Abstract:

The increasing depth of underground mines, driven by the scarcity of surface ore deposits, has led to higher horizontal ground stresses and subsequent rockwall closure, impacting underground mining operations. Cemented paste backfill (CPB) is commonly used to support excavations, but its response to multiaxial stress conditions in deep mines remains poorly understood. This research addresses this knowledge gap by introducing a novel multiaxial compression curing apparatus capable of simulating rockwall closure-induced stresses encountered in underground mines, particularly in deep mines. The newly developed apparatus applies two horizontal stresses (σ_H1 and σ_H2) resulting from rockwall closure and a vertical stress (σ_V) to CPB samples during curing. The efficacy and reliability of the apparatus were validated through comprehensive testing, confirming its ability to replicate rockwall closure conditions. Employing this apparatus, the study investigates the influence of rockwall closure rates on the strength development of CPB. Experimental results indicate that time-dependent rockwall closure significantly enhances the early-age unconfined compression strength (UCS) of CPB. Specifically, the UCS improvement at curing ages of 1, 3, and 7 days amounts to 49%, 58%, and 37%, respectively, compared to control samples without multiaxial loadings. This strength enhancement is attributed to the densification of the CPB's pore structure and the acceleration of cement hydration. However, it is crucial to note that excessive stress-induced by rockwall closure can lead to mechanical damage or failure of the CPB if it exceeds the CPB's load-bearing capacity. Conversely, appropriate rockwall closure rates contribute to further densification of CPB. Moreover, the study identifies that the development of horizontal and vertical deformations within CPB is significantly influenced by the stress evolution in each axial direction. The research outcomes hold substantial significance. Firstly, the novel apparatus fills a critical gap in experimental methods for investigating CPB behavior under multiaxial high-stress compression in real mine fields. Secondly, the findings provide valuable insights into the curing behavior of CPB under rockwall closure-induced stresses, facilitating an improved understanding and control of CPB performance in deep mining applications. This knowledge is crucial for optimizing backfilling practices, enhancing underground mine safety, and ultimately increasing mining efficiency in deeper ore deposits.

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Mr. Hongbin Liu