Research on mechanical properties and failure characteristics of loaded borehole specimens under static-dynamic coupled loading

ZHANG Yujiang; LI Shule; YANG Yongcong; FENG Guorui; ZHANG Shuai; DU Yunlou; WANG Qian

doi:10.13247/j.cnki.jcumt.20240590

Abstract：Borehole pressure relief is a primary method for preventing and controlling rock-bursts,with the diameter of the relief borehole serving as a crucial relief parameter.Conduc-ting research on the mechanical properties and failure characteristics of loaded specimens sub-jected to uniaxial compression with borehole pressure relief,under combined static and dynam-ic loading conditions,holds significant importance for optimizing borehole pressure relief pa-rameters and maintaining the stability of surrounding rock post-relief.In this paper,a three-dimensional static-dynamic multi-field coupling experimental system,acoustic emission(AE)equipment,and digital image correlation(DIC)devices were employed to conduct uniaxial compression tests on loaded specimens subjected to dynamic loading disturbances after bore-hole pressure relief.The effects of pre-static load levels,dynamic load amplitudes,and bore-hole diameters on the uniaxial mechanical properties and failure characteristics of the specimens were explored.The experimental results indicate:When the sum of static and dynamic loads is less than 73％of σuc(uniaxial compressive strength),the combined static and dynamic loading enhances the uniaxial compressive strength of the specimens.The elastic modulus of the speci-mens increases significantly after disturbance.Boreholes weaken the strength of the specimens in a positively correlated manner;as the borehole diameter increases,the weakening effect be-comes more pronounced.Boreholes and loads(both static and dynamic)influence fatigue strain.Fatigue strain increases linearly with the borehole diameter and dynamic load ampli-tude.Pre-static loads also affect fatigue strain.When the specimen is in the compaction stage,dynamic loading disturbances compact the original fractures inside the specimen,resulting in larger fatigue strain.In the elastic stage,with minimal fracture development,fatigue strain decreases.During the plastic stage,irreversible plastic deformation occurs,leading to an in-crease in fatigue strain.An increase in borehole diameter reduces the AE events(ring counts and energy)of the specimen and lowers the damage threshold.Dynamic loading disturbances compact the specimen,increasing AE events and raising the damage threshold.The energy re-leased instantaneously during failure increases,making the specimen exhibit stronger brittle-ness.An increase in borehole diameter alters the fracture development characteristics of the specimen.As the borehole diameter increases from 0 to 12 mm,the failure mode of the speci-men transitions from tensile failure to X-shaped conjugate oblique shear failure,with some specimens showing flaking on their surfaces.This research provides a theoretical foundation for revealing the failure mechanism of surrounding rock under borehole pressure relief and serves as an important reference for optimizing borehole pressure relief parameters.