A mixed-use development near the old milling district hit refusal on a dense boulder train at 35 feet. The original plan called for shallow footings. The site sat over a buried valley filled with compressible organic silts—something we see often when you get close to the Mississippi River corridor. In Minneapolis, the subsurface is never uniform. Glacial advance and retreat left behind a chaotic sequence of stiff till, outwash sands, lacustrine clays, and occasional cobble layers. The design of a pile foundation must account for that vertical variability. We often pair our pile foundation design with a CPT test to get a continuous profile of tip resistance and sleeve friction before selecting the final pile type and length.
In Minneapolis, the difference between a 40-foot pile and a 90-foot pile often comes down to a single layer of soft lacustrine clay that only a CPT will reveal.
