This standard provides guidelines for the design and construction of bored, cast-in-situ, under-reamed concrete pile foundations. It covers piles with single or multiple bulbs, which are particularly effective in expansive soils for anchoring against uplift and in soft soils for increasing bearing capacity.
Provides guidelines for the design and construction of under-reamed pile foundations, particularly suited for expansive soils.
Quick Reference Values
minimum longitudinal reinforcement0.4% of gross area
minimum clear cover50 mm
slump for tremie concreting150 mm to 200 mm
minimum spacing friction piles3 times pile diameter
minimum spacing end bearing piles2.5 times pile diameter
minimum grade of concreteM25
Key Formulas
Qu = Ap * Nc * cp + alpha * c * As — Ultimate bearing capacity of pile in cohesive soil
Qu = Ap * (0.5 * D * gamma * Ngamma + pd * Nq) + sum(K * pdi * tan(delta) * Asi) — Ultimate bearing capacity in cohesionless soil
Practical Notes
Always ensure complete bentonite flushing before starting tremie concreting to avoid mud-cake formation and structural discontinuity.
Concreting must be continuous; interrupting the pour risks creating cold joints and weakening the pile shaft.
Theoretical capacity calculations must be verified by initial and routine load tests on site as per IS 2911 Part 4.