Ground control conditions of the mechanized longwall mining at Alpu lignite deposit

Ground control is one of the four subsystems of underground coal mining. Beside the roof control, it covers also rib control, floor control, pillar design, shield design, overburden failures and subsidence. Ground control condition of the presumed mechanized longwall mining in study area was taken into the consideration in this study. Ground control condition of the study area was obtained by the following steps. Classification of the geotechnical units, rock mass classification, cavability index, required shield capacity, floor bearing capacity, critical cutting height and support design of gateroads. Geotechnical classification of the strata layers and rock mass classification was done due to the lithology of the boreholes and laboratory test analyses of them. According to layers position to the lignite seam and their lithological data, they separated into the geotechnical units. RMR rock mass classification was applied. Results classified major part of the structure as "poor rocks" and in some cases "fair rocks". Caving behavior of the roof strata was predicted by polish scientists' method. In addition, by applying the US National Institute for Occupational Safety and Health (NIOSH) roof rating system in possible roof strata results are compared. In conclusion roof strata is classified as "immediately caving" strata in all production alternative. Required shield capacity was estimated by detached roof method. The caving height, calculated due to the bulking factor of the lignite and roof strata. Low strength floor strata act as a limitation to mining height increasing in all production alternative. Possible mining height was determined as five and six meter at LTCC method. In normal longwall method inside the critical cutting height, floor strata in all production alternatives can provide the required bearing capacity. Required shield capacity in each production alternative is rising by increasing in cutting height. Stability of the coal wall in face analyzed in numerical model at different cutting height. Face daily advance was accepted as two meter per day. In this condition, critical cutting height was determined as three meter. Support design for main road and longwall panel headgate and tailgate was designed in numerical model. As a result, recommended support system in main road is selected as GI 140 profiles with 0.5 m spacing, wire mesh with 0.1 m spacing and 0.01 thickness and Shotcrete with 0.12 m thickness. In headgate and tailgate, support system is selected as GI 140 profiles with 0.7 m spacing, wire mesh with 0.15 m spacing and 0.004 thickness and shotcrete with 0.1 m thickness. To avoid failure during the production supports should be advance with pressure by touching the roof and right after the cutting. In addition cutting height should be control to the critical height.