CHENNAI: When construction of the outer walls for underground Central Metro started, engineers didn't expect that the mixed soil condition would impede work. Trenches were cut to build the walls that were inconsistent, the wall joints began to leak and lowering iron cages into the trench to pour concrete became difficult.
Adaptive irrigation technology saves 2 years for metro rail
Due to the deadline approaching, the engineers at Afcons Infrastructure, the company that is building the station, decided to adopt a method and machinery used to build dams and reservoirs. The requirements were a hydromill, a trench cutter with two cutter wheels, a new overcut method of construction and 2.2 lakh cubic metres of concrete. Around 250 concrete panels, each 1 m thick each, were built next to one another to build a 2,300m-long diaphragm wall for the station.
As the alternate concrete panels are built, excavation of the soil in between them begins. Engineers had to overcut into the already built adjacent panel for about 150mm to 250mm in width. The trench is then filled with concrete after reinforcement bars are fitted.
“In the overcut method, lowering and removal of stop-end tubes take less time and the cage is lowered only after trenching is complete. This was a cost effective as well as a time-saving method,” an engineer said.