The backfill engineering of open stopes with CPB revolves around the stability, pressure, drainage, and curing processes that allow for the development of CPB that can sustain itself and neighbouring mining operations. Studies performed in the field and in models have revealed that CPB behavior is greatly influenced by many factors, including the geometry of the stope, the composition of the binder, the filling rate, barricades, and the subsequent stope wall closure process. Therefore, a universal solution to backfilling cannot be applied here.
The first factor considered involves the geometric configuration of the stope and the filling method, because the paste’s behavior differs depending on the type of void in which it is placed. In particular, measured data suggest that there may be lower pressures near the brow due to arching, and the filling rates and drawpoints affect crucial design aspects, such as barricade loading.
Secondly, barricades or fill fences are another major engineering component since they should withstand the early-age total pressure that will be generated before the paste gains strength. Instrumented stopes revealed that although fence deflections were relatively low, there is a possibility that some operations have two-stage fills, where first pour forms a plug. This is a logical solution in case of uncertainties in the total pressures at an early age. From the field studies, another observation regarding total loads was that low pore pressures at the vicinity of the fence decrease total load; this implies that leaking water pathways and joint sealing become important components in fence design.
Third, paste mixes are not simply material considerations but are geotechnical design variables. In studying the CPB behavior, one finds that varying the binder amount in a paste mix changes the consolidation rate, hydration, pore pressures dissipation rate, and effective stress development rate. Therefore, it is critical to select the appropriate paste mixes based on the required exposure period and self-supporting strength, as well as mining sequence. In general, higher binder contents are used in plugs or early loaded zones, while lower binder contents are applicable in deeper parts of the stope.
Water management and drainage become essential due to the presence of the hydraulic loads and the fact that excessive water reduces the strength gain and increases the failure potential. CPB is generally more favourable than the hydraulic fill because the former produces little bleeding, yet there are many instances where seepage through barriers and the drainage regime play an important role in terms of affecting pore pressure and total pressure behavior. Thus, when designing, it becomes necessary to plan for drainage requirements, dewatering possibilities, and potential local water accumulation inside the stope.
Fifth, it is important to consider the impact of the curing process right from the beginning. The backfill pressure varies with time; field studies have shown that pressure increases during placement, and further pressure changes occur later due to thermal effects, shrinkage, and rock mass closure. It implies that in addition to testing the backfill for the ability to remain stable while being placed, engineers need to assess its performance over time, including wall convergence after the blasting operation.
Lastly, sound engineering for CPB backfilling involves not only empirical design but also monitoring and modeling. Finite element analysis along with effective stress analysis have been employed to simulate fill buildup, consolidation, cement hydration reactions, and arching, whereas field instrumentation confirms whether the simulation represents the real world scenario. From a practical standpoint, a safe design method would involve conducting strength tests in the lab, geomechanical modeling of the stope, checking barricades, and monitoring of the fill process itself.
