Marmaray: Asia-Europe Tunnel
Just a pointer to a fascinating project that recently achieved a major milestone: the underwater tunnel of the Marmaray project, connecting the European and Asian sides of Istanbul, was completed on October 20th:
This is an immense engineering feat, since (in the words of one of the managers) "I can't think of any challenge this project lacks". Istanbul is an earthquake zone, the Bosphorus is one of the world's busiest shipping lanes, the excavation continually runs into historical ruins, and Turkey is not one of the world's stablest countries politically or economically. Once up and running in 2012, this will provide both commuter services across Istanbul (which are currently limited only to ferries) and allow through service for long-distance trains from Europe through to mainland Turkey.
Wikipedia has a fairly good article, plus a good map showing how radically transport will change once Marmaray and a few other metro projects are ready, all projected for 2012:
But the official site has not been updated since 2005...
As I had seen a documentary about this project some months ago - an interesting fact on this tunnel is that it is in fact not a tunnel in the normal sense, that means a hole drilled through the soil or bedrock. Instead they descended pre-constructed concrete structures onto the seafloor and connected them there.
Originally Posted by jpatokal