Experimental study on seepage and mechanical properties of sandstone under different confining pressures and cyclic loads

In order to explore the lagging water inrush mechanism of deep coal seam floor and to clarify the seepage and mechanical characteristics of floor strata during mining，the Rock Top multi-field coupling tester was used to carry out stress-seepage coupling experiment of sandstone under different confining pressures(20，30，40 MPa) and cyclic loading. The results show that：(1) The complete stress-strain curve of rock under cyclic loading can be divided into five stages，including primary micro-fracture compression closure stage，elastic compression stage，crack stable development stage，crack rapid development stage and post-peak deformation failure stage；(2) Under different confining pressures，the peak strength of rock under cyclic loading decreases slightly compared with that under conventional triaxial compression，but the stress-strain curve shows obvious hysteresis；(3) With the increase of the number of cyclic loads，the dissipation energy periodically decreases，and the elastic modulus gradually decreases with the increase of the axial stress difference during the first cycle；(4) Under the same hydrostatic pressure，the permeability of sandstone after failure increases significantly compared with that before failure，and with the increase of the unloading level，the permeability increment is consistent with the growth rate；(5) Under different confining pressures and cyclic loads，the pre-peak permeability changes periodically with the increase of the stress difference，and the post-peak permeability decreases obviously with the decrease of the stress difference；(6) Under different confining pressures and cyclic loads，sandstone mainly shows shear failure，and with the increase of the unloading level，the degree of damage increases. Under 20 MPa confining pressure，sandstone shows a single shear failure. Under the cyclic load of 30 MPa and 40 MPa confining pressure，there is a crack network dominated by through shear cracks and supplemented by secondary tension cracks. © 2022 Academia Sinica. All rights reserved.