ASTM D1586-18 governs SPT execution across the United States, but in Casper Wyoming the standard takes on added weight. The city sits at 5,120 feet elevation on the North Platte River, underlain by Quaternary alluvium, terrace gravels, and interbedded clays that shift dramatically over short distances. Contractors unfamiliar with the basin’s depositional history often misinterpret refusal depth or assume uniform bearing, only to encounter bouldery lenses or groundwater at 12 to 18 feet below grade. A properly hammered split-spoon sampler with calibrated energy delivers N-values that feed directly into IBC Chapter 18 bearing-capacity calculations. When shallow refusal suggests bedrock, but the profile is actually cemented gravel — common on Casper’s west side near the river terraces — the SPT log prevents overconservative foundation sizing. For sites near Alcova or along the I-25 corridor where soil variability increases, we often pair the SPT program with a CPT investigation to capture continuous tip resistance and pore-pressure data across transitions that the split-spoon might miss.
Corrected N60 values from Casper’s alluvial terraces often reveal 25–40% higher liquefaction resistance than raw field blows suggest when energy calibration is applied.
