Irving sits squarely on the Eagle Ford Shale formation, which weathers into highly plastic, expansive clays. Anyone who has driven Loop 12 after a wet winter knows what volume change does to asphalt: longitudinal cracking, alligator patterns, and rutting that reappears two seasons after a mill-and-overlay. A CBR road subgrade assessment run on undisturbed Shelby tube samples tells us whether the native subgrade can carry traffic loads or whether we need chemical stabilization before placing the asphalt. When the plasticity index pushes past 25 — not uncommon near the Trinity River floodplain — we pair standard Proctor curves with triaxial resilient modulus data to calibrate the AASHTO 1993 structural number so the pavement section actually matches Irving's moisture regime. Our lab runs ASTM D1883 soaked CBR on every project because a dry-weather number is meaningless here; the clay swells, loses strength, and that is exactly when the pavement fails.
Soaked CBR values in Irving's Eagle Ford clay routinely drop below 3 percent — designing with dry-weather numbers guarantees a premature failure.
