Running a drill rig across Sioux City's bluffs and bottomlands, you learn quick that the subsurface doesn't read the textbook. We've pulled up fat clays sitting right on sand lenses in the Floyd River floodplain, and dense loess that looks solid until you punch through a paleosol. A standard SPT can miss those transitions entirely. That's why our team pushes the CPT test cone through those tricky profiles—it gives us a continuous resistivity and tip resistance log, so the fuzzy boundaries between the Peoria Loess and the underlying glacial till actually show up. When a developer down by the Missouri River needs bearing data for a mat foundation in three days, not three weeks, this is how we deliver it.
A CPT log catches the thin silt seams between loess layers that a split spoon skips, which matters when you're designing for the Big Sioux's 100-year flood.
Local ground factors
We run a 20-ton truck-mounted penetrometer with a continuous hydraulic push system—no hammer, no augers, just a steady 2 cm per second through whatever Sioux City's geology throws at us. The risk isn't the clay; it's the gravel stringers left by the ancestral Missouri River. Hit a cobble at 40 feet and you can bend a cone or lose a pore pressure transducer if the operator doesn't back off in time. We swap cones on-site and recalibrate against a load cell before every test, because a zero shift in the sleeve friction reading will corrupt the entire soil behavior type classification. Saturated loess near the Perry Creek bridge can trap excess pore pressure around the cone face, so we run dissipation tests at multiple stops—skip that step and your undrained shear strength estimate is fiction, not data.
Common questions
How deep can you push a CPT in Sioux City's soil?
It depends entirely on what's underground. In the loess that blankets most of Sioux City's east side, we routinely reach 60 to 80 feet without refusal. Down in the Missouri River bottomlands, we've hit dense sand and gravel at 45 feet that stopped the cone. We always bring a pre-augered option for sites where the top few feet are fill or frost-affected, so we don't waste push capacity on disturbed ground.
Is a CPT cheaper than drilling a boring with SPT?
For a straight stratigraphic profile, CPT in Sioux City typically runs between US$160 and US$220 per hour on site, plus mobilization and data processing. A single CPT can log 100 to 150 feet in a day, while a drill rig might get two borings to 50 feet. The cone gives you a continuous record, not samples every five feet, so you're paying for resolution, not just depth. On a tight site with limited access, the truck-mounted rig also saves you the cost of a separate mud pan and cuttings disposal.
Does CPT replace soil borings, or do I still need both?
CPT doesn't retrieve a physical sample, so you can't run Atterberg limits or moisture content directly from the cone log. In Sioux City we pair a CPT sounding with at least one sampled boring to calibrate the soil behavior type classification with actual lab index tests. The cone tells you where the boundaries are and how continuous the layers run; the boring gives you the soil in your hand. For a foundation design on the loess-covered bluffs, that combination is hard to beat.
How fast can I get the CPT data after the test?
The raw cone data downloads the moment the last push rod comes out of the ground. We run the dissipation corrections and generate a preliminary log onsite, so the engineer walking the site with us sees the profile before we demobilize. The final report with SBTn classification, corrected tip resistance, and any liquefaction screening plots is typically in your inbox within two working days, faster if the project schedule demands it.
