I can understand the use of RCC as the foundation for the main spillway. If they used any type of uncemented backfill, it would eventually consolidate and sink, causing problems. They could plausibly build a structure, which might ultimately be cheaper, but would take a lot of time and effort to engineer correctly. Laying layer upon layer of RCC which set quickly and requires no formwork appears to be the fastest method of construction.
The volume would be enormous. They would end up with a monolith of concrete more than 100 feet in every direction, which would have to be one of the biggest pores outside of dam construction in the world. You could build a couple dozen miles of freeway with that volume! I guess cost is no longer a concern. Even with RCC’s lower cement content, I think heat buildup could still become an issue that would have to be dealt with.
However, I can’t see the use of RCC to make an apron between the (yet to be constructed) cut off wall and the emergency spillway weir. They just finished dumping bags of rock and boulders cemented together with conventional PCC below the weir, leaving a relatively uneven surface. They would have to rip that out out and smooth it off before placing RCC, or fill it in with even more rocks and concrete. What would be the benefit of using RCC for this emergency spillway application?
Does RCC generally include any kind of reinforcement material (rebar)? Not my area of expertise.
I think the concept as mentioned above is RCC as a spillway covering below the emergency weir. That is proposed as a seamless full width cover. My concern is can it be placed sloped that much.
Something along the lines of flow-able fill could be an answer for the moonbeam canyon sub-grade. It could be delivered by chute, pump, or truck.
The whole thing is a crap shoot of choices. The design should take 12 months not 12 days.