Controlled Modulus Columns vs Deep foundations

[Pelotoner2]

We are seeing many VE contractors entering the scene to VE our deep foundation designs. Some of these are design-build with varying augercast pile sizes, or other deep foundation system, which are an in-kind exchange.

However, we just heard about a VE request to move from augercast piles (+/- 120 ton compression) to Controlled Modulus Columns (CMC) on a building. While we've entertained CMC in poor soils, debris areas, and heavy low-rise buildings, this request is for a 16+ story, concrete two-way flat plate, relatively heavy building.
It's also a moderately small footprint, where overturning is an important consideration.
Further, all of the lateral capacity will be taken by soil-interaction friction between the footing and the load-transfer platform (although passive pressure could be used, I would be hesitant due to the large movement required for full passive activation).

I would also be concerned about overall and differential settlement. CMC's bear into a shallower layer and due to the typical quantity of CMCs, partially act like a field of group-action piles.

Although this isn't a project for which we are EOR, I'm sure this will come up on one of my projects in the future. As of now, I would provide extreme resistance to this system for this size/weight building and would consider resigning as Structural-EOR if backed into a corner. I'm curious about other structural engineer's thoughts and experiences.

 

[ATSE]

CMCs have their place, but tend to be oversold.
Some CMCs have reinforcing, but the typical CMC is not reinforced. They have no ductility and no lateral load capacity. You know how a C39 concrete test cylinder normally breaks in the lab - classic 45 degree tension crack? CMC exhibit the same behavior when exposed to high top loads, and especially lateral loads.
If you are using CMCs, best if a deep, stiff aggregate cushion is provided between the top of the CMC and the bottom of foundation.
Knowing what I know now, I would never use a slender CMC without at least 0.25% reinforcing - which can usually be provided with a #9 to #11 bar in the center (like an under-reinforced ACIP_. And even then, with caution and restrictions.