The hydraulic rig anchors itself against the truck's weight, and the hardened steel cone begins its steady push into the Billings subgrade at a constant 2 cm/s. We monitor the digital readout as tip resistance and sleeve friction translate in real time into a stratigraphic profile of the Yellowstone Valley deposits. Unlike standard drilling methods that retrieve disturbed samples from discrete depths, the CPT string captures a continuous log of soil behavior, which is critical when delineating the interbedded silts, sands, and the underlying Colorado Group shale that defines much of the subsurface beneath Billings. Before placing footings on the South Side or designing deep excavations near the Rimrocks, the data from a CPT test provides the near-continuous profile needed to catch thin, problematic lenses that a conventional boring might miss entirely.
A single CPT sounding in the Billings area can replace three or four standard borings when the goal is to map stratigraphic continuity across a site.
