THE HISTORY AND HERITAGE OF
CIVIL ENGINEERING IN VIRGINIA
The Chesapeake Bay Bridge-Tunnel (1960-1969)
Like a 20th-Century Colossus, the Chesapeake Bay Bridge Tunnel stands astride the wide mouth of the Chesapeake Bay.
The American Society of Civil Engineers, impressed by the diverse and difficult problems that had to be overcome in order to create this gigantic, new fixed crossing-at the edge of the Atlantic Ocean where tides run strong and winds are high-has named the Bridge-Tunnel one of the seven wonders of the modern world. The ASCE choice was based on the seven projects' unusual engineering features, utility to mankind and size.
A complex combination of trestled roadways, bridges, man-made islands and tunnels, the 17.6 mile long Chesapeake Bay Bridge-Tunnel provides a two-lane highway between Cape Charles, on the eastern shore of Virginia, and the Norfolk-Virginia Beach area on the state's mainland. The Bridge-Tunnel closes the last water gap on the North-South Ocean Highway and cuts at least 90 minutes from the driving time between the New Jersey Turnpike and Jacksonville, Florida.
Too big to be built by a single firm, the Bridge-Tunnel is a result of the combined efforts of several leading engineering and construction companies. It was designed for the Chesapeake Bay Bridge and Tunnel Commission, the sponsoring authority, by Sverdrup & Parcel, St. Louis, Missouri, which also was the construction supervisor. Major contractor was a joint venture group consisting of Tidewater Construction Corporation, of Norfolk, Virginia; Raymond International Inc., of New York; Peter Kiewit Sons' Company, of Omaha, Nebraska and Merritt-Chapman & Scott Corporation of New York. The steel superstructure for the high-level bridges near the upper end of the crossing were made by American Bridge Division of United States Steel Company, Pittsburgh, Pennsylvania.
Although the individual components of the Bridge-Tunnel are not the longest or largest ever built, the total project is unique in the number of different types of major structures included in one crossing and the fact that construction was accomplished under the severe conditions imposed by hurricanes, northeasters and the unpredictable Atlantic Ocean, according to Percy Z. Michener, Sverdrup & Parcel Project engineer.
The Chesapeake Bay Bridge-Tunnel consists of 12.5 miles of low level concrete trestles, two one-mile tunnels, two steel bridges, four man-made islands, 1.5 miles of earthfill causeway, and approximately 5.5 miles of approach road. The roadway on the major portion of the project is 28 feet wide, with space for a parked vehicle next to the curb.
The major portion of the Bridge-Tunnel is low level trestle over relatively shallow water, approximately 20 to 30 feet in depth, in areas where there arc no established navigation requirements. The roadway on this structure is placed on a level grade at an elevation 30 feet above mean low water to accommodate small boat traffic and to keep the superstructure above wave action. The trestle structure consists of 858 precast, prestressed concrete spans of 75 feet each and precast bent caps supported on 54-inch diameter, hollow, precast, prestressed cylindrical concrete piles. The hollow piles, which have walls five inches thick, were filled with sand to enable them to withstand the shock of collision by small boats or ice floes which occasionally occur in this portion of the Chesapeake Bay. In fact, there have been two major accidents since the Bridge-Tunnel was put into service in 1964, the latest of which resulted from the storm of the first of October 1972 when the trestle structure was battered by a heavy steel barge which was lost in tow. However, repairs were made in record time and service reestablished without other incident.
Two primary considerations in the trestle design were duplication and ease and speed of fabrication and erection.
Trestle components were fabricated on an assembly-line basis at Bayshore Concrete Products Corporation, a special plant constructed at a cost of approximately 3.5 million dollars at Cape Charles, Virginia. The trestle superstructure units were designed as simple spans; fabricated as four separate double "tee" sections (TT), and tied together laterally with post-tension wire at the ends and third points of the span after erection. Curved spans were also precast as duplicates to fit a one degree curve and include super-elevation with transition from the level roadway section. The "tee" section girders were reinforced with straight, uncoated SevenWire Stress Relieved strands. Each strand was prestressed to 175,000 pounds per square inch. On all concrete structures an additional concrete cover of reinforcing steel was provided as insurance against possible chemical reaction on the concrete surfaces due to salt water exposure. All concrete in the superstructure units was designed for a compressive stress of 5,000 pounds per square inch.
