Posted on 02/12/2017 4:26:47 PM PST by janetjanet998
Edited on 02/12/2017 9:33:58 PM PST by Admin Moderator. [history]
The Oroville Dam is the highest in the nation.
Then I responded to your amphibolite post & pic to me with post 2,636 demonstrating a simple proof of structural & functional soundness when concrete, properly emplaced in amphibolite with a "flip" dispersal system at the end of the original spillway.
Was there a misread of my original post (2,362) in discussing the challenges of anchoring a "flip" design at the end of the damaged spillway?
My criteria has always been “what type of machine will get it out.”
Can we rip it? Hoe it? Break it out in layers with a big loader or excavator? How far we gitten with a point on a hoe-ran? I guess it’s time to get the rock drills and powder monkeys in here.
Your second picture only reinforces the evidence of a sharp "V seam" of weathered rock being removed revealing the hard amphibolite base. This would be normal for historic waterflows at these locations causing the weathering & thus becoming the "highly fractured weathered rock".
Keep in mind, that all of the observed eroded weathered rock is gone. Where did it go? It tumbled down the flow channel.
But don't take my word on all of this... look at the DWR geology video of the new mini-fault "seam" discovered at the bottom of the emergency spillway flow. The geologist explains how this seam was revealed by the erosion & the amphibolite that remained.
I didn’t comment on a flip or plunge pool, only on the hardness of the rock. Your reply discussed a flip at the end of the spillway. This was puzzling since I hadn’t commented on that. So I scrolled back to see where the flip pool was discussed and found the article which proposed trying to jump over the crater in the spillway. This differed from a flip at the end of the spillway, hence my comment.
We were talking about two different things and talked right past each other.
It is about time for the protesters to march across the dam. That will take solve the problems.
Yes it did. Water cut through the weathered brown rock and washed it away. Water continued cutting into the underling gray rock. Was some of the gray rock eroded by "weathered rock debris filled flow"? Of course, yet being softer how much damage did it cause? All of it? I don't think so. I don't dispute that the weathered rock contributed to erosion of the gray rock. I think much, if not most, of the erosion of the gray rock was caused by water and occurred after the overburden was washed away.
Well hopefully you should have keys to answers, or good reference information, to your questions at this point. You have good observation skills and have put in good work in graphics and artwork in your posts - including good questions. This is always fruitful in discussions that I consider valuable with other FReepers such as yourself.
How thick was the Amphibolite layer in the core sample?
That photo is a microcosm of the Lake Missoula scab lands floods.
As of this past Friday’s show Turin has quit and won’t ever work with Todd Hoffman again.
My mineralogy prof called Amphibolites “garbage can silicates” compared to most other less complex silicate minerals.
Yes, I saw that he won’t be coming back.
Thank-you!
Based on what I have read that is a great description.
When the grey rock has all of those fractures and veins
that run through it and underneath it, I don’t see how the
grey rock is very much more resistant to erosion than the
brown rock. It is still going to crumble away.
It is not a homogeneous layer of rock.
Similar to the concrete slabs on the spillway,
they did not “erode” away from the top side,
they washed out from the bottom side and fractured and crumbled away.
(IANAG - I am not a geologist)
I”m thinking, based on what I read, that the gray rock below might be a good foundation, but perhaps not a good water-flow surface, especially at 40,000++ cfs. I mean, that’s a LOT of water and thus a lot of potential to erode. I mean, it’s obviously harder and more resistant than the brown, looser rock above it, but I don’t think it’s up to the task of a high-speed water flow.
And just to note, I also am not a geologist. Nor a civil engineer.
Here is evidence to the question:
That core sample had fractures that would force any structural design to require a consolidation of the material via high pressure grout injection. But that still would be a poor option as this sample amphibolite is fractured there is a mixture of weathered rock present. This core sample is very unusual in that the amphibolite is "sandwiched" as a laminar layer fold or seam. It is not surprising there are fractures in this narrow "seam". In addition, that core sample is not a representative of large emplacements of blue grey bedrock (amphibolite) found in large sections of the original main spillway (image below).
The image demonstrates the resiliency integrity of large sections of good fresh blue grey Amphibolite - compared to "highly fractured weathered rock". This section took quite a beating from imbedded debris within a powerful hydraulic pounding when the spillway was operating at 100,000 cfs (note: part of the flow was still coming down this section with debris, even though a greater flow was forming the "canyon"). There were chunks still coming down in this section. Yet the #11 anchor rebar is observed intact within the Amphibolite and much of the spillway is still anchored into the Amphibolite foundation. The damage to the concrete reveals the jackhammering pounding debris environment during this flow (spalling & rebar entangling). If the Amphibolite was highly fractured, you would see a significant elevation difference from erosion compared to the leftover concrete slab grade.
Bottom line: The structural conditions of the main spillway and the emergency spillway hillside are complex. Before any proposed designs are suggested, care must be exercised in thoroughly sampling the geologic substructure to determine what stripping to do, what grout consolidation is required, and what areas are too risky to construct upon.
I encourage your insightful queries, discussion, and skilled technical abilities. In these FReeper discussions, and in decades of complex failure analysis, I have found the best input from great souls such as these discussions have yielded. No need for disclaimers here (degree/expertise/etc) & no questions/comments should be inhibited by such. btw- often times, it is a technician or some other person who notices something unusual, yet crucial to the failure investigation, that experts (some not all) have discounted. That is why I will interview the tech’s after getting the initial failure crisis challenge explained by the experts.
I don’t know my amphibolite from a hole in the ground!!!
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.