WEI Xuefei, DUAN Yunling, QIAO Nan, FENG Jinming
The Austrian tunneling method (NATM) is being used to construct underground structures in China. The methods main points are to 1) reduce the stresses, 2) provide appropriate flexible supports, 3) seal the stress sphere and 4) provide monitoring and measurements. Barton summarized the relationship between the rock mass quality index, Q, and the cavern excavation span and support type. Chinese construction specifications for underground excavations are similar; however, there have been 50 collapses of underground projects using the NATM method in China with this study indicating that many of the accidents were using strong supports in V-class wall rock even though such strong supports are not recommended NATM core supports. This indicates that designers do not fully understand NATM including a lack of knowledge of the optimal section and support types for the intact rock type, failure to use local reinforcement for fractured zones to form stable circumferential deformation of the wall rock, and failure to use reinforcements to block leaks as well as improper selection of support installations, inaccurate design predictions, and inappropriate equipment for the working face rock. The suggested countermeasures include avoiding excavating caverns in V-class wall rock, quickly grouting fractured zones to improve the rock mass strength in fractured zones, and sealing sections as quickly as possible.
