This study aimed to elucidate the damage mechanism of prestressed sandstone under uniaxial compression through the distribution characteristics of meso-structures. Four prestress levels, i.e., 0MPa, 15MPa, 30MPa, and 40MPa were selected. Nuclear Magnetic Resonance and Scanning Electron Microscope techniques were employed to observe the distribution characteristics of meso-structure within rocks and to further its damage mechanism. The results show that, compare with untreated specimens (0MPa), damaged specimens by 15MPa show a more porous meso-structure due to pores/cracks propagation which occurs between skeleton minerals and filler materials. Furthermore, specimens treated by 30MPa and 40MPa show low failure strength because micro-pores/cracks initiation inside skeleton minerals causes high deterioration. By meso-mechanics analysis, particle rotation leads to pores/cracks propagation and slightly modifies the meso-structure under low-prestress conditions. With the increase of the prestress, the transgranular cracks initiation and propagation will transform the skeleton structure of rocks, leading to significant rock deterioration.

To explore the evolution law of pores/cracks and meso-structures in rocks under stress, sandstones were damaged by different stresses to be studied here. The damaged specimens can be divided into two types by macro-mechanical characteristics: Low Damaged Specimens (LDS) and High Damaged Specimens (HDS). For the LDS, pore/crack propagation mainly occurs between skeleton minerals and filler materials. For the HDS, besides pore/crack propagation, micro-pore initiation inside skeleton minerals is the main factor for damage. According to the meso-mechanics model, particle rotation leads to pore/crack propagation under low-stress conditions, but the modification of specimens’ skeleton structure is limited. As the stress increases, particles will be under higher stress because the rotation of particles will gradually weaken, leading to the formation of transgranular cracks, which transform the skeleton structure. Therefore, under different stresses, the meso-evolution behavior of minerals controls the evolution law of pores/cracks and changes meso-structure of rocks.