Application of comprehensive detection techniques in leakage analysis of karst reservoirs
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摘要: 通过区域岩溶水文地质调查、地球物理探测和地质钻探对太平水库库尾岩溶渗漏进行探测,对太平水库渗漏原因和渗漏特征提出新认识:水库区域范围宝塔组(O2b)灰岩地层中发育一条NE-SW向横穿太平水库的地下河,在距离水库3.2 km的老龙洞出口排泄。左右岸落水洞发生塌陷后,库水通过岩溶管道快速渗漏至地下河,是导致库水位急剧下降的原因。地球物理探测结果显示库尾左右岸均有明显异常区域,且从左岸至右岸异常区域的高程逐渐降低, 符合地下河岩溶发育一般特征。结合钻孔验证结果认为, 太平水库库尾地下河发育高程为
1516.36 (左岸)~1513.36 m(右岸)。研究成果可为太平水库后续防渗工作提供指导,并对岩溶地区类似水库的渗漏探测工作提供借鉴。Abstract:The reservoir is located in Fengdu county, Chongqing Municipality. After impoundment, karst collapses occurred successively on both the left and right banks at the reservoir tail. Reservoir water rapidly leaked through sinkholes within the collapse pits, causing a sharp decline in the water level and severely impacting normal functioning of the reservoir. To identify the cause and characteristics of the leakage, this study employed a combination of regional karst hydrogeological surveys, geophysical exploration, and geological drilling techniques to systematically investigate the leakage problem at the reservoir tail. The following new insights were obtained: (1) Regional karst hydrogeological surveys indicate the presence of a NE–SW trending limestone belt of the middle Ordovician Baota formation (O2b) traversing the reservoir tail. Karst development is highly pronounced within this layer, commonly featuring solution fissures, caves, and conduits. Field surveys identified multiple sinkholes distributed in a bead-like pattern along the strike of this limestone formation. Tracer tests confirmed the existence of an underground river flowing through the reservoir in a NE–SW direction, with its outlet at Laolong cave, located 3.2 km southwest of the reservoir. The longitudinal gradient of this underground river system is steep, with a vertical drop of approximately 130 m. The development of various karst features at the reservoir tail and the direction of groundwater flow are both influenced by this underground river system. Reservoir impoundment induced the collapses of sinkholes on both banks, allowing reservoir water to directly access into the underground river and discharge at Laolong cave. This has been identified as the fundamental cause of the sudden drop in the reservoir water level. (2) Controlled Source Audio-Frequency Magnetotellurics (CSAMT) and the High-Density Resistivity (HDR) method were selected as geophysical exploration techniques to characterize the spatial distribution of the underground river. These two methods complemented and mutually validated each other's findings. Three CSAMT survey lines were deployed. The results revealed a relatively enclosed low-resistivity zone extending from the left bank to the right bank, with elevations ranging from 1,510 m to 1,500 m, showing a gradual decrease in elevation from left to right. Additionally, three HDR survey lines were conducted. The results indicated underground river elevations of approximately 1,530 m at the low adjacent valley on the left bank, approximately 1,515 m at the left bank of the reservoir, and approximately 1,500 m at survey line yd-4 on the right bank mountain. The gradient of the karst conduit within the reservoir area is inferred to be 1.5% to 2.0%. The alignment of anomalous zones identified by both methods generally follows a NE–SW direction, consistent with the bedrock strike. Furthermore, the elevation of these anomalous zones gradually decreases from the left bank to the right bank, further confirming that the underground river primarily develops along the bedrock strike, flowing from NE to SW. (3) Geological boreholes were drilled based on geophysical anomalies. These boreholes revealed significant vertical karst development within the Baota formation limestone at the reservoir tail. Borehole CZK1 intersected a karst cave; the elevated