Rochester's ground shifts with the seasons. The freeze-thaw cycles that chew up I-490 every March also alter near-surface soil structure in ways that a desk study simply won't catch. Glacial Lake Iroquois left behind a layered deposit of glaciolacustrine silts and clays punctuated by deltaic sands, and the contact between those units can vary by several feet across a single city lot. Running an SPT program here means penetrating those transitions with repeatable blow-count data. We mobilize a CME-75 rig with an automatic trip hammer calibrated to ASTM D1586, splitting spoon sampling at 5-foot intervals or at every stratum change. The N-value profile that emerges gives you a direct read on relative density in the sand lenses and consistency in the clay layers, feeding directly into bearing capacity equations under the IBC. For sites near the Genesee River gorge, where valley-wall colluvium masks bedrock depth, we often pair the SPT with seismic refraction to flag the top-of-rock before auger refusal surprises the drilling crew.
An SPT refusal at 22 feet in Rochester's drumlin till doesn't mean bedrock—it often means a boulder train; recognizing that saves half a day of misdirected coring.
Questions and answers
What does an SPT boring program cost for a typical Rochester commercial lot?
For a two-borehole program to 30 feet depth with standard sampling, the range runs US$540 to US$680 per borehole, including mobilization within Monroe County, hollow-stem auger drilling, split-spoon sampling, and a PDF boring log with corrected N60 values. Sites requiring traffic control on Monroe Avenue or extra depth due to deep fill will shift the upper end of that bracket.
How deep do you typically have to drill in Rochester to reach competent bearing?
It depends entirely on the landform. In the downtown core along Main Street, competent glacial till or bedrock often appears between 15 and 30 feet. Out in the Chili-Ogden area, where glaciolacustrine silts dominate, we have logged 60 feet of soft material before hitting anything drillable. We always recommend at least one boring that penetrates 10 feet into refusal material to confirm you are not sitting on a boulder.
How do you handle SPT refusal on boulders in the drumlin fields?
When we encounter refusal at an unexpected depth, we log the blow counts that led to it, offset the borehole by 5 feet, and redrill. If refusal repeats at the same approximate elevation, we classify it as probable bedrock and switch to a core barrel. If the second hole passes through, we flag a boulder and continue sampling. The distinction matters for pile design.
Do you provide N60 corrections or just raw N-values?
Both. Every log we issue includes the raw N-value and the corrected N60, with a footnote describing the hammer energy ratio used for correction. We calibrate our hammers to ASTM D4633 annually and can provide the calibration certificate upon request. For liquefaction studies, we also report (N1)60 normalized to 1 atm overburden.
Can you perform SPT borings in limited-access sites, like between two existing buildings?
Yes. We run a compact CME-45 track rig that fits through a 36-inch gate and can operate with 12 feet of overhead clearance. For interior drilling, we switch to a portable tripod setup with a safety hammer, though the energy calibration differs and we note that on the log.
