Application of water cutoff curtain in the seepage cutoff and drainage reduction of open-pit coal mine

In order to solve the problems of huge drainage volume,high production cost and high environmental risk in Zhanihe open-pit coal mine,four kinds of curtain technologies,such as underground concrete diaphragm wall,large depth vertical concealed laying of anti-seepage membrane,high-pressure rotary jet grouting and secant pile,are used for the first time to build an arc-shaped trench filling type and pile hole pressing type bottom cut-off curtain with a plane length of nearly 6 000 m,a maximum depth of more than 50 m and an effective thickness of more than 0. 6 m along the concealed outcrop in the north of the coal seam. During the implementation of the project,five technical problems have been solved,including low-strength (8 - 10 MPa) impermeable ( P6 grade) concrete mix proportion technology,ultra-long trench excavation and wall protection technology,geomembranes overlay laying and connection technology,high-volume fly ash cement mixed slurry grouting and filling technology,high-pressure jet grouting pile technology in gravel layer. During and after the construction of the curtain wall,the quality and water cut-off effect have been tested by four methods,such as drilling core method,pumping test,flow field observation method and drain- age change analysis method. The results show that the concrete pouring is continuous and uniform,the filling of fly ash cement mixed slurry is dense and the cementation is intact,the diameter of high-pressure rotary jet grouting pile and secant pile is up to the standard,and the pile body is complete. The permeability coefficient of the wall is 8. 34×10-7 cm / s,and the permeability reaches the very micro permeability level. The maximum water level difference between the inside and outside of the wall has reached more than 10 m. The drainage volume of the mine has been reduced by 60% , which is still in the process of reduction. The curtain wall has obvious water interception effect and meets the design re- quirements. The project is a successful demonstration of using a comprehensive curtain technology to solve the drainage problem in China’s open-pit coal mines,with significant social,economic and environmental benefits. The research re- sults of the project have important application value for the development of open-pit coal mine drainage work in China, and have reference significance for the ecological environment protection in the eastern grassland area of China.