We keep seeing the same mistake on Fargo job sites: a contractor runs a nuclear gauge on fat clay, gets a reading they trust, and then the pavement fails two winters later. The Red River Valley clays don't lie to a sand cone. That's the whole reason we still run ASTM D1556 field density tests here—there's no dielectric constant correction that fixes what our lacustrine silts do to indirect methods. When the Corps of Engineers specs a job near the Sheyenne diversion, they want a sand cone report, period. Pairing it with a Proctor test gives you the relative compaction number that actually holds up in court. And if we're checking subgrade for a heavy-load floor, we often recommend a CBR test beforehand to correlate density with bearing capacity.
A sand cone test in Fargo clay is a direct measurement—no nuclear calibration curve can compensate for montmorillonite's bound water error.
