I-70 Georgetown Incline, Georgetown, Colorado

Colorado Department of Transportation

The Georgetown Incline Rockfall Mitigation Project involved evaluation and recommendations of potential rockfall mitigation methods at select locations along I-70 at the Georgetown Incline. Many accidents, injuries, and fatalities have been reported due to rockfall events originating on the Georgetown Incline.

Yeh and Associates gathered geologic hazard data using existing information and by conducting a field reconnaissance. Outcrops and rockfall chutes were mapped and evaluated for potential rockfall. Many areas were identified as areas of needed mitigation. These areas were evaluated using the Colorado Rockfall Hazard Rating System (CRHRS), the Modified Q-system rock mass rating system, field observations, aerial photos, and geologic maps.

The Colorado Rockfall Simulation Program and Roc Science's RocFall software were used to evaluate rockfall behavior and in determining an appropriate means of mitigating the rockfall hazard. Risk analysis was also evaluated using probabilistic methods, which considered initiating events such as rainfall, snowmelt, wind, etc., the impact significance, potential number of fatalities, and amount of rockfall. An annual probability of occurrence was then developed.

Potential areas of mitigation were identified and recommendations on mitigation methods were provided. Georgetown incline mitigation options included: barriers, rock reinforcement, rockfall containment, rock removal, fences and attenuators, rock sheds, and tunnels. The mitigation areas and methods were selected based on feasibility, effectiveness, and cost.

Two sites on the Georgetown Incline were analyzed for mitigation. Mitigation methods selected were wire rope net rockfall fences with draped cable net and scaling. The fences are flexible systems that absorb the energy of the falling rock and either stop or significantly reduce the velocity of the rock. The draped cable net captures any rocks not stopped by the fence and keeps the rocks close to the slope face as they travel down the slope and into a ditch or catchment area. Rockfall fence plans and provisions were provided for the initial construction of the project. Yeh and Associates provided support and construction inspection during installation of the fences.

Yeh's key personnel who worked on the project included Rick Andrew who was the principal in charge and project manager and Ben Arndt was the project engineer for the design and installation.