How is stone column ground improvement designed and verified?

Stone column design: (1) Column spacing using area replacement ratio (15-35% typical), (2) Bearing capacity - composite ground approach or column/soil loads based on stiffness ratio, (3) Settlement reduction factor (n/[1+(n-1)*as]) where n = stress concentration ratio, as = area ratio, (4) Column capacity - limited by lateral confinement from surrounding soil (critical for soft clay), (5) Drainage - acceleration of consolidation using combined radial/vertical flow. Verification: full-scale load tests, CPT between columns, settlement monitoring. Design codes include FHWA guidelines.