Tremie Concrete (Underwater)

Tremie concrete is concrete placed underwater or in deep, narrow excavations using a vertical pipe (tremie pipe) to deliver concrete from above the water surface. The pipe ensures continuous concrete flow without segregation, water displacement of cement, or aggregate settlement. Per IS 456:2000 Cl. 13.7, IS 2911 (piles), IS 9556 (diaphragm walls), and IRC 78 (bridges), tremie placement is essential for: (1) Cast-in-situ piles (bored cast-in-situ); (2) Diaphragm walls; (3) Underwater concreting; (4) Deep narrow excavations; (5) Slurry-stabilised foundations.

Key tremie procedure: (1) Mix design — typically high cement content (380-450 kg/m³ for M30), high slump (150-200 mm), use of PCE superplasticisers; aggregate maximum 12-16 mm to prevent segregation in narrow pipes. (2) Tremie pipe — typically 150-300 mm diameter, made of mild steel; diameter at least 6× maximum aggregate size. (3) Pipe insertion — to bottom of excavation; ensures concrete is deposited below the water/slurry. (4) Concrete pumping — continuous from bottom up, displacing water/slurry from above. (5) Pipe extraction — gradual, maintaining concrete level above pipe outlet to prevent washing in.

The most-overlooked aspect of Indian tremie concrete: pipe management during pumping. The pipe must remain submerged in concrete (typically 1.5-3.0 m below the surface) to prevent slurry/water entering. If pipe is lifted too high, slurry is included in concrete causing voids and weak zones. Pipe management requires skilled operator + on-line concrete level monitoring. Pile load tests (PLT) and Pile Integrity Tests (PIT) detect tremie-related defects.