Abstract: In order to study the fracture characteristics and energy consumption characteristics of the fully tailings cemented backfill under impact loading, uniaxial impact tests on fillers with different cement-sand ratios at moderate strain rates were carried out with the help of a split Hopkinson pressure bar (SHPB) test system. The results show that the pre-peak strain energy, absorbed energy, prepeak strain energy density and absorbed energy density of the backfill body all increase exponentially as increase of incident energy when the cement-sand ratio is the same. When the incident energy is less than 16 J, the absorbed energy density, pre-peak strain energy density, absorbed energy and pre-peak strain energy of the backfill body with the cement-sand ratio of 1:6 are greater than those of the cement-sand ratio of 1:4 and 1:8. The fracture toughness of the backfill body gradually grows with the increase of the cement-sand ratio for the same peak strength, incident energy, pre-peak strain energy and absorption energy. The fracture toughness of the backfill body increases linearly with the increase of dynamic peak strength, absorbed energy density and pre-peak strain energy density, and increases exponentially with the increase of incident energy, pre-peak strain energy and absorbed energy. The increase of fracture toughness with energy absorption density and pre-peak strain energy density of the filled body with cement -sand ratio of 1:4 is two to three times that of cement-sand ratios of 1:6 and 1:8. Based on the growth law of strain energy density, energy consumption and strain, the damage and failure evolution process of the backfill can be divided into four stages: nonlinear compression, linear elastic deformation, elasto-plastic deformation and post-peak damage. Through regression analysis of the backfill body test results, a calculation formula for the fracture toughness is derived from the perspective of energy consumption, which can provide a reference for the stability analysis of the underground backfill body.

Key words: back fill body, fracture toughness, energy dissipation, impact load, strain energy density, energy absorption density