Study On Shallow Coal Seam Mining Overburden Strata Movement And Water Disaster Evaluation In The Condition Of Semi-Cementation And Low Strength Surrounding Rocks

In the conditions of semi-cementation and low strength, coal mining may bring many problems, such as overburden strata movement and evaluation of roof water disaster. To solve these problems, we took the first coal mine of Yi-Li as study object. Based on the drilling data, geophysical exploration data and physical mechanics test data of rock in study area, we used many methods, such as theoretical analysis, numerical simulation, similar material physical simulation and laboratory test, to have exploratory study on many aspects. And they were structure characteristics of overburden strata, overburden strata movement law, roof structural stability, water resisting capability of key aquifuge, roof water disaster evaluation, main technical ways of roof water prevention and control in study area. The main study results was as follows:(1)We systematically analyzed the primary mineable coal seams’roof aquifer thickness variational law, lithological characteristics, water abundance and conductivity characteristics. We also analyzed the aquifuge thickness variational law and lithological characteristics. And we analyzed the hydraulic connection of the aquifers during coal measures. We had analysis of the water abundance and conductivity characteristics of the quaternary bottom. The Quaternary pore aquifer was the main recharge source aquifers during coal measures.(2)We had studied on mining overburden strata movement law of the 5th coal seam under different conditions by many methods, such as discrete element numerical simulation, finite element numerical simulation, and similar material physical simulation. The simulation results showed that with the increase of mining height, the cutting roof caving risk increased. We used both the short voussoir beam theory and step beam theory to evaluate the 5th coal seam roof structural stability. According to the characteristics of semi-cementation and low strength, we put forward "semi-low" slide coefficient to modify the evaluation system. The result was coincident with the test.(3)On analysis of the overburden strata zoning, we held that the overburden zoning characteristics had two conditions in study area, and they were "semi-low" four zones and "semi-low" two zones. On the analysis of the relationship between fissure closure zone and time, we gave the calculation method of the fissure closure zone.(4)We discussed the concept of key aquifuge and determination ways. We had analysis of the key aquifuge thickness variational law and lithological characteristics. Moreover, we had analysis of physical and mechanical properties to the key aquifuge by swelling test, disintegrating test, softening test, tensile test, uniaxial compression test and so on. And we also evaluated the key aquifuge water resisting capability by rock mechanics test and triaxial stress-permeability test. To quantitatively evaluate the water resisting capability of key aquifuge, we put forward the water resisting index method. The results showed most study area were in middling water resisting capability partition.(5)According to the 5th coal seam’s roof aquifer thickness variational characteristics and lithological association characteristics, and considering the influence of roof lithology and structural characteristics to water abundance, we put forward the water abundance index method to have quantitative evaluation of the coal seam roof aquifer water abundance. Moreover, we divided the water abundance partition. The height of water flowing fractured zone was predicted by four methods. They were laboratory test prediction, regulation formula prediction, multi-linear statistical prediction and deformation prediction. Based on considering the influence of roof lithology and structural characteristics to aquifuge, we used the water resisting index method to quantitative evaluate the water resisting capability of the roof aquifuge and we divided the water resisting capability partition.(6)Based on the comprehensive analysis of factors affecting roof water inrush, we put forward "five maps" information fusion method to predict roof water inrush risk. And we developed the corresponding roof water inrush risk prediction software by VB6.0. According to the 5th coal seam roof aquifer condition in study area, we used two methods to predict the roof water inflow, and they were big well method and analogy method. We calculated the upper mining limit of the 5th coal seam.(7)Finally, we had analysis of the water filling conditions, and put forward technical ways of roof water prevention and control in whole study area.