more-in Building an extensive metro corridor in a city having a few dozen unstable buildings – those which precariously slant to one side due to adverse soil conditions or shoddy construction, is by no means a simple feat. That Kochi Metro services to the city hub resumed on Friday noon, within half a day of the collapse of a building that was under construction next to the metro viaduct at Kaloor, vindicates the pride of place accorded to safety and durability in constructing the 18-km Aluva-Maharaja’s College Ground elevated corridor. Work is under way to extend it by another nine kms up to Thripunithura. The Principal Advisor of Delhi Metro Rail Corporation (DMRC), 85-year-old E. Sreedharan who made it a point to visit Kochi to oversee metro works at least once every week, spoke to The Hindu of how the metro agency is not at all worried about structural safety of the viaduct which has been built to last 100 years. “This is because all piles are designed with a factor of safety of ‘three’ – meaning that they can support three times the design load. Their design is to safely support two fully-loaded trains (each having 900 commuters) and operating parallel to each other at the top speed of 90 kms per hour,” he said. Referring to specifications adopted for piling for Kochi metro, he said that each pillar (pier) stands atop four piles. Each pile has a diameter of one metre and is as deep as 35 to 40 metres in places like Kaloor which are slushy and have a soil comprising a mix of marine clay and sand. In such terrain, a steel pipe lining up to a depth of around 8 m is given so that piles do not collapse. The diameter of each pile at stations (which are cantilevered structures) is 1.50 m. Thus, the foundation will be stable even if there is a crack on the road surface. In non-slushy areas like Muttom, piles are anchored atop rocks, the Metroman said. Narrow roads The extra depth for piling often caused nominal delay in completing civil works in some construction sites. The metro agency’s Kochi Project Director Dani Thomas spoke of how Kochi’s narrow roads posed a major challenge to completing civil works in a time bound manner. “We overcame this challenge by substituting U-girders with I-girders, especially in the corridor leading from Edappally to the city hub. This is because launching pre-cast U-girders needs more space than is needed to launch I-girders. Cranes with up to 350-tonne capacity are needed to launch U-girders whereas 150-tonne ones are enough for I-girders.” Even after launch, I-girders have to be topped with a deck slab casting, a parapet erect and stitch concrete, making it time consuming and labour intensive. As for piling, reliance was on hydraulic rigs which come for a higher rent than tripod rigs, but which saved considerable time and subsequently lesser traffic disruption, Mr. Thomas said.

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