Click through to see each step of Bertha's extensive repair process. All photos from WSDOT Flickr page.

Bertha's 2,000-pound front end emerged from the repair access pit on March 30 thanks to a custom-built modular lift tower from Mammoet.

Two cranes were needed to lift Bertha's bearing block from the main cutterhead assembly and over to its own repair platform.

A worker cleaning one of Bertha's cutter drive motors.

A welder retrofitting a piece of Bertha's outer shield, which was removed before the cutterhead assembly was pulled up from the pit.

An aerial view of the repairs.

This is Bertha's new outer seal ring just before it is lowered and installed atop the cutter head, seen on the lower right. The inner and outer seal rings form the machine's new seal system which protects the main bearing.

Bertha's new inner seal ring is hauled from the waterfront over to the repair site.

Crews maneuver the new inner seal ring onto a platform.



The inner seal ring is installed atop the cutterhead.

After the inner seal ring is lowered, crews inspect the installation.

Meanwhile, crews refurbished the machine’s agitator, which mixes excavated material with conditioning agents in the chamber behind the cutterhead.

Here the machine's main bearing, responsible for rotating the cutterhead, is installed. The red substance is a lubricant.

The main bearing is then encircled by a gear ring.

Here, the main bearing and bull gear are seen encircling the center pipe. The pipe is part of the agitator seen before.

A milling machine prepares the surface of the SR 99 tunneling machine’s cutter column for reassembly.

A crane lowers Bertha's inner cylinder, which houses the machine’s agitator and the inner seal ring, into place.

Mammoet crews lift the machine’s bearing block into place atop the cutterhead and drive unit.

Crews finish up installation of the machine's motors.

With the last motor installed, lowering of the repaired front end back into the pit begins.

According to the WSDOT, the Mammoet crane rotated the 2,000-ton front end 90 degrees while lowering it into the pit.



With the front end in position to be reconnected to the rest of Bertha, the three outer shield pieces are reconnected.



Welders complete Bertha's reinstallation by reconnecting sections of the machine's outer shield.

A closeup view of the newly resurfaced cutterhead from inside the pit.

With the final repairs having been made earlier this summer and Big Bertha finally picked back together underground, Washington State Department of Transportation and Seattle Tunnel Partners crews are hopeful that their 18-month nightmare is nearing a close.

Now two years behind schedule, the world’s largest tunnel-boring machine is pegged for a return to digging in November. The machine went down in January 2014 one-tenth of the way through digging a 1.7-mile tunnel which will replace the Alaskan Way viaduct and carry a double-deck highway beneath Seattle.

In April we showed you the process of lifting the massive machine’s cutterhead through a 120-foot deep access tunnel and now, WSDOT has shared all the photos of the machine’s massive repair process.

Seven of the machine’s rubber seals meant to protect its main bearing became clogged by sand and water and steel casings around the seals “broke apart, sending fragments into the drive gears,” the Seattle Times reported back in May. Plus, some of the teeth in the machine’s bull gear, which rotates the drill face, were cracked as well as several pinion gears. Hitachi-Zosen, the machine’s manufacturer, resurfaced much of the front end to allow its circular parts to move smoothly and replaced the full set of 24 pinion gears and the outer seals of the main bearing.

The company also lengthened the mixing arms and equipped them with paddles, attached more steel blades to the cutting surface and ordered a replacement for the machine’s cracked center pipe. The full repairs are expected to be completed later this month.

In August the machine was lowered back into the pit and a resume digging date of November 23 was set. Between now and then, crews will be performing open-air testing on the machine.

Don’t miss the gallery detailing the extensive repairs, above.