Atlantic Cities

The Most Complicated Tunnel in the World Finally Opens

The Most Complicated Tunnel in the World Finally Opens
Reuters

There’s been much talk of huge future development projects in Istanbul recently. Today, one of them actually arrived.

After nine years work and $4 billion spent, Turkey's largest city opened its first tunnel underneath the Bosphorus Strait, a body of water that separates its European and Asian sections. The 8.75-mile rail tunnel is destined to be part of a new commuter network called Marmaray, capable of transporting 75,000 passengers per hour when at full capacity. The link will not just ease commutes and get people off congested roads and bridges, says Turkey’s government, but also ultimately form a key link between continents, an "iron Silk Road" that Prime Minister Tayyip Erdogan has grandly promised will "link London with Beijing."*


A view of the Bosphorus bridge that links Istanbul's Asian and European side. (Osman Orsal/Reuters)

Outsiders might well be wondering why the tunnel has taken this long to arrive. An alternative to road bridges and ferries has been desperately needed for some time. The existing two bridges over the Bosphorus are routinely gridlocked, and Istanbul has some of the worst traffic congestion problems in the world. At its narrowest, the Strait is less than 800 yards across. Plans to tunnel beneath it have been around since the reign of Sultan Abdülaziz, 150 years ago.

In a setting like Istanbul, however, nothing is ever simple. The city is built on layer upon buried layer of historical cities. When crews started excavating the tunnel, they smashed straight into the Byzantine Harbor of Theodosius, a long-buried medieval wharf stacked with the shipwrecks of 37 artifact-filled watercraft. Removing and preserving the over 40,000 objects discovered took years, with work carried out in the face of official exasperation and reluctance.

But while this held the project up, it's deep beneath the harbor that the tunnel's true problems began. 

Istanbul is famously in an earthquake zone. The tunnel itself passes just 11 miles from a major fault line. Because of this, the city dropped the tunnel more than 60 meters beneath the sea; it's thought to be deepest submerged underwater railway tunnel in the world. Yet even this far down, Istanbul's geology poses problems. The earth through which the tunnel passes is loose and soggy, and can become even looser and soggier during an earthquake, turning to liquid. To anchor the tunnel for this eventuality, engineers have had to take extreme measures. They encased the tunnel in steel and injected the earth around it with a thick layer of concrete. The undersea sections of the tunnel have also been book-ended with two flexible steel and rubber joints, so that the tube can jiggle rather than snap if the earth shakes. If all this fails, floodgates at either end of the tunnel will at least protect Istanbul's streets and subway network from a storm surge.

But while the tunnel’s safety measures sound stringent, some still feel it is opening too soon. Its launch is a publicity coup for President Erdogan, timed to coincide with today’s 90th anniversary of the Turkish Republic. Only three of the planned 37 stations will actually open this month. Completion of the rest of the Marmaray network remains a few years off. Crucially, Turkey's Chamber of Architects and Engineers have cast doubt on the water tightness of the tunnel's flexible joints and pointed to the lack of a security center. 

The chamber's criticism is part of an ongoing struggle with the current government. Earlier this year, Turkey's Parliament banned the Chamber from participating in city planning decisions, retribution for their opposition to government plans for Gezi Park. In light of this year's public upheavals, it's not surprising that the project is viewed with suspicion. Many grand plans currently intended for Istanbul have been bitterly attacked for threatening to displace poor residents and destroy the environment. The government's raw, authoritarian response to protest brought the country close to breaking point. While the tunnel may well help to ease some of Istanbul’s problems in the long run, its drawn-out, complex creation is tainted by association.

* Correction: An earlier version of this post mistakenly identified Tayyip Erdogan as President, not Prime Minister.

Top image: An engineer performs a last check on a train of Marmaray. (Murad Sezer/Reuters)

Feargus O'Sullivan covers Europe for The Atlantic Cities. All posts »

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