CSX BRIDGE OVER TENNESSEE RIVER SLOUGH NEAR BRIDGEPORT, ALABAMA BRIDGE REPLACEMENT AND TRACK IMPROVEMENTS. Introduction

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1 CSX BRIDGE OVER TENNESSEE RIVER SLOUGH NEAR BRIDGEPORT, ALABAMA BRIDGE REPLACEMENT AND TRACK IMPROVEMENTS AREMA PRESENTATION September 13, 1999 Presented by: Rick Garro, P.E. Assistant Chief Engineer Bridges, CSX Transportation Hal Lewis, P.E. Senior Project Manager, HDR Jacksonville, FL Introduction The existing bridge is made up of pinned connected truss spans and is located at the southern end of Bridgeport Yard, Bridgeport, AL. The bridge crosses the Tennessee River Slough, which is a braid in the Tennessee River, and ends on Long Island. The track then crosses CSX s single-track vertical lift span bridge over the Tennessee River. The bridge is on CSX's Chattanooga Subdivision, which carries approximately 30 trains per day. Norfolk Southern Corporation also operates on the line under trackage rights. The replacement of Bridge was accelerated after an eye-bar failure occurred in All of the pinned connections were then inspected and no other eye-bar cracks were found. The bridge was placed on a permanent 10-mph slow order to sustain it until replacement. The replacement plan had to address the maintenance of rail traffic, track alignment, property acquisition, constructability, environmental considerations, and cultural resources. CSX hired HDR for assistance in studying alternatives, right of way acquisition, developing construction plans and procuring all necessary permits. History The existing 1470-ft. long bridge was a single-track, ballasted deck structure consisting of nine pin-connected deck truss spans with a timber trestle approach on the south end. The existing masonry piers and abutments, originally constructed in 1851, have been modified over the years. During the Civil War the original bridge was the focal point of several conflicts between Union and Confederate forces vying for its strategic importance in transportation and communication. The bridge s superstructure was destroyed and rebuilt twice during this period. Five of the existing deck truss spans were reconstructed in 1887, and the other four spans were reconstructed in Center trusses were added to each span in 1930 to

2 increase the bridge s load capacity. Several of the stone foundations have been strengthened while others are the originals. During the past 30 years the bridge has needed continuous repairs to the floor system to correct fatigue cracks in the floor beams. The new bridge is 1,470-ft. long and consists of ten steel deck plate girders spans with a concrete ballast deck. The Town of Bridgeport had pushed to take ownership of the bridge in lieu of demolishing it partly due to its historical significance in being the namesake and logo of the Town. Furthermore, the Town plans to build a park on Long Island and use the bridge as access and vista to the Tennessee River Valley. The replacement of this bridge presented a number of engineering challenges and opportunities to improve CSX s track in this area. Obstacles and Challenges Alignment The existing track alignment approaching the bridge from Bridgeport Yard was limited to a 25 mph speed and had a curved #20 turnout. The replacement study looked at basically three alternatives: upstream offline, online replacement and reusing the existing substructure with modifications, and online replacement with all new substructures. All things considered, the offline upstream replacement was the most costeffective alternative justified by easier bridge construction, minimum impact on train schedules, and shortest construction schedule. Environmental/Permitting The preferred alignment had more challenges than the other alternatives and required significant coordination and patience. Acquiring the various permits and legal approvals required on-going communication and coordination between the various agencies and landowners. The final approvals were not obtained until April Some of the main challenges were: 1. Archeological and Historical Shell middens adjacent to the widened approach right-of-way had to be delineated and fenced off prior to construction. During the Civil War the original bridge was the focal point of several conflicts between Union and Confederate forces vying for its strategic importance in transportation and communication. The Alabama Historical Commission had to review and approve HDR s historical survey reports prior to construction. 2. Threatened and Endangered Species A federally listed Threatened and Endangered Species, Anthony s Riversnail, inhabits this stretch of the Tennessee River. Construction of the new piers would adversely affect the local population. HDR worked with the U. S. Fish and Wildlife Department to develop a mitigation plan that was satisfactory to the agency as well as CSX. 3. Wetlands A stretch of wetlands existed in the proposed approach alignment right-of-way. The existing wetlands were delineated and a wetland mitigation site had to be constructed.

