THE HISTORY AND HERITAGE OF
CIVIL ENGINEERING IN VIRGINIA
The Big Walker Tunnel (1967-1972)
The tunnel through Big Walker Mountain, on Interstate 77, with the 11.4 miles of roadway itself in approaches and adjacent roads, were, at the time of the letting of contracts involved, the most expensive single project ever taken on the interstate system in Virginia. Contract for the tunnel was let in September 1967 and all of the completed work included was dedicated by ribbon-cutting ceremonies on June 23, 1972. The 23 miles of I-77 between Wytheville and Bland cost almost $50,000,000 and now presents a much shorter route, straighter, wider and safer, and constitutes an important link in the Great Lakes to Florida Highway. It has been characterized by the president of this latter Highway Association as "one of the most important projects of the 20th Century for Southwest Virginia".
Preliminary engineering studies for the project were made by Brokenborough & Watkins, consulting engineers of Richmond, Virginia, and the final design of the roadway and tunnel was by Singstad & Kehart, consulting engineers of New York City.
The tunnel is located some seven miles north of Wytheville near the Wythe-Bland County line. The first grading contract for 3.2 miles of I-77 was awarded in December of 1966 to H. B. Rowe & Company of Mt. Airy, N.C., on a bid of $3,388,849. The second grading, for 2.1 miles, was let on a bid of $2,887,971 to Nello L. Teer Company, of Durham, N.C., which company as a subcontractor under the tunnel contractor, also graded the 2.3 miles of the tunnel and its approaches. The grading, bridgework and paving of 3.8 miles north of the tunnel was done on a bid of $6,537,600 by A. B. Rowe Company and Miller Engineering Company, of Mt. Airy, N.C. Pendleton Construction Company, of Wytheville, built seven bridges south of the tunnel on a $678,062 contract, and the remainder of the paving on a $2,101,646 contract. Rights of way cost $660,000; engineering fees, $1,600,000; legal and closing costs, $180,000; a truck stop, $85,000; and sewerage and wastes treatment plant, $90,000. C. J. Langenfelder & Son, Inc., of Baltimore, Maryland, executed the tunnel contract on a bid of $22,623,793; electrical equipment and wiring, by Walter Truland Corporation, of Alexandria, Virginia, for $2,288,000; and the transmission, fans, motors, and installation thereof, by the Westinghouse Electric Co., of Boston, Massachusetts.
Studies of methods and use of present day earth moving equipment lead to the decision to cut and fill on the roadway through Little Walker Mountain, a 300-foot cut with slope stakes set some 1,100 feet apart at the deepest portion. About 10,000,000 cubic yards of excavation was required in grading? half being in the Little Walker Mountain crossing, 3,000,000 cubic yards moved to the south entry fill and 2,000,000 cubic yards to the north entry. Estimated on an open cut through Big Walker it would have been 500 feet deep with a movement of 12,000,000 cubic yards of excavation. Actually some 163,000 cubic yards of rock were removed from each of the two tunnel tubes, for a total of 326,000 yards, all in solid rock. Excavation at the portals amounted to a million yards, and was moved into the nearby approach fills.
The major feature of this entire project was the Big Walker Tunnel itself, to provide two 26-foot wide roadways, 27 feet apart or some 64 feet on centers, 4,229 feet long with a vertical clearance of 16.5 feet, and sloping upwards towards the north on a 3.5% grade. The crest of the Mountain is at elevation of 3,650 feet and the greatest depth to paving is 800 feet. The cross section of the tunnel is an inverted horseshoe with a thin slab overhead to provide floor for the air ducts, both exhaust and intake for each tube. Twenty four fans, up to nine feet in diameter, provide ventilation with three blowers and three-exhausts at the intakes and exhausts of each tube. Of interest in design, the intake for the upgrade duct may require a maximum of 1,719,200 cubic feet of air per minute while the downgrade, only 956,700 cubic feet, and ducts are sized in relationship. Automatic sensing devices, with manual backups, analyze the carbon monoxide content of the tunnel air and adjust ventilation. The southbound tube can be cleared in one minute but two minutes are required for the northbound tube. Emergency diesel fueled generators provide back-up in the event of power failure.
Traffic lights, five per lane, control the traffic flow in case of accidents, and fire extinguishers are mounted every 110 feet, while the spacing of the 22 telephones along the tunnel is equalized. Interior lighting is controlled to permit visual transition for the entering driver. The building at the south portal houses offices, controls, garages and maintenance facilities, while that at the north portal is for storage. The National Park Service is providing a major recreational area adjacent and includes a lake, camp site and other conveniences, access to which is through an interchange between I-77 and Virginia Route 717 near the south portal. This is the longest above-ground vehicular tunnel in Virginia.
This interstate facility will provide travelers with one of America's most scenic and exciting rides. That, along with the impetus of the new road will greatly encourage economic development thus repaying many times over the outlay of initial costs.
Sources of Information:
Virginia Department of Highways, A. W. Coates, Information Officer (VDH)
South Portal of Tunnel-VDH.
Platform and Drills for Rock Excavation in the Tunnel-VDH.
Concrete Placing Equipment-VDH.
Welding Structural Ribs for the Roof of the Tunnel-VDH.
Reinforcing of Tunnel Lining-VDH.
Completed Traffic Tube-VDH.
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