The most common mistake we see on Eugene construction sites is relying on lab permeability values from disturbed samples. You get a clean Shelby tube from a Willamette silt, run a falling-head test in the lab, and the number looks reasonable. Then the excavation hits interbedded gravels and the inflow triples what the model predicted. The Lefranc and Lugeon tests exist precisely to avoid this disconnect. Eugene sits on a complex sequence of Quaternary alluvium, Missoula Flood deposits, and weathered volcanics of the Fisher Formation—materials whose in-situ hydraulic conductivity can vary by three orders of magnitude across a single project site. Running a field test captures the real mass permeability, including secondary porosity from root casts, desiccation cracks, and gravel lenses that no lab specimen ever represents. We combine these tests with CPT soundings when we need a continuous stratigraphic profile to select the proper test intervals, and with grain size analysis to correlate field results with soil classification for long-term dewatering design.
A Lugeon test does not just give you a permeability number—the shape of the pressure-flow curve reveals whether the rock mass will dilate, wash out, or self-heal under injection.
