The Oroville Dam, the highest dam in the nation, suffered major spillway damage during heavy winter rains in 2017.

The main concrete spillway at the 770-foot tall dam north of Sacramento, CA, was built in the late 1960s on poor quality rock. The spillway cracked in multiple places in the following years, allowing water to flow underneath. On Feb. 7, 2017, water from powerful winter storms rushed under the massive spillway, which forced up its giant slabs and ripped a huge hole in the structure causing one of the most serious dam emergencies in California history.

Reconstruction teams were mobilized with the goal of completion before the next winter rains arrived. More than 500 pieces of heavy equipment, 150 construction management staff and 500 craftworkers were ready to go in eight weeks.

On the main spillway, crews demolished existing concrete and excavated soil and rock to reach solid foundation. They then batched and placed more than 340,000 cu yd of roller-compacted concrete (RCC) to fill the excavation and 140,000 cu yd of structural and leveling concrete to reconstruct the spillway. A new underdrain system also was installed.

Primary work at the spillway included construction of a 706,000-cu-yd RCC splashpad, built in 1-ft lifts, for a total of 1.2 million sq ft—an area equivalent to 25 NFL football fields. The splashpad is supported by a 1,450-ft-long underground secant pile wall, built into bedrock at depths of 35 ft to 65 ft. The spillway was rebuilt and the dam was saved.

The $1.1 billion emergency spillway reconstruction was completed in late 2018.

The NEX® System was utilized at the Oroville Dam Emergency Reconstruction project to monitor concrete temperature, and for mass concrete specification compliance to keep construction moving quickly in its short time-frame completion.