Gravity Blind Backfilling of Abandoned Underground Mine Voids Using Suitable Mix Proportion of Fill Materials and Method of Filling

This paper aims at to establish a novel approach of gravity blind backfilling method for abandoned mine voids using suitable backfill materials. Gravity blind backfilling is an important aspect for controlled movement of the overlying strata and efficient reduction of surface subsidence over unapproachable water-logged as well as dry underground coal mines. In this investigation, studies have been carried out in a fabricated transparent scaled mine model of a section of the bord and pillar underground mine using gravity blind backfilling method. The objectives of the paper is to determine the appropriate method with suitable backfill material through laboratory trial studies to develop an empirical equation among void volume, solid flowrate and solid concentration in gravity blind backfilling method. Since sudden jamming is a major hurdle in filling-up of a large scale areas from one borehole, an attempt has also been made to develop an electric based alarm indication parameter. Empirical relationships have been developed for estimation of maximum filled-up void area covered by backfilled solids after filling. Practical observation have been recorded about shape of filled up area, filled up height and directional spread of slurry in gravity blind backfilling. Electric sensor-based alarm system can predict water levels at different head and indicate the arrival of final stage of filling after which not more than 25% of filling will be possible with the same flowrate and concentration. The best (i.e. bottom ash 30% and sand 70%) and second-best solid composition (i.e. bottom ash 40% and sand 60%) of bottom ash and sand for blind backfilling purpose are determined on the basis of the localized spread of backfill solids without any sign of sliding towards the dip direction, full compaction up to roof of the gallery and greater load-bearing capacity. The coefficient of correlation came to be 0.81 which showed the different parameters has a strong inter relationships amongst each other.