Study of rock NMR experiment and damage mechanism analysis under freeze-thaw condition

Taking granite as samples, a freeze-thaw cycle experiment (with the temperature ranged from - 40 degrees C to 20 degrees C) is conducted. The highest cycles are 100. Nuclear magnetic resonance (NMR) technology is employed to observe the rock damage changes. The results show that freeze- thaw cycle action will produce damages to the sample. Some samples crack after a certain cycles. Both the T2 spectrum and NMR image indicate that the action of freezing and thawing cycle redistributes the inner structure of sample. The T2 curves change greatly after the cracks emerged. Finally, damage mechanism is adopted to analyze granite damage principle in condition of freeze-thaw. An equation of material continuity and porosity is obtained. Then an equation between effective stress and porosity is established. Taking N-4 for example, the relationship between effective stress and cycles is obtained.