Novel Hydraulic Measurement Technique to Enable Reliable Strength Evaluation of Cemented Paste Backfill in Underground Mines

ABSTRACT: In this laboratory-scale investigation, a hydraulic fracturing approach was developed and validated for directly determining the tensile strength of cemented paste backfill (CPB), offering an alternative to standard strength testing techniques. Fracture initiation pressure (FIP) served as the main indicator of CPB strength, and the resulting data were compared against conventional strength benchmarks, namely uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), and critical Mode-I fracture toughness (KIc). Regression analysis demonstrated a robust linear correlation between FIP and these established measures, suggesting that FIP can reliably predict CPB strength. However, traditional linear elastic failure models substantially over-predicted tensile strength based on the observed FIP values. To resolve this, the Point Stress (PS) model was employed, yielding more accurate tensile strength estimates, particularly for smaller boreholes. The PS model also clarified how borehole size influences hydraulic pressurization behavior. Consequently, this study confirms that hydraulic fracturing, interpreted via the PS model, offers an effective, practical alternative to standard CPB strength testing methods.