Thursday, November 5, 2020

Anatomy of designing a complex repair: How we’re working to restore SR 203

Update: November 18, 2020
On Monday, Nov. 30, contractor crews will close all lanes of SR 203 south of Northeast Stillwater Hill Road between Carnation and Duvall. During the closure they will install drainage pipes under the roadway and in the hillside above. We expect these repairs, and the associated closure, to last through mid-January 2021. When this work is complete, we will open both lanes of SR 203 and spend the winter months finalizing a more permanent design-construction solution.

During this around-the-clock closure, a signed detour will route travelers onto local roads.

Why a full highway closure?
Several factors drive this decision for an extended closure of the highway. Our first priority is for the safety of the people on the jobsite and the traveling public. There is simply not enough space on this narrow roadway to provide a safe space for crews doing the work, the equipment needed and still maintaining a safe distance for an open lane for travel.
By Frances Fedoriska

We often talk about what's going on with a road project – it's usually visual so it's easy to do. But you may not know what happens before the actual work starts. So we want to peel back the proverbial curtain and show you how a highway project goes from being a reported roadway issue to a shovel-ready construction job.

In this case, the SR 203 repair.

Our efforts to repair the highway between Carnation and Duvall following a slide almost 10 months ago has mostly been happening behind the scenes at the makeshift home offices of dozens of our employees from across the state.

In January 2020, a major winter storm destabilized a hillside and damaged southbound SR 203 between Carnation and Duvall.
A winter storm in January 2020 led to significant damage on SR 203 between Carnation and Duvall.

In the weeks that followed, we installed temporary traffic signals to alternate travelers through a single open lane. Our crews installed monitoring devices into the roadway and surrounding area to find the source of the slide. Then it was March, and COVID-19 really arrived.

Unforeseen delays
In an effort to slow the spread of COVID-19, the state issued a mandate in March to halt all construction for most of the spring. When King County returned to Phase Two-type construction allowances, we were grappling with workforce reductions and state-mandated furloughs. Both situations set back our timeline for designing a solution to repair the highway and prevent future slides.
A look at the rainfall totals, including for the winter storm that contributed to
significant damage on SR 203.

The process
The pandemic doesn't know or care about our process for taking a roadway incident through the paces to becoming a construction project. Many Washingtonians don't either. Here are the eight steps we most commonly use for major highway repairs. For reference, we are at Step 6 for designing an SR 203 solution.
  • Step 1 – We recognize a problem with a highway following a report of an issue from a source such as a traveler or our own crews.
  • Step 2 – The problem/emergency is defined (in this case as a complex roadway failure requiring more investigating) and our Region Materials Engineer (RME), Region Maintenance and typically the Project Engineer Office (PEO) in the area will discuss if there is a quick repair or mitigation that our maintenance group can make.  In the case of SR 203, the issue was too involved for a quick maintenance repair and we determined we needed a more in-depth assessment of the area/situation. During this process, we installed monitoring equipment in the roadway to collect data regarding ground movement and water tables.
  • Step 3 – Once we determine the source of the failure, we discuss possible repairs. In this case, a typical repair would be a buttress (removing failing soil and replacing it with large rocks). For SR 203 this repair was not recommended due to potential environmental effects requiring possible further exploration. A geotechnical engineer (GE) was assigned to this incident to start recommending other possible structural repair options.
  • Step 4 – Our geotech engineer collected additional information about what's happening under the roadway from the meters we installed,  field visits to the highway, field explorations (borings drilled below the ground surface) and laboratory tests on collected soil samples. This exploratory process was on hold until July due to COVID-19 restrictions. With more information, our engineering geologist (EG) and geotech engineer worked together to determine the layers of soil beneath the roadway. Think of it as building a layer cake, with the icing on top being the asphalt. Using this model, they can determine which layers of the cake failed. From there, our team can consider what type of repair is best for this given location.
  • Step 5 – We evaluate the proposed structural repairs based on which best balances feasibility and limiting cost to the taxpayer. At this point, our Bridge and Structures Office (BSO) gets involved to discuss the designs and which are cost-prohibitive to build. For SR 203, this step produced two feasible designs: a buttress, or a retaining wall/ground improvement hybrid solution. This combination of structural solutions is relatively unique for this type of project. 
  • Step 6 – Our geotechnical engineers get help from the project engineering and bridge and structures offices to put together plans and an estimated cost for the repair. Because this SR 203 project has two repair options, both have their own feasibility and estimate assessments. Ultimately, the project engineering office will lead the decision on which alternative to carry through to construction.
  • Step 7 – We develop a final design, cleaning up any loose ends from the preliminary design. At this step we are double-checking our work before …
  • Step 8 – The project goes to "Ad" – we advertise the opportunity for contractors to examine the scope of the work and bid on the project.

When working on a repair to SR 203, our engineers determine the layers of soil
beneath the roadway to determine where the failure occurred.

We know showing the steps being taken to restore SR 203 to a two-lane highway won't change anyone's experience on the road tonight or tomorrow. Like many highway projects, the earlier pause and resulting challenges that COVID-19 presented set us back and that's been frustrating for all of us. We don't have an exact timeline for when this will all get done and road work will begin, but we must do the job right, so we are doing all we can to make sure the right people are overseeing the right design to restore this highway and prevent future emergency closures.


CuriousInDuvall said...

1) In Step 3, a buttress is not recommended, but it is one of the feasible alternatives in Step 5. Explain. 2) Assuming the figure represents soil layers, describe them (especially Soil Units 1,2,5), and please explain which “layers of cake” failed (as described in Step 4).

PL said...

Since the closure date is set, can you tell us which you went with? Buttress or retaining wall? Will these solutions be used on hill below the road only or on the hillside above as well? Do you have a work up on the cost of each and the amount of time for 'permanent' repair? Can we expect a permanent repair next summer? After the drainage is installed, will the lane be paved and full width or will there be a narrowed lane like was done on the Novelty Hill collapse? Thank you for your speedy response!! _ Paula

WSDOT said...


Starting Monday, Nov. 30, contractor crews will install drainage under the roadway and up on the hillside over SR 203. The work being done is a temporary fix that will allow us to use the winter months to finish going through the design-construction process for a permanent solution, while reopening all lanes of travel in this area.

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