Napa County has completed the construction of a new retaining wall and backfill to stabilize the hill at the site of a 2017 landslide above the Silverado Trail at Pratt Avenue in St. Helena, California. The new construction is intended to protect the roadway, increase public safety, and reduce Napa County’s maintenance needs.
After heavy rainfall in 2017, a portion of Silverado Trail at the eastern end of Pratt Avenue was closed due to a slope failure and the resulting roadway damage. A temporary catchment wall was constructed to allow Pratt Avenue to be re-opened while a long-term solution was developed.
WRECO worked as the lead designer for the permanent solution in coordination with Biggs Cardosa Associates and Miller Pacific Engineering Group.
The project included the following elements:
Approximately 0.16 acres of slope grading, slide removal, and rock slope protection;
Coordination with subconsultants on the design of the approximately 280-foot-long and 10- to 20-foot-high retaining wall;
Installation of approximately 50 linear feet of guardrail and transition railing;
Removal of traffic stripes, Type K concrete barriers, and guardrail;
Installation of 12-inch-diameter drainage pipe and flared end section;
New traffic stripes and roadside sign; and
Revegetation with native species, slope stability, and erosion control measures throughout the site.
WRECO was responsible for leading the design team and developing the plans and estimate for the roadway and drainage improvements, including grading, striping, temporary water pollution control, and permanent erosion control.
The new drainage features are intended to improve drainage, reduce water infiltration under the pavement, and facilitate future maintenance.
Biggs Cardosa Associates provided structural engineering and construction inspection services and Miller Pacific Engineering Group provided geotechnical services for the duration of the project.
The project was funded by Federal Highway Administration (FHWA) Disaster Relief through the California Department of Transportation (Caltrans) and local funds.