Weakening mechanism and fragmentation characteristics under uniaxial compression of sandstone with different saturations
Strength weakening of rock mass caused by water rock interaction is a common cause of disasters in mining engineering.Water rock interaction weakening characteristics and its mechanisms are the key to preventing and controlling engineering problems related to water rock interaction.On the basis,the characterization methods such as acoustic emission(AE),scanning electron microscopy(SEM),and nuclear magnetic resonance(NMR)were used to study the characteristics and mechanisms of water immersion weakening in sandstone with dif-ferent saturations(0,25％,50％,75％,100％).It was found that the average uniaxial com-pressive strength of rocks from dry to saturated has decreased from 93.613 4 MPa to 19.255 7 MPa with a decrease of 79.43％.The plasticity of highly saturated sandstone has been enhanced.The AE count and cumulative energy from dry to saturated decreased from 23 186 and 29 495 to 8 504 and 3 695,respectively.The damage variable B also decreased from 1.00 to 0.57,and the spatial distribution density of AE signals decreased.As the saturation increa-ses,the fragmentation degree of sandstone decreases,and the main fracture surface gradually evolves from tensile failure to shear failure.The fractal dimension of fragmentation decreases from 1.716 5 to 1.376 2.NMR results indicate that as the water absorption saturation increa-ses,the capillary water ratio gradually increases,causing a decrease in the cohesion and friction of the rock sample,and promoting the formation of weak structures in the rock sample.SEM results show that the dissolution of mineral components inside the rock sample causes an increase in internal pores and the proportion of macropores.The above-mentioned wa-ter rock interaction causes changes in the form of rock sample failure,it gradually evolves from transgranular cracks to intergranular cracks.The macroscopic manifestation is that the rock sample evolves from tensile failure to shear failure,resulting in a decrease in rock strength.
water rock interactionacoustic emissiondamage variablefragmentation charac-teristicswater weakening mechanism
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