The cost of Chattanooga's downtown freeway makeover - estimated at $85 million in 2006 and bid at $126.3 million when it got underway in November 2015 - has climbed to $143 million as issues were encountered along the way, TDOT's Ken Flynn said Monday.
The Highway 27 project to provide three lanes in each direction from the I-24 split to the river was already the most expensive highway project in the state's history at the starting price.
Mr. Flynn, TDOT Region 2 Director of Operations, told members of the Chattanooga Engineers Club that the project is now 71 percent complete with a new target for finishing of January, 2020.
He said, “This is a very expensive 2.3 miles. The massive cost of building 43 retaining walls has contributed to the high price, along with replacing nine bridges and adding an extra lane and shoulders along the Olgiati Bridge. When finished there will be three lanes in each direction. The “S” curve will also be removed and a collector or frontage road will be constructed southbound from the Olgiati Bridge to MLK Boulevard that will solve the problem of ramps running in and out of the highway. There will be exits to 4th Street, 6th Street and MLK Boulevard from the frontage road."
The geology around Chattanooga has been a big challenge in building the road. The contractors found 10 times more rock than was anticipated. “The area really is a boulder field,” said Mr. Flynn. This has caused the necessity of drilling through alternating layers of rock and soil to set pilings - one of the reasons that the completion date has been extended. Other problems are man-made. The area underneath the largest retaining wall, which is 40,000 square feet, 70 feet tall and runs from 6th Street to the Olgiati Bridge, was filled in over the years and used as a makeshift landfill.
Mr. Flynn said, "This area had a lot of voids and a mixture of good and bad soils, rock, etc. The very tall retaining wall required the placing of anchors into this material to support the retaining wall. To fill the voids and strengthen the soils, holes were strategically drilled and 300,000 cubic feet of grout was pumped into the slope for stabilization. This, too, increased the original time and cost."
Another man-made problem came to light when foundry sand was encountered while constructing other retaining walls. This sand was tested and it was determined that to dispose of it properly it had to be taken to a certified landfill, thus increasing time for disposal and costs. Another increase came when it was determined that, due to new design requirements, struts needed to be added to the river piers of the Olgiati Bridge to reinforce existing sandwich beams so they would not sag.
An attempt was made to contain the footprint of the whole project that prevented the need to acquire additional property along the road. Instead of the customary sloping of adjacent land, retaining walls are being used to prop up the new roads. Only about 17 tracts of land had to be bought.
Funding for rebuilding this road comes from an 80/20 match between the state of Tennessee and the Federal Highway Administration. As costs have changed, TDOT has gone back to get the extra funding.
Mr. Flynn said maintaining two functioning lanes in each direction in order to keep traffic moving is accomplished by building a little and then shifting a little. While Phase 2 is under construction, lanes are being shifted to make room for the work that will be done in Phase 3.
Reasons for rebuilding the road were that the capacity needed when the road was originally designed was much lower than what it is now. As traffic increased, the ability of the road to function has been reduced. Due to the age of the roadway the bridges were in need of constant maintenance.
Another road project is also underway in the area, which is repairing the highway up Signal Mountain. This work is only to stabilize what is already there, not to increase capacity, Mr. Flynn said. And, it is not the last project that is planned for the road. A lot of voids have been discovered under the road, which has required pumping a lot of grout to fill them. The work is about on schedule, said Mr. Flynn. TDOT is considering improvements to other areas fairly close to the current job, while the equipment is already there.
The future big project will include making improvements to drainage and adding new guardrail in addition to stabilization. A public meeting will be held next year to discuss what work is planned for this project.
Mr. Flynn told the club a new approach will be taken for road building in Tennessee roads in the future. The new method, called “Design Build,” will reduce the customary 12 years that it typically takes to get a highway under construction. The traditional method is that all phases of a road project are done separately because each step, such as environmental studies, preliminary design, finalized design, right of way acquisition, and construction, is funded individually. In Design Build, different phases are done concurrently. The first step will be to get qualifications and review them before picking design build teams to bid. TDOT provides a 30 percent plan and the designer builder is encouraged to find better ways to do the project faster and less expensive than conventional means. The project for replacement and reconfiguration of the I-75/I-24 Interchange is a Design Build project and should be awarded after the first of next year. Work could begin in the spring.
Another method is Construction Manager/General Contractor (CM/GC) and is it is being used for replacing the I-24 Bridge over Germantown Road along with the Belvoir Road Bridge over I-24. This method hires a contractor to serve as a part of the design team to bring innovative ideas and techniques into this phase of the project. Accelerated construction ideas such as pre-building a bridge and installing it in one or two weekends, he said. "We design the parameters and the contractor does the details," said Mr. Flynn.
Mr. Flynn said TDOT is always looking for ways to save the taxpayers’ money so that it can be used to fund and build other needed projects.