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Evaluation of groundwater flow through a high rockfill dam foundation in karst area in response to reservoir impoundment
International Journal of Rock Mechanics and Mining Sciences ( IF 7.2 ) Pub Date : 2022-11-15 , DOI: 10.1016/j.ijrmms.2022.105268
Yi-Feng Chen, Jingjing Yuan, Guohui Wang, Jianhua Xu, Ran Hu, Zhibing Yang

Constructing high dams in karst valleys remains a challenging issue as karst conduits provide preferential channels for flow through the foundations. The uncertainty of the karst system drastically increases the risk of leakage and hence the difficulty in seepage control at the foundations. This study examined the transient flow behaviors through a karst foundation on which a rockfill dam with a height of 219 m had been constructed. During reservoir filling, an abnormal pressure rise occurred in the foundation downstream the grout curtains, typically with a magnitude of 53∼69 m higher than the pore pressure head at the neighboring positions. This phenomenon was comprehensively investigated by site characterization, inverse modelling, numerical simulation and cross-correlation analysis, demonstrating that the abnormal pressure rise is locally induced by eroded fault (left bank) or contact zones between karst formations (right bank). These conduits have an effective permeability value one order of magnitude higher than that of the karst formations, which quickly transmit the reservoir pressure pulse across the grout curtains, as evidenced by a higher cross-correlation and a smaller lag between pool level and piezometer measurements. The grout curtains have sufficiently low permeability in limiting the amount of leakage through the foundation, and hence ensure the safety of the reservoir operation in spite of the pressure rise. This study confirms the applicability of the equivalent continuum model in addressing groundwater flow problems in karst formations, as long as the site conditions are properly characterized.



中文翻译:

水库蓄水响应下岩溶地区高堆石坝基地下水流评价

在喀斯特河谷建造高坝仍然是一个具有挑战性的问题,因为喀斯特管道为流经地基提供了优先通道。岩溶系统的不确定性大大增加了渗漏的风险,从而增加了地基渗流控制的难度。本研究检查了岩溶地基的瞬态流动行为,在该地基上建造了一座高 219 m 的堆石坝。储层充填过程中,灌浆帷幕下游地基出现异常压力升高,通常比邻近位置的孔隙水头高53~69 m。通过场地特征、逆向建模、数值模拟和互相关分析对这一现象进行了综合研究,表明异常压力升高是由侵蚀断层(左岸)或岩溶地层之间的接触带(右岸)局部引起的。这些管道的有效渗透率值比岩溶地层的有效渗透率值高一个数量级,它可以将储层压力脉冲快速传递到灌浆幕上,水池水位和测压计测量值之间的互相关性更高,滞后更小。灌浆帷幕具有足够低的渗透性以限制通过地基的渗漏量,因此尽管压力升高也能确保水库运行的安全。这项研究证实了等效连续体模型在解决岩溶地层地下水流动问题方面的适用性,只要现场条件得到适当表征。

更新日期:2022-11-15
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