There will be at least 2 levels of braced walers. The first level will be a few feet from the top of the sheet piling and the second level will be about 9'-10' below the top of the sheet piling.
As an example of what the contractor is asking, at one location the sheeting may extend down 6' below the second level of walers/struts at which point it hits rock and he can't get any embedment. He is required to excavate down hto this point, but He doesn't want to pin it to rock, instead he is asking whether the flexural strength of the sheeting can act as a cantilever and resist the bottom 6' of soil/water pressure.
I have always pinned it, but this contractor is indicating that he has done this before. I'm just not sure how to analyze it.
If I understand what you are recommending, a better solution would be to push the perimeter of cofferdam out and use that additional clearance to slope up from the rock and provide an embedment that way? With a sloped embedment, that woudl probably require a significant offset to get the required embedment depth, so I'm assuming the contractor won't be thrilled with this option.
cntw1953: I'm not sure I understand what you mean by treating it as a 4' ring.