Abstract: The creep acoustic emission (AE) location tests of red sandstone were carried out, and the evolution of AE source along loading direction and perpendicular to loading direction was analyzed. On this basis, the fractal characteristics of source zi value and ri value were studied with fixed time window and time step. The results show that when the creep stress is equal to or greater than the damage stress, the spatio-temporal evolution law of AE source reflects the process of micro-cracks initiation, nucleation, expansion and coalescence. The initiation of micro-cracks mainly occurs in the stage of decelerating creep. During this process, the micro-cracks evolve from the end surfaces and the outer wall to the center of the specimen along the loading direction and the vertical loading direction, and the fractal dimension of zi values and ri values generally decrease. The nucleation process of the micro-cracks appears in the stage of steady creep, and nucleation area locates in the center of the specimen. Then, with the increase of the creep time, the micro-cracks step into the expansion stage, in which the evolution of the micro-cracks is manifested as the expansion process from the center of the specimen to the direction of the end surface and the outer wall, and the fractal dimensions of the corresponding zi values and ri values are at low levels, which can be used as a marker for the process of micro-cracks nucleation and expansion. The coalescence of micro-cracks occurs in the accelerated creep stage. During this process, the micro-cracks are mainly distributed in the axial upper and lower part of the specimen along the loading direction, while in the vertical loading direction, the micro-cracks are distributed all over the radius of the specimen. However, the fractal dimension of source zi value and ri value both increase slightly with the increase of creep time, which can be used as a symbol of micro-cracks coalescing process. The findings in study can provide theoretical and experimental support for exploring rock creep micro-mechanism and creep failure prediction method.

Key words: red sandstone, creep, damage strength, acoustic emission source, fractal dimension