Some 30 years after the Appalachian Regional Commission approved the designation of Corridor X from Fulton, Miss., to Birmingham, Ala., the project is finally nearing completion. There are good reasons why it has taken this long to complete the final segment connecting Corridor X to I-65 in Birmingham. The challenges were enormous: The interchange is geometrically complex, the environmental context is sensitive, I-65 currently carries 85,000 vehicles per day through the project area and several major utility lines run right through the interchange area.
To complete this massive undertaking, the Alabama Department of Transportation (ALDOT) enlisted the services of Volkert and Associates Inchttp://www.roadsbridges.com/30-Years-Young-article9334., headquartered in Mobile, Ala., and with offices throughout the southeast. The Corridor X portion of the interchange area begins 1.4 miles northwest of I-65 and extends 2,000 ft southeast of I-65 to U.S. 31. The I-65 portion begins at 16th Street, just north of I-59/I-20, and extends 5.4 miles north to Walkers Chapel Road. Faced with an estimated construction cost approaching $300 million, ALDOT and Volkert realized that it would be cost-prohibitive to design and construct the project as a single entity. Thus they divided the project into six plan sets.
Sensitive angle
The first challenge of the I-65/Corridor X interchange area is the shear geometric complexity. The main interchange will be four levels and fully directional. To accommodate the projected traffic, the interchange requires collector-distributor roads paralleling I-65 northbound and southbound. Just northwest of the interchange, Corridor X is shoehorned in between an established residential neighborhood and a Norfolk Southern railroad line. The neighborhood streets are as much as 100 ft higher than Corridor X, while Corridor X is as much as 60 ft higher than the natural drainage channels located in the valleys between these same streets. After passing under I-65, Corridor X climbs rapidly to pass over Lewisburg Road and tie in to U.S. 31.
The second challenge of the I-65/Corridor X interchange area is the sensitive environmental context. The New Georgia Landfill (an active city-of-Birmingham facility) is located in the northern quadrant of the interchange while the T.M. Burgin Landfill (a closed construction-debris facility) is located in the eastern quadrant of the interchange. Furthermore, an abandoned firing range is located in the vicinity of the I-65 southbound to Corridor X westbound ramp. In order to minimize the risk of disturbing lead or other potential contaminants, ALDOT and Volkert agreed early in the design process that there would be no excavation in the northern quadrant—all roadways and ditches would be constructed entirely with fill.
The T.M. Burgin Landfill in the eastern quadrant posed a different challenge. While the goal in design was to minimize disturbance of this landfill, the area could not be completely avoided, since a major drainage system flowing northwest from U.S. 31 toward I-65 is routed under the middle of this landfill. The outlet of this system, located just east of existing I-65, is a 1/4 -in.-thick, 5-ft by 5-ft steel-box culvert with diagonal bracing conveniently placed inside to catch trash and reduce flow capacity. Excavating and replacing this system was not an option—ALDOT had no desire to acquire and disturb a closed landfill.
Volkert was understandably reluctant to connect to this system at the upstream end west of Lewisburg Road. The solution? Most of the flow entering this system is diverted into a new system running northwest along Corridor X from the U.S. 31 interchange area to the west side of I-65.
Two major creeks passing under I-65 also were areas of environmental concern. Village Creek passes under I-65 south of the Corridor X interchange, while Five Mile Creek flows east to west under I-65 north of Corridor X. One of the biggest concerns at Five Mile Creek is an in-place 10-ft by 6-ft box culvert that empties into a 460-ft-long concrete channel that subsequently empties into Five Mile Creek on the east side of I-65. This culvert collects storm-water runoff from under almost a mile of I-65 and has a design flow of approximately 700 cu ft per second (cfs). Because of right-of-way constraints, detention is difficult, but Volkert designed two ponds within the infield areas of the I-65/U.S. 31 interchange. This reduces the design flow in the culvert by over 100 cfs. Being concrete and steep, the in-place outfall channel flows fast, and scour is evident where the channel empties into Five Mile Creek. To alleviate this area, Volkert designed a riprap energy basin and outfall channel to replace the existing concrete channel.