position of this conduit and its proximity to a sinkhole on the right bank suggest that it is a branch conduit connecting the right bank sinkhole to the underground river. Borehole CZK3 encountered a cavity nearly three-meter high, located near the bottom of the Baota formation limestone at elevations between 1,519.26 m and 1,516.36 m. Water level monitoring in the boreholes indicated shallow water levels within the conduits and significant silt accumulation, supporting the interpretation that this feature represents the underground river karst conduit. (4) Based on integrated geophysical exploration and geological drilling, the elevation of the karst conduit floor of the underground river in the reservoir area ranges from 1,516.36 m on the left bank to 1,513.36 m on the right bank. The estimated conduit dimensions are approximately 2.7 m in width and 2.9 m in height. Near the reservoir head and surrounding areas, the Shizipu formation (O2s) serves as a relatively impermeable layer. On the left bank, the underground river conduit near the reservoir tail passes through the Baota Formation limestone, where the burial depth of the relatively impermeable layer increases closer to the tail. Weakly karstified rock masses on this side act as the lower impermeability boundary. The recommended anti-seepage floor elevation for the left bank is approximately 1,516.0 m. (5) During the investigation phase of karst reservoirs, comprehensive regional karst hydrogeological surveys must be conducted to accurately characterize groundwater flow paths. Only through this approach can the impoundment conditions of the reservoir be clearly understood. In reservoir leakage investigations, relying solely on a single geophysical method or a single borehole to identify leakage pathways and directions is suggested be avoided. This study has elucidated the causes, pathways, and key channel characteristics of leakage at the reservoir. The findings provide a direct foundation for the subsequent design of anti-seepage engineering measures for this reservoir and offer valuable reference for the detection and prevention of similar leakage issues in reservoirs located in karst regions. -
Key words:
- Taiping reservoir /
- karst leakage /
- underground water /
- hydrogeology /
- geophysical detection /
- geological drilling
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表 1 水库库区出露地层岩性表
Table 1. Lithology of the reservoir area
系 统 组 地层代号 地层厚度/m 岩 性 简 述 第四系 Q 0~20.0 冲洪积层,主要为红褐色、黄褐色粉质黏土夹碎石;残坡积层为灰黄色粉质黏土夹全风化页岩 志留系 下统 龙马溪组 S1ln 486.0~613.0 上段为灰绿、黄绿色泥质胶结的粉砂岩、粉砂质页岩及页岩,下段黄绿色粉砂质页岩及页岩;主要分布于库尾 奥陶系 上统 五峰组 O3w 11.6~12.8 灰褐色页岩,黑色炭质页岩,含碳量高,手摸染手,在陈家湾冲沟处出露 临湘组 O3l 4.2~6.1 灰至深灰色泥灰岩,纹理状构造,局部含白云质;主要分布在库尾 中统 宝塔组 O2b 28.8~40.1 灰白色、灰色裂纹状、龟裂纹灰岩,分布在库尾 十字铺组 O2s 10.0~20.4 灰至深灰色泥质灰岩,钙质泥岩,局部夹灰黄色粉砂质页岩,分布在库尾 下统 大湾组 O1d3 O1d3-3 3.5~16.3 黄褐色页岩,薄层状构造,分布于库首 O1d3-2 14.8 深灰色页岩,含钙质胶结,局部含生物化石 O1d3-1 20.0 灰黄色、灰绿色薄层状页岩,薄层状构造,夹深褐色生物碎屑薄层 O1d2 19.2 灰白色灰岩,厚层构造 O1d1 87.0 上部黄绿色页岩,中部深灰色泥质生物灰岩,下部灰岩页岩互层,分布于库首 表 2 示踪剂投放信息表
Table 2. Information on the tracer delivery
示踪剂 投放位置 投放点高程/m 运移距离/m 投放量/g 荧光素钠 田家湾
落水洞1554.79 4360 300 罗丹明 水库左岸
落水洞1548.80 3370 310 表 3 地球物理探测测线布设参数
Table 3. Layout parameters for geophysical detection lines
探测技术 测线名称 布置位置 测线长/m 探测
方向可控源音频大地电磁法 cs-1 河床右岸 75.0 库首至库尾 cs-2 河床中间 55.0 库首至库尾 cs-3 河床左岸 65.0 库尾至库首 高密度电法 tj-2 左侧田家湾 172.5 库首至库尾 zd-4 库尾左岸 345.0 yd-4 右岸 345.0 表 4 钻孔揭示岩溶发育情况表
Table 4. Karst development revealed by boreholes
孔号 孔口高程/m 钻进深度/m 溶蚀发育高程/m 掉钻高程/m 钻孔漏水位置/m 地下水位/m czk1 1560.73 45.4 1544.13 ~1536.43 1531.73 ~1526.73 1538.13 ~1537.23 1527.53 ~1527.03 1543.93 1527.20 czk2 1551.87 30.7 1547.42 ~1539.62 无掉钻 全返水 1546.32 czk3 1559.66 47.3 1552.86 ~1544.96 1530.26 ~1516.36 1552.56 ~1552.06 1548.96 ~1548.66 1548.16 ~1547.86 1545.36 ~1544.96 1526.16 ~1525.96 1519.26 ~1516.36 1552.00 1516.44 -
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