Experimental investigations on the failure characteristics of brittle sandstone containing various heights of rectangle cavities under biaxial loading

Abstract

Spalling failure commonly exists during the excavation of underground structure and lead to tremendous losses of life and property. Therefore, to simulate the failure initiation and development during the underground excavation, the sandstone samples with various heights of rectangular cavities are prepared and applied in the biaxial compression test. The surface deformation field is monitored by the Digital Image Correlation method, and the acoustic signal is captured simultaneously. Research results indicate: 1) The relatively intensive secondary failure is activated by the first AE burst incident, which is reflected in the relatively high signal amplitude and low b-values; and the most severe damage occurs at the peak stress status, accompanied by the highest AE counts and energy releases. 2) As the cavity height increases, the samples’ failure mode transfers from the pure fracture failure to the mixed fracture-spalling failure, and finally to the typical V-shaped spalling failure. 3) In previous studies finished by the sample with the circular cavity, the failure shape and distribution remain unchanged when the excavation area (section diameter) is fixed; while the position, development process, and mode of secondary failures in the surrounding rock of rectangular cavity gradually change as the cavity height increases (to simulate the mining stope excavation). 4) Based on the PFC simulation results, the spalling failure is constructed through two stages; shear cracks adjacent to the internal free face contribute to the first round of spalling failure, and the internal tensile cracks result in the second round of spalling failure.