Numerical simulation analysis of closure effect of large curtain work with complex hydrogeological conditions

The hydrogeological conditions at Zhuxianzhuang Coal Mine are complex,and the mining of No. 8 coal seam is threatened by the strong water-rich aquifers of Ordovician and Archaean era limestone,which seriously threatens the safe mining of the coal mine. The method of building large curtain closure walls,cutting off the hydraulic connections between them and carrying out drainage and pressure reduction,was put forward. In order to predict the overall closure effect of large-scale curtain wall,a numerical simulation analysis of large-scale curtain closure engineering effect under complex hydrogeological conditions at Zhuxianzhuang Coal Mine was carried out in view of the shortcomings of previ-ous curtain effect tests in local area. Three-stage drainage test was carried out underground. Based on this,a numerical simulation analysis of large-scale curtain closure engineering under the hydrogeological conditions of multi-layer,com-plex contact and composite boundary in Zhuxianzhuang Coal Mine was carried out. The result shows that the water lev-el of fifth aquifer inside of the curtain wall shows a “flat disc” drop phenomenon. The water level difference between inside and outside the wall is obvious. At the end of the drainage test,the water level difference between inside and outside the wall is about 200 m. The “lag” phenomenon appears in the change of water level of fourth aquifer,indica-ting the weak hydraulic connection between them. The parameters of fifth and fourth aquifer are determined to be 4 and 2 zones respectively. The high-angle unconformity contact relationship between fourth and fifth aquifer is generalized by assigning the second and third layers to the same parameters. And the contact zone between Ordovician ash and fourth aquifer is generalized as the boundary of variable water head,and the contact recharge between Archaean era limestone and fifth aquifer,and between Ordovician limestone and fourth and fifth aquifer is generalized as a recharge item. A large-scale numerical model of 420 rows×260 rows×3 layers of large curtain closure project is established,and the model is calculated by using WHS solver of MODFLOW software. Because of the complex stratum contact relation-ship in the study area,the numerical model is prone to non-convergence. The convergence of the model can be well controlled by adjusting the damping coefficient of the dynamic algorithm between 0. 8 and 0. 5. The numerical simula-tion analysis of the curtain closure wall shows that the overall permeability of the curtain closure wall is poor,and the overall permeability coefficient is 0. 6 Lu (equivalent permeability coefficient is 0. 005 m / d). It is predicted that the residual water amount is 91 m3 / h when the water level of fifth aquifer drops to -350 m,and the closure rate is over 95% . The comprehensive analysis of the closure effect of curtain wall is obvious. This calculation method and technolo-gy can provide reference for the construction,calculation and fast convergence of large-scale numerical models under similar multi-layer,complex contact and complex boundary hydrogeological conditions,and enrich the mine geological support technology under the background of precise coal mining.