Deformation characteristics of sandstones during cyclic loading and unloading with varying lower limits of stress under different confining pressures

Varying lower limits cyclic loading and unloading tests with different confining pressures were carried out to reveal the influence of confining pressures on deformation characteristics of sandstones. Increasing confining pressures reduced the development of radial irreversible strain, and increased axial irreversible strain, which prolonged the process of volumetric strain from compression to expansion. The evolution of volumetric strain is sensitive to the division of crack closure, and stable or unstable growth of cracks. Increasing the confining pressure inhibited the development and connection direction of cracks, which decreased the length of the final fracture surface.