| China is the largest coal mining country all over the world,which coal resources are very rich and distribute widely.China has approved the construction of 14 large coal bases with a capacity of 100 million tons,including 5 bases of Ningdong,Shendong,Shanbei,Huanglong and Xinjiang,which mainly mine Jurassic coal resources.The shallow coal seam in the Jurassic coal field is generally faced with the problem of roof sandstone water disasters;Ningdong coalfield is especially typical among them.The Maiduoshan coalmine is located in the south of Yuanyanghu coal area in Ningdong coalfield.The aquifer in the lower section of Zhiluo formation has the complicated hydrogeological conditions,such as the thickness is large and the water-abundance is good.The water disasters with different scale occurred many times in the process of excavating,and the threat of roof water disaster is seriously.According to the underground practical situation,the hydrogeological conditions of aquifer in the lower section of Zhiluo formation on the 2#coal seam has a big discrepancy with the early geological exploration,hydrogeological supplement exploration results.The hydrogeological data obtain from early exploration cannot meet the needs of mine production safety.The aquifer hydrogeological conditions on 2#coal seam was need to research deeply,the overlying rock failure rule of strata on the 2#coal seam need to find out,and then the water disasters control and prevention technology of tunnel excavating and working panel mining was developed to realize the safety of coalmine mining.This paper takes the roof sandstone composite aquifer on 2#coal seam as the research object,through the“one-hole two-section”dewatering test underground,hydrochemistry and tracer test,rock hydrology test,underground water inflow numerical simulation with“double stage and double water level”,overlying failure numerical simulation by FLAC3D,laboratory test and other methods,combining pumping test on the ground with dewatering test underground,field test with indoor test,macro analysis with micro research,analytical method with numerical method,a systematic research has been carried out on the hydrogeological characteristics of the thick sandstone aquifer on the coal seam and water disasters control and prevention.The following research results have been obtained:1)The permeability coefficient of the Yenan formation aquifer between 1#and 2#coal is1.741?2.511m/d,and that in the lower section of the Zhiluo formation is 3.673?6.297m/d.The unit water inflow of borehole in the lower section of the Zhiluo formation was calculated by analytical method as 4.7353,3.7383 and 2.2092 L/s·m,respectively.The results obtained by graphic method are 3.8970,3.4456 and 2.2467 L/s·m respectively.From the analysis of the time and space response characteristics,hydrogeological characteristics and hydrochemical conditions of the aquifer in the lower section of Zhiluo formation to the dewatering test of the Yenan formation aquifer between 1#and 2#coal,it is concluded that the two aquifers have close hydraulic relations.By analyzing the change of water quantity and water level during the dewatering test,analyzing the long-term change of the water level of the surface long-term observation hole,and analyzing the response of the water level of the surface long-term observation hole to the long-flow drainage water,it is concluded that the aquifer in the lower section of the Zhiluo formation on the 2#coal seam has certain drainage feasibility.2)The hydrogeological parameters of the roof in the lower section of Zhiluo formation aquifer on 2#coal seam in the 11 mining areas can be divided into 6 zones,with horizontal permeability coefficient of 0.9?4.5m/d,vertical permeability coefficient of 0.09?0.45m/d,water level of 0.1?0.2,and water storage rate of 1×10-7?5.5×10-7.The permeability coefficient in the dewatering test area obtained by numerical method was 4.5m/d,which was 9.23%different from that obtained by analytical method.The permeability coefficient of the lower section of the Zhiluo formation calculated based on the dewatering test is 15.9 times that of the pumping test.Compared with the pumping test,the hydrogeological parameters obtained from the dewatering test are more consistent with the actual conditions,so as to realize the fine exploration of the hydrogeological conditions of the roof aquifer.3)The test and analysis results of physical and mechanical properties of roof strata provide scientific basis for roof water hazard prevention and control.Grouting has certain effect on the change of hydrogeological conditions such as the permeability and porosity of the original formation.Grouting reinforcement technique is suitable for sandstone aquifer with local fissured roof of coal seam.It is necessary to drill with the following pipe to prevent hole collapse when the roof drainage borehole is exposed to the mudstone waterproof layer.The calculated height of the water-conducting fracture zone on the 110207 working panel calculated by empirical formula,theoretical analysis and numerical analysis is basically the same.The height of the water-conducting fracture zone on the 2#coal working panel is58.62?62.6m,and the ratio of the height of water-conducting fracture zone to the thickness of the coal mining is 15.42?16.47.4)Based on the research results of the hydrogeological conditions of the thick sandstone aquifer and the overlying failure rules on the working panel,taking the first working panel of Maiduoshan coal mine as an example,the water disaster control and prevention technology were developed during tunnel excavating and working panel mining.During the tunnel excavating,the comprehensive water disaster control and prevention technology was adopted,including long-distance directional drilling to explore the water-rich area of aquifer,water drainage by conventional drilling,grouting bolt and reinforced support of U-shaped steel shed.The water drainage technology of“long time dispersion drainage+short time concentrated drainage”was adopted before the mining of working panel.The water drainage scheme is optimized by using the numerical model of underground water flow.Through the above researches,the fine exploration of the hydrogeological conditions of the thick sandstone aquifer on the coal seam,the quantitative analysis of the characteristics of the overlying failure rules,and the development of the water disaster control and prevention technology system of the thick sandstone aquifer was formed. |
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