West Area CSO Tunnel
United States, Atlanta, GA
2005 – 2007
Clean hard rock tunnelling

The US Environmental Protection Agency (EPA) has laid down the law: the overflow of untreated sewage into rivers and streams, known as "Combined Sewer Overflows", must stop. Since the capacities of sewage plants are inadequate, especially after heavy rainfall, large cities such as Atlanta have decided to initially store the mixed water underground and divert it afterwards to sewage plants for treatment. The two tunnels planned for this purpose in Atlanta will be 13.4 kilometers long and will be able to store about 670 million liters of mixed water.

Two Herrenknecht Gripper TBMs, each with a diameter of 8.23 meters, commenced tunnelling under Atlanta through the gneiss and granite rock in July and September 2005, respectively. The two machines (S-288 and S-289), which were of identical design, achieved tunnelling performances under the former Olympic city of up to 187.5 and 208.5 meters per week respectively. In spring and summer 2007 the two Gripper TBMs successfully finished tunnelling.

Data Sheet

Country, Location

United States, Atlanta, GA


2005 – 2007




Gneiss, granite

Tunnelling length

13,733 m

Machine Data

2x Gripper TBM:
Diameter: 8,230 mm
Lining method: Rock support
Cutterhead power: 3,150 kW
Torque: 6,315 kNm

Your contact person Contact us

Steffen Dubé President and General Manager Herrenknecht Tunnelling Systems USA Inc.
Gerhard Goisser Commercial Manager Herrenknecht Tunnelling Systems USA, Inc.