Controlled modulus columns (CMCs) are used as a ground improvement solution for weak, compressible, or otherwise soft soil. Some commercial projects require high load-bearing capacity, but the soil that the structure will be built upon cannot stand up to the weight of the structure. In order to remedy this issue, you can use controlled modulus columns.
Since their development in the 1990s, CMCs have become known as a sustainable, cost-effective choice for improving soil stability.
Controlled modulus columns are essentially concrete columns that are installed by drilling into the earth. The actual CMC installation process, however, is a bit more complicated.
A reverse flight displacement auger utilizes high torque capacity and down-thrust to bore these holes, known as rigid inclusions or semi-rigid inclusions, into the ground on a grid. These inclusions are roughly 10 to 18 inches in diameter about 3 to 10 feet apart. The auger drills these inclusions up to 40 meters (roughly 130 feet) into the ground; it moves past soft soil down to more stable soil or dense sand or silt.
As the auger drills, it moves soil laterally, thus avoiding the soil displacement that can be typical of other ground improvement systems.
The auger is hollow, which allows us to fill the inclusions with grout or concrete all the way down to the bottom of the inclusion.
Once all of the inclusions are drilled and filled, there is essentially a grid of stone columns reaching far down into the earth. Because the CMCs are drilled on a uniform grid, they offer optimal distribution of loads between the inclusions and the surrounding soil.
Before the foundation is poured, the CMCs are covered with a load transfer platform, also known as a granular mattress, to create a smooth, even layer for the foundation.