Experimental study of uniaxial compressive strength (UCS) distribution of hydraulic backfill associated with segregation

Stope backfilling with mine wastes has become a common practice in underground mines worldwide. Despite the increasing popularity in paste and rock fills, hydraulic fill made of classified mill tailings or sands remains commonly used in many mines. When such a slurried material is placed in a mine stope, a phenomenon known as segregation can take place associated with the quick drainage and consolidation of the hydraulic fill, thereby leading to a heterogeneous fill mass. While numerous publications have focused on the alleviation of segregation, there are few studies on the characterization of the distribution of geotechnical properties within hydraulic fill due to segregation. It is particularly scarce to quantify the spatial variation of the segregation and the resulting geotechnical properties after a backfill is placed in an opening. There is also a gap to quantitatively describe the degree of segregation using an appropriate expression or definition. The aim of this study is to investigate the effect of the segregation on the spatial variation of the geotechnical properties of hydraulic fill. Laboratory tests were performed with the cemented hydraulic backfill prepared with columns of different heights. The experimental results indicate that the segregation takes place and the resulting physical and mechanical properties can vary throughout the columns for samples higher than twice of the standard size. These results also indicate that the mechanical properties of a hydraulic fill obtained in a laboratory following the current practice with standard samples may not be representative of the fill mass placed in mine stopes. Expressions are proposed to quantify the degree of segregation associated with the spatial variation of particle sizes of mine hydraulic backfill.