I am currently working as the geo on a new development. I have given initial recommendations to undercut 6 feet of the underlying CH material. The CH has PI's up to 27, and I am approximating 1800 psf swell pressures. The owner and SE have pitched the use of rammed aggregate piers, and we shot that down due to the possibility of transferring the shrink/swell forces from the pier to the shallow footings. Our response recommendation was to do additional borings to a greater depth to entertain the idea of micropiles. Shot down due to cost ineffectiveness. Our last recommendation was to use a 3' undercut in conjunction with a monolithic slab on grade and grade beam scenario, hoping that the 3' will provide enough cushion from swell pressures. I would greatly appreciate it if anyone could weigh in with some ideas and or other concerns. Thanks in advance.
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