How does pile group behavior differ from single pile behavior?

Pile group effects include: (1) Group efficiency - capacity may be less than sum of individual piles due to stress overlap; efficiency factor = group capacity / (n * single pile capacity), typically 0.7-0.9 for friction piles, (2) Settlement amplification - group settles more than single pile at same load per pile, (3) Block failure mode - closely spaced piles may fail as a block, (4) Lateral load distribution - leading piles take more load. Minimum spacing is typically 2.5-3 times pile diameter. Group effects are analyzed using efficiency factors or block analysis.