Abstract
Backfilling is widely used to control surface subsidence and stope stability to improve pillar recovery. Furthermore, it is also an effective way to process and dispose of mining waste such as coal gangue and tailings. In this study, the hydraulic-mechanical properties of cemented paste backfill materials (CPB) were investigated. Twenty-eight cemented coal gangue-fly ash backfill mixtures were prepared with different water, cement, fly ash and coal gangue content and the slump, segregation and water bleeding ratio tests were conducted. Increasing fly ash content increased the slump value and decreased the segregation value of the slurry. The uniaxial compressive strength (UCS) of the cemented coal gangue-fly ash backfill samples were tested at different curing times. Based on the test results, an optimized recipe was used for the field trial. Longwall cut and backfilling mining method was used in the 2300 mining district to recycle the coal pillar between longwall 2301 and 2302. Both stress and displacement meters were installed in the goaf and their performance was monitored continuously. An increase in stress and displacement values were observed to occur with the working face advanced (up to 325 m and 375 m, respectively); thereafter, a trend of stabilization was observed. The monitoring results suggest that the backfills can efficiently control the roof movement and surface subsidence as well as improve pillar recovery.
Highlights
Backfilling is an effective way to control surface subsidence introduced by underground mining activities [1,2,3]
Cemented paste backfill (CPB) materials are produced with three ingredients: mining tailings or coal gangue; hydraulic binders, e.g., ordinary Portland cement (OPC), slag, fly ash, etc.; and water [15,16,17,18]
The early strength can meet the requirement of holding the weight of the direct roof
Summary
Backfilling is an effective way to control surface subsidence introduced by underground mining activities [1,2,3]. Surface subsidence is especially obvious when coal mines are operated at a relatively shallow depth. Another attractive aspect is that the materials usually used in backfill mining are tailings or coal gangue, which are generated during ore or coal processing in plants. Cemented paste backfill (CPB) is a widely used backfilling method that can significantly improve mining stopes stability in underground hard rock mines, or reduce surface subsidence in underground coal mines [10,11,12,13,14]. CPB materials are produced with three ingredients: mining tailings (in underground hard rock mines) or coal gangue (in underground coal mines); hydraulic binders, e.g., ordinary Portland cement (OPC), slag, fly ash, etc.; and water [15,16,17,18]
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