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Archive for Thursday, May 23, 1996

TRAFFICWAY BRIDGE SETTLING CREATES CRACK

May 23, 1996

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State transportation officials say they'll take steps to counteract settling on the new bridge over U.S. Highway 40.

Settling underneath the approach slabs on the new U.S. Highway 40 bridge over the South Lawrence Trafficway won't affect the integrity of the structure, engineers say.

The settling is visible on the south edge of the eastern approach, where the concrete barrier railing has separated from the platform beneath it. The gap, which is at least half an inch wide in places, is about three feet long.

Ralph Gripka, the Kansas Department of Transportation's construction engineer for the Lawrence area, said mudjacking would be used to elevate the approach slab back to the level of the bridge itself.

``On almost every bridge built there's settlement ... and it usually shows up pretty quickly,'' Gripka said. ``This isn't a major problem.''

The five-lane bridge was completed in September.

The bridge itself rests on pilings driven into bedrock while the approach slabs float on fill dirt. Gripka said the settling of an approach slab accounts for the bump that motorists feel when they drive onto a bridge.

However, in this particular instance the silicon sealant in the seam between the railing and the approach slab didn't hold. A peculiarity in the bridge design allowed water that seeped through the gap to collect under the approach slab, accelerating the settlement.

Gripka said a slight modification in the design of the other three bridges over the trafficway would prevent that from happening elsewhere.

KDOT has not developed an estimate for the mudjacking cost.

``I hope it's just a few thousand (dollars) at most,'' Gripka said.

The bridge was designed by HNTB Inc., the Kansas City engineering firm that is designing the trafficway.

Even though the design contributed to the problem, ``KDOT's going to pay in this instance,'' he said.

``It's not entirely the the designer's fault because KDOT oversees it,'' Gripka said.

Douglas County Engineer Frank Hempen disagreed that the design was to blame.

``There are thousands of bridges designed just that way that function very well,'' he said.

In any case, John Pasley, a civil engineer who is the trafficway project manager for Douglas County, said he was satisfied that KDOT was taking care of any problems.

``You always get settlement between the bridge and the pavement,'' he said. ``It's a normal thing to have happen.''

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