Abstract: The layering phenomenon in filling is very common in the process of stepwise or subsequent backfilling. Different cemented filling specimens are prepared with four concentrations (65%, 70%, 72% and 75%) and backfilling times of 1, 2, 3 and 4, separately. Uniaxial compression tests are conducted to study mechanical properties and failure modes of specimens. The research demonstrates that: (1) When the concentrations of different filling specimens are the same, the weakening effect of the uniaxial compressive strength (UCS) increases with increasing the filling time. When the concentrations vary from 65% to 75%, the corresponding strength reduction coefficients are in the range from 0.592 to 0.967. (2) The relationship between UCS of the specimen and the filling time fits the quadratic function, whereas the relationship between UCS and concentration fits the logarithmic function. (3) Main failure modes of different filling specimens are characterized by conjugated shear failure and tensile failure along the layer plane. Low-strength interlayer may result in decreasing the strength of layered cemented filling specimens, which can also be considered as theoretical reference for designing the strength of mine backfilling.

Key words: subsequent backfilling, cemented filling, layering phenomenon, uniaxial compressive strength (UCS), strength reduction