Deformation,failure,and acoustic emission response characteristics of fractured sandstone under cyclic loading and unloading
ZHU Ningqiang
LI Xuelong
CHEN Shaojie
CHEN Deyou
MEI Chengwei
MA Xingzhi
Abstract：In coal mining activities,periodic mining disturbances cause fractured rock mass to bear cyclic loads.In this paper,cyclic load-ing and unloading tests of fractured sandstone under different loading and unloading amplitudes are carried out,and the mechanical charac-teristics,deformation and failure characteristics,acoustic emission response characteristics and damage evolution rules of fractured sand-stone under cyclic loading and unloading are analyzed.The mechanism of strengthening and deterioration of mechanical properties of frac-tured sandstone under cyclic load is revealed from the aspect of macro and micro structural changes.The results show that:① With the in-crease of cyclic loading and unloading amplitude,the peak load,elastic modulus and peak strain of fractured sandstone increase first and then decrease;After cyclic loading and unloading with the amplitude of 40%uniaxial compressive strength(σ0)and 60%σ0,the strength of sandstone is high,the time of deformation localized misplaced momentum surge is relatively late,and the final damage degree of sand-stone is severe.When the cyclic amplitude increases to 80%σ0,the localized misplaced momentum is relatively active during loading and unloading.② The sliding friction between particles leads to more acoustic emission events in the samples with 40%σ0 and 60%σ0 amp-litude.When the cyclic amplitude is increased to 80%σ0,the large scale nascent fissure occurs in the sample,and high amplitude acoustic emission events occur.The AF/RA value of the specimen indicates that the final failure type of the specimen after cyclic loading changes from tensile failure to shear failure with the increase of cyclic amplitude.③ Combined with the SEM analysis of the fracture section of fractured sandstone,a generalized model of strength strengthening and deterioration mechanism of fractured sandstone under cyclic load-ing and unloading is proposed:fracture effect of weak structure and compaction and consolidation effect under medium and low amplitude disturbance lead to compaction and severe failure of fractured sandstone;Under the disturbance of high amplitude,the shear crack grows when the sandstone is loaded and the tension crack develops when it is unloaded.④ There is a threshold value between 60%σ0 and 80%σ0,when the cyclic amplitude exceeds this threshold value,the damage variable of sandstone increases rapidly,and the dissipative energy and the proportion of dissipative energy increase gradually with the increase of the cyclic amplitude.The research results can provide data ref-erence for monitoring,warning and prevention of coal and rock dynamic disasters.
Keywords：cyclic loading and unloadingfractured sandstonelocalized deformation bandcrack propagation formacoustic emissionfatigue damage mechanism
Publication Date：2025-12-31
Online Publishing Date：2026-01-16(First online date of this platform, not the publication date of the document)
Pages：19( 67-85 )