The list of environmental concerns is rather extensive. Joe Money Machinery is located in the southern quadrant of the I-65/Corridor X interchange. Two of the interchange bridges are located right over and are designed with bents in Joe Money’s distilling ponds, where water from washing heavy equipment was formerly collected. Some contamination was found in the northern end of the two ponds, and ALDOT has already acquired and filled that pond under a different contract. No contamination was found in the southern pond, and it is to be drained and filled as part of this project.
The entire project area along I-65 was historically important for coal mining and industry. The mines are closed, but even today the entrance to one is still visible within the interchange area. Based on the mine studies conducted for this project, it can be expected that more historical evidence of mining could be encountered during construction. One final item of environmental interest was the discovery of small traces of trichloroethylene in the vicinity of the ramp gore from the northbound CD road to westbound on Corridor X. The source could not be identified, so once again Volkert raised the elevation of some drainage structures and designed a ditch in fill in order to avoid disturbance in this area.
Heavy sheet traffic
The third challenge of the I-65/Corridor X interchange area is maintenance of traffic, primarily vehicular on I-65 and its ramps but also rail traffic on the six active lines passing under I-65. The design goal for the traffic-control plan was to keep all ramps and six lanes on I-65 open at all times. During development of the traffic-control plans, it became apparent that some ramps would have to be closed temporarily and detours provided. But the goal of keeping six lanes open on I-65 was attained, aside from brief temporary closures for setting bridge girders and for blasting. For Plan Set 2, covering the heart of the interchange, over 150 plan sheets representing approximately 10% of the entire plan assembly are devoted to the traffic-control plan.
Lines start here
The fourth challenge of the I-65/Corridor X interchange area is the presence of several major utility lines, most notably those of the Alabama Gas Corp. (AGC), Southern Natural Gas Co. (SNGC) and the Alabama Power Co. (APC). AGC has 4-in. and 12-in. high-pressure lines running adjacent to the Norfolk Southern railroad line on the west side of I-65 through the Corridor X interchange. SNGC has a 24-in. high-pressure gas line crossing Corridor X about one mile west of I-65, passing north of the New Georgia Landfill and crossing under I-65 at Five Mile Creek.
SNGC had 20- and 22-in. high-pressure gas lines passing right through the I-65/Corridor X interchange. After extensive deliberations and negotiations, ALDOT and SNGC agreed that the best course of action would be to relocate the 20- and 22-in. lines within the same easement as the 24-in. line. This project has now been completed, clearing the way for construction of the interchange. APC had power lines that crisscrossed the Corridor X alignment throughout this project. Like the gas lines, this has required a major relocation effort.
Construction is already under way on Plan Set 1. The R.R. Dawson Bridge Co. was awarded the construction contract in September 2007. New bents on the west side of I-65 for widening the bridge over Daniel Payne Drive and the newly graded northbound off-ramp from I-65 to Daniel Payne Drive need to be completed early for coordination with the construction efforts on Plan Set 2, which is scheduled for letting later this year.
Extensive erosion-control netting to protect the cut slope until vegetation is established also will be used, as well as the use of riprap on the widening of the I-65 bridge over Village Creek to protect the creek banks during construction. ALDOT intends to use similar erosion- and sediment-control measures during construction in the vicinity of Five Mile Creek on Plan Set 2.
Most of the other plan sets also are nearing completion. Plan Set 3 is scheduled for letting soon. Plan Set 4 is scheduled for letting in 2009. Design of Plan Set 6 is approximately 70% complete, with letting scheduled for 2010. West of Fulton, Miss., U.S. 78 is already a controlled-access facility to the Tennessee state line southeast of Memphis, Tenn. It is expected that eventually this controlled-access facility will be connected to one of the interstates near Memphis, thus completing the I-22 link all the way from Memphis to Birmingham.
