Stabilization of a Rock Cut with Ore-grade Uranium Mineralization

摘要

During 1988, the New Hampshire Department of Transportation (NHDOT) remediated a 100-foot high rock slope located on Interstate 89 near Lake Sunapee in New London, New Hampshire (N.H.). The stabilization work was part of a larger roadway project and consisted of removing 100,000 cubic yards of potentially unstable rock, which was dangerously close to the northbound lane. This site was unique in that the granite rock contained anomalous concentrations of uranium and thorium. In 1968-69, high concentrations of secondary uranium minerals were found in the rock during the initial excavation for this roadway cut. The uranium minerals generally occurred as fracture filings and coatings along east-west trending, steeply dipping joint surfaces. After construction, the highly soluble uranium minerals in the granite rock migrated downward when the water table dropped and were re-deposited at lower elevations in the rock cut. Due to the naturally occurring radioactive minerals in the rock, a Health and Safety Plan was implemented to protect the construction workers and the general public. The Plan included sampling, testing, on-site monitoring and training of personnel involved in the construction phase of the project. This is the first time in the United States that health and safety precautions were implemented on an engineering project for the removal of uranium bearing rock. The challenges were formidable which included presplitting the entire height of the rock slope in a single lift, locating and designing a disposal site for the uranium rich rock, and protecting the workers and public.