Damage Evolution of Rocks under Triaxial Compressions: An NMR Investigation

To investigate the damage characteristics of rocks subjected to triaxial compression, marble specimens were prepared and subjected to varying levels of axial compressions with identical confining of 20 MPa. The loaded specimens were then tested using Nuclear Magnetic Resonance (NMR) technique to obtain their micro NMR parameters. The changes in transverse surface relaxation time (T-2) distribution, peak area, porosity and microcracks structure distribution of the specimens due to varying compression ratios were systematically analysed. It is found that with the increase of the axial compression, the size and the number of the microcracks, porosity and the peak area increase, indicating that severer damage is induced at high compression ratio. The proportion of the large microcracks area to the total T-2 area exceeds 96% in spite of the increase in compression ratio, indicating that the large microcracks dominate the degradation of the specimen. Based on the Magnetic Resonance (MR) images, the variation of the microcracks distribution can be visually presented under the different compression loadings. The NMR method presented in this study shows a good way of identifying meso-damage evolution characteristics of rock.