Flatiron West is in the midst of enhancing a three-mile section of Interstate 5 in southern Orange County for Caltrans and the Orange County Transportation Authority (OCTA). Traveling through the cities of Mission Viejo and Laguna Hills, the I-5 Oso Parkway Project is improving the freeway by adding one general purpose lane in each direction, from Alicia Parkway in the north to Crown Valley Parkway in the south.

The scope of work on this $130-million project includes constructing seven bridges in three locations, large scale paving operations, and significant improvements to drainage and electrical infrastructure.

Along with putting innovative engineering solutions in place to accommodate construction of these new structures, Flatiron is also working on active commuter and passenger rail lines – Metrolink and Amtrak, plus freight rail traffic, and various waterways.

The new El Toro Bridge crosses over a pair of live railroad lines.

Massive shoring work has already been completed on 22 retaining walls, which included permanent soil nails, vertical and horizontal ground anchors, and mechanically stabilized earth (MSE) systems.

New northbound retaining walls, above, have been successfully constructed. To ensure the stability of the homes at the top of the slope, extensive shoring was required.

Project Manager Jacob Cadmus stated that the entire job is moving more smoothly thanks to a great working relationship with HDR’s Clay Walker, who is serving as the Caltrans Resident Engineer on the project. “Clay is extremely knowledgeable, experienced, and Old School, which is greatly appreciated and proves to keep everything moving.”

Work on the Oso Parkway Project began in July 2019, and in order to make the completion date of May 2024, the bridge construction work is being accelerated. Once the current stage is completed, traffic will be shifted over 80 feet onto the new bridge to enable the start of the final phase of the project.

Alternate ramp closures are taking place at night to keep access to the freeway convenient without having to travel too far to enter or exit I-5. For northbound La Paz, a temporary off-ramp was constructed to accommodate the critical railroad work windows. “We are also able to maintain commuter traffic in both directions of the interstate with minimal interruptions during the day,” Cadmus stated.

The La Paz City Road Bridge deck pour is shown here underway.

But even with all of the strategic advance planning, there was still an unexpected challenge.

“While we were excavating for 60-foot drilled piles for the La Paz City Road Bridge, contaminated soil from leaking gasoline tanks was discovered,” said Cadmus. “The remediation work that had to be done – and continues to be done, threw a temporary monkey wrench into the schedule,” he continued. “But we’ve been able to make a few changes to accelerate the project in other areas.”