Minneapolis subgrades don't forgive guesswork. The local glacial till and lacustrine clays can lose half their bearing capacity with just a small moisture increase. We've pulled samples from sites near Lake Nokomis that tested CBR 12 at optimum moisture, then dropped below CBR 4 after a 96-hour soak. That's the difference between a 6-inch aggregate base and a 14-inch section with stabilization. The grain-size distribution of these fine-grained tills often points to frost susceptibility, but the CBR value is what actually sizes the pavement layers. Our lab runs the soaked CBR per ASTM D1883 on remolded specimens compacted at the Proctor density you'll hit in the field. No generic correlations. We test the material your contractor will actually place, using the same compactive effort your spec requires. For city street reconstructions in Minneapolis, that soaked value is often the controlling number in the MnDOT flexible pavement design equation.
A 96-hour soaked CBR on Minneapolis glacial till can be half the unsoaked value. That single number changes your entire pavement section.