The substructure bent caps were cast with exposed reinforcing steel for the connection to the piling. The prestressed 54-inch diameter cylindrical piles were cast by the "Cen-Vi-Ro" process in 4-, 8-, 12-. and 16-foot lengths. They were joined after curing by threading 12 prestressing wires (diameter .192") through each of the 16 holes formed in the S-inch thick pile wall. The wires were prestressed to an average of 165,000 pounds per square inch by jacks; grout was forced into the holes under a pressure of not less than 100 lbs. per square inch. An epoxy was applied at the joints between sections as a seal.
The piles ranged in length from 80 to 172 feet and weighed from 800 to 1,000 pounds per foot of length. Approximately 2,600 of these pilings were used on the project.
The 54" piles were driven from a special DeLong type barge, nicknamed the "Big D." Seventy feet wide by 150 feet long, this "walking" pile driver was supported on four 100-foot long steel pipe spuds which could be raised or lowered into the sea bed by 500-ton capacity air jacks. This provided a fixed platform for the pile driving operation.
The precast caps which tie the tops of the piling together to form a rigid pile bent were placed from a traveling bridge 175 feet long with a stiff-leg derrick mounted at each end. The bridge called the "two-headed monster' moved forward on a wheel assembly mounted on bonnets which were temporarily placed on the two outside piles of a bent. Steel railroad rails on the under side of the bridge moved over the wheel assembly as the bridge propelled itself forward with its deck hoist engines. The forward derrick handled the equipment for cutting off the piled to the correct elevation. After the cap was set in its final position, concrete was placed in the pile through a 9-inch hole in the cap over each pile.
Each "double-tee" slab section' weighing approximately 65 tons, was set in place on the bent caps by a 75-ton capacity, stiffleg, self-propelled derrick mounted on a steel box girder which spanned the completed bents.
The length of piling required was determined from a soils, profile developed from 120 exploratory borings at strategic locations along the project centerline, some to a depth of 300 feet. Data from the borings were supplemented by a sonar reflective survey which permitted interpolation of the boring data to indicate subsurface conditions for the entire crossing.
All piles were driven to bearing in the tertiary formation of the Miocene age. The average length of all piles driven was 110 feet; the longest pile was 172 feet. Each pile in the trestle was designed to carry 160 tons load. At selected locations along the project centerline, test piles were driven and loaded to twice the design capacity onto 320 tons of compete blocks as a static load. The test load was applied to the pile with a 500-ton jack in predetermined increments, and a pile was considered satisfactory if the net settlement was no more than 0.25 inch after 60 hours of loading.
All low level trestle prestressed concrete "double-tee" superstructure units were seated on steel reinforced neoprene rubber bearing pads, to give resilience to the superstructure units and allow free expansion movement.
The trench-type tunnels which are constructed under each of the two major ship channels are identical in construction details.
The Thimble Shoal tunnel has a portal-to-portal length of 5,738 feet and provides a 1,900-foot ship channel with a minimum 50-feet depth and a 2,500-foot channel with a 40-foot minimum depth. The Chesapeake Channel tunnel is 5,450 feet long and provides a 1,700-foot channel with 50-foot depth and a 2,300-foot channel with a minimum 40-foot depth. The maximum roadway grade in the tunnels is 4 percent. The roadway width is 24 feet plus a 2'-6" sidewalk on one side and an overhead clearance above the roadway of 13'-6".
The tunnel structure consists of prefabricated composite structural steel and reinforced concrete tube sections 37 feet in diameter approximately 300 feet long, sunk into place in a prepared trench and covered with a minimum of 10 feet of selective backfill material. The structural steel portion of the tube sections consists of a 35-foot diameter steel tube supported inside a 37-foot square box section. The double steel form shells were fabricated and the interior reinforcing steel tied in place at Orange, Texas, then towed approximately 1,700 miles to the fitting-out yard at Norfolk, Virginia.
