Mechanical Behavior of a Granite from Wuyi Mountain: Insights from Strain-Based Approaches

A series of monotonic and cyclic loading tests were conducted on granite samples from Wuyi Mountain to investigate the mechanical behavior under different confinements and damage states. The irreversible axial and radial strains were computed to characterize the development of the damage state, and three characteristic stages were detected according to the average gain rate. The evolution of the apparent deformation parameters with the deviator stress level was investigated to determine the linear elastic stage, but no substantial progress was achieved. In addition, two typical approaches (transitional region and same gradient region of hysteresis) were also found to be unsuitable for determining the elastic parameters to complete the cyclic loading test. Therefore, a secant approach was proposed based on volumetric strain to identify the lower bound of the nominal linear elastic stage with the upper bound established by linear regression. The results indicated that both elastic parameters and stress thresholds showed positive correlations with confinement. With the accumulation of the damage state, the peak stress and crack initiation threshold decreased, crack damage threshold and elastic parameters first increased and then decreased, and the crack closure threshold showed a tendency to decrease–increase–decrease. In addition, the strain softening stage showed a higher slope and minor stress drop value under larger confinement, and a transition from plastic compaction to plastic dilatancy was also detected.