Investigations on the distress to the pavements/pqc slab around monorail piers, Wadala, Mumbai-Paper

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The paper investigates cracking and level displacement in pavement-quality concrete (PQC) slabs near Mumbai Monorail piers on the Sion–Koliwada and Anik–Wadala roads. The distress appeared soon after the monorail became operational, while pavement farther from the piers remained largely intact, prompting initial concerns that the pier caps had heaved.<br /><br />Geotechnical records showed fill overlying soft to very soft, high-plasticity marine clay, generally 5.5–11 m thick, above basalt and breccia. The monorail piers are supported by piles founded in rock, whereas the road pavement rests on the compressible soil. Stone columns had been installed beneath the pavement to improve the ground.<br /><br />A September 2014 level survey found average settlements of approximately 250 mm on Sion–Koliwada Road and 110 mm on Anik–Wadala Road, relative to original road levels. Investigation indicated that the pier foundations and caps remained stable. Instead, the surrounding pavement and underlying soil settled over time under the fill and pavement loads. Slabs supported at pier caps therefore remained near their original elevation, creating relative level differences and cracking that resembled pier-cap uplift.<br /><br />Ongoing mass excavation and dewatering at a nearby site may also have accelerated settlement by lowering groundwater levels, increasing effective stress in the clay, or causing loss of soil fines. The authors note that stone columns can reduce settlement but cannot eliminate consolidation in soft clay.<br /><br />The study concludes that the observed pavement distress resulted primarily from consolidation settlement of the soft marine-clay subsoil, with nearby dewatering a possible contributing factor—not failure or movement of the monorail structure.

Keywords

pavement-quality concrete

cracking

level displacement

monorail piers

marine clay

consolidation settlement

stone columns

dewatering

geotechnical investigation

soft subsoil