基于高掺量粉煤灰防渗墙的露天矿水资源保护技术

Water-preserved coal mining technology in open pit based on cutoff wall with high fly ash content

蒙东某露天矿矿坑涌水量高达100000 m^3/d,补给源主要为海拉尔河,河水经深厚砂卵石层沿煤层隐伏露头渗入煤层,进而涌入矿坑,采用疏干井疏排矿坑涌水,造成水资源的巨大浪费和环境严重破坏,并增加露天矿生产成本。为截断补给通道、减小矿坑涌水量、保护水资源和矿区生态环境,通过试验、理论分析研究了高掺量粉煤灰防渗墙材料的强度、抗渗性能、黏度、粉煤灰激发剂效果,并针对露天矿煤层厚、补给范围广的特点,进行了现场帷幕截水试验。研究结果显示,水固比0.7∶1.0时,防渗墙材料的抗压强度和抗渗性能与水泥掺量呈正相关关系,粉煤灰掺量为80%的充填材料前期强度增长缓慢,后期强度增大较快,60,90 d抗压强度分别为28 d的1.90倍、3.25倍;CaCl2和NaCl可加快粉煤灰活性发挥、促进水化反应、减小颗粒间孔隙,显著提高充填材料的早期强度和抗渗性能,具有良好的激发效果;防渗墙材料的黏度随着剪切速率的增大具有明显的剪切变稀现象,剪切速率为30 s^-1时出现拐点,呈现剪切增稠现象;膨润土可增加充填材料的黏度,消除其剪切增稠现象,并提高材料的抗渗性能。通过露天矿北侧补给区域进行高掺量粉煤灰防渗墙截水试验,矿坑涌水量减少24000 m^3/d,截水效果显著,水资源得到保护;防渗墙内外水位差逐渐增大,墙外水位逐渐恢复,水位埋深达到-6^-7 m,水位恢复到植被所需的生态水位,生态水位得到保障。在露天矿采用高掺量粉煤灰防渗墙可截断渗水通道、减少矿坑涌水量、保护生态环境,实现露天矿绿色、保水开采。

The water inflow of an open pit mine in eastern Inner Mongolia is as high as 100000 m^3/d.The main supply source is Hailar River,which penetrates into the coal seam along the hidden layer of coal seam through the deep exposed sandstone and then flows into the pit.The drainage shaft is used to discharge the water,however,the method wastes a lot of water resources,damages ecological environment and increases production cost.A curtain wall can be built not only to cut off the water conduit route and reduce the mine water inflow,but also preserve water resources and mining environment.Therefore,the strength,impermeability,viscosity and the effect of high-content fly ash curtain wall building material are studied through experiments and theoretical analysis,then applied in the field for water cut.The results show that the compressive strength and impermeability of the filling material are positively correlated with the cement content when the water-solid ratio is 0.7∶1.0.The strength of the filling material with 80%fly ash content grows slowly in the early stage,but increases rapidly in the later stage.The compressive strength at 60 d and 90 d is 1.90 times and 3.25 times of that at 28 d respectively.CaCl 2 and NaCl could accelerate the activity of fly ash,promote hydration reaction,reduce inter-particle porosity,and significantly improve the early strength and impermeability.As the shear rate increases,the viscosity of the paste backfilling material has an obvious phenomenon of shear thinning.When the shear rate is 30 s^-1,an inflection point appears showing shear thickening phenomenon,during which the bentonite could increase the viscosity and improve the impermeability by eliminating the phenomenon of shear thickening.The water cutoff test on the high content fly ash paste backfilling material is conducted in the field of north side recharge area of the mine.It is found that water inflow is reduced by 24000 m^3/d.The water level difference between inside and outside the curtain wall gradually increases,and the level outside the wall gradually recovers to normal with a water level buried depth of-6^-7 m,which means it has recovered to ecological level required by vegetation.In conclusion,the notable effects have been achieved in cutting off water and preserving water resources and environment,offering some ideas and references for green and water conservation coal mining in open pit mines.