CREC 160, a Φ 6.3m Slurry TBM supplied by CREG for Nanchang Metro Line 2 completed its crossing beneath the Ganjiang River in Nanchang. On March 27, the machine met its target ventilation shaft precisely after a drive of 1,736m. The 1342m river-crossing section thereof, 400m longer than that of Nanchang Metro Line 1, refreshing the TBM river-crossing drive.

Major challenges

The project faces many challenges, Chief among them are:

Complex geological conditions
The TBM launching location is close to highly permeable sand strata beneath Ganjiang River. The machine has to cross Ganjiang Dike and fault zone. Constant and real-time monitoring is needed to prevent water and sand ingress as well as ground settlement. 

Long distance drive
Moderately weathered pelitic siltstone featuring upper soft and lower hard binary stratum comprises a major part of the tunnel section. The long distance drive is quite demanding for the machine given the potential risk of cutterhead clogging, slurry treatment problem and upper sandstone collapse. To address that, secondary grouting is adopted. Measurement like increasing the number of centrifuge and the use of quickly solidified slurry successfully solved the aforementioned problems. The best monthly performance of CREC 160 was 436.8m.
 

The contractor of this project is China Railway Tunnel Group (CRTG), one of the most experienced and leading Chinese tunneling contractors operating in the Chinese and international market today. With the completion of the River-crossing part, CREC 160 is nearing the end of its overall tunneling. The final trial operation of Nanchang Metro Line 2 is therefore a big step closer.

A video featuring the breakthrough of CREC 160 can be found here:

http://tv.cctv.com/2017/03/28/VIDE6aMMHHbJRtMF5tKk5Oj8170328.shtml