Construction of Phase II of the Palmetto Parkway/Interstate 520 project in Aiken, South Carolina, has been under way since January 2007. Running 6.5 miles from US Route 1 to Interstate 20, the $126-million four-lane divided interstate facility is a 31-month fast-track design-build project with three interchanges and 15 bridges.
Under the leadership of United Contractors, Inc., local firms U.S. Constructors, Inc.; R.E. Goodson; Triplett-King & Associates, Inc.; Coleman-Snow Consultants, Inc.; Florence & Hutcheson, Inc.; F&ME Consultants, Inc.; S&F Engineering, Inc.; Palmetto Safety Solutions, Inc.; and Public Strategy, LLC have combined to form the design-build partnership Team United to construct the project. In addition, Team United provides on-the-job training, utility coordination and community relations with leadership and oversight provided by the South Carolina Department of Transportation and The LPA Group.
Awarded the contract in November 2006, Team United initially had access only to small portions of the job due to permitting issues. Work began in January 2007 with some minor clearing and grubbing at the south end of the project.
With only a 31-month schedule, Jim Ewart, chief operations officer with U.S. Constructors, Inc., explains that clearing and grading work began with a set of review plans that had been developed through the right-of-way acquisition, while Triplett-King & Associates began bridge design and Florence & Hutcheson began roadway design plans for the team.
"The preliminary design had not gone under any particular major review process," says Ewart. "We took that design as a guideline, and we changed it to match our schedule and to give the most cost-effective solution to the design."
Proceeding with only preliminary plans meant that Team United undertook "construction at risk" in order to meet the aggressive schedule.
"Because of doing work at risk — not having a complete set of plans — we have had occasions where we have had to re-engineer and redo work that we had in place," says Ewart. "By the time these (preliminary) plans went through the review process, what we originally proposed was not what was ultimately agreed to. But that's just the nature of design-build work. You either wait until you have a complete set of plans — and with only 31 months we just couldn't do that — or you work at risk. We elected to work at risk."
However, Team United could only proceed with clearing and rough grading on the project. Work could not proceed on any structures until plans were in place.
In general the soils on the project have been excellent on the job. The soils are typically composed of sand varying in depths from 2 feet to 3 feet to 20 feet to 30 feet. The sand primarily overlays sandy clays, although some chalky kaolin material has been encountered.
The project has essentially been a balanced job. Team United hauled in approximately 200,000 cubic yards of borrow on the south end of the project to facilitate the schedule. However, the rest of the job has included 5 million cubic yards of balanced cut and fill. Staffing levels have continued to climb as more work is available. Last week, Team United had 244 people and 174 pieces of equipment the size of a backhoe loader or larger on the job to move the dirt.
With clearing complete and mass grading ongoing, nearly every phase of construction is under way including work on a large box culvert and seven of the 15 bridges.
Maintaining the clean water flow of an existing creek and working with two very different elevations have been just two challenges during construction of a large cast-in-place box culvert. The topography of the culvert's location resulted in a deep cut in 40 feet of sand on the left side of the right of way and a corresponding amount of fill on the right side. Wet soil and sliding dirt complicated the process of keeping the creek clean during the cut and fill process. Team United temporarily piped in the entire length of the creek to ensure it did not get polluted and stabilized the soil in the creek bed with stone to construct the culvert.
These sandy soils led Triplett-King & Associates to design the bridges on the parkway with pipe piles — one of the more innovative aspects of the project. These circular steel piles vary in diameter from 24 inches to 36 inches and are used on the interior bents of the bridges rather than a typical pile and footing. These pipe piles also act as the columns for the bridges.
The steel piles are hollow. Depending on the soil type, some of the piles are open, while others have points or cleats on the bottom to facilitate the pile driving process. The pipe piles are then filled with sand to a certain elevation and topped with a concrete plug. Of the seven bridges under construction, there are about eight 24-inch piles and three 36-inch piles per bent.
Ten months into the project, work continues on the side roads, which are asphalt, and the bridges. The next big thrust along the I-520 mainline will be fine grading in preparation for concrete paving. The project is scheduled for completion in July 2009.