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ROCKFALL HAZARD AND EVALUATION METHODS, THE GEORGETOWN INCLINE, COLORADO
Road cuts and natural outcrops high above the interstate generate rockfall along this segment. These outcrops consist of the metamorphic Idaho Springs Formation with intrusions of Silver Plume Granite. Glacial activity carved and shaped the present landscape, leaving oversteepened slopes through which the highway system now stretches.
The conditions causing rockfall were determined in an attempt to select appropriate mitigations measures to reduce the risk of rockfall affecting motorists along the Georgetown Incline. The conditions causing rockfall fall into 2 categories, one occurs when rockfall is controlled by structural conditions, and the other occurs when rockfall is controlled by erosion. The Colorado Rockfall Hazard Rating System and a modified Q-rating system were used to evaluate the conditions causing rockfall along the Georgetown Incline. Results of these systems show a high rockfall hazard rating for the area. A quantitative method of calculating the likelihood, consequence and risk of rockfall affecting a vehicle was performed as a part of this evaluation.
The results of these evaluations, along with cost considerations were used to determine appropriate mitigation measures and to prioritize locations for mitigation. Protection, stabilization, and avoidance measures were considered for segments with high rockfall ratings. Due to the size, unpredictability, and rockfall mechanisms of the site, protection methods are the most feasible for the Georgetown Incline. Currently, $1,000,000 has been allotted for mitigations efforts. Mitigation to this point includes construction of 2 rockfall fences, rock scaling and installation of draped wire mesh. Additional scaling and installation of draped wire mesh is scheduled for the summer of 2002.