Study On Mechanical Properties And Acoustic Emission Characteristics Of Red Sandstone Under Water-bearing Conditions

Water–rock interaction usually has a crucial influence on the mechanical properties and failure mechanism of rock mass.Taking sandstone as the research object,the uniaxial compression test was conducted,and the changing laws of the mechanical properties and macroscopic failure shape of sandstone under different water contents were analysed.The fracture morphology was observed by scanning electron microscopy(SEM),and the relationship between crystal fracture surface roughness and mechanical properties was observed and analysed.The characteristics of the dominant frequency and amplitude during sandstone failure were analysed based on acoustic emission(AE)technology,and the response mechanism,as well as the development of internal fracture,was determined.Subsequently,the mechanism of the variation of the dominant frequency characteristics of sandstone was revealed based on the low-field nuclear magnetic resonance and mineral composition analysis.Results reveal that the uniaxial compressive strength and elastic modulus of sandstone exhibit a nonlinear decreasing trend with an increase in water content.The deterioration to the sandstone structure by water is divided into three periods: intense,stable growth,and calm.The macroscopic fracture shape of sandstone gradually changes from singleshear failure to axial-split failure,whereas the roughness of the crystal fracture surface positively correlated with the water content,with the mechanical strength negatively correlating.There are four types of AE signals in the process of sandstone fracture: low frequency and low amplitude(LF-LA),low frequency and high amplitude(LF-HA),intermediate frequency and low amplitude(IF-LA),and high frequency and low amplitude(HF-LA);correspondingly,there are four response mechanisms: sliding friction between the mineral particles or crystal fracture(transgranular or intergranular crack)corresponds to the LF–LA signal,friction of microcracks corresponds to the IF–LA signal,fracture of microcracks corresponds to the HF–LA signal,and large-scale macroscopic cracks correspond to the LF–HA signal.Based on the analysis of the dominant frequency variation characteristics of sandstone,it is confirmed that the mineral composition and pore structure of sandstone jointly affect its response mechanism.Research results can enrich the research content of sandstone damage characteristics under water-bearing conditions and provide new perspectives and approaches for quantitatively describing the water–rock interaction mechanism.