A study of mineral compositions and micro-structure characteristics for the Jinping marble

To study the evolution law of internal pore structure of Jinping marble under loading, the mineral composition and uniaxial compression test were first conducted. Then, the nuclear magnetic resonance (NMR) tests were carried out on the samples subjected to different axial pressures, and the corresponding test results were further analyzed. Finally, the functional relationships of the damage degree and effective stress ratio with the axial compression ratio were established according to the NMR porosity parameters. It is found that the pore distribution in the marble has multi-scale characteristics. During the loading process, the T₂ spectrum distribution curve of NMR shifts to the right as a whole, and the proportion of small-sized pores decreases while the proportion of medium-sized pores increases. There exist multi-fractal structures of pores inside the rock samples, and the fractal dimension and connectivity of pores are affected by the small pore proportion. When the small pore proportion is low, the pore structure is relatively simpler and the fractal dimension is lower. When the small pore proportion is high, the pore structure is more complex and the fractal dimension increases. Both the porosity and damage degree of the marble increase exponentially with the increase of load, and the effective stress ratio of damaged and undamaged state also increases. This study has important guiding significance for revealing the mechanism of rock damage and failure, and also own certain reference value in rock damage detection.