Rockfall Mitigation at the Pillar Mountain Slide, Kodiak, Alaska

摘要

The Pillar Mountain slide in Kodiak, Alaska, has been a site of persistent rockfall hazard for several decades. At the base of the slide, Rezanof Drive traverses the site. Rezanof Drive is a critical lifeline representing the only road linking the community of Kodiak to the northeast with the airport and U.S. Coast Guard Base to the southwest. In addition, piers are located on the downslope side of Rezanof Drive. The slide is located on a southeast-facing slope. The maximum width of the slide is approximately 1,400 feet, and the maximum height of the slide reaches to approximately 760 feet elevation. Steep bedrock cliffs form a complex geometry to the crown and flanks of the slide. The main body of the slide consists of a talus slope. Pillar Mountain is composed of argillite that steeply dips into the slope. The bedrock is part of the accretionary prism complex associated with the Aleutian subduction zone. The bedrock is mantled by loess and vegetative mat. As part of a Highway Safety Improvement Project, the Alaska Department of Transportation and Public Facilities (ADOT&PF) completed a rockfall hazard mitigation project with the primary objectives of reducing rockfall hazards associated with the slide, reducing maintenance efforts associated rockfall cleanup, and maintaining traffic flow along Rezanof Drive. This paper focuses on providing a historic review of the slide, a detailed look at the field investigation and the use of Light Detection and Ranging (LiDAR) elevation data to characterize the slide, and discussion of the rockfall modeling completed to support the development of rockfall mitigation design alternatives. The results of these efforts supported the selection and ultimate construction of an innovative, mechanically-stabilized earth (MSE) rockfall berm to intercept rockfall and protect travelers and workers along Rezanof Drive.