Date:
Tuesday, December 11, 2007
Contact:
Greg Phipps, WSDOT Communications, 206.440.4702 (Shoreline)
Travis Phelps, WSDOT Communications, 206.440.4472 (Shoreline)
RENTON – WSDOT engineers are working on an emergency plan to replace a failing culvert that runs underneath I-405 in Renton. If the culvert is not repaired, more rain could lead to more significant erosion and possibly undermine I-405 near Benson Road S. and Main Avenue S.
“The Dec. 3 rainstorm overwhelmed many of our culverts. Nearly all handled the load well. A couple, like this one, did not,” said Dave McCormick, WSDOT Assistant Regional Administrator for Maintenance and Operations.
In the days after the storm, crews discovered a large 30-foot-deep by 30-foot by 80-foot sinkhole just 12 feet from the southbound shoulder of I-405. Crews immediately closed the lanes and poured about 700 cubic yards of rock into the hole to prevent more sliding. The slope at the sinkhole site is now secure.
Upon closer examination, they determined the 400-foot long culvert that carries Thunder Hills Creek from the east side of I-405 to the west was failing. The culvert collapsed and the sinkhole formed immediately above it. WSDOT engineers are designing a plan to replace the culvert. That work could take up to eight weeks.
The more immediate problem is winter storms. Because the culvert is not working, water from the creek has nowhere to go. If a significant storm were to hit the Puget Sound, the water could potentially lead to a collapse of the roadbed.
To prevent this from happening, crews will begin work Thursday night to build a pump and pipe system that will divert water around I-405. To install this drainage system, crews will close one right northbound lane 20 hours a day for up to two weeks. The round-the-clock lane closures could begin as early as this Friday. WSDOT recognizes the significant amount of traffic in the area and we will make every effort to open all lanes in the northbound direction during the peak morning commute.
Crews need to lane to store equipment and personnel as they build the pumping station and lay the pipe.
“We know this will lead to congestion in Renton. There are only three lanes in the area,” said WSDOT Project Engineer Lisa Hodgson. “But if we don’t have these pumps in place and we get another big storm, we could be forced to close I-405 entirely. And that simply isn’t an option.”
WSDOT traffic engineers are studying the plans and working with project engineers to find ways to do the work as quickly as possible with the least amount of disruption to traffic.
Once the pipe is in place, crews will begin the long-term repair work. This work involves replacing this 48-inch culvert under the freeway. Although engineers haven’t exactly settled how they will get the new pipe into place, they know it will likely NOT involve closing lanes on I-405. However, it is very likely the work will be noisy. WSDOT will work with local officials and residents to minimize the inconveniences that noise can cause.
Because this is emergency work, the nature of the lane closures is changing. WSDOT advises drivers who use this freeway to stay on top of the closures by:
Engineers do not have a firm cost for this work, but repair work alone is estimated at $5 million.
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