Arizona Inn Landslide Mitigation
The Arizona Inn Landslide lies on the southern Oregon Coast along US101, near the town of Gold Beach. In the late 1990s, a vertical drainage gallery was installed near the center of the landslide consisting of an approximately 200-foot-deep shaft with arrays of horizontal drains to stabilize the landslide. In January 2023, the landslide moved over 20 feet, completely shearing the existing shaft. Delve Underground designed a new shaft to replace the original and restore active drainage to the landslide.
- Mitigation of a major landslide impacting a critical highway link on Oregon Coast.
- Construction of a 200-foot-deep, 20-foot-diameter shaft and installation of approximately 60,000 linear feet of horizontal drains.
- Final Design, Geotechnical Investigation, Initial Ground Support, Cost Estimating, and Geologic and Geotechnical Evaluations.
Scope of Work
The Oregon Department of Transportation retained Delve Underground to design mitigation measures to restore the landslide drainage system. Following an alternative analysis that included reestablishing the previously damaged drainage shaft, the team selected a mitigation approach consisting of a new shaft and horizontal drain array located outside of the active landslide. Services provided include subsurface field investigation and instrumentation of the slide, geotechnical and structural design of the shaft, and hydrological modeling of the effectiveness and density of the proposed drainage system. Delve Underground prepared contract documents for the project and provided engineering services during construction.
Challenges & Innovations
The project was delivered in a compressed timeframe to minimize the risk of continued landslide movements impacting US101. Design of this landslide mitigation included subsurface exploration and interpretation of complex geology and a detailed evaluation of the effectiveness of the horizontal drainage system as well as the constructability of the proposed shaft. The selected shaft site and shaft design simplified construction and reduced risk and safety hazards during construction.
