Mechanical properties and acoustic emission characteristics of sandstone under natural and saturated conditions

In order to study the mechanical properties and acoustic emission (AE) characteristics of sandstone with different grain sizes in the process of damage and failure under saturated and natural conditions, we carried out uniaxial compression tests and AE tests on three kinds of sandstone under saturated and natural conditions to study the mechanical properties and AE characteristics under the uniaxial stress state. The test results show that the average compressive strength of coarse-grained sandstone, medium-grained sandstone, and fine-grained sandstone are 54.23 MPa, 53.56 MPa, 59.46 MPa respectively under natural conditions, and 35.62 MPa, 31.79 MPa and 29.10 MPa under saturated conditions. After saturation, the elastic modulus of them decreases by 19.6%, 32.7% and 33.7%, respectively, and the Poisson’s ratio increases by 9.6%, 10.4% and 19.5%, respectively. The variation trend of AE energy curve of all samples at each stage is consistent with the degree of stress failure at each stage, and the peak value of AE energy appears near the peak value of stress. The total AE energy in the elastic deformation stage of saturated samples decreases to 67.4% for coarse-grained sandstone, 32.4% for medium-grained sandstone and 29.3% for fine-grained sandstone. Compared with that of sandstone in the natural state, the total AE energy in the damage evolution stage of saturated samples decreases significantly by 73.5% in coarse-grained sandstone, 36.0% in medium-grained sandstone and 62.0% in fine-grained sandstone. The value of AE energy in the unstable rupture stage also reduces by 30.7% in coarse-grained sandstone, 29.5% medium-grained sandstone and 38.3% fine-grained sandstone. The changes of mechanical properties and AE characteristics of sandstone after saturation are the reflection of microstructural changes in the macro level. The peak value of AE energy in the process of uniaxial failure of sandstone can be used to characterize the brittleness of sandstone, providing reference for the study of rock brittleness.