Get ready to see Mammoet’s crane back in action, as crews stand ready to lower the front end of Bertha, the world’s largest tunnel-boring machine, back into its tunneling pit after repairs wrapped up on the machine over the weekend.

Already the 2,000-ton front-end has been connected to the custom-built Mammoet crane and final tests stand as the last step before the lift can begin at some point on Monday morning. Crews expect the lifting and then lowering of the piece—essentially in the reverse order it was brought up—into the 120-ft-deep pit could take about 14 hours.

The front-end section isn’t the only piece needing to return to Bertha, but it is the largest of the four pieces required for reassembly this week. The piece contains the machine’s cutterhead, new motors and the new main bearing assembly.

Once the front end returns to the rest of Bertha at the bottom of the pit, crews can reconnect wires, hoses and cables. The three pieces of the machine’s outer shield will be lowered into the pit just days after the front end.

Once all the pieces have returned to Bertha and been reassembled, expect a long series of tests before crews attempt to restart tunneling by late November.

The TBM has sat idle since December 2013, when it overheated; then, it was shut down, so crews could search for a cause and a solution. Bertha stopped just 1,083 ft into a 9,270-ft (1.7-mile) course to create space for a new Highway 99, which will replace the aging and seismically vulnerable Alaskan Way Viaduct.

With the 57.5-ft-dia machine’s cutterhead now under repair and reassembly, the Seattle Tunnel Partners joint venture of New York-based Dragados USA, Spain-based ACS Group and California-based Tutor Perini Corp. believes it can have Bertha digging again this fall.

With Bertha potentially churning earth again in late fall, STP plans to have the tunnel open to drivers in spring 2018, which is beyond the state's original target date of November 2016 and STP's original target date of December 2015. STP expects that, once Bertha relaunches her tunneling efforts, she will take approximately one year to go the remaining 8,000-plus ft, north to the project’s end point near Seattle’s Space Needle.

STP has worked with machine manufacturer Hitachi Zosen, Japan, since the 326-ft-long TBM exhibited trouble. After an investigation, crews discovered damage to the seal system and the main bearing. The cause of that damage has yet to be determined. To access Bertha for repairs, STP did not disassemble the machine from the rear and reach the front cutterhead through the already tunneled portion of the project; instead, STP dug an access shaft in front of the machine and, in March, lifted the TBM's front end from the 120-ft-deep pit.

In addition to the main bearing, STP crews have installed portions of a new seal system, which includes the addition of reinforced steel, a new monitoring system and, to help prevent clogging, upgrades to the soil-conditioning system.

Inside the machine, bigger openings in the cutterhead, longer mixing arms to stir dirt, a heavier bearing, and steel rods and plates to reinforce the front end will give Bertha a new robustness.

Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.