The mechanical properties of backfill are the key indexes for filling ratio design and maintaining the stability of underground stope. The variation of the loading rate and the environment (humidity, temperature) in which backfill is located can affect the mechanical behavior of the backfill. In this work, uniaxial compressive strength tests with variable loading rates (0. 1 mm/min, 0. 25 mm/min, 0. 5 mm/min, 1 mm/min and 2 mm/min) were carried out for backfill with different water content (dry, saturated and nature). The mechanical parameters and failure modes of fillings under state change and loading rate were obtained. According to the energy conservation theorem, the relationship between the energy evolution and stress-strain behavior of backfill under different conditions was studied. On this basis, the damage variable of backfill based on energy was established. The results show that: (i) as the loading rate increased, the compressive strength of backfill first increased and then decreased, and there was a critical loading rate. The dry and saturated had strengthening and weakening effects on the compressive strength and elastic modulus of backfill respectively. The dry led to the transformation of backfill from ductility to brittleness, and the stress-strain curve decreased rapidly after reaching the peak stress. Although the saturated state was conducive to the ductility of backfill, the weakening effect of water makes it destroy under small strain. (ii) When the loading rate increased from 0. 1 mm/min to 2 mm/min, the failure mode of the dry backfill gradually changed from tensile shear mixed failure to tensile failure (less shear failure). The saturated filling body is mainly tensile failure, while the nature backfill showed tensile shear mixed failure as a whole. (iii) Increasing the loading rate accelerated the energy exchange of backfill. The effects of drying, saturation and nature on the energy evolution of backfill were mainly reflected in the plastic yield stage and failure stage of the corresponding stress-strain curve. The slope of the energy dissipation strain curve is dry, saturation and nature from large to small. (iv) The damage strain characteristic curve based on energy evolution showed four stages: initial damage, stable damage development, accelerated damage and failure. Increasing the load rate shortens the initial strain in the accelerated damage stage, and the dry and saturated aggravates the damage development of backfill. This study can provide a theoretical basis for further understanding the load change caused by mining disturbance and the mechanical behavior and stability of backfill under different humidity conditions. © 2022 Cailiao Daobaoshe/ Materials Review. All rights reserved.
