John if I am understanding your problem correctly I think it might be just as cost effective to entirely take off the top part of the dam down to the old dam. Then cut a core down into the old dam however far you need and replace the top of the dam while compacting it properly.

I may be all wet in that suggestion. But I am thinking of machine operation and ease of the job. It may take no more machine time for a dozer to take the top off, a backhoe to core a couple feet into the old dam, then have the dozer and whatever compaction method you can come up with to recreate the top portion of the dam. The dozer could simply push the top off to the backside slope so a very short push with minimal material movement.

I'm just thinking you may be overthinking this problem (based on your sketch). If it is much harder to core and compact within a narrow core all the way to the top of the dam, it may be just as cost effective to redo the entire upper portion of the dam. I'm just thinking of machine time and ease/difficulty of the job.

Just an idea. Worth every penny you paid for it.

John

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