US 20 Bridge Piers
The Oregon Department of Transportation (ODOT) let a design-build contract to realign an 11-mile segment of Highway 20 in the Oregon Coast Range. The alignment involved soil and rock cuts up to 200 feet high, embankment fills up to 150 feet high and several bridges, all of which traverse ancient landslide terrain. During construction, ODOT retained Cornforth Consultants (CCI) to evaluate the impact of proposed cuts and fills on the discovered landslides and the design approach to landslide stabilization. CCI provided ODOT with landslide modeling, stability analysis and mitigation expertise to further understand the potential impact of construction on landslide stability.
CCI 's supplemental investigation work included over 60 instrumented geotechnical borings; down-hole imagery; laboratory testing of soil, rock and shear zone materials; interpretation of imagery; and geologic reconnaissance. Geotechnical instrumentation to investigate landslide conditions included slope inclinometers, standpipe piezometers and vibrating wire piezometers. Geologic models of the subsurface conditions were then conceptualized and further developed to enable analysis of potential landslide instability.