How Engineers Sank a 180,000-Ton Tunnel Under a Live Shipping Lane

How do you sink a 180,000-ton tunnel piece onto a shifting seafloor and get it within two centimeters — under one of the busiest shipping lanes on Earth? This is how engineers did it twice, failed, and got it right on the third try. The Hong Kong–Zhuhai–Macau Bridge is a 55-kilometer bridge-island-tunnel system crossing the Pearl River Estuary, built to carry highway traffic while leaving room for 300,000-ton vessels and Hong Kong International Airport's flight paths above. At its center is a 6.7-kilometer immersed tunnel, assembled from 33 individually sunk elements weighing up to 80,000 tons each. We follow the installation of element fifteen — turned back twice by seabed sediment before succeeding on the third attempt — and the September 2018 test that followed just weeks after the crossing opened: Super Typhoon Mangkhut. The bridge opened to traffic on October 24, 2018, after nearly a decade of construction, at a cost of roughly $18.8 billion USD. #Engineering #Megaprojects #Infrastructure #TunnelEngineering #ImmersedTunnel #AtlasAgainstOdds