3 4. Permits HDR assisted CSX in obtaining the required permits from the US Army Corp of Engineers, Tennessee Valley Authority, and the State of Alabama, as well as the U.S. Coast Guard. 5. Right-of-Way New right-of-way had to be purchased for the new alignment and wetland mitigation site. A submerged land lease had to be negotiated with the State of Alabama. Also, an easement had to be granted by the TVA since they control the river system in this area. Bridge Design The new substructure consists of hammerhead piers founded on steel 14 x 89 H-piles. Each pier column is 7 6" in diameter with an average column height of 45 ft. Both abutments are founded on 14 x 117 H-piles; wing walls are founded on 14 x 89 H-piles. Based on the results of the test borings, Piers 1 through 5 were intended to be friction piles with an estimated depth of 100 ft. Piers 6 through 9 were intended to be bearing piles since rock is closer to the surface. However, the geology of the site is karstic with variable weathering of limestone and dolomite. The rock is variable and contains solutions, which are filled with soil. Due to the variability of the rock and soil, dynamic testing of piles was used to verify pile capacities. In some locations piles were driven to lengths of up to 150 ft. The superstructure consists of four deck plate girders spaced on 4-ft. centers with a reinforced concrete deck. The span layout consists of two end spans at 147 2" and eight interior spans at ". The girders are 9-4" deep and use over 4,000,000 lbs. of A709 weathering steel. CSX typically uses painted A709 steel instead of weathering steel. However, weathering steel was selected for this project because of the its location, height above the river and the use of a concrete ballast deck. Bridge Construction The Project was bid in April 1997 and the low bid was received from Scott Bridge Company. The Contractor proposed an 18-month construction schedule for completing the work in early November The project utilized an informal partnering process with the intent of maintaining the project s schedule, budget and minimizing impacts on train operations. The partnering process included monthly site meetings of key team members involving the Contractor and representatives from CSX's Bridge, Design and Construction, Transportation, Maintenance and Signal Departments. Monthly progress reports were provided to all team members. The partnering process is credited with keeping all parties focused on the project s goals: safety, quality construction, and project completion under budget and on schedule. The bridge pier s were constructed by the use of barge mounted cranes. This complicated the construction process due to the delivery of materials and the seasonal fluctuations of the Tennessee River in this area. The Contractor used three 150-ton barge

4 mounted cranes during the river pier construction and during superstructure construction. The construction at the three river piers closest to Long Island encountered irregular rock layers, which required explosives for removal. The rock had to be removed to permit the cofferdam and footing installation at the three piers. The proximity of the new piers and the existing piers, which were constructed in 1851, was of particular concern when considering the use of explosives for rock removal. A controlled demolition plan was developed that would adequately fracture the rock in the new pier areas without damaging the existing piers. Seismographs were installed on the adjacent piers and on adjacent residences to monitor the effect of the explosions. The results of the seismographs indicated minimal vibrations as a result of the controlled demolition. The new 9-4 deep deck girders were 148 long and arrived in fully assembled beam pairs loaded on rail cars. The girders were staged in Bridgeport Yard on the rail cars along the outside track to facilitate the Contractor s installation of lifting clamps. Then, Work Trains moved the cars onto the existing bridge where the barge mounted cranes were waiting to lift the girders off the rail cars. The cranes were positioned to swing the girders directly onto the new piers where the new bearings where already in place. This process expedited the installation and avoided the double handling of materials that would have occurred if the girders had to arrive by barge to the construction site. The new 12 thick concrete ballast deck was progressively placed from the Bridgeport end of the bridge. This sequence permitted the use of the new bridge as a material and manpower supply route during the last phases of bridge and track construction. Track Design The approach to the new bridge on the north side of the project required 8,600 cubic yards of excavation. The south approach required 19,900 cubic yards of backfill and 5,600 cubic yards of rock to widen the existing approach embankment. Approximately 1,500 ft. of new track was needed across the new bridge and approximately 1,100 feet of new main line track was needed on the approaches. Approximately 1,400 ft. of main line track would be re-aligned in advance of the new approaches. One advantage of constructing a new off-line alignment is improved configuration of the South Bridgeport interlocking. Currently, a power operated No. 20 turnout is located

5 immediately north of the bridge. At this location the single-track main line splits into a two-track main line. The existing No. 20 turnout is located on a curve and requires more maintenance than similar turnouts located on tangent track. The new design improves the alignment by replacing the curved No. 20 turnout with a standard CSX No. 16 turnout on tangent track. In addition, the design improves the train speed on both approach alignments from 25 miles per hour to 30 miles per hour. Track Construction Realigning tracks in Bridgeport Yard required close coordination with CSX s Transportation Department. The new track alignment was constructed with minimum impact on through trains and on Yard operations. The trackwork effort was completed in only three (3) weeks. This project s schedule coincided with the CSX's Chicago to Willard, Ohio B&O double tracking improvement project and required considerable coordination to get materials and trackwork resources to construct the improvements in the allotted timeframe. The new track was put into service in November 1998 which was right on schedule. Challenges and unforeseen conditions were encountered on the project, and countermeasures were taken as necessary to keep the project on schedule. Concrete ties were selected for the realigned track on the approaches and across the bridge to reduce future maintenance. The project was originally bid using timber ties and the use of concrete ties was substituted during construction. Asphalt Underlayment was used below the ballast on the bridge approaches. Building the project offline made the installation of asphalt underlayment very easy. The asphalt was selected to improve the track substructure strength and reduce future maintenance. The asphalt underlayment used on this project is part of an ongoing research project in conjunction with the University of Kentucky. Team Effort This was a project where all facets of the Railroad were brought together and coordinated to make a very successful project. The project was completed below budget and the comments from the various CSX Departments and the Contractor were generally the same We wish all projects went this smooth.

6 Team Members: CSX Transportation All Departments HDR Engineering Project Design, Permitting and Construction Monitoring Scott Bridge Construction Prime Contractor Carolina Steel Primary Steel Supplier Queen City Trackwork Subcontractor