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NE Tolt Hill Road Slide Repair Project
May 30, 2024: The bridge is open to all traffic but requires temporary single lane closures at the west approach of the bridge. 24 hours a day, 7 days a week a portable traffic light is alternating two-way traffic into the one open lane.
Overview
Road Services is replacing the existing and damaged retaining wall with a new deep retaining wall that is designed to prevent erosion and will provide better protection for flood events. This project improves safety for travelers and restores the stability of soil under the west approach to the Tolt Bridge, over the Snoqualmie River near Carnation, WA. King County is removing the existing 55-foot-long gabion retaining wall and replace it with an updated 80-foot-long soldier pile retaining wall. This will shore up the soil under the southwest bridge approach and improve the stability of the nearby slope. This bridge is an important part of the east/west corridor in the Snoqualmie River Valley and a critical part of the flood evacuation route. Once repairs are made, the shoulder that was closed in March 2023 will reopen.
Status update
May 30, 2024
Lane restrictions began on Thursday, May 30th and will last for three-and-a-half months. A temporary signal at the bridge is alternating two-way traffic into the open lane 24 hours a day, 7 days a week.
Check MyCommute to see lane restrictions and road closures throughout unincorporated King County.
Project location
The active construction zone takes place west of and under the bridge. Construction equipment is stored on one of the two lanes of the bridge. The Tolt Bridge is located over the Snoqualmie River to the west of Carnation, WA. View larger image (661KB)
What to expect during construction
- Crews are working Monday through Friday.
- The bridge is open to all traffic and requires temporary single lane closures at the west approach of the bridge. 24 hours a day, 7 days a week a portable traffic light is alternating two-way traffic into the one open lane.
- Construction equipment is staged on the roadway requiring one lane to be closed.
- People living or working nearby may hear noise from jackhammers, trucks, generators, and other construction equipment.
Frequently asked questions
In February 2020, following a significant rainstorm, settlement and movement of the gabion wall was discovered, and engineers implemented survey and visual monitoring of the ground movements from that time. In addition, a real-time monitoring system was installed on the tilted wall and the west approach to the bridge to allow the engineers from their office to monitor the movement of the impacted area.
Gabion retaining walls are shallow walls built of rectangular wire mesh boxes filled with rock or other materials, then stacked in “cells.” They are most commonly used as retaining wall structures and can often be seen along the sides of roads and highways holding back cliffsides to retain soil.
Soldier Pile retaining walls are designed by geotechnical/structural engineers to prevent soil settlement, lateral movement, and erosion that can undermine an existing structure. During construction crews will place large steel piles in pre-drilled holes deep in the ground and then place panels between the piles.
Sample photo: gabion retaining walls are made of wire mesh boxes and filled with rocks.
Deep soldier pile retaining walls are built to prevent the lateral movement of soil.
Project photos
November 2023: Orange traffic cones were in place to block vehicles from using the shoulder of the bridge directly above the existing wall.
Construction will require temporary single lane closures and will alternate two-way traffic into the one open lane using a portable traffic light. Once construction has concluded, the current shoulder restriction will be removed. View larger image (3MB)