The most expensive mistake in Miami construction is not the SPT test. It is the excavation that floods because nobody checked the blow count at the water table. Miami sits on a razor-thin margin. The Biscayne Aquifer is just a few feet down. You hit it wrong and the whole site turns into a pond. That delays the job. That bleeds money. We run SPT tests that map exactly where the soil transitions from dense sand to soft limestone. The rig penetrates standard 18-inch increments. The hammer drops 140 pounds from 30 inches. The number of blows tells you everything. Builders across Dade County use this data to design dewatering systems, size footings, and avoid the kind of surprises that bankrupt a project. When you need CPT testing for continuous profiling in saturated zones, or a test pit to visually confirm the strata, we coordinate both from the same mobilization.
In Miami, the difference between 8 blows and 15 blows at 12 feet is the difference between a dry excavation and a flooded one.
Common questions
How much does an SPT boring cost in Miami?
A single SPT boring to 20 feet depth in Miami-Dade typically runs between US$600 and US$850. That includes the drilling crew, the split spoon sampling every 2.5 feet, field logging, and the final typed boring log with N-values and soil descriptions. Cost goes up if you need deeper borings, multiple boreholes, or specialized access like a limited-access rig for tight urban lots in Brickell or Coral Gables.
How deep do SPT borings need to go in Miami?
It depends on the foundation type and the site location. For a typical shallow foundation east of I-95, we usually drill to 20 or 30 feet. That gets you through the Miami Oolite into the underlying sand or Fort Thompson limestone. For deep foundations or sites near the bay with liquefaction concerns, we go to 50 feet or until we hit consistent refusal (N>50 for 18 inches). The Florida Building Code requires the boring depth to extend below all unsuitable layers.
What makes Miami SPT testing different from other regions?
The water table. In most of Miami-Dade, groundwater is at 4 to 6 feet below grade. That means half your boring is underwater. We use mud rotary or hollow-stem augers to keep the hole open and collect undisturbed samples below the water table. The other factor is the limestone—Miami Oolite is soft and porous, with cavities. You can lose circulation suddenly. Our drillers know how to case off the rock and keep the boring advancing.
How long does an SPT investigation take?
A single boring to 30 feet takes about half a day of field work. We mobilize the drill rig early, set up, drill, log, and demobilize. The lab work on the split spoon samples takes another 2 to 3 business days. You will have the draft boring logs within 3 to 4 days of the field work. A full geotechnical report with bearing capacity and settlement analysis takes about 7 to 10 business days from the date of drilling.
