Much has been made of Elon Musk’s recent interest in boring tunnels under America. He is even advising the Trump administration to use tunnels as part of its $1 trillion infrastructure project, saying he could bore his way across America and create a lattice of tunnels 30 levels deep to solve the country’s traffic congestion problems.
Talking about boring holes in the ground is one thing. Doing it is something else entirely. In 2001, an earthquake damaged the elevated highway along Seattle’s waterfront, making it unsafe for cars and trucks to use. That highway was a vital part of the city’s infrastructure and served as the primary link between the southern and northern sections of the city. A new roadway would have to be constructed. There was only one problem. The city of Seattle was in the way.
The Washington Department of Transportation decided the only solution was to bore a 9,720 foot long tunnel under the city. WSDOT and main contractor Seattle Tunnel Partners STP enlisted the help of the Hitachi Zosen Corporation of Japan to build the world’s largest tunnel boring machine. Nicknamed “Bertha,” it was 326 feet long and 57.5 feet wide and weighed 7,000 tons. One April 4, Bertha completed its mission as it broke through a reinforced concrete barrier at the end of its journey. New Atlas was there to record the event.
“At first, the only sign that Bertha was approaching was a deep grinding, screeching noise that came from behind the plug that dominated the south end of the 90-ft-deep pit that had been built to receive the steel behemoth. On one seam of the plug, a trickle of foam was seeping out as the soapy conditioner used to make the soil easier to dig through tried to escape.
“At 9:45 am, the scene suddenly changed as a sudden jet of suds and muddy water shot out of the base of the plug, flooding the pit. At the same time, the giant cutting disc of the machine apparently made contact with the inner surface of the plug and clouds of very fine white dust rose and was trapped in the confines. This reduced visibility to zero for many minutes and members of the press were asked to retreat to cleaner air while Bertha paused and the dust cleared under sprays of water.
“Then at about 11:15 am EDT, Bertha broke through as section by section chunks of concrete and rebar were ground up and fell away into the water below. Within 20 minutes, most of the plug was gone and the cutting disc, once a bright mosaic of green, red, and yellow covered with sharp cutting heads, was now revealed as a worn metal surface with blunted edges.”
Now the problem is getting Bertha out of the ground. First the contractor will removing the giant support struts from the pit dug at the end of the tunnel. Over the next 5 months, Bertha will be broken up into 20 ton chunks that can be transported over city streets. Some parts will be salvaged and sold back to the manufacturer but most of the steel will go to a local iron foundry to be melted down. It will be reused to build the roadway inside the new tunnel. The pit itself will be converted into a ramp connecting the tunnel to the road network.
“This is a historic moment in our state’s transportation history,” said Washington State Governor Jay Inslee. “Innovation and perseverance are the engines that keep Washington in the forefront. There is still more work ahead but this moment is one worth celebrating.”
To hear Elon Musk tell it, boring tunnels is as easy as planting bulbs in your garden. The video below suggests there may be slightly more to the process than that. Musk says his engineers are going to figure out how to make boring machines that are ten times faster than anything available today. If true, that should be quite a sight to see.
Source and photo credit: New Atlas