Boise sits on a geological patchwork that changes fast — you can go from coarse gravels near the Boise River to dense basalt float within half a mile. Standard drilling can be slow and messy in those cobble-rich lenses, which is why CPT has become a go-to here for stratigraphic profiling. The cone pushes through softer alluvium cleanly, giving us continuous tip resistance and sleeve friction data in real time. When the probe hits refusal on basalt or a thick gravel stringer, you know exactly where that transition sits, no guesswork. We run the rig on commercial lots in the Bench, warehouse pads out by the airport, and multi-story footprints downtown where space is tight. Pairing CPT data with a few test pits helps verify refusal depth in gravelly zones, and when you need dynamic properties we add MASW to tie shear-wave velocity to the same profile.
Continuous cone data catches thin clay seams and loose sand lenses that an SPT spoon skips right over — and in Boise's layered alluvium, those seams control settlement.
Our approach and scope
Local ground factors
One pattern we see across Treasure Valley jobs is a thin gravel stringer at 8 to 12 feet that stops a standard cone cold — and inexperienced operators mistake refusal for bedrock. That gravel is usually just a channel lag sitting on softer silts, and you can push through it with a pre-drill or a thicker push rod. Missing what lies underneath means you never see the loose sand lens at 18 feet that could liquefy under a 2,475-year seismic event. Downtown, where the water table sits only 6 feet down in spring, CPT pore pressure readings catch zones where excess pressure builds fast — a red flag for cyclic softening in silty soils. We also see a lot of fill on old orchard land along the Bench: uncontrolled, variable, with buried organic pockets. A cone refusal map across the footprint tells you where that fill transitions to native material without guessing from three borings spaced 80 feet apart.
Relevant standards
The analysis adheres to ASTM D5778-20 for CPT logging and reporting, IBC 2021 and ASCE 7-22 for seismic site class and liquefaction screening, Robertson and Cabal (2015) for soil behavior type classification, and Boulanger and Idriss (2014) for CPT-based liquefaction triggering evaluation.
Other technical services
Stratigraphic CPT soundings
Continuous tip, sleeve, and pore pressure logs to refusal or target depth, with real-time soil behavior type classification.
Pore pressure dissipation testing
Stop-and-hold tests at clay and silt contacts to estimate coefficient of consolidation for settlement rate calculations.
Liquefaction screening package
CPT-based cyclic resistance ratio profiles using Boulanger & Idriss (2014), mapped to IBC site class and design ground motions.
CPT-boring correlation suite
Parallel CPT soundings next to SPT borings to calibrate local soil behavior type charts with lab index testing.
Typical parameters
Common questions
How deep can a CPT go in Boise soils before hitting refusal?
It depends block by block. In river terrace silts and sands, 60 to 80 feet is common. On the Bench or near the foothills, basalt float and dense gravels can stop the cone at 10 to 20 feet. We often pre-drill through the upper gravel cap so the cone can profile the softer soils underneath.
What does CPT cone penetration testing cost per sounding in the Treasure Valley?
Can CPT data replace borings for foundation design in Boise?
Partly — CPT gives you continuous stratigraphy and direct bearing estimates in sands and silts, which covers a lot of Treasure Valley sites. But you still need physical samples to check gravel gradation or run Atterberg limits on clays, so we typically pair CPT with a few targeted borings rather than rely on cone data alone.