Study On The Mechanism And Engineering Application Of Seepage Cutoff And Drainage Reduction Of Diaphragm Wall In Open-pit Coal Mine

In open-pit coal mine process,ground water level needs to be lowered and controlled.The commonly used methods are water draining and curtain grouting.At present,the open-pit coal mines which under construction and production in China all adopt water draining to reduce or unwatering the water level.Because of the long period of big flow drainage,the water table surrounding the mining area is reduced rapidly,which cause the vegetation dying,the wells drying and the land desertification.The damage to the natural environment of the mining area is serious,and the residents living in the surrounding area have problem in domestic water.At the same time,the large amount of drainage groundwater causes great waste of groundwater resources,and the discharge of mine water causes the deterioration of surface river water quality.It is easy to cause water loss and soil erosion during the process of stripping the surface layer and aquifer,and the stability of the slope is reduced.All those bring difficulties to the drainage project and slope maintenance and management.In addition,the drainage project occupied a large number of manpower and equipment.The cost of drainage project in tens of millions of yuan every year,which brought serious economic burden and increased the production cost of the open-pit coal mine.In order to solve a series of problems such as"ecological environment,production safety and economic benefits"caused by groundwater draining,and realize the green,safe and sustainable development of open-pit coal mine,in case of Zhanihe open-pit coal mine was studied as an example,diaphragm wall technology was used to replace the commonly used drainage technology,the seepage supply channel of open-pit coal mine is cut off by curtain grouting,and the drainage of mine is basically reduced.The following researches were mainly carried out:1.Based on the hydrogeology and engineering geological conditions of the mining area,combined with the construction process of the diaphragm wall,the necessary conditions,favorable conditions and economic conditions for the construction of the diaphragm wall of the open-pit coal mine were proposed.The diaphragm wall was divided into many forms from the aspects of wall structure,plane distribution and section shape,such as pile hole pressing-type and groove pouring-type,linear-type and arc-type,bottom-type and suspension-type.2.Main control factors which influence the seepage cutoff and drainage reduction effect were analyzed.Based on the groundwater seepage theory,by means of complex variable function theory,the formula for calculating the lateral flow rate of the two ends and the bottom of the diaphragm wall and the formula of the seepage flow through the body of the wall were derived.The results show that the lateral flow is in direct proportion to the aquifer permeable coefficient K and head loss H,has a negative correlation with the length l and depth d of the diaphragm wall;the seepage flow has a negative correlation with the thickness B and a positive correlation with seepage coefficient K₂ of the diaphragm wall.3.Indoor seepage physical model was established to simulate the process and law of groundwater flow field and seepage flow along with the changes of groundwater head and continuous length of diaphragm wall.The function relation between seepage flow and the length of the seepage wall was fitted,and the relationship between the effect of cut-off reduction and the closure degree of the diaphragm wall was established.The results show that there is a three function relationship between the seepage cutting effect and the diaphragm wall closing degree,the seepage cutting effect is significantly increased with the increase of the diaphragm wall lenghth.4.Influences of the length,depth,thicknessand permeability coefficient of the diaphragm wall on groundwater flow field and volume of water drainage were studied based on the numerical simulation software MODFLOW.Simulation results ware consistent with the theoretical calculation results.The results show that the longer the diaphragm wall,the smaller the amount of water needed to lower the water level of the pumping center to the same level.The rate of water withdrawal decreases with the increase of diaphragm wall length.The influence of the depth of the seepage wall on the pumping amount mainly depends on the stratum at the bottom of the diaphragm wall,the relation between the thickness of the diaphragm wall and the pumping amount can be expressed by the two polynomial function.The speed of the pump water decrease gradually slows with the increase of the thickness of the diaphragm wall,when the permeability coefficient of the diaphragm wall decreases to less than 0.001m/d,The effect of decreasing the permeability coefficient on the seepage reduction is not significant.The research of seepage cutoff and drainage reduction mechanism was further improved.5.Zhanihe open-pit coal mine was studied as an example to carray out the diaphragm wall construction test.The feasibility of diaphragm wall construction in open-pit coal mine was verified by 400 m long wall construction engineering test.Flow field observation and pumping test were used to test the seepage prevention performance,analyze the control function of the diaphragm wall construction on the groundwater flow field.The drainage amount of the open-pit coal mine,the rationality and accuracy of the seepage cutoff and drainage reduction mechanism weres proved.6.The effect of seepage cutoff and drainage reduction after the completion of the engineering test and the completion of the wall was simulated by the MODFLOW numerical simulation software.Based on the research results,the optimization model was set up,and the key technical parameters of the main body of the seepage proof wall in Zhanihe open-pit coal mine were designed and optimized.The purpose of this paper is to:?1?Derive the calculation formula of the around flow and seepage flow of the diaphragm wall;?2?Study the influence degree of the main controlling factors of the diaphragm wall,and establish the mechanism of seepage cutoff and drainage reduction;?3?Carry out the diaphragm wall construction engineering test;?4?Form a set of diaphragm wall construction theory and method of the analysis and design,construction technology and optimization,and effect test and forecast for open-pit coal mine.Technical support for open-pit coal mine of the water disasters prevention and water resources protection were provided.