Between May 3 and Nov. 18, 2024, Denver Water and its contractor, Kiewit Barnard, placed 269 vertical feet of roller-compacted concrete, or RCC, to raise Gross Dam.
With the progress made during the 2024 season, we are still on schedule to finish RCC placements in 2025. We plan to restart placement in spring 2025, once temperatures are consistently above freezing.
To complete the Gross Reservoir Expansion Project, we are raising the dam 131 feet above the existing crest, or top, of the dam. We are doing this by building 118 concrete steps from the bottom of the existing dam to the new dam crest. Each step is 4 feet tall with a 2-foot-long setback from the step below.
We are using RCC to raise the dam. RCC gets its name from the way it's applied in the construction process. Workers place the concrete with mini-dump trucks, spread it with a small bulldozer and then roll and compact it into place with a smooth drum compactor.
Construction of the new steps is expected to last through 2025. In 2026, workers will complete the top of the dam, which will include a control building, electronics, concrete railing and a bridge over the spillway.
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Making RCC on-site
We have built an on-site quarry, crusher plant and batch plant to make RCC. This reduces the number of truck trips by about 70%.
What is RCC?
RCC is a mixture of rocks, cement, fly ash and water - the same materials used to make concrete found in sidewalks and buildings. The difference is RCC uses less water, so it looks more like dirt before it is compacted into place.
You can learn more about RCC in our article practice makes perfect when putting concrete in place.
The quarry
Rock is excavated from the on-site quarry and brought to the crusher plant where it will be turned into aggregate and sand for the RCC.
The crusher plant
The crusher plant breaks up rock from the quarry into aggregate and sand that will be mixed with the RCC. The crusher equipment turns boulders into rock no bigger than 2 inches.
The batch plant
The batch plant mixes the materials together to make concrete. It will take nearly 740,000 cubic yards of RCC to raise the dam. The entire batch plant is almost the length of two football fields.
What to expect during construction
In 2022 and 2023, the work on-site was in preparation for the dam raise. Here's what to expect during RCC placements:
Trucks
Up to 30 more trucks delivered cement and fly ash daily in 2024. We hired dedicated drivers for these deliveries who went through training to drive safe through the canyon. Trucks hauled throughout the day and night; however, we did not haul cement or fly ash during school bus hours, 7-8:30 a.m. and 3-4:30 p.m.
Noise
Raising the dam requires an on-site quarry, crusher plant, batch plant and conveyor system, as well as more deliveries, equipment and support staff. While you can expect an increase in noise on-site, we continue to assess noise levels to make sure they stay below allowable limits.
Lights
RCC placements are a 24/7 operation. Lights are needed to illuminate the roads, produce and crush aggregate, batch and convey concrete, and maintain and support operations. We continue to downcast lights as much as possible while maintaining the safety of our workers.
Workers
We had up to 375 workers on-site daily in 2024. This number will increase to approximately 450 workers in 2025. To meet our goal of 50% carpooling, we will continue our shuttle program. The shuttle program brings workers to site in 15-passenger vans from the Northwater Treatment Plant.
This is the largest dam raise in the U.S. and the largest RCC dam raise worldwide. When complete, Gross Dam will be the tallest RCC dam in the country and the tallest dam in Colorado.