Columns with Mixed moduli CMM® is a ground improvement method using low deformation modulus columns or a rigid inclusion constructed through compressible soils with a stone column head and thus creating an element with materials of different modulus of compressibility. to reduce settlement and increase bearing capacity.
The objective of CMM® is to reduce foundation settlement. The stone column head primarily allows a more efficient design for the load transfer platform and also reduces the risk of any direct lateral impact on the rigid inclusion due to any post construction activity.
After the working platform is prepared, the rig is moved into place and data recording starts. Generally a displacement auger or vibrated tube is used to penetrate down to the designed depth. Concrete is pumped as the tool is pulled upwards. Once the rigid inclusion is installed up to the designed level, a column of gravel or crushed stone, is installed on top. Its length is adapted to the characteristics of the project (bottom level of the shallow foundations, rafts and slabs; stratigraphy of the soil). Typically it is between 1.0 and 1.5m, even though it can be contemplated to install it deeper.
Mixed columns are controlled before, during and after installation to ensure the highest quality solution. A variety of tests can be carried out including:
- Field trials for verifying columns production parameters
- Digital recording and logging of the execution parameters
- Column load test, column material compressive strength tests, column diameter verification
The type and frequency of tests varies based on the size of the project and the geotechnical context.