The need to widen Interstate-20 in the northeast Richland County of S.C. has been talked about for at least a decade, and in 2012 work finally got underway. Now, contractors are closing in on the August completion date on a job that’s called for expediency and smarts.
"The traffic on this segment is very heavily traveled for a four-lane interstate," said Paul Miller, project manager of the South Carolina Department of Transportation. The heavy travel, increasing traffic and accelerated schedule kind of made things difficult. It took some good thinking and coordination to get things done in a timely fashion."
The section of I-20 under construction runs through an area just north of Columbia. It is already heavily developed, with additional development continuing. The interstate currently sees about 61,000 vehicles daily, and that number is expected to rise to 117,000 by 2029.
"The project is basically five projects in one," Miller said. "The first is the widening project. That’s 6.3 miles of widening. We added an additional lane eastbound and westbound and reconstructed the concrete pavement. In addition to that, we demolished and reconstructed a 280-feet interstate bridge. We also widened another bridge to accommodate an additional lane of travel. We also installed a noise barrier wall for approximately 6 miles and intersection improvements on one of the exit ramps, where we added a dual left hand turn lane."
One of the main challenges of the job was maintaining two lanes of travel while constructing the new lanes.
"It’s remodeling the house while you’re still living in it basically," said Curtis Schwartz, project manager of Zachry Construction Corporation.
To do so, the company cut the project into five stages, Schwartz said.
Zachry Construction Corporation split the traffic so that it traveled on opposite sides of the median and barrier wall, with a treed area in the middle of the job.
"They come to the job side by side, split one in the new east bound and one in the new west bound and then come back together," Schwartz said. "That allowed us to demolish and remove and replace entire existing lanes. First we built the widened part to the inside and that is where we put the traffic so we could build the outside portion."
There were no real surprises in the work, but some of the existing conditions, such as the amount of groundwater and unsuitable materials from it, were new to some of the crew, Schwartz said.
"There are natural springs. We had some undercut areas, had to remove the material and go back with a stone base and underdrains," Schwartz said.
The state also added another component to the job after rare snow and ice storms wreaked havoc on the asphalt on the existing westbound segment, sparking a number of damage claims.
"While we were here and already disrupting traffic, we decided it was in our best interest to the public to get it done now and complete this project rather than start a new project after Zachry moved out," Miller said.
Because time was of the essence, the SCDOT put the job out as an A plus B bid, which is not something the agency does often, Miller said. With an A plus B bid, contractors assign a dollar figure to each component of the job. That’s the construction cost. The B portion is the number of days in which the contractor estimates it will take to complete the job. The state then assigns a dollar figure for each day.
"For our project, the days were charged $15,000 each," Schwartz said. "We bid 600 days, or 20 months … Our construction costs totaled around $64 million, then they add 600 x $15,000, or $9 million to the $64 million. They do this for all bids and the lowest bid wins.
"Theoretically, your construction price could be higher and days lower and get the job. This job also had a C portion, so it was A+B+C. The C portion was the number of days utilizing a detour route for eastbound I-20, charged $20,000 per day. With our revised staging we eliminated this detour. We bid 20 days for the C, and used 0. The DOT will usually offer an incentive as well. We could finish earlier than 600 days and receive an incentive of $15,000 per day, up to 45 days.
"On the flip side, there are liquidated damages for going over the 600 days, also charged at $15,000. The incentive was a no-excuse, meaning additional scope / change orders, etc. could increase the duration and move the liquidated damage date, but the incentive is fixed at the 600 day mark. This type of bid allows the contractor to be innovative and think of different ways of performing the work. There is also the risk of going over the allotted days and paying liquidated damages. With the market being so competitive right now, these type of jobs can give some contractors an advantage if they are able to plan and perform the work efficiently."
The equipment used on the project included a Guntert and Zimmerman 850 concrete paver with a dowel bar inserter, a Leica Grade Control for the concrete paving, a Rexcon Batch Plant and the typical graders, dozers and loaders. At its peak, the job created about 85 jobs, with an additional 40 subcontractor employees.
Workers are set to switch to final stage of paving, casting the median barrier in place and striping before opening travel in all six lanes. The completion date is set for August 15.
"I think the public is going to be happy," Miller said.
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