The designer of a road construction project on the Intercounty Connector (ICC) in Montgomery and Prince George’s counties, Md., was able to adapt the original plan to better suit the environment and save money by using engineering innovation to solve problems with existing natural conditions.
The project’s original design went through an “alternative technical concept process,” in which each of the design-build teams can propose ideas to modify the plan. Dewberry, the designer, pitched an idea that would reconfigure the interchange by reducing the number of flyover ramps—and save about $75 million.
The main alignment approaching I-95 was near an old quarry, with many wash ponds in the area.
“We ended up realigning the mainline of ICC to the south a few hundred feet, allowing us to avoid some of the adjacent wash ponds and provide a different interchange configuration, thus avoiding a large amount of bridge structures,” Dave Mahoney, the project manager, told ROADS & BRIDGES.
The state’s original design placed bridges over those wash ponds, which Mahoney said were 40-50 ft deep and contained sediment from the gravel-pit operations.
“We used wick drains to slowly fill in those wash ponds and pull the water vertically out of the material, dry the material and turn it into an embankment for the roadway,” Mahoney said. “We avoided the need to build long bridges with very deep foundations to reach the bottom of the wash ponds as well as the need to find material to set the bridge in. That was a real strategy, to improve that area instead of building a bridge.”
The realignment of the interchange and use of wick drains helped to reduce the bridge structure area by more than 200,000 sq ft. Originally, 29 storm-water-management ponds would have been affected by the design; after redesigning and rerouting drainage, only 14 ponds were affected, reducing impact to the surrounding property owners and the environment.
