Experimental study on failure behavior of tunnel in jointed rock mass under excavation

The purpose of this study is experimentally to investigate the failure behavior on the disturbed zone around anopening in non-persistent jointed rock masses. The jointed specimens are modeling material with hole being drilled under a certain stress level to simulate underground excavation. In our experimental studies, the failure process with the time is fully observed: (1) For deformation around the opening after excavation: With a constant ratio of lateral loading to axial loading 'lambda', crack initiation occurs away form the opening first. But the final failure is dominated around the opening by sliding along the joints, and by the coalescence between the joints and the opening. (2) For the failure time: When the applied axial loading keeps about 75% of the peak force, the time for the failure of an opening is decreases with the increase of lambda. Our observation contradicts the common observation that a higher confinement leads to a longer failure of time.