Purdy Creek Fish Barrier Removal

In the Pacific Northwest, management of natural resources, including the extensive network of streams and rivers, are of utmost concern. We rely on these resources for generating power, food, drinking water, and transportation of goods, and many local economies are dependent on their long-term sustainability. As growth and expansion continues, management of these resources becomes more complicated, with the need to improve existing and outdated infrastructure.

The summer construction season brings many fish passage improvement projects. These projects often involve temporarily bypassing existing streams to remove and replace outdated or failing culverts. The benefits of these projects are twofold: they allow infrastructure improvement while also removing barriers to migratory fish that travel upriver to spawn each year.

D.H. Charles Engineering was recently tasked with designing temporary excavation shoring for a fish passage project on SR 16 in Pierce County, WA. The project involved removal of an existing 6’-diameter culvert pipe running through the roadway embankment, and replacement with a natural streambed. Traffic would ultimately be routed over two new bridges, spanning roughly 200’ over the streambed below. To allow for construction without disruption of traffic, a staged approach was used, which maintained one direction of existing SR 16 while the other direction was diverted onto a temporary bypass. Due to the staged construction, temporary excavation shoring was required to support and protect the roadway and allow construction of the bridge foundations.

Our scope consisted of designing cantilever and tie-back soldier pile shoring at depths ranging from 10’-35’ for construction of the bridge piers. The Contractor elected to use W14x120 piles already in their fleet. Piles were spaced at 8’-4” on center to accommodate steel road plates between the pile flanges at bays without tie-back anchors penetrating though the shoring. Where tie-back penetrations were required, timber lagging was used to shore between piles. At depths of approximately 12’ or less, cantilever piles were used without the need for bracing. Beyond 12’, double channel walers and tie-back anchors were used to support the piles. Tie-back loads ranged from 90-115 kips. Engineered solutions like this anchored soldier pile shoring system allow for safe support of deep cuts with significant surcharge loads, while offering maximum flexibility of layout and materials to fit the Contractor’s needs.

As a native of the Pacific Northwest, I love working on these types of projects. They always bring unique challenges ranging from the complex ground conditions to the tight in-water work windows. Partnering with great contractors to tackle these projects and improve local infrastructure is one of the most satisfying parts of my job and always keeps me coming back for more!