Crews lower world's largest tunneling machine into pit

SEATTLE -- The Alaskan Way Viaduct replacement tunnel is a step closer to be drilled below the city of Seattle.

Five stories tall, big Bertha, the world's largest tunneling machine, weighs more than four 787 Dreamliners.

On Friday crews from the Washington State Department of Transportation lowered Bertha's gigantic, green, 838-ton cutterhead into place- just a few inches at a time into an 80-foot deep pit.

Chris Dixon, who's in charge of State Route 99 tunnel project construction said so far, everything's on schedule.

The only thing left- is to fit the last pieces together then test everything out.

"We plan on having that completed in July to start tunneling in July," Dixon said.

Here's how big Bertha will work:

Red and yellow grinders and thick steel cutters will churn Bertha's path underneath the city.

Right behind, huge red arms will rotate to install huge slabs of concrete to create the actual tunnel-while massive, black pistons will push those slabs tightly together- at the same pushing Bertha's cutter head forward.

All the rock, sand and dirt will flow through the many cutter heads, then through massive middle and rear sections.

The rock, sand and dirt will be loaded onto conveyor belts before its loaded onto barges and taken away.

The whole process is extremely slow--Bertha will average just 30 feet per day,

But there shouldn't be traffic delays.

The next road change is coming in 2014 - when they shift lanes of State Route 99 near Century Link a tad bit north, said Matt Preedy with WSDOT.

"It will look a little different, but the number of lanes you'll have and the ramp locations are going to be the same," he said.

After Bertha starts digging in July, she'll keep digging for a little more than a year.

The tunnel is scheduled to open in late 2015.