Soldier Pile Retaining Wall and Slope Slide Stabilization on Hwy 49

California Highway 49 used to be the main route for gold diggers of the 1850’s. The picturesque region around the historic route continues to be a touristic attraction, especially around the American River.

The California Department of Transportation (CALTRANS), the owner of State Route 49, detected and recorded landslide movements over the years at mile post (MP) 37.82, near the city of Auburn, El Dorado County, 0.4 mile south of the North Fork American River Bridge. CALTRANS’ original slope stabilization design specified slope stabilization consolidated with micropiles.

The project was awarded to the experienced contractor Condon-Johnson & Associates, Inc. (CJA), Oakland, CA. CJA realized that challenging conditions would be encountered with the original design, so they developed a Cost Reduction Incentive Proposal (CRIP) design. They hired specialized structural engineer P B & A Inc. of San Anselmo, CA to finalize the design of the retaining wall.

The final project specified passive permanent, 46mm (#14) grade 517 MPa (75 ksi) DYWIDAG THREADBAR® tieback anchors with a 35-ft unbonded zone, working in conjunction with structural steel soldier piles and a cast in place concrete grade beam. The tieback anchors were produced using the DYWIDAG double corrosion protection system.

In order to monitor future slope movements, twelve DYNA Force® Sensors were installed on the bars, close to the anchorage at alternate locations. Up to 30m long lead wires were conducted to a waterproof box where the CALTRANS instrumentation team will have access for future load monitoring. Proof and performance load (666 kN) and lock-off load (0 kN) produced by the stressing equipment were verified by the reading unit.

The soldier piles and anchorages were embedded inside the concrete grade beam and the entire area was covered with original soil which was brought to the initial slope.

Supplytechnical assistance

California Department of Transportation (CALTRANS), Sacramento Office, USA

PB& A Inc., Structural Engineers, San Anselmo, CA, USA