At the fitting-out yard the two-foot-thick interior concrete stress ring and the roadway slab were poured and the tube section was sealed preparatory to sinking. Before towing to the tunnel site, sufficient exterior pockets between the interior and exterior steel shells are filled with ballast concrete to lower the tube to about 6 inches of free board. The tube was then towed to the construction site for sinking in its final location.
Prior to sinking, a trench was dug in the sea bed and shaped to the correct tunnel grade and alignment by placing a two-foot thick layer of pea gravel on the trench bottom and screeding to the correct grade by dragging an oversized bulldozer blade along the surface of the foundation material. The foundation bed for the tube, which in some locations is approximately 100 feet below the Bay water surface, was finished to a tolerance of one tenth of a foot.
At the construction site the tube was placed between two railroad car ferry floats which supported two heavy bridge cross girders, fitted with lines and blocks for lowering the tube into the prepared trench. Additional ballast concrete was placed in the exterior tube pockets to give the tube a negative buoyancy of approximately 250 tons. The tubes were guided into position on the instructions of deep-sea divers working on each side of the tube where the connection was to be made.
Executed at the time of slack water to insure a minimum of underwater current forces on the tube, the connection between tubes was made in this way: a 7-inch diameter fixed pin on the floating tube was guided into a slotted hole in a steel casting on a tube which had earlier been positioned in the trench. The positioned tube had a hood plate on the lower half which extended under the tube being placed. The tube to be placed had a hood plate on its upper half, which extended over the tube already in position. Thus, the tubes that make up a tunnel overlap.
With the tube in correct position in the trench, the remaining exterior pockets along its sides were filled with tremie concrete to give an additional 300 tons of negative buoyancy. The tube joints were further sealed on the exterior by pouring a thick concrete envelope around the joint. After that, the interior of the tube joint was sealed by welding together the overlapping hood plates and by completing the interior stress ring reinforced concrete to make all joints continuous. When the tubes were jointed in their final position, sand backfill was placed along the sides and to a minimum depth of ten feet over the top to insure permanent stability. Thirty-seven tunnel tube sections were placed in the construction of each tunnel.
After the tubes were placed and joined, the watertight bulkheads of each tube were cut out progressively from one end of the tunnel; the interior of the tunnel was finished with ceramic tile, lighting system and other appurtenances.
The tunnel ventilation was accomplished by a transverse distributional system which supplies fresh air uniformly along the tunnel length from a duct beneath the roadway, and removes air through a duct above the ceiling.
Tunnel roadway lighting is provided by two continuous lines of fluorescent tubes, with the intensities varied by zones to provide control at the portals to help vehicle drivers adjust their vision from daylight to artificial light.
The ends of the tunnels are anchored on man-made islands constructed in 35 to 45 feet of water. These islands provide a transition from the trestle roadway to the tunnel tubes. Each of the project's four islands is approximately 1,500 feet long and 230 feet wide at the top, providing about 5.5 acres of real estate at a cost of about 5 million dollars. The general surface of the islands is 30 feet above mean low water. A ventilation building, shaft and garage for an emergency crash truck are located on each island.
The islands were designed to resist the forces of a hurricane with 105 miles-per-hour wind velocity. Scale models in wave tank tests withstood hurricanes of 135 miles-per-hour wind velocity.
The islands were constructed by first placing hydraulic fill on the Bay bottom to an elevation of 17 feet below mean low water. A rock dike, approximately 10 feet in height, of 0.75 inch to 6-inch stone then was constructed around the perimeter at elevation minus 17 in accordance with the planned shape of the finished island. The enclosure created by these dikes then was filled with sand to form the second lift of the island. A 4-foot thick layer of Quarry Run stone, ranging from 500 lbs. to 2,000 lbs, was then placed outside the previously constructed dike, followed by a 5-foot layer of heavy riprap stones weighing not less than 10 tons each. With some weighing as much as 25 tons each, these stones act as the protective armor surface of the completed island. The process of constructing dikes and placing hydraulic fill and outer layers of protective stone was repeated until the island reached its final elevation of 30 feet above mean low water. On the completed island the heavy armor stone extends from 20 feet below to 20 feet above mean sea level and subsequent severe storms have proven this protection more than adequate.
