Research On Failure Modes Of Recry Stallized Phosphogypsum Used For Backfilling And The Stope Safety

The phosphogypsum poses potential threatsl to humans and environment, which is the industry by-product. The comprehensive utilization of phosphogypsum has many problems such as the difficulty of purifying treatment, complex process, high energy consumption, large investment and high cost at home and abroad. In response to the national call of building the harmonious and uniform mines with resources exploitation and ecological environment protection, this paper considers the phosphogypsum is processed by simple calcination method to obtain the recrystallized material for filling gob without cement. By doing this, achievement of large and effective utilization of phosphogypsum resources can be made. Besides, the problem of handling gob in phosphate mining can be addressed. This improves the recovery utilization rate of phosphate rock resources and reduces the cost of filling. This paper gives focus on the preparation of phosphogypsum for material recrystallization and the subsequent mechanical properties tests. Following research were conducted:1) Through the analysis of the preparation parameters affecting on recrystallization mechanics properties, the best preparation parameters are obtained. By using the orthogonal test method to establish experimental samples, the strength of recrystallization is predicted by the improved neural network with genetic algorithm. The results provides a theoretical reference for the preparation parameters of phosphogypsum recrystallized material in engineering.2) Based on the mechanism of backfill in the stope, the stress state, the stress distribution, the independence intensity and the self-reliance height of the phosphogypsum recrystallization backfill in the stope are analyzed. The analysis results show that the backfill has very good independence and its strength can ensure the stope to be filled at higher safety.3) By the analysis of observed phenomena in the experimental process and the uniaxial compressive stress-strain curve of the phosphogypsum recrystallization, its failure characteristics is researched. With the aid of the statistical mechanics and the continuum damage mechanics methods, the two kinds of recrystallization damage constitutive models are derived. The models with the test curves are comparatively analyzed. Finally, the damage constitutive models for very good fitting whole test process are gained after the model updating.4) The FLAC3D numerical simulation software is used to respectively simulate the filling processes of the phosphogypsum recrystallized filling material and the filling materials originally used in mine, which is combined with the actual engineering in the Maluping mine. Through the comparative analysis, changes of stress, displacement and plastic zone in surrounding rocks of the stope roof and floor are investigated after using two kinds of filling materials. The advantages of using phosphogypsum recrystallized filling material are analyzed, facilating industrial utilization.5) Based on the comprehensive study of the key elements influencing stope safety, the geological factor, engineering factor and environmental factor are set at the first-order evaluation index, and13factors are set at the second-order evaluation index. The application of multistage fuzzy evaluation theory and AHP method is used to establish the second-order fuzzy comprehensive evaluation model assessing the stope safety, which comprehensively evaluates the safety of stope filling phosphogypsum recrystallization.