Loading rate effect on the uniaxial compressive strength (UCS) behavior of cemented paste backfill (CPB)

Underground mined-out areas and tailings are the two major harmful consequences from metal mining industry. Cemented Paste Backfill (CPB) method, refilling the tailings back to the underground mined-out areas, has been widely used worldwide. Clear understanding on the uniaxial compressive strength (UCS) behavior of the CPB is very important for the stability analysis of the backfill structure and the parameters optimization of backfill plan. However, the UCS tests can be markedly affected by the testing loading rate. And few papers reported the effect of different loading rates on the UCS of CPB. In this study, the UCS behavior of 14-day cured CPB samples are investigated using five different loading rates: 0.1, 0.25, 0.5, 1, 2 mm/min. The digital image correlation (DIC) method and scanning electron microscope (SEM) analysis were also carried out to help clearly understand the different loading rates effect on the deformation behavior and failure surfaces. The findings show that, the increase of loading rate has a strengthening effect on the UCS. The correlation between the loading rates and the UCS is more in line with an exponential function when the loading rates are between 0.1 and 2 mm/min. During the loading process with different loading rates, the axial deformation characteristics of all the tested CPB samples can be divided into uniform and non-uniform phases. And the loading rates of 0.5 and 1 mm/min resulted the smallest standard deviation for both the axial displacement and the axial strain observed from the three preset monitoring points. As the loading rate increased, the Ca/Si parameter on the fracture surface of the samples also increased slightly. The findings of this research clearly demonstrated the behavior of UCS under different loading rates, and also provided a key research evidence in selecting appropriate loading rate in assessing USC of CPB sample for laboratory tests