Did you get a chance to study the slab remains in Ray’s post 1811.
That is very enlightening. Now, I imagine that this is from prior to the 14th when the spillway was shut down for assessment and not later as the spillway is still flowing as far as I am aware.
All evidence of slab sub-base has washed away but it appears obvious that some of the slab areas appear to have been placed on competent rock cut to slab subgrade. It also appears there were slab areas where competent rock was not available to provide the grade needed for slab placement. This means that water that got under the slab under pressure would have wedged under that portion placed on rock and lifted it.
When placing a large concrete apron in an area where rock strata underlaid a PART of the area, I have never had a designer not require a substantial overcut of the rock so that all concrete pavement is on a similar sub-base for drainage purposed, uniformity of performance, heave characteristics and the like.
Now at the time of this picture, all sub-base would have washed away but it seems to clearly show slab on rock in a lot of areas.
Now, I will once again state that I am talking of large concrete bearing aprons of this size for large truck traffic or military vehicles. That being said, I don’t like the design I see.
Photo of spillway as of yesterday (22nd)
In the first photo part of the slab is on a sub-slab. In the second photo the slab is directly on the grey rock.
You can zoom in quite a lot on these photos, particularly the first one.
Given the amount of erosion what are your thoughts regarding the feasibility of the spillway remaining at this location?