D3 Rockfall Mitigation Project Interstate 15, Helena to Great Falls, Montana

摘要

Numerous rock slopes adjacent to Interstate 15 (1-15) between Helena and Great Falls, Montana have a history of hazardous rockfall activity requiring high levels of maintenance. The Montana Department of Transportation (MDT) is in the process of reducing the rockfall hazards in this corridor. In January 2011, MDT Geotechnical Section evaluated historical performance and existing conditions of the rock slopes in the corridor to develop rockfall ratings for prioritizing mitigation. MDT retained Landslide Technology (LT) of Portland, Oregon to conduct an independent rockfall evaluation of the corridor, and 15 sites were chosen for mitigation. LT developed conceptual mitigation options for each site. MDT selected mitigation options for development of final designs and divided the project into three phases to accommodate funding. Final design work began in 2014 and is ongoing. Mitigation includes slope scaling, rock bolting, draped mesh, rockfall attenuators, flexible rockfall barriers, and catchment area improvements via rock slope excavation. The development of temporary rockfall protection and traffic control designs was a significant challenge given the vital nature of the 1-15 corridor and MDT's requirement to perform the majority of the work, including scaling under live traffic. Construction of Phase 1 began in 2015 and was completed in June of 2016. Phase 2 began construction in the spring of 2016 and is projected to be completed by the fall of 2016. LT provided construction engineering (CE) services for Phase 1 and is currently providing CE on Phase 2. LT is developing final plans, specifications and engineer's estimate for the Phase 3 designs, which is currently projected to be let for construction in 2017. As with any design and construction project, several lessons have been learned on this project including items such as: unique nature observation of construction efforts for rockfall mitigation measures.