Numerical simulation of the acoustic emissions and released energy in the tunnel surrounding rock subjected to a localized failure considering dilatancy

Evolution of the acoustic emissions and released energy during the process of the localized failure of the surrounding rock of a tunnel is simulated after the tunnel is excavated considering the post-peak dilatant nature of rock.The method to introducing the dilation angle into FLAC is discussed and the maximum principal plastic strain increment for shear failure is related to the dilation angle.The method to calculating the acoustic emission counts and released energy is presented.The former only considers the number of events,while the latter the magnitudes of events.It is found that higher dilation angle leads to larger number of failed elements in shear and corresponding released energy in the tunnel surrounding rock.Higher dilation angle results in bigger,less sharp and deeper V-shaped notches because the angle between the maximum principal stress and the shear band becomes larger.The tensile strength is set to be a constant.However,the tensile strain-softening occurs and the tensile elastic strain energy is released.The reason for this phenomenon is explained.Generally,the precursors to failures of V-shaped notches can be found from the released energy,while does not from the acoustic emission counts.This reflects that the magnitudes of events should be considered necessarily.For zero dilation angle,the number of failed elements and corresponding released energy can be underestimated,while it is easier for the surrounding rock of the tunnel to reach the static equilibrium.