Stone columns have a threefold effect in soil :
- Compaction of compatible layers.
Layers of clean sand and gravel and slightly silty sand (up to 20 % fines content) are compacted during the process of stone column installation. - Reinforcement of the soil.
Column and soil form a reinforced matrix with instantly increased shear resistance and stiffness modulus. The high friction angle of the column material gives an immediate overall increase in shear strength to the composite of soil and column. - Drainage.
The columns accelerate drainage (consolidation) of the cohesive soil, i.e. the columns work as vertical drains and thereby accelerate reduction of harmful excess pore pressures