[EarthResearcher333]

>>HerringBone Drain Pipe - Fracture pattern in Main Spillway...

Hi Jim 0216, Perhaps this image may clear this up (re: question discussion). The fractures reveal an "upward" pattern where the drain pipe is still under the slab, but angled slightly upslope to facilitate flow. Key: Pipe is angled "upslope" with respect to the resulting "downslope" flow of drainwater. If the drain pipe were constructed strictly horizontal there were design considerations discussed of "self-cleaning" and "better flow".

These series of fractures follow design information on the placement of the drains under the main spillway slabs. These fractures likely occurred after the original blowout failure. The downstream hydraulic turbulence would have pounded these slabs. As Freeper abb has provided prints on the gravel & drain pipe placement in the dimensions of the slabs, this becomes a narrowing area of the thickness of the slabs. Thus the cracks below the blowout area offer insight into many factors (stagnation pressures, thin section in slab concrete, strength of hydraulic pressures from turbulence, etc).

Of course, these insights are from an after-failure. The spillway was not designed for the after-failure - BUT - this after blowout failure cracking gives an indication of what the actual design may perform to in extreme destructive conditions (i.e. useful as a form of a destructive test to provide data in original safety factor margins & design vunerabilities).

[Jim W N]

Thanks ER. Maybe I’ll need to take an engineering class to understand how a drain pipe angled slightly upslope “facilitates flow”. My simple mind would think a pipe angled upslope would tend to back up the flow.

[EarthResearcher333]

>>Spoke too Soon: Possible Drain Pipe Cracks & multiple patches Present in Main Spillway BEFORE Failure…

Going back to prior images before the Main pre-spillway, there are numerous sign of the "HerringBone drain pipe" alignment in Maintenance repair cracks on the surface concrete of the Main Spillway.

Why is this important? The drain pipe, & enveloping drain gravel around the pipe, reduces the thickness of the main spillway slab (see blueprint data posted by abb in post 2,132). This reduction of slab thickness would represent a weaker structural zone vs the full slab height. The very strong indicators of these Maintenance repaired cracks, in a "herringbone" type of pattern, leads to the question of if this is a leading contributor (combined with subsurface erosion, stagnation pressure, WEAK point in concrete slabs from drain design, expansion/contraction stresses, etc).