Effect of water saturation on mechanical characteristics and damage behavior of cemented paste backfill

In this study, a series of experiments was conducted to examine the mechanical and damage properties of cemented paste backfill (CPB) with different water saturations (ws = 0%, 22.1%, 47.0%, 65.3%, 82.8%, and 100%). The results reveal that the UCS, peak strain, and elastic modulus first increased and then decreased, and the porosity and fractal dimension of cracks first decrease and then increase with the increase of ws. In addition, the UCS, peak strain, and elastic modulus is maximum, and the porosity and fractal dimension are minimum when the ws is 65.3%. The UCS increases with the increase of peak strain and elastic modulus, and decreases with the increase of porosity and fractal dimension, and the UCS present good quadratic polynomial functions relationship with the porosity and fractal dimension. The SEM images show that with the increase of ws from 0% to 65.3%, the hydration products increases and the pore structure decreases. When the ws exceeds 65.3%, and the pore structure begins to increase. The failure mode of the CPB is mainly tensile failure. A new damage constitutive model of CPB with different ws was constructed. The total damage D of the CPB is composed of initial damage Dp and load damage DL. The total damage evolution curve shows an S-shaped distribution, and the total damage rate evolution curve shows a normal distribution. With the increase of ws, the damage rate and the peak value of damage rate of CPB first increases and then decreases.