Basic theory of cold load and storage functional backfill in mining

Heat damage in deep mine is an important problem for mineral resources exploitation. To improve the effect of mine cooling and the utilization efficiency of cooling capacity,a cooling method by applying cold load and storage functional backfill for deep mine,which based on the consideration of the cooling demand in deep mine and the char- acteristics of backfill mining,was proposed in this paper. Compared with the traditional method of mine cooling,this method eliminates the terminal device of underground air conditioning system and the conveying system of cold load medium,and creates the overall low-temperature environment of the stope,with obvious economic and safety benefits.The overall implementation plan had been formulated which consists of four stages,filling material preparation,slurry transportation,phase change and cooling of backfill and consolidation strengthening of backfill. In the aspect of materi- al preparation and formulation optimization,the three constraint conditions which were chosen as the optimization goals are the flow characteristics of slurry,the heat transfer characteristics of backfill and the mechanical strength character- istics of backfill. In the aspect of phase change cooling of backfill,a phase change heat transfer model based on the en- thalpy model,porous medium model and hydration heat releasing model was established and verified experimentally. By using this model,the distribution characteristics of temperature and liquid phase ratio changing with time during the phase change process of cold load and storage backfill in underground conditions were calculated. By comparing the two influencing factors of initial liquid phase ratio and slurry concentration,it was calculated and concluded that the main influencing factor of cooling is the initial liquid phase ratio. In the aspect of filling slurry transportation,the ex- periment showed that with the decrease of the initial liquid phase ratio,the ice content increases,the yield stress and the plastic viscosity coefficient both increase. The Bingham model and the yield stress and plastic viscosity coefficient measured by experiments were used to obtain the calculation formula for predicting the shear stress characteristics of pipeline transport in engineering practice. In the aspect of strength of backfill,the experimental results showed that the relationship between compressive strength and initial liquid ratio is characterized by stages. As the initial liquid ratio decreases from 100% to the critical value,the strength increases gradually. While the initial liquid ratio is lower than the critical value,the strength decreases with the decrease of the initial liquid ratio. The influencing factors and influ- encing mechanism of dominance under different conditions were analysed.