滇东高原罗平湾子水库岩溶渗漏机理及库外补漏设想

Karst leakage and its sealing at Wanzi reservoir in Luoping county on the plateau of eastern Yunnan

在总结和分析前人研究成果的基础上,结合云南省罗平湾子水库地层岩性、地质构造、水文地质工程地质条件、岩溶发育特征、水库汇流条件、多次补漏未遂等因素,对影响水库渗漏的主要因素进行分解,结果表明:岩溶强发育带地层中溶蚀孔、洞发育,土工膜铺盖封闭库底,蓄水后便在土工膜之下、地下水位之上的岩溶空隙中形成真空,在库水位频繁、大幅度波动条件下易发生真空吸蚀作用,充填物部分被淘空;库底以上的蓄水压力与库底以下的真空产生的负压叠加后形成附加应力,当附加应力大于孔洞之上岩土体的抗剪强度,或大于孔、洞充填物与洞壁之间的粘结强度时发生冲切破坏,这是导致水库多次补漏未遂,且同一渗漏片区重复发生岩溶塌陷、出现落水洞的主要原因。在库区内补漏具有很大的局限性,而在库区外适当部位设置防渗帷幕,不仅可根治渗漏,还可明显抬高地下水位,改善蓄水条件,扩大原设计库容数倍。

Built on the Dagan river-a three-tier tributary of the Nanpan river from the Zhujiang river system,Wanzi reservoir is located at Wanzi village on the edge of Luoping basin 13 km from the southwest of Luoping county of Yunan Province.It is a typically karst-damaged reservoir in eastern Yunnan,with its lateral leakage toward lower adjacent valley.The landform of this reservoir belongs to erosion-corrosion alpin and medium-height mountains of eastern Yunan structure.The control drainage area of Wanzi reservoir is 10^(4) km^(2) with the average runoff of 8,843×10^(4) m^(3).This medium-sized reservoir covers a designed irrigation area of 2,133×10^(4) m^(2) with its designed height of 23.5 m and normal capacity of 1,046×10^(4) m^(3).It has experienced four times of leakage sealing since its construction in 1959,but the leakage reaches more than 0.5 m^(3)·s^(−1) at medium water level with water supply of only 141.7×10^(4) m^(3).In order to provide the theoretical foundation for further successful sealing and even the expanding of reservoir capacity,we investigate the main causes of the failure of leakage sealing.Meanwhile,we also profoundly analyze the factors of leakage according to the previous studies as well as the data about Wanzi reservoir such as stratum lithology,geological structure,geological conditions of hydrogeological engineering,characteristics of karst development,conditions of flow concentration,the failure of sealing,etc.Results show that because the study area is located on the strong karst development zone controlled by stratum lithology and structure,the vacuum suction erosion and the groundwater erosion caused by frequent and substantial water-level fluctuation result in corrosion fissures and the scouring of holes.The additional stress,composed of the water storage pressure and the negative pressure caused by the vacuum due to the coverage and enclosure of reservoir bottom,is larger than the shear strength,or larger than the strength bonding karst cave fillings and cave walls.Consequently,there exist failures of leakage sealing,sinkholes and the repeated karst collapse in the same leakage area,all of which are the main causes of leakage.In spite of several relatively separate leakage belts inside the reservoir area,all the leakage belts outside converge into the karst pipelines on both sides of the reservoir.These karst pipelines characterized by bedded development are narrow due to the holdup of clastic rocks.The leakage sealing spots scattering over a large area bringing huge engineering work and the failure of leakage protection.However,the water-tight curtain properly laid out outside the reservoir area can not only eradicate the leakage,but it can also effectively raise the groundwater level to improve storage conditions.In the way of laying out water-tight curtain,the reservoir capacity can be expanded more than 3 times as large as the previous one,equal to 3 other medium-sized reservoirs.