In Seattle, No Simple Answers For A Stalled Tunneling Machine

By January 24, 2014NPR News
In this photo made with a fisheye wide-angle lens, "Bertha" is shown in July as it prepares to begin tunneling in Seattle. Ted S. Warren/AP

In this photo made with a fisheye wide-angle lens, “Bertha” is shown in July as it prepares to begin tunneling in Seattle. Ted S. Warren/AP

Ever wonder what happened with Bertha — the world’s biggest tunneling machine, stuck under Seattle? We last checked in on the story right before Christmas, when engineers were preparing to send down inspection teams to identify the blockage. People (OK, the media) were having a grand time, floating ridiculous guesses about what the mysterious object might be. An old ship? Dinosaur bones? Bigfoot?

One month later, there’s still no clear answer. Certainly nothing headline-grabbing.

At first, the blame was directed at a steel pipe: On Dec. 3, Bertha’s cutting face hit the 8-inch diameter, 119-foot-long casing for a research well drilled a dozen years ago by teams working for the state department of transportation. The casing was never removed, and/or someone forgot that it was directly in Bertha’s path. The blame game on that is just getting started.

You might wonder why a pipe would matter, since Bertha is designed to chew through boulders. But Bertha’s five-story-tall rotating cutting face is meant to fracture rock, not ductile materials like steel. That pipe bent when Bertha hit it — imagine running over a jump rope with your lawn mower.

But now it seems the pipe may not have been the only cause of Bertha’s troubles.

Even though the pipe fragments have now been removed, the giant tunneling machine remains stationary. For the past week, specially trained crews have been performing “hyperbaric inspections” in the claustrophobic space around the cutting head, and they’ve found more potential snags, including a rock that was almost exactly 3 1/2 feet wide. The rock was slightly too big to be “digested” by the conveyor system that moves rubble away from the cutting face, but too light to be fractured into smaller pieces by the cutting face. It’s not something that could stop Bertha by itself, but it’s a symptom of a bigger problem.

It’s like trying to crack a nut with a hammer without being able to hold the nut down. Bertha has a harder time fracturing rocks when those rocks are light — or loosely compacted. At the moment, the machine is only about 50 feet down, in the loosely compacted fill of Seattle’s waterfront. Once the machine gets deeper under downtown, engineers assume the more tightly packed soils will hold rocks in place firmly enough to let Bertha chew through.

So, no dinosaur bones. And to be clear, Bertha isn’t really stuck. The department of transportation describes the situation as one of “increasing resistance” at the front end, and operators want a full picture of the situation before they put the $80 million machine back in gear.

Or, as the project manager put it to an impatient legislative committee (one more metaphor!): “If it was your car, and all your warning lights were on and you still needed to make a trip, would it be wise to make that trip?”

Copyright 2014 NPR. To see more, visit http://www.npr.org/.image
Read original article – Published January 23, 2014 6:05 PM
In Seattle, No Simple Answers For A Stalled Tunneling Machine

Recent headlines

  • An Alaska Airlines plane at Juneau International Airport.

    Alaska Airlines pilots plan picket over lack of compensation

    Alaska Airlines pilots have reached a breaking point in negotiations with the company, and now have plans to picket outside Ted Stevens Anchorage International Airport. The pilots plan to picket starting at 1 p.m. Monday outside the airport in Anchorage.
  • Obadiah Jenkins tries to help Daniel Hartung pull himself from Six-Mile Creek in Hope. (Photo courtesy James Bennett)

    Homer resident saves kayaker’s life on Six-Mile Creek

    Jenkins was taking a practice run through the class four rapids when a bystander filming the event, noticed another participant, Daniel Hartung, 64, of Indian Valley, flipped out of his kayak and became pinned under a log.
  • Vigor Alaska Shipyard Development director Doug Ward talks with Marine Transportation advisory board member Greg Wakefield inside the not-quite-finished Alaska Class ferry Tazlina. (Photo by Leila Kheiry/KRBD)

    Alaska class ferry Tazlina on track at Ketchikan shipyard

    The Tazlina is the first of two new Alaska Class ferries that the Ketchikan Vigor Alaska shipyard is building for the state. Its two halves are complete and welded together, and shipyard workers are busy getting interior spaces done.
  • The Matanuska sits in drydock for maintenance.

    Fall-winter-spring ferry bookings begin

    The Alaska Marine Highway is taking reservations for October through April sailings. The schedule changed so the Matanuska can get new engines.
X