Salvage of TBM by ground freezing

Rescue of tunnel boring machine by ground freezing

Cairo, Egypt Dipl.-Ing. Michael Löffler

In 2009, during a large infrastructure project in Cairo/Egypt (subway line #3) and caused by the collapse of a tubbing segment ring, large amounts of water and soil ingressed into the subway tunnel. This not only created a massive crater in the city center but also lead to the tunnel boring machine to be buried under 25-30m of ground.

Located between the stations El Gaish and Bab El Shaaria in Cairo’s district Bab Al-She’riya, an already established tubbing segment ring collapsed midway of the 4.3km long drivage of the tunnel boring machine (TBM). Approximately further 1.2km of tunneling would have been needed to finish. The collapse was caused by a single segment of the tubbing segment ring dropping out. Therefore, water and ground were able to ingress into the tunnel, provoking loss in soil and with it creating a massive crater at the surface.

frost body length

25 ^m

frost body length

^°C

ground temperature

-10 ^°C

ground temperature

^2009-2010

project duration

^2009-2010

project duration

First of all, the affected area had to be filled and stabilized. Afterwards the recovery was carried out by means of a vertical, 97m deep slurry trench wall shaft. The ground freezing was performed from this vertical recovery shaft by planning, installing and operating for several months a brine freezing tapered towards the tunnel. This freezing allowed for the TBM to be cleared, for the broken ring to be repaired and for the TBM to finally be recovered. CDM Smith was in charge of the complete technical processing by order of Bauer Spezialtiefbau and supervised the ground freezing on site.