Wednesday, August 5, 2020

Elementary, my dear WSDOT

Some cool tools – aka underground detectives – do the dirty work under SR 203 when we aren't able to

By Frances Fedoriska

A level of "subterranean sleuthing" will help us determine why a portion of State Route 203 suddenly shifted earlier this year. Without Sherlock Holmes around, we can't crack this case without the help of some devices designed for undercover dirty jobs like the one unfolding under the highway between Carnation and Duvall.

Following a landslide in early 2020, we planted multiple devices under mounds of dirt, rocks and debris under the highway. Since then, they've been collecting information needed to design a fix for the slide – in places and times when we can't access the area.
Exhibit C – for "cracks." This gash in the asphalt on SR 203 shows how much the ground underneath
the roadway moved during a slide earlier this year.

Exhibit A: The timeline
Here's a quick recap of how we got here:
  • Early 2020 – A slide causes part of the southbound lane between Carnation and Duvall to give way. Since then the lane has been closed with traffic alternating through northbound SR 203.
  • March 23, 2020 – The global pandemic prompts the Governor to issue a "Stay Home" order to slow the spread of COVID-19, halting most construction in our state to keep workers safe and at home. 
  • June 19, 2020 – King County enters Phase 2 of the "Safe Start" reopening plan. This gives our personnel permission and new guidelines to safely get back to work in the field, investigating the cause of the slide.  
  • July 15, 2020 – SR 203 closes for a day allowing crews to access the area and collect subsurface information from devices installed into the sinking side of the roadway. We also searched for a historic waterline in the northbound shoulder.
Star witnesses: inclinometers and piezometers
Inclinometers measure embankment movement. The metal casing – basically a large, specialized pipe – is placed inside a hole drilled into the roadway and then bends when the ground or road around it moves. A probe is lowered into the casing to measure any deformations to determine how much movement happened since the previous reading.
Two key devices, both resembling metal coffee tins, tell us what is happening under the highway by
measuring movement without tearing up the road.

Piezometers monitor groundwater levels underneath the road. This is crucial to predicting future movement needed to prevent future slides. An open standpipe piezometer -- a long, narrow pipe placed inside a bore hole -- collects groundwater. Periodic manual readings of how deep the water level is shows whether there's a change – or movement – in the ground below that allows water to seep up or out of the ground.
In late July we took manual readings from the piezometer to monitor groundwater levels under the roadway.

Next steps
It will take a few weeks to assemble all the clues and translate the data we've collected into a confirmed source of the slide. Once we know the cause, engineers will design a solution that fixes the damage done and prevents future occurrences so we can safely reopen all lanes of SR 203.
Masked up and physically distanced, a crew member enters measurements into the system. The data logged in the
field will be analyzed by our geotechnical team in Olympia.

Thank you for your patience
We understand travelers are frustrated with the delays and speed at which this project is unfolding. We are too. At this time, there is no date for when construction may begin, but our goal remains getting started before the next rainy season.

To stay up to date on the developments, sign up for WSDOT's King County updates. A project webpage will be added to the WSDOT website once this mystery is solved.

1 comment:

Linz said...

Is there an update on this project? Rainy season is here...

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