Groundwater control technology in open pit mines and its impact on stability of end-slopes

Abstract

There are many rich water open-pit mines in China and the water inflow is large, if the mine groundwater or slope is not properly treated, it will face the dilemma of “water disaster, difficult strengthening of slope, and difficult mining of mines”. Open pit mines in China have developed a variety of groundwater control technologies such as vertical hydrophobic holes, horizontal hydrophobic holes, large diameter hydrophobic holes under the pit and well group hydrophobic and other pumping and draining methods, drainage alleys at the bottom of the pit, pit precipitation and radiation well draining, as well as water interception curtains and water curtains such as borehole slurry curtains, concrete diaphragm wall curtains, pile-row curtains and impermeable membrane curtains to solve the flooding and slope instability encountered in open pit mines. The effects of groundwater control techniques on groundwater level, changes in geotechnical properties of end-slope, changes in slope stress and slope stability coefficients in open pit mines were studied, and the effects of groundwater level lifting on slope stability under the action of water curtain were analyzed. The research results show that draining or de-watering the groundwater in the open pit can effectively reduce the depth of the groundwater, reduce the water content of the slope geotechnical body, improve the cohesion and internal friction angle of the slope geotechnical body, reduce the hydrostatic pressure and horizontal thrust of the slope body, and improve the overall stability coefficient of the slope; however, de-watering a large amount of groundwater can cause waste of water resources and pollution. The water cut-off curtain can solve the problems of too large a drop in groundwater level, huge volume of water drainage, waste of water resources and pollution caused by water drainage and precipitation. Under the action of water interception curtain, the water level on the outside of water interception curtain in the open pit mine keeps rising, which causes the water content of geotechnical body on the outside of water interception curtain to increase, the cohesion and internal friction angle to decrease, and the hydrostatic pressure and horizontal thrust of slope body to increase; while the water content of geotechnical body on the inside of water interception curtain decreases, the cohesion and internal friction angle to increase, and the hydrostatic pressure and horizontal thrust of slope body to decrease, which causes the stability coefficient of slope in open pit coal mine to slightly decreased. The slope stability coefficient is still within the safe range, and it also protects the groundwater resources of the open pit mine.

Keywords

• open pit coal mine
• groundwater control
• water cut-off curtain
• end-slope
• slope stability coefficient
• slope instability