County Road 31 Rockfall Mitigation

larimer county, colorado

AVI Professional Corporationretained Lithos Engineering to provide construction management services for the rockfall mitigation project along County Road 31.  A large expansion crack was observed parallel to the undercut rock face that overhung County Road 31 adjacent to Carter Lake. Larimer County closed the road immediately to reduce rockfall risk to the travelling public. During construction, Lithos was on site approximately four hours per day to document daily activities and assist the Contractor in identifying the limits of rock removal and scaling. Approximately 250 linear feet of the overhanging rock was removed. An additional isolated rock outcrop to the north that also posed a rockfall risk was removed.  Following removal of the overhanging rock, the outcrop was scaled further to remove additional hazardous material. A buttress of removed material was placed against the undercut shale layer to protect against further erosion. A trench was also cut at the base of the buttress to promote drainage away from the outcrop. 

 Lithos staff documented the approximate volume of removed material as well as the condition of the remaining outcrop face. More material was removed than anticipated, primarily due to the exposure of additional expansion cracks during mechanical scaling activities. Excess material was hauled to a quarry site managed by Larimer County located just north of the project location. The completed site consisted of a scaled rock outcrop and rock buttress. The project has been successfully completed, and County Road 31 has re-opened to the travelling public.


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