This map shows the South Lawrence Trafficway interchange at Bob Billings Parkway. The dashed red lines represent existing culverts that have caused a delay in the project's completion. The red rectangle shows the areas where the portions of the roads crossing the culverts must be repaved.

The South Lawrence Trafficway interchange at Bob Billings Parkway will require a few weeks longer — and $2.1 million more — than planned because portions of the constructed roads had sunk.

Kim Qualls, a spokeswoman for the Kansas Department of Transportation northeast district, said portions must be redone on the eastbound and westbound lanes of the extended Bob Billings Parkway west of the SLT, as well as on the nearby southbound ramp.

The roads will cross the top of an existing culvert. Foam was put in place to provide a cushion between the culvert and the subgrade earth, and the roads were paved on top of the foam, Qualls said.

Qualls said foam is a relatively new technology, but it is used frequently in construction situations such as jacking up pavement that’s approaching bridges or filling in where concrete panels settle in highways.

This map shows the South Lawrence Trafficway interchange at Bob Billings Parkway. The dashed red lines represent existing culverts that have caused a delay in the project's completion. The red rectangle shows the areas where the portions of the roads crossing the culverts must be repaved.

In this case, the foam between the culvert and pavement crushed further than it should have, Qualls said. The curbs stayed in place, but the roadway started to sink.

Qualls said all the pavement and curbs had to be removed as well as the foam, which she said was like pulling packing peanuts out of the ground.

“It’s been a pain getting (the foam) out,” she said.

To remedy the problem, reinforced concrete slabs will cover the culvert. The slabs will be covered with earth, and the roads will be paved on top of that.

“It’s a more traditional approach to do the slab, the earth, and then pave back over,” Qualls said.

Qualls said this is an isolated problem caused by the pre-existing culvert. It will not affect other stretches of the road, nor was foam used in any other portions of the interchange project.

Fixing these unforeseen issues will cost an additional $2.1 million on top of the total cost of the interchange — approximately $18.23 million. Qualls said the cost will be added to project construction costs to be paid by KDOT.

“It is definitely a chunk of change, for you and I,” Qualls said. “But in that magnitude of the project, and how long this project will live into the future, it is important that if that happens, we get it corrected.”

The interchange at Bob Billings Parkway was expected to open in late November. Only arterial roads and bike paths on the east side of the SLT will be open Nov. 25, Qualls said. As with any major construction project, scheduled dates are dependent on the weather.

Ramps to and from the SLT will not open until Dec. 18, at which time the arterial roads on the west half will open, also weather permitting.

Adjacent work near the interchange will continue until Jan. 30. That’s what Qualls said KDOT typically calls “finishing work” — the last of the seeding and cleanup in the area surrounding the road. She said that work won’t cause any major shutdowns.

Pavement markings will depend on what kind of weather the winter brings, also. Markings may have to be temporary until spring, but permanent markings are scheduled for completion by May 6.

“Sometimes that’s just what happens when you get so close to winter, so they’d just go back and apply those permanent pavement markings in the spring, as needed,” Qualls said.

Qualls said KDOT would not have expected the foam that’s used so frequently to crush.

“Traffic’s traveling over the foam underneath the concrete,” she said of other locations where the foam has been used. “It’s a technique that’s used quite a bit, but in this particular case, the foam just condensed and didn’t hold up.”

She said in any project, “even in the best of worlds,” nature can present unexpected circumstances.

“It’s a lesson learned, and that’s something that can then be applied to other projects,” she said.