In situ measurements of cemented paste backfill at the Cayeli Mine

Cemented paste backfill (CPB) is accepted as the optimal backfilling material for many underground mines. However, the lack of in-stope backfill pressure data poses fundamental problems from both operational and research standpoints. In response to the requirement for in situ data, a comprehensive field instrumentation project has been conducted. Results are presented here for two stopes at the Cayeli Mine, where geotechnical instruments were installed at the barricades and throughout the stopes. Measurements from a large (slow rise rate) stope with high binder content CPB demonstrated a rapid departure from hydrostatic loading, resulting in relatively low barricade pressures. Conversely, data from a smaller (fast rise rate) stope with lower binder content CPB demonstrated that when cement hydration is retarded, high barricade pressures occur. These examples illustrate the relationship between CPB rise rate and the moderating effect of cement hydration on in situ pressures, which ultimately control barricade pressures. Once CPB gains shear strength, arching of pressures occurs. In situ pressures were reduced with proximity to stope walls and further, under stope access brows, demonstrating that barricade location influences barricade loads. The application of real-time pressure monitoring of pastefill barricades has been demonstrated as an important tool in optimizing operational backfilling efficiency.