Stability Analysis Of The Second-step Pillar Mining Stope In Thick Broken Orebody

The deep V# orebody of Xincheng Gold Mine in Shandong province is a gently inclined large broken orebody. In-580m level of the orebody extraction is divided into two steps mining. First-step room with 8 meters wide is mined by mechanized panel upward horizontal slice cut-and-fill method, because of deep burial depth, high crustal stress, Jiaojia Fault Zone in the roofs, and the orebody of second-step pillar is extremely broken and unstable. On the other hand filling water from the backfilling in first-step room deteriorates both sides of second-step pillars. The mining safety of second-step pillars mining is seriously challenged. In order to extract second-step stope safety and efficiently, mining method called medium-length hole blasting extraction by pre-controlling roof and first-step filling is put forward. In order to gurantee the safety of mining second-step pillars, it is essential to perform the stability analysis on free-standing of backfill in first-step rooms and the roof stability of second-step pillars. Major works in this paper are listed as follows:1. Investigating mechanical parameters of rock mass at great depth are and classifying rock mass quality is carried out according to the obtained parameters.by field investigations of engineering geological conditions and rock mechanical sampling experiments.2. Analysis internal stress and required strength of free-standing backfill based on the mechanical model of backfill in first-step rooms.3. Calculating the height of free-standing backfill in first-step rooms related formulas. And discussing the free-standing cemented backfill in first-step rooms, as the height of medium-length hole blasting is designed as a sublevel height in current second-step pillars of Xincheng Gold Mine.4. Numerically simulating according to the effect of different sublevel heights and excavation lengths on roof stability of second-step rooms by using geotechnical finite element software Midas/GTS. After that, comparing with field measurement results in the testing stope.