The arrival of the last tunnel boring machine (TBM) in the Boulak shaft, on Monday, marks the end of tunnelling for the CML3 project, phase 3, in Cairo, Egypt. It took two TBMs to achieve the three 9.45-metre diameter tunnels, running a distance of 7 kilometres through sand, silt and clay. The mud-pressure TBMs successively crossed through the eight underground stations (entrance and exit under a steel bell), the diversion structure and the eight auxiliary drop shafts.

A whole host of challenges had to be overcome, including pressures of almost 4 bars, a trajectory with a radius of curvature of only 200 metres in some instances and navigation between bridge piles at times. Despite this, the performances were spectacular, particularly on the last 3-km-long 3C section, which was completed in 8 months and included three station crossings, with record outputs of almost 210 metres in seven days and 42 metres in one day!

Congratulations to the teams who took part in this project!