Eugene’s development along the Willamette River has always been shaped by its underlying geology—fertile floodplain deposits that make the valley productive also hide layers of loose, saturated silts and sands. When the city expanded outward from its 19th-century mill town core into areas like the Bethel-Danebo basin and the flatlands south of the Santiam Pass corridor, builders started encountering ground that behaves well under normal conditions but becomes a serious liability during a seismic event. The Cascadia Subduction Zone, roughly 100 miles offshore, is capable of producing a magnitude 9 rupture, and the Oregon Resilience Plan has identified Eugene as a community where unconsolidated alluvium poses a significant liquefaction hazard. Our soil liquefaction analysis combines site-specific SPT blow counts from spt-drilling with laboratory fines content and plasticity data to calculate the factor of safety against liquefaction at each critical layer, so structural engineers have defensible numbers for foundation design rather than generic assumptions.
Liquefaction isn't just about sand boils—in Eugene's interbedded silts, it's the loss of bearing capacity beneath footings that causes the structural damage most owners never anticipate.
