NV5 - Gypsum Ditch Bridge

Sandy & Gypsum Ditch Bridges for Wind Energy Project

The Ocotillo Express Wind Farm had been approved, and site grading was under way. Because the gypsum plant in the area had direct access to heavy rail delivery directly to their plant, the Ocotillo Express Wind project made use of the rails and the plant to have all their turbines and other materials shipped by rail and stockpiled at the plant for trucking directly to the site, which was less than a couple of miles away. To get to the project site from the gypsum plant, all trucks had to cross over two old timber structures (Sandy Ditch Bridge and Gypsum Ditch Bridge) that are owned and maintained by the County of Imperial, Department of Public Works. The wind energy contractor, Blattner Energy, needed a permit from the county to use these bridges. Due to the age (80+ years) of both structures, and the fact that the trucks would be carrying much heavier loads than standard highway loads, the county tasked Blattner with the preparation of a load rating analysis of both bridges before allowing any trucks to cross.

Blattner asked NV5 to thoroughly inspect the bridges and perform a load rating analysis to determine the feasibility of having these overloads go across. NV5 performed the investigation and prepared a recommendations report that would address all deficiencies to allow the use of both bridges by Blattner Energy.

NV5 was also tasked with inspecting the work performed by the contractor to ensure compliance. After some heavy rains and flash flooding, the sandy soil around one of the exterior columns at Gypsum Ditch Bridge had been scoured by over 2 feet, exposing a large vertical crack. Upon closer inspection, we noticed that the wood had rotted from the inside out, and the column was buckling every time a loaded truck was going over it. Construction was halted, and traffic over that column was immediately shut down. Traffic control was set up for one lane at a time over the bridge. NV5 recommended casing the column and injecting it with high strength grout from the bottom. Four thousand psi strength was attained within 5 days, and traffic was opened in both directions. When all construction was complete, NV5 was tasked with monitoring the first crossing of the heaviest load, approximately 384,000 pounds. Every truck was stopped at the approach end, and crossed at 5MPH to eliminate the effects of impact loading.


Imperial County, CA


Blattner Energy


Bridge Design & Inspection Services

Key Facts

  • 80+ Years Old
  • 384,000-lb. Payload
  • 4,000 psi Strength