Mumbai is about to record a milestone. Every day for the last two years, ‘Mavala,’ a gigantic machine weighing 2,800 tonnes—the cumulative weight of about 460 male elephants—has been burrowing under the Arabian Sea and Mumbai’s iconic Malabar Hill. It inches forward by about four or five metres daily, shattering the strong basalt rock in its way to smithereens. In the next seven to nine days, Mavala will have made its way to the other end, wrapping up the challenging task it has been at for the past two years. When it does, Mumbai will have created history for building…