Microstructure characteristics and the damage evolution rule of sandstone under triaxial compression test using Nuclear Magnetic Resonance (NMR)

The complex microstructure of rock is very important for the stability of geotechnical engineering. However, the current research on the microstructure of rock mass can't be monitored in real time. In this paper, rock microstructure under triaxial compression was studied using an online Nuclear Magnetic Resonance (NMR). The specimen was subjected to confining pressure of 10 MPa, then five levels of axial pressure were applied, and NMR is performed in real time after each axial compression is loaded.Research indicates: When the confining pressure is constant, the peak of T2 spectrum distribution curve decreases with the increase of axial pressure. The micropores grow in a parabolic fashion while the macropores grow in a quartic polynomial fashion. NMR porosity can be divided into three stages: initial growth stage, pore compaction stage and stable pore expansion stage. Macropore expansion plays a decisive role in porosity change in the initial growth stage and stable pore expansion stage, while micropore compaction plays a decisive role in pore compaction stage. NMR images can clearly and intuitively display the microstructure characteristics of specimens online.