Slope Stability Of Open Pit To Underground Mining In Tiegukeng Mining Area Considering Deformation Parameters Of Filling Body

The slope stability is a necessary condition for the first stage of underground mining at Tiegukeng mining area.In order to ensure the production safety after the mine is transferred to underground mining and reduce the impact of underground mining on open-pit slope stability,the goaf need to be backfilled.The main function of filling body in open pit to underground mining is to restrain deformation with the surrounding rock for reducing the influence of underground mining on the stability of open-pit slope.And the ability of the filling body to constrain deformation is related to its deformation parameters.Based on the mining technical conditions of the Tiegukeng mining area,the theoretical analysis and numerical simulations are used to carry out the study on the open-pit slope stability of the open pit to underground mining by considering the parameters of backfill deformation.(1)By establishing numerical models,the local strength reduction FEM is used to calculate the safety factors(F)of open-pit slope top including hanging wall and footwall under the various working conditions in the first stage.The calculation results show that The first stage mining has a greater influence on the stability of the hanging wall slope and less influence on the stability of the footwall slope.And the hanging wall slope has a risk of instability.(2)By establishing the filling body’s loading model,the mechanics theory was used to analyze the model to calculate the functional relationship between the deformation parameters of the filling body and the surface deformation caused by underground mining.This formula shows that the elastic modulus(E)and Poisson’s ratio(v)of the filling body are inversely proportional to the surface deformation.Underground mining caused uneven settlement deformation of the hanging wall of the open-pit slope.The deformation settlement from the top to the foot of the slope firstly increased and then decreased.(3)According to the ratio of cement-sand(1:16,1:8,1:6,1:4,1:2)of the filling body that may be used under the conditions of the Tiegukeng mining area.The variation range of the deformation parameters of the filling body was determined: 0.09 GPa ≤ E≤ 0.69 GPa,0.20 ≤ v≤ 0.36.The relationship between the deformation parameters of different filling body and the deformation settlements and safety factors of open-pit slopes was studied by using the numerical simulation.The results show that the deformation of open-pit slope gradually decreases,and the safety factor gradually increases,and the stability of the open-pit slope becomes better with the increase of the elastic modulus and Poisson’s ratio of the filling body.The elastic modulus and the Poisson’s ratio of the filling body affect the open pit slope stability together.When 0.09 GPa ≤ E<0.49 GPa,the safety factor increases with the increase of Poisson’s ratio.When E ≥ 0.49 GPa,Poisson’s ratio changes within 0.20~0.36 have less effect on the open-pit slope safety factor.The actual project uses the filling body with cement-to-sand ratio of 1:6.Its elastic modulus is 0.29 GPa and Poisson’s ratio is 0.26.And the safety factor under this filling condition is 2.2.In the cement-sand ratios that may be used in the project,filling body with cement-sand ratios of 1:8 or higher can ensure the stability of open pit slopes in the first stage.The range of deformation parameters of the filling body satisfying the engineering requirements of the slope stability(F ≥ 1.2)of the project is: 0.20 ≤ v ≤0.36 and E ≥ 0.18 GPa to 0.10 GPa,and the minimum value of the elastic modulus is related to the Poisson’s ratio.