Study on numerical simulation of groundwater flow field and slope stability in multi-aquifer open pit mine

Water is one of the most important influences on slope stability in open pit mines. In order to solve the problem of slope stability analysis in multi-aquifer open pit mines, the open pit mine in Block I of Thar Coalfield in Pakistan with multiple aquifers was taken as the research background. The groundwater flow field at different excavation phases was analyzed by numerical simulation method. Based on the seepage theory of groundwater, the distribution law of hydrostatic pressure in phreatic aquifer and confined aquifer was analyzed. Based on the rigid body limit equilibrium method, the slope stability analysis method under the action of hydrostatic pressure of multiple aquifers was proposed. Based on the water level distribution within the slope body obtained by numerical simulation, the slope stability at different excavation phases was calculated, and the influence of aquifers on slope stability was analysed. The research results show that: With the excavation and drainage of the mine pit, the groundwater flow field in the open pit mining area changes significantly, and a descending funnel was formed at the mine pit. When mining reached the pit bottom boundary, the water level dropped by about 155-163 m in the mining area. The hydrostatic pressure action of aquifer on slope is related to water level, quantity and location of aquifer. Under the condition of considering hydrostatic pressure of aquifer, the slope stability coefficients are all reduced. And the slope stability coefficients of the three different mining phases were reduced by 6.74%, 11.87%, and 5%, respectively. The more aquifers the sliding surface crosses, the greater the effect of hydrostatic pressure on slope stability. When mining to the boundary, the combined sliding surface passed through two aquifers, and the slope stability coefficient decreased by 5% under the hydrostatic pressure condition, and the arc sliding surface passed through three aquifers, and the slope stability coefficient decreased by 8.74% under the hydrostatic pressure condition. The stability of slope with arc sliding mode is more affected by aquifer hydrostatic pressure than that with combined sliding mode. When mining to the floor of the coal seam roof confined aquifer, the stability coefficient of slope with combined sliding surface decreased by 11.87%, while that with arc sliding mode decreased by 16.32%.