Bertha’s punch to repair pit lifts hopes for tunnel progress
Tunnel-boring machine Bertha’s slow and successful breakthrough into its repair vault Thursday raises hopes that the great dig toward South Lake Union could resume by late summer.After being stranded underground for more than a year, the damaged machine wormed through a 20-foot concrete wall in less than two days, without overheating and without stalling as feared.As a precaution, the tunnel team ran the Highway 99 machine much slower than its design calls for. That strategy worked, helping the team dodge further delays to a job already nearly two years behind schedule.
Based on the current pace, with crews working two 10-hour shifts per day, the world’s largest-diameter tunnel-boring machine should reach the center of the vault within a couple of days, allowing for the front end to be dismantled and hoisted to the surface for repairs, a 4 million-pound lift.
“We’re very pleased with the progress we’ve made” this week, said Matt Preedy, deputy Highway 99 tunnel administrator for the Washington State Department of Transportation.
Chris Dixon, project director for the Seattle Tunnel Partners (STP) contracting team, told reporters he wasn’t surprised with the machine’s performance.
“Not really. Not with the detailed planning involved,” he said.
The machine stalled Dec. 6, 2013, as temperatures spiked around the cutter drive. Wet sand and grit penetrated the rubber seals and may have damaged the main bearing, which is to be replaced.To some Seattleites, anxious about whether Bertha would ever move again, its progress this week seemed curious.
But the grind really wasn’t so fast.