ITD devises plan to address byway cracks

SANDPOINT — The Idaho Transportation Department has developed a plan to address settlement of the Sand Creek Byway.

A reinforced soil embankment settled more than anticipated, causing cracks in an approach slab to the byway’s mainline bridge over Sand Creek, according to documents obtained by The Daily Bee.

Settlement also created a vertical offset between the south end of the approach slab and a sleeper beam, a reinforcing structure which helps support the slab. A vertical offset also developed between the bottoms of a dual-tube metal guardrail as it transitions from the approach slab to the mechanically-stabilized earthen wall coping south of the approach slab.

“We always expected some settling on the whole project. That was sort of a given,” said ITD spokeswoman Barbara Babic.

Babic said the approach slab settled less than the fill did, which was compounded by the dissimilar settlement rates of concrete and asphalt.

The North Idaho Community Action Network, a group which formed to oppose the U.S. Highway 95 rerouting project in order to protect Sandpoint’s waterfront, also predicted the project would settle.

Terry Howard, a geotechnical engineer hired by NICAN in 2004, predicted that some retaining walls would settle by as much as a foot.

“There will be adjustments of each structure to the settlement that will require repair and/or replacement and more likely than not the roadway surface will be undulating due to the differential settlement,” Howard said at the time.

However, the settlement does not appear to be as pronounced as Howard predicted.

Project officials have outlined a 13-point reconstruction procedure to address the cracks and offsets.

“It’s still subject to change before they finalize exactly what they’re going to be doing,” Babic said.

The plan proposes removing and reconstructing the approach slab and coping to match the original design profile. The reconstructed approach slab will include a continuous inverted curb to allow future slab jacking in case the embankment continues to settle, according to ITD’s modification plan.

A horizontal void will be created between the underside of the approach slab and the roof of an abutment to allow for future settlement, the plan further states.

The top of the sleeper beam will be removed and recast to match the original profile, although reinforcement in the sleeper beam will be retained and protected, according to the plan.

Babic said ITD will pay for the modifications since the settlement was not the fault of Parsons RCI, the project’s lead contractor.

“It’s just part and parcel of the project,” Babic said.

A cost estimate for the modification was not immediately available because the finer points of the plan are still under review.

“ITD has provided with a set of revised drawings that we’re reviewing right now that details some corrective action they would like to see on the south end,” said Shane Webley of Parsons.