Bored Cast-in-situ Pile

Bored cast-in-situ pile is a deep foundation element constructed by drilling a hole into the ground (usually with a rotary drilling rig under bentonite slurry to stabilise the borehole), then placing reinforcement and concrete via tremie pipe. Per IS 2911 Part 1 Section 2:2010 (revised 2024), bored piles are the dominant pile foundation type in Indian urban construction. Diameters 300-2400 mm; depths 10-60 m (occasionally deeper). Major Indian bored pile contractors: L&T Heavy Civil, Tata Projects, Punj Lloyd, Foundation Engineering.

Construction sequence: (1) Survey and stake out pile location. (2) Drill borehole using rotary auger or down-the-hole hammer; bentonite slurry stabilises wall in cohesive/granular soils. (3) Install reinforcement cage (8-12 mm vertical bars + 8 mm hoops). (4) Tremie pipe inserted; concrete pumped from bottom up, displacing slurry. (5) Concrete sets; pile cap construction begins. Sequencing: typical Indian site achieves 1-2 piles per day for 600-900 mm dia × 25 m depth piles. The most common Indian bored pile defects: (a) Necking — local reduction in diameter due to soil collapse during drilling; detected by Pile Integrity Test (PIT). (b) Voids — air pockets in concrete due to inadequate tremie sequencing; detected by PIT or core test. (c) Misalignment — verticality off design; detected by post-construction survey.

Design per IS 2911 Part 1: (a) Pile capacity from soil parameters (skin friction + end bearing). (b) Group action when piles spaced < 3× diameter. (c) Pile load test (PLT) for verification. (d) Pile Integrity Test (PIT) for defects. The most-overlooked aspect of Indian bored pile construction: bentonite slurry quality. Improper slurry (wrong density, contaminated, too thick) causes wall collapse, slurry inclusion in concrete, or inadequate displacement during tremie. Proper slurry management requires daily testing and adjustment.