NMR TECHNOLOGY BASED STUDY ON PORE EVOLUTION PATTERN OF GUIYANG RED CLAY SHEAR WHOLE PROCESS

This paper studies the evolution of pore structure of Guiyang red clay during the whole process of shearing under conventional triaxial compression conditions, explores and analyzes the changes of fine-microstructure morphology of Guiyang red clay, and reveals the correlation between macroscopic damage morphology and fine-microstructure changes of Guiyang red clay. A fully automatic triaxial instrument, low-field NMR technique and SEM scanning electron microscope are used to conduct the whole process shear test on Guiyang red clay, and to analyze the specimens before and after shear by combining with the Particles(Pores) and Cracks Analysis System(PCAS).The research results show that the T₂ spectrum of Guiyang red clay shows three types of peaks, corresponding to large pores, medium pores and small pores. The deformation and damage of Guiyang red clay specimens under the action of load are mainly based on the adjustment of the relative position between internal particles. The pore volume shows an overall decrease. With the intensification of stress, the red clay gradually forms small folds visible to the naked eye, the large scale pores gradually develop into small scale pores, the number of small pores gradually increases, the number of large-medium pores gradually decreases, and the pore direction becomes more and more confused. When the small folds gradually expand and penetrate to form a large slip surface, the pore morphology shows transient directionality. Afterward the compression of the slip surface can reduce the number of small pores and increase the number of large-medium pores. During the whole shearing process, the pore morphology of Guiyang red clay gradually tends to be similar and the pore boundary tends to be complex.