How Japan Built the $7B Seto-Ohashi With 1970s Engineering — Inside a 10-Year Human Triumph

Built with late-1970s engineering across the Seto Inland Sea, Seto-Ohashi became a landmark road-and-rail connection between Honshu and Shikoku. From underwater rock excavation and giant marine foundations to towers, cables, deck lifting, railway systems, and load testing, this documentary reveals the full construction process step by step. #EngineeringDocumentary #BridgeConstruction #MegaProjects #SetoOhashi How did Japanese engineers complete this enormous sea-crossing system over nearly ten years—without modern digital positioning, computer-controlled lifting, or real-time construction monitoring? Seto-Ohashi is not a single bridge. It is an interconnected system combining three suspension bridges, two cable-stayed bridges, and one continuous steel-truss bridge across the Seto Inland Sea. Construction began in 1978, and the route opened in 1988, carrying highway traffic on the upper level and railway lines through the lower structural level. From surveying deep water and fractured seabed rock to installing marine caissons, anchorages, steel towers, main cables, hangers, trusses, road decks, and railway infrastructure, this documentary follows the complete construction journey. What you will see: ✅ How engineers surveyed currents, tides, seabed depth, and foundation rock ✅ How controlled underwater blasting prepared the seabed ✅ How enormous steel caissons were fabricated, floated, towed, and lowered ✅ How massive concrete anchorages and steel towers rose above the sea ✅ How pilot ropes, catwalks, strands, main cables, and hangers crossed the channels ✅ How cable-stayed spans were erected through balanced cantilever construction ✅ How giant steel-truss sections formed the double-deck road-and-rail structure ✅ How road systems, railway tracks, and structural load tests completed the crossing The challenge was not simply building above water. Engineers had to manage strong currents, wind, deep foundations, active shipping lanes, heavy offshore lifting, narrow installation tolerances, and the limitations of construction technology available during the late 1970s and 1980s. Watch until the end to see empty sea channels transformed into a continuous engineering system—an achievement created through precision, physical effort, patience, and human determination. TIMESTAMPS 00:00 1970s Engineering Against the Sea 00:32 Rewind: The Seto Inland Sea Before Construction 01:26 Marine Survey and Geotechnical Investigation 02:25 Underwater Rock Excavation and Seabed Preparation 03:24 Giant Caissons and Marine Foundations 05:10 Anchorages and Suspension Towers 07:26 Pilot Ropes, Catwalks, Main Cables, and Hangers 09:27 Cable-Stayed Bridge Construction 11:13 Yoshima Steel Truss and Double-Deck Structure 12:07 Suspension Deck Erection and Structural Closure 12:40 Road, Rail, Safety Systems, and Load Testing 12:56 Final Seto-Ohashi Engineering Reveal If you enjoy real engineering, bridge construction, heavy machinery, and full-process infrastructure documentaries, subscribe to Engineering Revealed. AI & Production Disclosure: This video uses digital visualization and AI-assisted imagery for educational documentary storytelling. Research, structure, writing, editing, and production direction are created by Engineering Revealed. Educational Note: This content is created for educational and documentary purposes. It is not professional engineering advice or an official construction record. #CivilEngineering #HeavyConstruction #JapaneseEngineering #InfrastructureDocumentary