青藏高原东缘水库绕坝基渗流化学溶蚀研究

Chemical dissolution of seepage around dam foundation of a reservoir in eastern margin of the Tibetan Plateau

研究了青藏高原东缘某大坝基础遭受渗流场与化学场破坏的过程。通过氯离子示踪、温度电导示踪以及人工示踪方法,确定混凝土防渗墙中存在缺陷,库水通过非全封闭式防渗墙绕坝基渗漏,渗水通过坝后区的反滤层排泄;酸溶解试验和X射线荧光分析证明,坝后区地表的白色颗粒物主要是CaCO_3;结合化学反应过程,确认析出物来自于防渗墙中的水泥,渗漏水中的CO_2与水泥中的Ca(OH)_2发生反应生成可溶性Ca(HCO_3)_2,然后被渗漏水带到地表,并在常温下分解形成CaCO_3。通过地表水中CO_2含量的测试分析发现,参与水岩反应的CO_2具有除大气降水之外的其他来源。结合地质构造推断来自深部碳库中的CO_2通过断裂带进入到了地下水与库水中,并参与了水岩反应,对大坝的侵蚀速度大幅度增加。研究表明深部CO_2进入地下水并参与渗流过程,对大坝及水工建筑物的化学侵蚀作用将大幅度增强。

The foundation failure of a dam on the eastern margin of the Tibetan Plateau during seepage and chemical processes is studied.By using Cl-tracing,temperature-conductivity tracing and artificial tracing techniques,it is determined that there is leakage through the non-closed concrete cut-off wall,where the reservoir water leaks through the dam foundation,and excretes through the filter layer after the dam area.The acid dissolution experiment and X-ray fluorescence analysis show that the precipitated white particles on the surface after the dam are mainly composited of CaCO3.Combined with the chemical reaction process.It is confirmed that the precipitation comes from the cement of cut-off wall.The CO2 dissolved in the leakage water reacting with Ca(OH)2 in the cement can generate soluble Ca(HCO3)2,which is taken to the surface by the leakage water and decomposed to CaCO3 at normal temperature.Through the measurement and analysis of CO2 content in surface water,it is found that CO2 in the water-rock reaction has other sources except atmospheric precipitation.Considering the local geologic structure,it is inferred that CO2 mainly from the deep carbon pool enters the groundwater and reservoir water through the fault zones,and participates in the water-rock reaction.This results in a faster erosion of the dam.The chemical erosion of the dam and hydraulic structures will be greatly enhanced if the deep CO2 enters the groundwater and participates in the seepage process.