Research On Induced Caving Method In Gentle-Dipping And Unstable Thick Gypsum Deposit

Lanling gypsum deposit locates in the southeast of Han Zhuang-Si Hu graben basin,Linyi city,Shandong province.The deposit distributes widely,with rich amount of resource,low-angle dip and large thickness.Room and pillar method has been used as the main mining approache with large ratio of permanent pillars reserved and large ore loss.Moreover,the gypsum pillar can be easily weathered and weakened,resulting in large-scale collapse of stope roof.The primary cause of the "12·25" accident was the destabilization of gypsum pillar and the roof collapse.Aiming at the No.7 mine field of Shandong Lanling Gypsum Group Company Ltd,the induced caving mining scheme was proposed in the present paper to ensure safety and increase recovery ratio.The "Three Law"(Law of roof caving,Law of ore and rock flowing and Law of ground pressure activity)were analyzed and an efficient induced caving technology for gentledipping and unstable thick gypsum ore body was proposed.The work can be summarized as the following:(1)Structural plane survey and Point Load Test were carried out.The ore bodies are at grade IV-level and the rock beds are at ???-level.Both the ore and rock have structural characters of easy-caving.(2)According to the mechanical characteristics(uniaxial compressive strength,tensile strength,elastic modulus and Poisson's ratio)of ore rock and orthogonal regression method,the proportion tests of river sand,cement,gypsum and rosin were carried out and the similar material proportion was obtained.Then similar material simulating experiments of caving method for gentle-dipping and unstable thick gypsum ore were carried out to reveal the caving mechanism of overlying rock.The caving span of overlying strata and caving outline were also obtained,which could provide basis for the determination of stope structure parameters.(3)The stress variation of overlying strata during stoping by caving method was also numerically simulated by RFPA software,based on which the stope structure parameters were determined.(4)Based on ore-drawing tests,the drawn-body form and granular flowing parameters were obtained,and the ore loss process and controlling method were also studied.By setting induced caving layer to delay the incorporation time of waste rock and controlling ore drawing to adapt to caving velocity,the ore recovery was enhanced and the ore dilution was reduced.(5)According to the "Three Law",two induced caving methods by flat-bottom trench and series trench were proposed respectively.Induced caving method by flat-bottom trench can be used for ore deposit with thickness greater than 15m,in which stress relief engineering was implemented for stope stability.Induced caving method by series trench trench can be used for ore deposit with thickness less than 15m,in which trench and ore-drawing roadway were arranged alternatively to settle the height difference of bottom structure.Ore body was mined from top down along the tendency,during which the gob area was enlarged continuously to induce the roof strata caving fragmentarily and form covering layer.The analysis shows that the induced caving mining method proposed in the present paper can adapt to the mining conditions of LanLing gypsum deposit with safety and high efficiency.