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00000181-fa79-da89-a38d-fb7f2a000000Bertha, the world's biggest tunneling machine, is a five-story-tall monstrosity of drilling tasked with digging out the tunnel for State Route 99 to replace the Alaskan Way Viaduct. It's journey to the center of the earth underneath downtown Seattle began in July 2013, and since then the project has seen its fair share of successes and failures.Follow the progress of the $3 billion megaproject with KUOW.

Still No Answers For Stuck Bertha

So far, crews trying to determine what’s stalling the State Route 99 tunnel machine have found a hard object more than three feet wide lodged in it.

They’ve also found metal and plastic piping. But what exactly is causing the stoppage is still unknown.Crews from Seattle Tunnel Partners have made more than two dozen hyperbaric inspections on various parts of the tunnel machine known as Bertha. They’re using air pressure to stabilize the ground in front of the machine. It allows crews to work in areas that would otherwise be filled with soil and water.

The work is laborious, time consuming and expensive.

Standing at the entrance to the tunnel Friday, Washington State Department of Transportation's Matt Preedy said he was concerned about the delay. “You know one of the fundamental purposes of the viaduct replacement project is that it’s a safety job. If we didn’t have a vulnerable structure on the waterfront we might not be under such a time crunch," he said.

Tunneling on the project has been halted since early December.

Preedy wouldn’t speculate about how much the delay will add to the $3.1 billion project or who might be on the hook for the costs.