Hwy 101 Johnson Creek Landslide Investigation
Landslide Technology was retained by the Oregon Department of Geology and Mineral Industries (DOGAMI) to investigate the Johnson Creek Landslide, located 3½ miles north of Newport, Oregon. The project is a collaborative effort of DOGAMI and the Oregon Department of Transportation (ODOT) to research causative factors for coastal landslides impacting US Highway 101. This research project is aimed at understanding the continued slide movements and determining remedial options that are appropriate with regard to environmental, geotechnical, and economic factors. The landslide is being studied as a typical example of a large, translational landslide in seaward dipping Tertiary sedimentary rocks along the Oregon coast. Data and interpretations from this investigation will be incorporated into one or more DOGAMI publications. The US Geological Survey (USGS) has been monitoring the slide real time at USGS.gov.
Landslide Technology developed a field investigation program with extensive instrumentation consisting of slope inclinometer installations, vibrating wire piezometers with automatic data collection devices, and coaxial cables for Time Domain Reflectometry measurements. A rain gage was installed on the site to acquire localized precipitation data.
Landslide Technology evaluated slope stability using a two-dimensional, limit-equilibrium analysis, including the effects of several contributory factors for the ongoing movement of the Johnson Creek Landslide. This analysis incorporated high quality geotechnical data on landslide geometry, hydrology, and correlation of movement to such factors as rainfall, groundwater pressure changes, seasonal deposition/removal of beach sand, and bluff erosion at the toe. Conceptual remedial options were developed, along with opinions regarding effectiveness, constructibility and estimated costs.