Abstract: The damage evolution and deformation characteristics of marble are studied by cyclic loading and unloading tests with varying amplitude under different confining pressures, and the crack volumetric strain and dilatancy characteristics are analyzed emphatically. Some conclusions are drawn as follows. (1) With the increase of cycle number, the elastic modulus of marble first increases and then decreases, and the generalized Poisson's ratio first stabilizes and then increases rapidly. (2) Comprehensive analysis of the crack volumetric strain curves from the 3rd to 6th loading shows that as the number of loading increases, the initial crack volumetric strain of the marble increases, the initial position of elastic deformation stage is delayed, and the expansion point gradually advances. Moreover, the relationship between the increment of crack volumetric strain caused by a single cycle and stress amplitude is exponential. (3) The dilatancy index of variable amplitude cyclic loading and unloading is different from that of monotone loading at a high confining pressure. With the increase of confining pressure, the proportion of crack volumetric strain increases gradually, and the proportion of crack volumetric strain under variable amplitude cyclic loading and unloading is greater than that under monotonic loading. The failure mode of marble changes from shear failure under monotonic loading to bulging failure under variable amplitude cyclic loading and unloading.

Key words: marble, cyclic loading and unloading, triaxial test, crack volumetric strain, dilatancy