Stress Increase Anomaly in Cemented Paste Backfill: Risk Identification from Monitoring

This paper presents a preliminary analysis of the stress increase anomaly observed in Cemented Paste Backfill (CPB) within mine stopes. This anomaly occurs during rest periods when no additional CPB is placed into the stope, leading to an unexpected rise in stress that is not accounted for in traditional backfill design. Such stress increases can impose additional loads on the stope barricade wall, posing potential risks. Recent field monitoring data has repeatedly demonstrated this phenomenon, which is hypothesized to be linked to thermal expansion caused by temperature increases during CPB hydration. Laboratory experiments have confirmed that temperature-induced volumetric expansion within semi-confined spaces, such as stopes, can lead to elevated internal stresses in CPB.In this study, fifty-six (56) instances of stress increase anomalies were collected and analyzed. A new parameter, the Stress Anomaly Ratio (SAR), is introduced, defined as the ratio between the maximum stress increase anomaly and the maximum stress recorded after filling. The analysis revealed that SAR values can reach up to 3.25, with an average of 1.2. Probability density functions and histograms of the data are presented, showing a significant probability (71.4%) that SAR exceeds 1. This indicates that the stress increase anomaly is a critical factor that must be considered in backfill design to ensure structural integrity.The findings of this study provide valuable insights for geotechnical and mining engineers, enabling safer and more effective design of CPB-based mine stope backfilling. By accounting for the stress increase anomaly, engineers can mitigate the risk of barricade wall failure and enhance the overall safety of underground mining operations. Further research into the risks associated with CPB stress increases is essential to ensure the long-term stability and safety of mining environments.

Keywords: Cemented paste backfill, Stress increase anomaly, Temperature change, Stope, Underground mine, Risk.