.
How Many Soil Borings A Site Needs And How Deep They Go
There's no standard count. The number and depth follow the structure and the loads it will put on the ground. A single-family residence may need two borings. A mid-rise building needs a grid across the footprint, extended below the depth where the building's weight still affects the soil.
For shallow foundation commercial work in Florida, borings commonly run 20 to 50 feet deep. Deep foundations and sinkhole work go much further. On Bechtol's sinkhole evaluation at Wiley Nash, borings ranged between 48 and 115 feet to reach the limestone and locate a solution cavity. The deepest boring on Bechtol's record is 137 feet, drilled in Ocala.
Site conditions can add borings too. If the first round finds muck or an unexpected soft zone, the engineer may add holes to define how far it extends.
Environmental Soil Borings And Monitoring Wells
Some borings have nothing to do with bearing capacity. Environmental borings look for contamination, so samples are screened in the field and selected intervals go out for chemical analysis.
During a Phase II environmental site assessment, borings are placed at a suspected source, such as a former fuel tank, and along the path contamination would likely travel. Some of those holes are finished as monitoring wells so groundwater can be sampled and tracked over time. Bechtol's crews drill most Phase II borings and handle well installation and sampling.
How Boring Results Shape The Geotechnical Report
The logs and lab results are raw data. The engineer turns them into bearing pressure, settlement estimates, foundation depth, and earthwork criteria such as undercut depth and target compaction. All of that is documented in the geotechnical report, along with the boring location plan and the logs themselves, and sealed by a licensed Florida PE.
Typical timing is one to two weeks to mobilize, one to three days in the field, and seven to ten business days for the sealed report.
Scheduling Soil Borings For Your Florida Project
A soil boring is the most direct way to learn what sits under a site. Samples are recovered at set depths and logged with N-values and groundwater levels, then classified and tested in the lab. The number and depth of borings depend on the structure and the ground, and the results feed the foundation and earthwork recommendations in a sealed report.
Bechtol Engineering and Testing provides geotechnical drilling services and soil boring tests across Florida, with engineers directing every boring and samples tested in its own DeLand laboratory. For residential soil investigations, commercial geotechnical investigations, or environmental borings for a Phase II, call 386.734.8444 or send your site plan to request a proposal.
