A half-mile corridor of CA-70 adjacent to the Feather River had long been prone to washout by high river flows during the rainy season. Scope of work on this $28.3-million stormwater and safety improvement project included a half-mile soldier-pile retaining wall that averages 17 ft in height with a 12-in.-thick cast-in-place wall facing. The wall, which also protects a newly realigned section of highway and prevents bank scour, features a rock pattern finish to match the native environment.

The bidding process was delayed as a result of the second-largest wildfire in state history, the Dixie Fire, which burned nearly 1 million acres on and around the project location. That left the site unsuitable to visit for the contractor’s estimators, so the project’s scope couldn’t be evaluated as planned in July 2021 and instead had to be pushed to November. This forced the contract timeline to be pushed back to a less optimal midsummer 2022 start, shortening the time to perform work before winter.

Photo courtesy Q&D Construction

Delays created additional challenges as the beams for the soldier pile wall had a more than six-month production timeline because of supply chain impacts. But the contractor was able to expedite the beam production by accepting a staggered beam delivery schedule.

When drilling began on the project’s 30-in. shafts, crews quickly realized that underground conditions did not match project bore logs. This issue played a part in nearly all of the project’s subsequent challenges, doubling the duration of work in all remaining phases. As a result, the owner and contractor formed a proactive committee working to resolve cost implications, giving the contractor confidence to continue moving forward as back-end contractual issues were completed.

With the river located adjacent to the soldier pile wall’s footprint, the traditional process of digging a bench for the foundation was not possible. To maintain adequate room for the traveling public and to complete work, the project team used a top-down construction method. An 80,000-lb drill rig on the existing roadbed was equipped with down-hole hammer attachments in order to drill through the boulder-filled embankment.