With annual rainfall of less than 100 mm (4 in.), 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 sq km (65 sq mi) aims to ensure improvement in the southern section of the city populated by half a million people.
Two Herrenknecht TBMs are driving a tunnel 20 to 30 m (65 to 100 ft) underground for the Abu Hamour Southern Outfall Project. The EPB Shields with a diameter of 4,470 mm (14.6 ft) are designed for Doha’s soft limestone soil. Muck comprising excavated material serves as the support medium for the shield, 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.
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 4 km (2.5 miles) of tunnel with an outer diameter of 3.6 m (11.8 ft) was excavated with the pipe jacking method in 2008. This is a remarkably large diameter for pipe jacking.
With its “Vision 2030”, Qatar aims to offer its citizens the highest possible standard of living. Some projects are already being implemented and range from surface water discharge to traffic infrastructure. Herrenknecht is also involved in the new Doha Metro System with a total of 21 EPB shields, many of which have already been delivered.