The tunneler was supposed to come up for repairs in September or October, but crews reportedly are having a harder time than expected digging a shaft to the damaged cutter head.
Crews were installing concrete rings into the 120-foot-deep shaft, but then work began to slow down.
State Department of Transportation officials said there are several reasons the work is taking longer than anticipated.
One factor is the addition of 11 piles to the shaft's design, bringing the total number of piles to approximately 84.
Also, crews are also working with exceptionally large interlocking piles, which are necessary to make the pit self-supporting without tiebacks or other reinforcements. The large piles take longer to install than standard piles.
Once the shaft is complete, workers will hoist the 2,000-ton front end of the tunnel machine to the surface, and begin repairs damaged seals and bearings.
Officials said Monday that Bertha's new main bearing has arrived in Seattle and will be assembled closer to the time it's needed, likely this fall.
Other repair pieces, such as the new outer seal ring, the thrust seal ring and bearing block are nearing completion. After these pieces are fabricated and inspected, they will be shipped to Seattle.
Cranes to lift the damaged cutter head to the surface still need to be assembled.
Bertha ground to a halt in early December about 1,000 feet into the 1.7-mile Highway 99 tunnel that will replace the Alaskan Way Viaduct.
Despite the latest delays, Seattle Tunnel Partners says it will resume digging the tunnel as originally scheduled in March 2015, because it built in extra time for the repair process.
The tunnel is expected to be completed and open in November 2016.