Study On Drainage Effect Of Blind Ditch In Gangue Dump Of Coal Mine By Physical Model Test

Groundwater drainage in landfill gangue slope is related to the safe operation of tailings reservoir.At present,seepage blind ditch is the main drainage measure of underground water in the accumulated body,and plastic blind pipe is still rare.In order to study the underground drainage capacity and drainage efficiency of the new type of plastic blind pipe,and to summarize the influence of water infiltration in the accumulation body on the material of blind ditch,the engineering geological conditions of the site were investigated in detail by taking the No.3 dumping site of Hecaogou Coal Mine in Zichang City as the research object.Combined with site investigation and previous comprehensive treatment design of Hecaogou gangue dump,the paper thoroughly discusses the seepage rules and the material transfer characteristics of underground water in gangue slope when adopting new plastic blind pipe and traditional blind seepage ditch to subsurface drainage,and analyze the influence of leachate carrying fine coal gangue particles on underground blind gully materials by using reduced scale physical model test indoor.On this basis,the advantages and disadvantages of the two drainage measures are analyzed to select a more reasonable underground drainage scheme and optimize it.The research results obtained are as follows:(1)The variation law of pore water pressure in gangue slope is summarized:(1)At the beginning of rainfall,the infiltration of rainwater leads to the downward movement of wetting front,and the pore water pressure starts to increase rapidly to the peak value and fluctuates slightly around the peak value.It starts to decrease slowly with the cessation of rainfall,and lags behind the cessation time of rainfall for about 80?100 minutes.(2)For the barometer buried in the same section,the pore water pressure decreases with the increase of depth,gradually increases to the peak value with the continuous rainfall,and fluctuates at the peak value.When the rainfall stops,the time when the pore water pressure begins to decrease appears different degrees of lag,but the upper osmometer responds faster than the lower osmometer.(3)For the osmometer with the same buried depth,the pore water pressure measured by the one at the axis is higher than that of the ones buried on both sides of the axis,while the osmometer at the slope is higher than that at the platform for the one buried at the same level.(4)The permeability coefficient and porosity of the upper gangue layer and the lower gravel layer are different greatly,and the water supply and loss of the gravel layer are unbalanced,which leads to the occurrence of negative pore water pressure and the subsidence deformation of the gangue layer.While at the foot of slope,there is no negative pore water pressure possibly due to the small thickness of upper gangue layer and the large amount of vertical and horizontal infiltration of rainfall.(2)Summarize the material transfer characteristics of gangue pile slope.Under the effect of rainfall infiltration,the leaching effect of rainfall on the surface gangue and the osmotic scouring effect of the bottom gangue lead to a relatively large reduction of the fine particles of the bottom gangue in the surface layer,while the leachate carrying fine coal gangue particles migrates downward and the fine particles are enriched in the middle layer due to seepage filtration effect.(3)Summarize the influence of coal water carrying fine coal gangue particles on the materials of underground blind gully.It can be seen that coal water immersion has no influence on the plastic blind pipes due to the short time in model test,but the strength loss rate of rubble(sandstone)in blind ditch is about 6%,which has a little impact.However,after a long time of soaking,rubble(sandstone)will be softened and mud and eventually block drainage channel.(4)The drainage effect of seepage blind ditch is better than that of plastic blind pipe in a short time.But considering the suitability of the site,the characteristics of gangue bulk,the efficiency of blind trench drainage and the economic and environmental protection of the treatment project,adopting the underground drainage method of "new speed-drainage pipe and reverse filter layer" shows more obvious advantages.