Stope depth effect on field behaviour and performance of cemented paste backfills

Cemented paste backfill (CPB) has been extensively used as a popular mine fill system for underground mining operations. Understanding the CPB’s in situ properties as an element of ground support is indeed really important for developing a well-organised mine design in terms of costs and security. In this paper, a comprehensive experimental work was conducted to better understand the effect of stope depth on in situ behaviour and performance of CPB having three different binding agents (ordinary Portland cement alone, slag-based cement and fly ash-based cement) over different curing times. A stope depth of 0 (it replicates the stope’s top), 5, 10, 15 and 20 m (it replicates the stope’s bottom) were virtually simulated by using an improved laboratory set-up, escorting with conventional plastic moulds. Results show that the highest compressive strength is obtained from CPB having slag-based cement. The strength of CPB increases with increasing stope depth mainly due to resulting improved geotechnical properties, such as reduced water content, degree of saturation and porosity as well as increased specific surface area retained at the bottom of a simulated stope. Geochemical testing shows that sulphate SO4−2 and calcium Ca contents increase with increasing curing time and reduce with increasing stope depth. As a critical point, a number of experimental relationships considered typically for different curing times, overburden pressure, arching stress and binder contents within CPB material were expressed and discussed.