WorldWide Drilling Resource

A Tale of Two Spillways Adapted from Information by Kiewit Infrastructure West Co. In February 2017, heavy rain and rapid snowmelt compromised the main spillway of California’s Lake Oroville, leading to the emergency spillway being used for the first time. Nearly 200,000 people were evacuated from the city of Oroville and multiple downstream communities as the hillside began eroding. Kiewit Infrastructure West Co. won the contract to complete an emergency repair and rebui ld of the two massive spi l lways for the Cal ifornia Department of Water Resources (DWR), and they needed to do it in less than 18 months. Portions of the 3000- foot main spillway had to be repaired and rebuilt in less than 165 days. The team was mobilized to the site of the nation’s tallest dam within a month. More than 700 Kiewit employees worked over 1.6 million hours at Oroville, and hundreds of other regional subcontractors, suppliers, vendors, and DWR employees also worked at the site. All involved were striving together to reach a common goal: get both spillways built to final design by November 1, 2018. To prevent uphill erosion, if the emergency spillway ever needed to be used again, crews constructed an emergency spill- way system (ESS) made up of a secant pile wall, splashpad, and buttress. In Phase 1, ESS work focused on the secant pile wall - a 1450-foot-long under- ground wall built into bedrock at depths of 35-65 feet. Once crews finished the wall, they could finally place roller-com- pacted concrete (RCC) into the splashpad. To crush the 1.2 million tons of aggre- gate required for the RCC production, the team processed over 2 million tons of on- site materials. Using one-foot lifts at a time, crews placed 706,000 cubic yards of RCC in a total area so big 25 regulation foot- ball fields could fit within the splashpad. “When Kiewit finished the first phase in November 2017, the compromised 3000- foot main spillway was back in working condition,” said Project Director Todd Orbus. “But the project was only 40% com- plete. We had to wait until May of 2018 to start finishing more than half our scope.” At the start of Phase 2, all the tempo- rary walls constructed along the spillway in Phase 1 had to be demolished. A three- foot layer of structural concrete was placed on top of the 1050-foot RCCmiddle section of the chute, and the temporary walls were replaced with permanent structural con- crete walls. Additionally, the top 730 feet of the spillway had to be demolished and replaced with structural concrete and hydro blast, then crews had to resurface the ener- gy dissipaters (or dragon’s teeth as they called them) at the base of the spillway. “We entered the winter season know- ing we had a tremendous amount of work to complete in 2018 - nearly double the amount of concrete to place than crews completed in 2017,” Orbus said. “But through extensive planning, execution, diligence, and hard work, we met all of our project milestones ahead of schedule. This proj- ect is proof of what can be accomplished when you have the right team focused on a common goal.” 63 WorldWide Drilling Resource ® DECEMBER 2019 C&G