Construction of Diaphragm wall by Using Trench cutters with overcut construction joints-Paper

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The paper presents the construction of diaphragm walls for Royapettah Station on Chennai Metro Rail Phase 2, using trench cutters and overcut construction joints. The walls serve as both deep-excavation retaining structures and permanent elements, designed for a 120-year-plus service life.<br /><br />Construction followed a sequence of guide-wall installation, pre-excavation, bentonite-supported trench excavation, cleaning and de-sanding, reinforcement-cage placement, and tremie concreting. Primary panels were excavated and cast first; secondary panels were then cut into the primary panels to form overcut joints, avoiding conventional waterstops at these joints. M40 concrete and carefully controlled reinforcement and slurry properties supported quality requirements.<br /><br />Trench cutters were selected to improve excavation performance, particularly at depth and in hard ground. Verticality was monitored using onboard inclinometers and KODEN trench profiling, with reports retained for each panel. Deviations beyond the specified 1:200 limit required remedial treatment and re-excavation. Concrete placement was monitored by comparing theoretical and actual volumes, while tremie embedment was maintained to prevent bentonite contamination.<br /><br />Key construction challenges included preparing stable working platforms for heavy machinery during monsoon conditions, managing traffic and staged work areas, locating and diverting known and unknown utilities, and coordinating reinforcement cages and concrete deliveries in a dense urban setting. Settlement markers, building survey points, vibration sensors, inclinometers, and dial gauges were used to monitor surrounding roads and structures.<br /><br />The authors conclude that detailed planning, stringent quality controls, and close instrumentation monitoring enabled the diaphragm walls to be constructed while providing insight into ground and wall behaviour.

Keywords

diaphragm walls

Chennai Metro Rail Phase 2

Royapettah Station

trench cutter

overcut construction joints

deep excavation

bentonite slurry

tremie concreting

verticality monitoring

instrumentation monitoring