Rescue of tunnel boring machine by ground freezing

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.

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.