On the morning of October 15, 2012, a massive rockfall buried both lanes of US Route 4 in Fort Ann, New York, near the Vermont border. After it was reported that a car might be buried under the rock pile, a State Police helicopter equipped with thermal imaging equipment was brought in, and it was determined that there was no vehicle present. Cleanup operations commenced and over the next 48 hours, the New York State Department of Transportation's (NYSDOT) emergency contractor removed over 1,700 cubic yards of fallen material. Engineering Geologists from the NYSDOT evaluated the remaining rockslope and determined that the slope was stable enough to temporarily reopen the road. However, they also recommended that the slope be remediated quickly and not be allowed to go through another winter of destabilizing freeze-thaw cycles and high groundwater conditions. Due to the tight time frame, it was decided to remediate the slope under the existing emergency contract. For the first time at NYSDOT, airborne and terrestrial LiDAR (Light Detection And Ranging) were combined with traditional ground survey and photogrammetric mapping to create a DTM (Digital Terrain Model) of the rockslope and the surrounding area. This DTM proved invaluable in the design of the remediation of the slope and for estimating rock removal quantities for the immediate cleanup and new rockslope construction. This paper will discuss the rockfall and the design and construction of the new slope under the emergency contract.
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