Burbank Water and Power Plant

Retaining stormwater is a massive challenge in the dry Southern California climate and stormwater retention and infiltration infrastructure is a critical piece of the water puzzle. However, placing these large preconstructed basins underground presents another challenge in itself. There are only a few ways to get a 275,000-gallon stormwater storage basin 20 feet underground after all. At D.H. Charles Engineering, we specialize in one of these ways, designing safe and efficient excavation shoring systems to facilitate these installations. And recently, I had the opportunity to help design one of these systems.

At the Burbank Water and Power Plant near Los Angeles, our client requested engineering for this exact scenario – getting a large preconstructed stormwater basin underground. Through coordination and teamwork with our client, we were able to narrow in on a system that would allow for this install. The end result was a roughly 150’-long, 68’-wide, and 22’-6”-deep braced beam and plate shoring system, using large steel beams and even larger steel pipe struts.

However, the project was not without its challenges. There were a few conditions that required our design team to exercise our expertise with our design. The first challenge was the presence of a large crane which was used to lower these heavy preconstructed modular retention basin blocks into place. Exerting a ground load at each outrigger of approximately 162,000 lbs, designing the shoring system to withstand these large surcharges required our design to be more detailed than a typical beam and plate design, specifying and detailing additional web stiffeners, bearing plates, and splices to ensure we were getting maximum capacity out of the components.

Another challenge was obtaining materials that were easier for our client to track down and maneuver. At a large span of 68’, getting standard steel beam struts to check out was not a possibility. Therefore, we were tasked with specifying the most effective steel members that checked out under these large loading conditions, but still obtainable for our client. The result was installing large 2’-diameter steel pipe struts. Lastly, clearance issues dictated the spacing of struts and the spans of walers, limiting our options. Since the retention structure consisted of preconstructed modular blocks, the system had to be lowered into the pit via crane, requiring enough clearance to safely lower the retention structure blocks into place.

Large excavation shoring jobs, such as this one, present many challenges. But they also provide a high level of excitement that our team thrives on. Designing these large and complex shoring systems while also anticipating and fielding challenges ahead of time to provide a smooth design process is a hallmark of our efforts here. And seeing this one lead to a successful install of critical infrastructure is an awesome achievement, especially with this project being so close to our Southern California office location.