复杂水文地质条件下大型帷幕截流工程效果数值仿真分析

朱仙庄煤矿水文地质条件复杂,其8煤开采受到奥灰和太灰强富水含水层的补给影响,严重威胁煤矿的安全开采。提出了建造大型帷幕截流墙、切断它们之间的水力联系、进行疏水降压的水害治理方法。针对前人单点局部检验帷幕效果的不足,为预测大型帷幕墙的整体截流效果,在井下开展了三阶段放水试验,以此为基础,开展了朱仙庄煤矿多层、复杂接触、复合边界的水文地质条件下大型帷幕截流工程数值仿真分析。结果表明:放水试验期间,帷幕墙内"五含"水位呈现"平盘式"下降现象,墙内外水位差明显,放水试验末期墙内外水位差约200 m,"四含"水位变化出现"滞后"现象,判断了它们之间水力联系微弱,确定了"五含"和"四含"的参数分别为4个和2个分区。针对朱仙庄煤矿复杂的水文地质模型,通过将第2和第3层赋值为相同参数概化了"四含"和"五含"的高角度不整合接触关系,奥灰与"四含"的接触带概化为变水头边界,同时将太灰与"四含",奥灰、太灰与"五含"的接触带概化为源汇补给项,建立了420行×260列×3层的大型帷幕截流工程的大型数值模型,运用MODFLOW软件的WHS求解器进行模型计算。由于研究区复杂的地层接触关系,数值模型在计算中容易出现不收敛现象,通过动态调整算法的阻尼系数在0.8～0.5可以很好地控制模型的收敛性。帷幕截流墙的数值仿真分析发现,帷幕截流墙整体渗透性能较差,整体渗透系数为0.6 Lu(折合渗透系数为0.005 m/d)。预测了"五含"水位疏降至安全水头-350 m时的残余水量为91 m~3/h,截流率达95%以上,综合分析帷幕墙截流效果非常明显。本次计算方法和技术可为类似的复杂水文地质条件下大型数值模型的构建、计算及快速收敛提供参考,同时丰富了煤炭精准开采背景下的矿井地质保障技术。

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 previous 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,complex contact and composite boundary in Zhuxianzhuang Coal Mine was carried out.The result shows that the water level 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,indicating 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 relationship 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 simulation 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 m3/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 technology 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.