Interstate Technical Group on Abandoned Underground Mines
Fourth Biennial Abandoned Underground Mine Workshop
Abstract: Virginia Department of Transportation
Stanley L. Hite
On Friday February 27th, 1998 a depression formed in the outside travel lane of Eastbound Route 250- a 40,000 ADT 6-lane highway. The resulting 3-vehicle accident led to the discovery of a complex of abandoned underground mines below three of the travel lanes, a right-turn lane, and a portion of the grass shoulder. The site lies within the Deep Run Mining District, in Henrico County , Virginia where Huguenot settlers produced the first commercial coal in what would be the USA, in 1748. This area is in a faulted separation from the main Richmond Basin, which is a Triassic half-graben developed along one of the east-coast cataclastic zones. Attempts to better delineate the mines included micro gravity and pattern drilling of 50 ft deep borings at a staggered l0 ft interval in each lane. Once the workings were defined, the repair option chosen was installation of cast in place pressure grouted columns. The 30-inch diameter ballistic nylon bags were adapted from the Fabriform pile jacket construction process. A total 45 columns were installed over approximately 3 weeks, working four nights per week. The cost of the grouting contract was approximately $79,000 and the overdrilling (including stand-by time) and management of the grouting contract came to $18,300. The grand total cost for the repair alone was $96,800. This does not include the pattern drilling, microgravity survey, traffic control, lighting, or project supervision that the department provided.