Failure Characteristics and Support Optimal Design of Columnar Jointed Rock Mass at a Diversion Tunnel

Columnar joints are native rupture structures which are ordered columnar forms in basaltic lava. The cracks and joints inside them are well-developed which lead to the weak self-supporting ability after excavation. At present, loose and collapse of columnar rock mass are the main problem in the hydraulic diversion tunnel. Based on field observation and test, this paper studied the failure characteristics of columnar joints in the diversion tunnel and simulated the failure mechanism. Based on this discussion, optimized support measures have been taken to ensure the safe construction of the diversion tunnel.