Effect of filling interval time on the mechanical strength and ultrasonic properties of cemented coarse tailing backfill

An experimental study is conducted to investigate the effect of filling interval time (FIT) on the uniaxial compressive strength (UCS) and ultrasonic pulse velocity (UPV) of cemented coarse tailing backfill (CCTB). A total of 72 CCTB samples with diameter × height of 50 mm × 100 mm prepared at different solid contents (70, 72, and 75 wt%) and water-to-cement ratios (3.00, 2.72, and 2.33) were subjected to UPV and UCS tests at 12, 24, 36 and 48 h of FIT. The UCS and UPV values of the CCTB samples increased with the increase in the solid content. However, an increase in FIT led to a decrease in the UPV and UCS of the CCTB samples. Different types of curve fittings were conducted to obtain the correlation between UPV and UCS versus FIT at different solid contents. A polynomial function can explain the relationship between UPV and FIT. Moreover, the UCS and UPV values exhibit a linear function. CCTB also shows a failure mode of tensile failure-tensile shear failure transition-tensile and shear mixing failure modes, which provides a theoretical basis for the strength design and stability control of backfills.