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Robertson Ranch Wildlife Crossing

Carlsbad, California

Wildlife Crossing


Toll Brothers


O'Day Consultants


Nove Engineering


Fall 2014

Technical Description:

• Diameter: 18'
• Length: 226 ft.

Robertson Ranch is a master planned community owned by Toll Brothers and located just three miles from the beach in Carlsbad, California. The 400-acre development offers “luxury coastal living” and contains single-family homes between 1,500 and 5,000 square feet. In order to fulfill requirements from the California Department of Fish and Wildlife and the Army Corps of Engineers, a wildlife crossing was needed beneath Gage Road. The new structure provides vehicular access over the structure so that residents may access their homes, while enabling a safe crossing for wildlife below.

Multiple structure options were evaluated, including but not limited to, cast-in-place concrete, precast concrete and structural plate. Due to the height of cover being over 35’, it was determined that a structural plate solution was the most cost effective solution, and an 18' diameter MULTI-PLATE®, 226' in length, was selected as the best option. Additionally, the round MULTI-PLATE option negated the pile foundation requirement that would have been required with other types of structures. In order to size the structure properly for both a wildlife crossing and a 100 year storm conveyance, an openness ratio was utilized.

During the design phase, the location of the project was also taken into account in order to determine the best way to maximize the life of the structure. With the project located so close to the Pacific Ocean, there was a strong potential for corrosive soil conditions, so the PH and resistivity levels were considered. During collaboration meetings between Toll Brothers, the on-site geotechnical firm, LGC Valley Inc, and Contech Engineered Solutions, it was determined that a more suitable non-corrosive backfill, sourced from within the project site could be utilized resulting in significant savings to the overall project, while achieving the desired 100 year design life for the structure.

In order to maintain continuity for wildlife while encouraging them to use the new structure, native foliage was planted both outside and throughout the interior of the structure, concealing the wildlife passage from the public eye and creating a private space for animals to inhabit. In the end, the project was a great solution for the site, and Toll Brothers and O'Day Consultants, the project's engineer, were pleased with the outcome.

Technical Description:

• Diameter: 18'
• Length: 226 ft.

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