PB&A, Inc. was hired by AECOM during the bidding stage of the Carroll Canyon Project in San Diego CA in order to find a better, more economical solution to the Permanent Retaining Walls needed on both sides of the Direct Access Ramp that would take traffic under the 805 Freeway onto Carroll Canyon Road. With our innovative design and cutting edge analysis programs we were able to come up with a design that would save the project millions of dollars in construction costs. The wall across the freeway had been designed and constructed previously at a cost of $20 million dollars more than the estimate to build the PB&A walls.
AECOM was the successful bidder and PB&A was retained to design the walls. Innovative design elements contributed to the success of these walls:
- V-Nails – PB&A used V-Nails to add additional stability during construction of the wall, which took place under a live freeway.
- PB&A proposed an alternative design for the traffic barrier that would be integrated into the permanent Soil Nailed Retaining Wall that would eliminate the back slab needed for the conventional traffic barrier solution. We had previously used this design successfully with Caltrans approval for Permanent Retaining Wall #301 along the I-15 in San Diego.
Some praise from our Client, AECOM
“Here are some comments for you regarding PB&A’s work with us on the I-805 North Design Build project.
- PB&A’s design for the soil nail and ground anchor retaining walls for the Carroll Canyon Direct Access Ramp was very innovative, especially when compared to the retaining walls TY Lin designed for Caltrans for a similar Direct Access Ramp just to the north of our project. I’m sure their innovative design and associated cost savings had a big part in our successful bid for the project.
- The soil nails and ground anchor walls for our project are approximately 1,200 ft long and up to 45 ft high. And the walls are located in a very sensitive location as they support the I-805 freeway lanes and two bridge abutments immediately behind the walls. Their innovative design for these wall also included vertical soil nails, which when analyzed by a finite element method, have a predicted max displacement of 0.41 inches! (This is absolutely remarkable for a wall this tall!)
- So, PB&A designed an innovative wall that saved millions of dollars, and is expected to perform much better than a traditionally designed soil nail / ground anchor wall. They certainly understand retaining walls, and temporary shoring, better than anyone that I have worked with in my 35 years as a civil engineer!
- Their original design included an integral concrete barrier on top of the wall that saved approx $1,000,000 dollars and reduced the space needed to construct the wall. They provided supplemental calculations to show that this design was feasible. When Caltrans did not approve this concrete barrier concept, PB&A provided documentation showing that Caltrans had previously approved this concept on another project in San Diego which helped Skanska successfully obtain additional compensation for this project change in a dispute settled by the DRB.
If you have a technically tough project that needs to be completed cost efficiently, then I would recommend PB&A to you! I have enjoyed our work together on the I-805 project and hope to work again with them again soon.”
Thanks, Mike Crull,
Design Manager for the I-805 Design Build Project