• Spanning Denmark’s Great Belt
    Awake!—1999 | February 8

    • Planners’ Headaches

      Actually, the Danish Parliament began debating the subject of such a bridge in the 19th century. Over the years, planners were occupied with questions like these: Do we want a bridge or a tunnel? Should the connection be for trains, cars, or both? What’s wrong with just using ferries?

      Thousands of calculations were made, and millions of words were spoken. The expression “Great Belt debate” became synonymous in Denmark with a never-ending discussion. But finally, in 1987, an agreement was reached. The connection, joining the two large islands at their closest points, would be for trains and cars. The project would consist of two bridges and a tunnel—an 11-mile [18 km]-long combination—together called the Great Belt Link.

  • Spanning Denmark’s Great Belt
    Awake!—1999 | February 8

    • The Double Tunnel

      The tunnel, the second phase of the project, is a great accomplishment in itself. Twin tubes, each 25 feet [8 m] in diameter, were built for trains. The tubes were bored through 4.6 miles [7.4 km] of clay, rock, and marine deposits. And the tunnel builders were not able to determine in detail the nature of this underground material before they started drilling.

      The tunnel lies between 30 [10] and 130 feet [40 m] beneath the seabed, depending on the undersea terrain—the deepest part being 250 feet [75 m] below the water’s surface. The tunnel drilling machines used were each over 600 feet [each approximately 200 meters] long, including support trains. The finished tubes are lined with 60,000 curved concrete segments, each weighing nearly eight tons.

      Starting the tunnel simultaneously from both ends, the builders masterfully succeeded in meeting in the middle with a deviation of less than an inch and a half [4 cm]. It was a long-awaited special occasion when, on October 15, 1994, Prince Joachim of Denmark officially connected the two halves of the tunnel by stepping from one boring machine into the other one, which had been digging toward it. From Sprogø in the middle of the Great Belt, the two finished tunnel tubes now extend all the way eastward to the coast of Sjælland. Since the middle of 1997, trains rapidly cross the Great Belt, providing regular service.

      Problems Encountered

      The drilling of the double tunnel under the seabed was well under way when suddenly the nightmare of all tunnel workers became a reality—water started to rise in the tubes. The tunnel personnel made it out safely, though it was a narrow escape. The two tunnel holes, however, filled completely with seawater, and much equipment was lost. What had happened? The drilling machines encountered an unforeseen pocket of water in the seabed. This chilling experience naturally set the whole project back, and new techniques had to be devised to get around the problem.

      Then one day an explosive fire broke out, and one of the tubes quickly filled with smoke. As a foreman put it, “the smoke got so thick that Pinocchio couldn’t have seen his own nose.” The site was cleared, the fire extinguished, and the work stopped until the cause was determined—hydraulic oil had caught fire. These and other troubles meant that the whole project was delayed time after time.