Cemented Paste Backfill (CPB) Material Properties for Undercut Analysis

A longstanding mine backfill design challenge is determining the strength required if (partially) cured subsequently undercut. Mitchell (1991) called undercut a sill mat and proposed an analytical solution that still often used, at least for preliminary design, has motivated subsequent empirical methods. However, fully employing requires knowledge of material’s Unconfined Compressive Strength (UCS), tangent Young’s modulus (Et), tensile (?t), as well estimates stope wall closure. Conducting high-quality UCS test poses challenges but relating result to remaining material parameters more difficult. Some new testing data presented compared available published results. Using parameter mi=UCS/?t range found be mi= 3 22, however, most compelling obtained when Mohr’s failure circle in tension tangential corresponding Mohr–Coulomb envelope determined from other tests. In these cases, value 4 materials tested, which much lower than 10 commonly assumed implies limiting 60% conventional assumption. It also relationship between Et described by power function close linear, values constant exponent depend on tested. given tailings independent void ratio, binder type or concentration, curing time, water salinity, within ranges were investigated. Therefore, used it should correlated with using appropriate function. These correlations are then measurements closure strains estimate solution’s applicability based its underlying assumptions, similar analysis extended “empirical method” solution. demonstrated existing approaches have limited applicability, generally full support rational will require numerical modeling incorporates effect confining stress stiffness mobilized strength.