Effects of height/diameter ratio on failure and damage properties of granite under coupled bending and splitting deformation

摘要

In underground mining, rock roofs with different thicknesses have distinct failure patterns under the complex stress. To understand the height/diameter ratio (H/D) on failure properties and damage characteristics under the coupled bending and splitting deformation, a series of point-bending tests were conducted on granite disc samples with the same diameter but different heights. The micro-crack evolution during the test was measured and recorded by acoustic emission experiments. Test results indicated that the height/diameter ratio determines the failure mode of granite samples. The sample with the H/D less than 0.4 is primarily fractured in the bending mode. Once the H/D exceeds 0.4, the failure pattern transforms into the splitting pattern. According to analysis of the ringing count rate in the acoustic emission signals, more than 60% of the damage accumulates rapidly in the yield stage, while the damage in other stages increases steadily. In addition, the damage evolution curves calculated from the plastic region are consistent with those calculated by the ringing count rate, so that the damage properties of the granite disc samples are obtained under the complicated stress. The rapid accumulation of the damage indicates the sharp change of the stress inside the rock sample, which is the precursor information of the failure of rock samples.