After 18 cantilever piers across three under-construction metro corridors — Gurgaon, Noida and Badarpur -— were found to have cracks in July, all these metro corridors connecting the NCR have seen rapid changes over the last two months.

The reinforcements and changes in designs, however, come as a challenge for Delhi Metro Rail Corporation (DMRC). The designs of the cantilever piers on all three corridors are different and so, the corrective measures need to be customised.

As a precautionary measure, the DMRC has set up metal structures around and under the piers for support. But while piers on the Noida line are being fattened, those on the Gurgaon line are likely to undergo “pre-stressing” — a process in which concrete structures are placed under compression in those regions where load causes stress.

Work has already started on the Central Secretariat-Badarpur section — which witnessed a mishap in Zamrudpur on July 12 due to a cantilever pier collapse. Of the eight piers found to have cracks, six have been identified for pier cap demolition and reconstruction with a different design. All six pier caps were similar in design to that of pier 67 which gave way.

The new design will have additional couplers — joints between piers and pier caps — to be tied with more re-bars to consolidate the concrete structure, said a DMRC official.

The process is being done with sophisticated mechanical hammers, so the adjoining areas are not damaged. Metro officials had also announced that the cantilever load on a few of the piers on the Badarpur stretch adjoining Pier no. 67 will be reduced. The cantilever width will be reduced from 3.88 m to 2.5 m.

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