From elevation plus 16 to 28, a reinforced concrete splash wall with a return lip was constructed around the perimeter of the island to protect against possible wave overtopping.
Although only a relatively small part of the total project, the 3,800 foot long North Channel bridge provides a single navigation opening of 300 feet horizontal clearance and 75 feet vertical clearance above mean high water to accommodate the local fishing fleets. The approach grades are 3 per cent.
In addition to the main truss span, the approaches on each side consist of two, four-span, continuous riveted steel deck plate girder units with reinforced concrete roadway surfaces. The bridge is located in water up to 60 feet in depth in an area where there are many variations in the Bay bottom due to shifting channels. The piers consist of metal cans filled with tremie concrete from 5 feet below the water surface to the bottom of the pier, supported on 14 inch steel bearing piles 130 feet long driven into the sea bed to 80 tons bearing capacity each. The piers were constructed without cofferdams. This was achieved by excavating to an elevation slightly below the theoretical bottom of the pier. A precast template supported on temporary timber piles was placed in the excavation at the exact pier location. The 14 inch steel bearing piles were then driven to the required bearing capacity through holes which had been precast in the template allowing about 10 feet of the piling to project above the top of the template.
After the pilings were driven, a steel shell can, with all reinforcing steel tied in position on the inside, was lowered and secured to the top of the precast template on the exact pier alignment. The openings in the concrete template through which the steel piles were driven were sealed with steel plates by a deep sea diver and the steel shell was filled with tremie concrete.
When the pier was completed to the water surface, the remainder of the structure above water was completed by standard construction methods.
FISHERMAN INLET BRIDGE
The 460-foot long Fisherman Inlet Bridge is over one of the U.S. Inland Waterway dredged channels. The center portion of this structure consists of a three-span, continuous, all-welded steel deck plate girder with reinforced concrete roadway surface. The center span of 175 feet provides an opening of 110 feet horizontal clearance and 40 feet vertical clearance above mean high water. The approaches to this structure are on a three per centigrade and are of the low level trestle type construction. The main superstructure spans are supported on a cluster of eight battered 54" prestressed concrete cylinder piles tied together with a poured-in place oversize cap.
FISHERMAN ISLAND CAUSEWAY
Between the North Channel Bridge and the Fisherman Inlet Bridge the project roadway across Fisherman Island is carried on an earth-fill embankment 15 feet above mean low water. The side slopes of the embankment are protected from wave action and erosion by a blanket of stone riprap.
Modern toll collection facilities are located at both ends of the project. The administration and shop maintenance facilities are located at the north end of the project on the Eastern Shore peninsula near Wise Point, at Cape Charles.
The entire structure is equipped with roadway lights from shore to shore, with illumination provided by four hundred watt, 20,000 lumen mercury vapor lamps mounted on prestressed reinforced concrete standards. They are spaced at 225 feet centers on alternate sides of the roadway. A study of various types of poles subject to hurricane wind velocities indicated that the prestressed reinforced concrete poles would better resist vibration due to wind and thus reduce the replacement of luminaires with subsequent reduction in maintenance cost.
Navigation lights and signals for marine traffic are provided in accordance with U.S. Government regulations.
Emergency telephones at approximately one-half mile intervals are provided along the entire project.
The complete electrical system for the project including operating power for the tunnels, navigation and roadway lighting systems, and telephone cables is carried in especially designed
aluminum trays attached to the outside of the precast low level trestle superstructure and bridges. This type of construction provides easy installation and ready access for maintenance.
Sources of Information:
The Chesapeake Bay Bridge-Tunnel Commission, Cape Charles, Va.
Sverdrup & Parcel, Consulting Engineers, St. Louis, Mo.
Man-Made Wonder as Seen from the Eastern Shore Terminus.
Core of Tunnel.
Construction in Progress on a Man-Made Island in the Bay.
Construction of the Entrance and Facilities on One of the Islands.
Trestle Piling in Place Ready for Caps.
Barge Being Removed from Bridge After the Storm of October 1972 (Courtesy Virginia Department of Highways).
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