Chemically Induced Changes in the Shear Behaviour of Interface Between Rock and Tailings Backfill Undergoing Cementation

Tailings are man-made soils generated by mining activities. When mixed with cement and water, they form a cemented soil called cemented paste backfill (CPB). CPB is commonly used to backfill underground cavities created by ore extraction. The shear behaviour and resistance of the CPB–rock interface are important parameters for the geotechnical design of underground CPB structures. However, CPB can contain a relatively high amount of sulphate, and no studies have been performed to investigate the effect of the initial sulphate content of CPB on the behaviour and resistance of the interface between rock and tailings backfill that is undergoing cementation. The main objective of this experimental investigation is to, therefore, examine the effects of the initial sulphate content (0 ppm, 5,000 ppm, 15,000 ppm, and 25,000 ppm) of CPB on the shear behaviour of the CPB–rock interface at the early ages of curing (1 day, and 3 and 7 days). The obtained results show that, for samples at a very early age of 1 day, an increase in the sulphate content reduces the shear strength of the CPB–rock interface, whereas, for those cured for a longer period of 7 days, the sulphate can either positively or negatively affect the shear strength of the interface depending on the sulphate content.