At 57 feet in diameter, it's touted as the world's biggest tunneling machine. It was even given a name, Bertha.

But now, after digging just over 1,000 feet, Bertha is broken down and stuck underneath Seattle's downtown waterfront.

And fixing the massive mess could cost taxpayers millions.

The tunneling machine is the key workhorse in a $3.1 billion tunnel project aimed at replacing the Alaska Way Viaduct, a double-decker elevated highway that was damaged in the 2001 Nisqually earthquake. Bertha's meltdown, though, has put the project in jeopardy of being the West Coast version of the biggest public works boondoggle in U.S. history, Boston's "big dig" -- which cost taxpayers $14.6 billion, nearly four times the original price tag.

"People should be very worried about what's going on right now," said Dori Monson, a radio host on KIRO in Seattle. "To have the state saying, 'we're not paying for the overruns.' You have the contractor saying, 'we're not paying.' The contractor has a provable history of making other people pay. So that means it's going to be the taxpayers."

The contractor, Seattle Tunnel Partners (STP), already has put in for $190 million in additional pay due to unforeseen problems.

Among the issues the project has encountered are: too much groundwater; a labor dispute involving the International Longshore and Warehouse Union; and a well that Bertha ran into, damaging her massive cutter head and main bearing. The steel pipe was put there by the state, and STP thinks the state should pay.

How exactly Bertha got stuck underground is an open question. The running theory is the machine overheated when it hit the well pipe, but the issue will be argued by the attorneys.

"Who's ultimately responsible and liable for that time and cost is going to be determined by a review of the contract," said Chris Dixon, of Seattle Tunnel Partners.

State officials say the contractor knew about the well and hit it anyway. The Department of Transportation gave Fox News documents supporting its case.

The issue is critical, because fixing the tunnel-boring machine is expected to take until March 2015 and cost $125 million. That's $45 million more than STP paid for Bertha.

State officials say they're trying to protect taxpayers.

"We have written the most robust contract we could possibly write with the best experts from around the country," said state DOT Secretary Lynn Peterson. "And we brought a team together on the legal side to make sure we're protecting taxpayers at every step of the way."

The state has denied a majority of the contractor's change orders, but that doesn't end the dispute.

A court ultimately will decide who's responsible for the delays and cost overruns. That puts taxpayers in danger of being on the hook for a project some fear may never get finished.