Dement Construction Co. Keeps Tennessee’s Most Expensive Road Project on Track
The $126 million reconstruction of U.S. 27 in downtown Chattanooga, the Tennessee Department of Transportation (TDOT)’s most expensive project to date, is progressing well.
“It’s a big project and is one of the main access points for people to come to Chattanooga,” says Ken Flynn, TDOT Region 2 Director of Operations. “It was time to bring it up to new standards.”
The 2.3-mile project, from Interstate 24 to the Olgiati Bridge, aims to improve safety and add capacity to the 1950s-era, elevated roadway, which was designed for about 20,000 vehicles daily and is now beginning to deteriorate. The road currently carries 70,000 vehicles per day. The road is about 10 to 15 feet above the city.
TDOT selected Dement Construction Co. of Jackson, Tennessee, to add lanes, so there will be three in each direction, and straighten the freeway by removing an “s” curve. Work began in November 2015, is about 17 percent complete. It is scheduled to finish in July 2019.
“It’s gone really well,” says Manuel Abello, P.E., with Dement Construction. “We have a really good team between the department, the CEI, us and some really good subcontractors. Communication has been good.”
The department has worked with city leaders about the design and artwork on the retaining walls. Plans have been discussed for years. At one point, a roundabout was considered for one of the interchanges, but that was not pursued.
The scope includes widening nine bridges with prestressed concrete girders over other roads, and adding ramps and a travel lane and shoulder in each direction on the road. The main road will be paved with asphalt, and the ramps are concrete.
Dement Construction also is expanding the 0.6-mile steel-plate girder Olgiati bridge, spanning the Tennessee River. Crews are removing by hand about 2.5 feet of concrete around the existing rebar, so rebar for the new decking can tie into the old rebar.
“We have to clean it off by hand,” Abello says. “We cannot use heavy equipment on it, because the structure stays in place. We have to use low-weight jackhammers.”
About 30 percent of the bridge is over the river, and that will require barge work. The approach spans are built on land.
The bridge substructure for the expansion was constructed as part of a separate project in 2003, knowing that the widening would occur in conjunction with the U.S. 27 corridor improvements. Some of the exit ramps to the surface streets will start on the bridge.
Additionally, the project includes building new frontage roads; modifying several interchanges; reworking the drainage; adding curbs, gutters and sidewalks to six cross streets; and constructing more than 270,000 square feet of retaining walls.
“In normal construction, you would build a slope,” Flynn says. “Basically, the whole project is being built with retaining walls to keep the footprint small.”
Building Retaining Walls
The project splices through a highly developed area, with large office complexes and limited right of way.
“It’s been challenging piecing in the walls at the edge of right of way, next to buildings,” Abello says. “There’s a lot of subsurface exploration and things you have to deal with below ground.”
Dement Construction is responsible for designing the retaining walls.
“We give the contractor the parameters for the design and options on different types of walls,” Flynn says. “That way they can give us the most economical wall for the situation.”
The walls on this project contain a mix of mechanical stabilized earth, poured-in-place concrete, and soldier piles with tie-backs, depending on the situation and soil. In some places, the crews are limited with more traditional sheet piling, Abello explains.
The soil needed to be improved before the wall could be constructed in certain areas with multiple voids. Grout is being injected into those spaces.
“We have a wall that is 48,000 square feet and at its highest point is 70 feet tall,” Flynn says. “There’s an area that was an old landfill, full of debris. Instead of excavating it out, we are pumping grout into the area to stabilize it, so it can hold up the wall.”
That wall is a soldier pile with tie-backs, excavated from the top down. Timber lagging is put in temporarily to hold back the material. Every 6 feet, crews drill in a tie-back to counteract the forces of the dirt pushing the wall over.
“It stabilizes itself as you go down,” Flynn explains.
Abello says some walls on this project employ multiple methods, including soil nailing.
“It’s been really neat,” Abello says. “It’s very rare that you get to do it all on one project.”
Dement Construction subcontractor GeoStabilization International of Grand Junction, Colorado, is using a specialized hydraulic percussion rock drill from John Henry for the tie-backs. The “Steel Drivin’ Machine” is mounted on an excavator. It uses a water-injection type dust suppression system.
A couple of walls have a Geopier foundation. Geopier MSW walls and embankment support increases the composite stiffness of soft soils and adds shear reinforcement to increase bearing capacity and stability. The elements also act as vertical drains. Ramming the Geopier foundation elements into place also adds stiffness to the surrounding soil. The result is faster settlement during construction and less settlement over the long term.
TDOT and Dement Construction are keeping traffic flowing, with traffic shifting during three phases. The job is currently in the first phase, with traffic in the center and construction on the northbound. The second phase will move traffic to the part of the project already complete, and then all traffic will shift again during the third phase while work takes place on the southbound. Lane closures occur at night. Going forward, Dement Construction may need to build some temporary ramps.