After 4 Years, Seattle's Giant Tunneling Machine Finally Breaks Through

Bertha has broken through.

After four long years underground,

Seattle's massive tunnel-boring machine

completed its epic, arduous 1.7-mile journey

by chewing its way to daylight.

The 57-foot-diameter blades cut through the concrete wall

of a 90-foot-deep deconstruction pit.

Just check out the people here

for a sense of the scale of this behemoth.

It's a long-awaited triumph.

Of the four years that Bertha spent below the earth,

it was stuck for two of them, waiting on major repairs.

Now, work can really get underway

in the tunnel that Bertha left behind

to move SR-99, a dated and potentially dangerous section

of elevated highway underground

to open up Seattle's waterfront for public enjoyment.

Here, at the start of the tunnel,

crews are already installing the double decks

which will carry the new road.

But as we move through the tunnel towards the cutting head,

we enter Bertha itself.

The trailing end of the machine is five stories tall

and the whole thing is 300 feet long,

so those rotating teeth are still way up there.

This is where the crushed soil

and earth is transported out on a conveyor

and where machinery hoists in the preformed

curved concrete sections that make up the tunnel wall.

Each time a full ring is completed,

hydraulic jacks push the whole assembly forward.

Six operators control the tunnel-boring machine,

three per shift.

At 1.7 miles, Seattle's new underground roadway

isn't the longest

and it definitely wasn't the fastest to build;

but for Bertha at least,

there is finally light at the end of the tunnel.