Flatiron West recently completed work on the Interstate 5 Oso Parkway Project and the newly widened roadway in Mission Viejo and Laguna Hills, from Alicia Parkway in the north to Crown Valley Parkway in the south, is now fully opened to traffic. This section of I-5 is the third-most traveled roadway in the Untied States, carrying an average of 415,000 vehicles daily.

Looking southbound over the newly completed JPCP lanes of I-5.

“The success of the project,” said Flatiron West Project Manager Jacob Cadmus, “was thanks to the effective collaboration between Caltrans and Flatiron throughout the entire construction process. Specific challenges came to light once we got into the work that required modifications. Caltrans was great to worth with.”

The La Paz Undercrossing Bridge and the newly paved I-5 freeway.

The scope of work included widening nearly three miles of Interstate 5, adding extra general-purpose lanes in each direction, together with ramp auxiliary lanes to alleviate current and future transportation demands. Compounding the normal difficulties encountered when working on a heavily traffic highway, Flatiron also had to work above busy roadways and active commuter and passenger rail lines – Metrolink and Amtrak, plus freight rail traffic, and various waterways.

Along with Caltrans, Flatiron worked with the Orange County Transportation Authority (OCTA) on the project.

Seven new bridges in three different locations were built. While constructing the foundations at the La Paz Bridge, hazardous materials were discovered and the drilled spoils generated from the Cast-in-Drilled-Hole (CIDH) installations had to be monitored, contained, and hauled offsite; especially difficult work due to the tight site constraints.

Jacking operations take place at the abutment of the La Paz Undercrossing Bridge.

Two of the seven new bridges required a call to Flatiron’s Construction Engineering Group. The two bridges required the superstructures to be built high and then lowered into their final position once the superstructure was at strength and stressed, enabling the falsework to be removed. The Construction Engineering Group developed plans that included jacking bents, 100-ton and 200-ton hydraulic jacks, jack stands and shims, and a robust lateral and vertical restraint system. An innovative new computerized system was employed to allow precise motion control and lowering of each jack in sync together at ¼” intervals, with 20 carpenters on site to support the operation.

The La Paz Bridge superstructure was lowered into its final position in ¼” increments.

More than 43,000 cubic yards of Jointed Plain Concrete Pavement (JPCP) was placed.

Additional work featured the installation of 22 retaining walls, with soil nails, vertical and horizontal ground anchors, and mechanically stabilized earth (MSE) walls. All drainage and electrical systems were upgraded as well. The project value was $148 million.

Big thanks and a tip of the hard hat go out to Flatiron Project Manager Jacob Cadmus for all of his generous contributions to this story.