Replacement begins Monday of washed-out culvert in Renton on northbound I-405 to Bellevue

Starting Monday, crews will begin installing the new culvert that will carry Thunder Hills Creek underneath Interstate 405 near Benson Road in Renton.

Last December’s rain storm created a torrent of water that resulted in a sinkhole along the I-405 and the collapse of the old Thunder Hills Creek culvert. New culvert installation will occur between 7 a.m. and 4 p.m. on weekdays, and should continue for four to six weeks. Replacing the culvert will protect I-405 against flood damage during future storms.

When the old culvert collapsed crews set up two emergency systems to divert Thunder Hills Creek away from the culvert to protect the stability of I-405: One system pumps creek water into a storm drain along the I-405 shoulder. A second system engages when creek levels rise and pumps water into a 2000 foot-long pipeline that carries water into wetland on the other side of I-405.

The new culvert installation involves pushing steel pipe sections into the ground underneath I-405 using a boring machine. Crews will weld the 20-foot-long sections together to create a continuous pipe underneath the freeway. When complete, the new culvert will be 470 feet long and 51-inches wide. The new culvert will be 140 feet longer than the old culvert to accommodate widening of this section of I-405.

During culvert installation drivers should expect intermittent weekday single-lane closures from 9 a.m. to 2 p.m. on Benson Road. Additionally, from 10 p.m. to 5 a.m. on Monday, June 16, and Tuesday, June 18, crews will close the northbound I-405 HOV lane in the vicinity of State Route 515 to complete work to fill and seal the old culvert.

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