Installation of Large Diameter Bored Pile Socketed in Hard Rock with RCD for MTHL, Mumbai-Paper

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The paper presents the use of reverse circulation drilling (RCD) for constructing large-diameter, rock-socketed piles on Package 1 of the Mumbai Trans Harbour Link (MTHL), a major sea-crossing bridge project. The marine alignment contains soft marine clay over weathered rock and strong basalt, while breccia is more common on land. Because conventional hydraulic rigs struggled in the hard marine rock, RCD rigs were selected for their faster penetration and efficient bore cleaning.<br /><br />The project required 2.2 m diameter piles, generally 35–50 m long, to support substantial bridge loads. RCD rigs were mounted on steel liners, which had to be firmly embedded to provide a stable platform and prevent liner movement or rig tilt. In practice, liners encountered stiff clay and unexpected hard layers, causing clogging, premature refusal, and difficulty reaching the intended embedment. The team used grabbers to remove obstructing material and proposed combining vibro-hammers with grab excavation, impact hammers, or pre-boring to seat liners in competent strata. A temporary access bridge supported the heavy equipment in the inter-tidal zone.<br /><br />The paper also describes a bi-directional pile load test, chosen because conventional kentledge testing was impractical and potentially hazardous for the very high test load. The test reached 9,800 metric tons, reported as the heaviest pile load test in India at the time.<br /><br />Overall, the case study finds that RCD can be efficient and economical for deep, large-diameter piles in hard rock, but its success depends on securely seating the liner and adapting installation methods to actual ground conditions.

Keywords

reverse circulation drilling

large-diameter piles

rock-socketed piles

Mumbai Trans Harbour Link

marine clay

basalt rock

steel liners

pile load test

bi-directional testing

marine bridge construction