Pile Foundation

Pile foundation is a deep foundation system using long, slender structural elements (piles) driven or cast into the ground to transfer building loads to firm soil or rock at depth. Used when shallow foundations are inadequate due to weak surface soil, high water table, or heavy column loads. Indian Standard IS 2911 (multiple parts) governs pile foundation design and construction; IS 1904 covers settlement and bearing.

Main pile types: (1) Driven precast piles (IS 2911 Part 3) — pre-fabricated concrete piles driven into the ground by hammer or vibration. Common sizes 300-450 mm diameter, 8-25 m depth. (2) Driven cast-in-situ piles (IS 2911 Part 1 Section 1) — driven hollow casing then filled with concrete. (3) Bored cast-in-situ piles (IS 2911 Part 1 Section 2) — drilled hole filled with concrete and reinforcement; diameters 300-2400 mm, depth up to 60 m. Most common for urban Indian construction. (4) Driven precast pre-stressed piles — for marine and heavy-duty applications. (5) Steel piles — H-pile, pipe pile; used in cofferdams and specialty.

Load transfer: (a) Friction piles — load carried by skin friction between pile shaft and soil; suitable when soil has uniform moderate strength to depth. (b) End-bearing piles — load carried at the pile toe on firm strata (rock, dense sand, dense gravel); suitable when firm strata is at depth. (c) Combined friction + end-bearing — actual behaviour of most Indian piles. Pile capacity computed per IS 2911 + IS 6403 from soil parameters. Group action: when piles are spaced at < 3× diameter, group efficiency factor reduces individual pile capacity. Indian practice: routine bored cast-in-situ piles 600-1200 mm diameter in groups of 4-9 under each column. Major Indian pile foundation projects: Mumbai metro (1500 mm bored piles), Delhi metro, Atal Setu (sea bridge piles), all multi-storey buildings on weak soil. The most-overlooked aspect of Indian pile foundations: pile integrity testing. Pile load test (PLT, IS 2911 Part 4) and Pile Integrity Test (PIT, sonic) verify in-situ capacity and detect defects. Many private projects skip these tests; major commercial and infrastructure projects require both.