Doha, Qatar / Schwanau, Germany, 24.07.2014 With annual rainfall of less than 100 mm, Qatar is one of the driest landscapes on earth. But individual driving rain showers lead to extensive flooding in the densely populated capital of Doha. A comprehensive drainage system covering an area of 170 km² aims to ensure improvement in the southern section of the city populated by half a million people.

Two Herrenknecht tunnel boring machines (TBM) are driving a tunnel 20 to 30 meters underground for the so-called Abu Hamour Southern Outfall Project. The EPB Shields with a diameter of 4,470 mm are designed for Doha's soft limestone soil. Muck comprising excavated material serves as the support medium for the so-called Earth Pressure Balance Shield (EPB), providing the requisite pressure balance at the tunnel face. Protected by the shield skin, the tunnel is excavated using ring-shaped reinforced concrete segments. The individual segments are transported through the tunnel as it is completed and connected to form closed rings (segmental lining process) directly behind the TBM with an erector.

Via the main tunnel extending 9.5 kilometers, up to 16.5 cubic meters of water per second will later be conveyed to a central pump station near the New Doha International Airport.

Herrenknecht tunnelling technology was also used in designing some of the inlets during an initial construction phase. Using a slurry AVN machine from Herrenknecht, a total of four kilometers of tunnel with an outer diameter of 3.60 meters were excavated with the pipe jacking method in 2008. This is a remarkably large diameter for pipe jacking.