[EarthResearcher333]

Blasting at Upper Main Spillway - very close - Why? - Clue may be a spillway charged Water basin - but Why the Risk?

DWR photo shows a drill rig setting up an array of blast holes nearly 100ft near the Upper Main Spillway. This very close blasting is NOT for the DWR stated reason of "protection of workers" for the carved canyon as this is well upslope from the canyon walls. This blasting, so close, may likely "jar" the broken part of the spillway. Why risk more damage when there is another spill projected soon? It may be understandable in the closeness of the blasting for the vertical cliff - but this risk has seemed to be resolved by blasting that has already occurred (wider angle of this photo).

To take such a risk of destabilizing & possibly tumbling the 50+ end section of the damaged upper spillway must have a reason. But to potentially destabilize the fragile upper main spillway? I've lived adjacent to a rock quarry less than 1/4 mile away. I could hear large rock crashing through trees after blasts. We were warned before blasting & would go inside just in case. The shock to the house foundation was amazing. You felt the shock before you heard the blast (a split second difference). I can't image intentionally "shocking" the critical upper main spillway right now - especially so close - and when it is in an area that seems unnecessary.

Putting on a "wild idea" hat…. Perhaps someone wants to get ahead of the game and feels the risk is worth the head-start…. Perhaps they need to figure out a sneak drain path (possibly eroded in the hillside rock) of the large residual waterflow from a side hill basin of the spillway… If so, why can't this wait?

Blasting right next to Upper Spillway - risking destabilizing & tumbling of 50+ ft section of end of spillway - risking damage to rest of spillway - Note the significant waterflow in the drain outlets and in the damaged lower left drains on the shotcrete.

[abb]

Maybe constructing a level area for a batch plant work pad? (thinking out loud again) Maybe a batch plant on both sides of the spillway, so as to have access and delivery locations on each side?

[meyer]

I wonder if they’re planning to use low-power blasting, deep down like they did in another area as shown in a previous video. Something to break up the weathered rock. But even that could have an effect on the bedrock under the spillway.

I hope that it’s well thought-out.

[KC Burke]

Okay, you asked for speculation. I will try.

IF they are drilling holes for blasting it might indicate the following:
1.) They are planning to cut that parallel access road down lower to the elevation of the adjacent spillway floor to provide access.
2.) They want to do that in a matter of days not weeks when they do start it.
3.) They know that area has rotten rock in one layer and then various layers of solid concomitant rock below.
4.) They are drilling to place a weak charge at a precise shallow depth in say the first solid layer so that the rotten layer and the first shallow layer peals away like a well broken egg shell.
5.) This way they get in there with big scrapers with teethed equipment ahead of it to pull all that material out and make a 15 foot cut at that roadway in a matter of days because all the material is pre-broken.

They then end up with a parallel access-way at the same elevation as the slab they want to remove when starting later this year.

This avoids the procedure where the soft material comes out and then hoe-rams have to be brought in to peck away at a new layer of removal, then excavators have to take it out in big shovel batches, etc.

Charges of precise small amounts are used to make cuts in that manner all the time when roadways are cutting across an elevation that has such rock.

Doing it adjacent to an earth-fill dam — Just Damn, I don’t know. They blast all the time when they are building these puppies — I will wait and see.