TBM Activities

The South Cobb Tunnel TBM was assembled underground in a chamber called the starter tunnel. This chamber, just large enough to assemble the 27 foot diameter, 328 foot long machine, is located at the bottom of the Sweetwater Construction Shaft. The assembly of the 1300 ton TBM was completed, and tunneling begin in early September, 2009.

The TBM portion of the South Cobb Tunnel project entails constructing approximately 5.5 miles of 27-foot excavated diameter tunnel (located in hard rock), with depths ranging from 150 feet to 400 feet below the ground surface. This TBM, whose cutter head is turned by 10 electric motors which total 4760 Hp, has over 6100 Hp by the time you include the hydraulic system and other miscellaneous systems. As the cutterhead rotates, it produces rock chips which are collected and transported to the surface by conveyor belts.

The TBM holed through at the South Cobb Construction Shaft March 14, 2011. Disassembly took approximately three months, and concrete lining of the tunnel is approximately 35 percent complete.

This is a picture of the TBM cutterhead as it entered the South Cobb Construction Shaft at the end of it's 28,890 foot long journey. 

The main tunnel alignment begins near the intersection of Maxham Road and Old Alabama Road and heads to the southeast along the Cobb County line then turns to the east just north of 1-20 and continues to the east until it reaches the South Cobb WRF. To view a map of the project and the final TBM location, click here.

This is a picture of the cutterhead as it was being moved to the face (the area where tunneling is going to begin)

This is the cutterhead and gripper/main beam section of the TBM at the Moody yard where it was rebuilt. The section of the machine that is visible in this photo is only about one-fourth of the length of the machine.

This is a photo of the TBM as it enters the round tunnel it has just bored. The section of the machine that is visible in this photo is part of the trailing gear.

This is a photo of the tunnel the TBM creates as goes along the right of way. Yes, it can make it around a bend, this is called a reverse curve since it bends one way and then back. That technique is used to offset the tunnel to fit the alignment. The machinery on the right side of the photo is the conveyor belt that removes the cut rock (muck) from the tunnel, and the pipes and wire are the utilities that supply electricity and water to the TBM, and remove dirty water from the heading (the end of the tunnel where the excavation is taking place).