Gross Dam is being raised with what is called a downstream buttress raise, where the new concrete will be placed on the downstream face of the dam from the bottom up. First, our team is establishing an on-site office and staging area to store equipment, followed by development of an on-site quarry that will be used to obtain most of the aggregate materials needed to build the dam.
Crews will then prepare the existing dam surface for the new concrete using high-power water jets and will excavate rock at the base and abutments of the existing dam to prepare the foundation to support the expanded dam surface. Concrete will be produced at an on-site concrete batch plant and conveyed to the dam site where it will be added to the structure using a process called roller compaction.
The concrete mix for most of the new dam — roller-compacted concrete (or RCC) — uses less cement, more fly ash and has a lower water content than conventional concrete. This mix also has superior physical properties, which include lower curing temperatures, lower embodied carbon and a final product that is less susceptible to cracking.
In addition to the main dam expansion, a saddle dam will be added to process extreme flood events.