Oroville Slab Design - 6" Drain Pipe causes drastic thinning from O.D. & Bell Joint dimensions..
Hat Tip: meyer, abb, Repeal The 17th..
Specifications for the outside diameter and the bell coupling diameter of the Vitreous Clay Drain Pipe used on the Oroville spillway creates severe thinning zones in the Spillway slab. To confirm the original specs on the 4" drain pipe dimensions, detailed measurements on documents & scale revealed a near perfect match to a modern Pipe catalog of the same type of pipe for the 4 inch Inside Diameter (4" I.D.). This means that the actual thickness of the outer dimensions of the pipe need to be factored for a net slab thinning. Thus, shifting to the catalog 6" drain pipe specs (6" I.D. was used in the Oroville slab design) the thinning results were stark. Unless there was a cutting into the foundation layer to compensate for the larger diameter pipe, there was not much spacing in the thin zones for rebar (~2.5" down - centered) at the "bell coupling" areas.
Worse, penetration of water into such thin region(s) could cause persistent cracking, and even spalling (chipping) of the slab concrete surface from Stagnation Pressure ("hydraulic jacking").
Spontaneous Holes ("chipping" failures) occurring in Upper Main Spillway… Pics have indeed revealed that spontaneous "chipping" areas have occurred in the upper main spillway - in slabs close to the Upper Main Spillway Gates. It should be noted that "Standing waves of water" form "rooster tails" of mixing in the merging water induced by the 5ft thick concrete columns in the Gate structure. These hydraulic dynamics (& slab stress forces) settle out further down in the flow in the Upper main spillway. A design weakness has been discussed regarding a "thinning" dimension caused by using 10.43inch height drain pipe in a spec design 15 inch slab thickness. Thus, the rebar would be forced into a "thin" zone below the upper surface of the concrete slab(s). See prior post/discussion images/info at link. It is possible that
this thinning and "chipping" prone design weakness would be at its greatest near the Main Spillway Gate - due to these powerful hydraulic dynamics - besides the issue of "hydraulic jacking" pressures from water penetration below/into the slabs called Stagnation Pressure. This effect was the culprit to Dam Spillway chute failures where two prominent examples are the Big Sandy Dam, Wyoming, 1983, (spillway chute failure) - Dickinson Dam, North Dakota, 1954 (spillway chute failure).
These "chipping" holes occurred recently in 2017. This evidence means that other slab areas may "chip" in re-activiation of the spillway. Cavitation erosion may accelerate damage to a spontaneous "chip". Thus another important reason for "eyes on the upper spillway" during its operation. There is no time to address this design weakness as only a full reconstruction of the spillway is required to eliminate these design weakness/flaws. (note that water was redirected to allow "dry" access to these TWO spalling "chipping" failures. A "THIRD" "chipping" failure is present in another image (not shown here) very close to a seam close to the Main Spillway Chute Gate.)
IMPORTANT: A similar "chipping" failure defect was observed in the area at/near the "blowout" failure location, prior to the catastrophic Main Spillway blowout. See post 2,092 or the second link below. This "chipping" defect failure was captured in a picture taken in the last week of Jan 2017 - just before the blowout failure in February.
Oroville Slab Design - 6" Drain Pipe causes drastic thinning from O.D. & Bell Joint dimensions..
Clip from FRPost link: This means that the actual thickness of the outer dimensions of the pipe need to be factored for a net slab thinning. Thus, shifting to the catalog 6" drain pipe specs (6" I.D. was used in the Oroville slab design) the thinning results were stark. Unless there was a cutting into the foundation layer to compensate for the larger diameter pipe, there was not much spacing in the thin zones for rebar (~2.5" down - centered) at the "bell coupling" areas. Worse, penetration of water into such thin region(s) could cause persistent cracking, and even spalling (chipping) of the slab concrete surface from Stagnation Pressure ("hydraulic jacking").
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Years of Warnings at Blowout Area? Missing drain water/slabs being repeatedly repaired at leakage..
Clip from FRPost link: Having this defect present would have likely initiated very damaging cavitation erosion from spillway flow (jackhammer effect on the concrete)….. = = reference notes: 1. Stagnation Pressure' as described by the Bureau of Reclamation: "Stagnation pressure refers to two conditions that can result in damage and/or failure of the spillway: (1) High velocity, high pressure flows enter cracks or open joints in the spillway flow surface (such as a chute), which results in uplift pressure that lifts (displaces) portions of the spillway conveyance feature; and (2) High velocity, high pressure flows enter the foundation through cracks or open joints in the spillway flow surface, which results in internal erosion of the foundation and loss of support of portions of the spillway conveyance feature [26]."
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Spontaneous Stress Induced "chipping" failures in the Upper Main Spillway (from spillway use 2017). Third "chipping" failure not shown (in another DWR image) in slab close to Main Gates.
