Water seepage collection and measurement early warning system for earth-rock dam on deep overburden foundation

Abstract

The application discloses a kind of for deep overburden layer earth-rock dam's seepage collection and measurement early warning system, belong to water conservancy and hydropower engineering monitoring structure design construction technical field.Provide a kind of can effectively combine downstream cofferdam of earth-rock dam with downstream seepage monitoring structure, further significantly reduce investment cost and implementation difficulty for deep overburden layer earth-rock dam's seepage collection and measurement early warning system.The measurement arrangement structure includes earth-rock dam, downstream cofferdam and construction diversion tunnel or construction period ecological water supply hole, also includes dam foundation seepage interception structure, seepage collection output structure and seepage measurement structure, dam foundation seepage interception structure is sequentially arranged in the center position of downstream cofferdam and the overburden layer below it along the width direction of river course, seepage collection output structure is arranged between earth-rock dam and downstream cofferdam, and seepage measurement structure is arranged in construction period ecological water supply hole;Seepage collection output structure is connected with seepage measurement structure by diversion tunnel.

Description

Technical Field

[0001] This invention relates to a seepage collection and measurement early warning system, and more particularly to a seepage collection and measurement early warning system for earth-rock dams on deep overburden foundations, belonging to the field of design and construction technology of monitoring structures for water conservancy and hydropower projects. Background Technology

[0002] The design concept of earth-rock dams is to block seepage upstream and drain downstream. Upstream, cohesive soil, concrete, geomembrane, and other media combined with foundation treatment measures serve as the seepage prevention system. Downstream, drainage structures are installed to divert and discharge any potential seepage, and seepage measurement systems are installed at the locations where seepage is most likely to accumulate to monitor the leakage of the earth-rock dam and dynamically evaluate the safe operation of the dam.

[0003] Seepage from earth-rock dams can spread downstream across the entire riverbed surrounding the dam foundation. For dam foundations with deep overburden, deep seepage is difficult to monitor. Therefore, engineering measures are typically implemented downstream of the dam to intercept water and alter the seepage path, creating a concentrated seepage outlet at an appropriate location downstream of the dam. This outlet collects all seepage from the dam and its foundation, and a seepage monitoring system is then deployed there to accurately monitor the actual seepage flow.

[0004] Earth-rock dams on foundations with deep overburden typically employ a fully enclosed seepage-cutting structure, such as a cutoff wall, within the overburden foundation downstream of the dam toe. An opening is created at an appropriate location, and a measuring weir is constructed adjacent to this opening to monitor seepage flow. Earth-rock dam construction generally utilizes a cofferdam and bank diversion scheme, with cofferdams upstream and downstream of the dam to impede floodwaters and riverbed seepage, meeting the requirements for dam foundation treatment and dry land filling. However, due to various reasons, the downstream temporary cofferdam and the measuring weir must be arranged separately. For earth-rock dam projects with deep overburden layers in the riverbed foundation, separating the downstream cofferdam and measuring weir is neither economical nor environmentally friendly, and also presents certain implementation difficulties.

[0005] Earth-rock dams constructed on thick overburden layers often require ballast at the downstream toe to ensure the dam body and foundation's anti-sliding stability. For economic and environmental reasons, the downstream cofferdam and ballast are typically integrated, with the ballast's crest elevation often significantly higher than the cofferdam's crest. If the goal is to utilize the downstream cofferdam's seepage control system for a seepage monitoring system, two methods exist: 1) After the ballast is constructed, partial excavation is carried out to near the top of the cofferdam's seepage control system. A measuring weir is then built and installed for seepage monitoring. The excavated ballast is then restored. However, this method presents significant challenges for weir maintenance and repair. Furthermore, considering the downstream ballast's height can reach tens of meters, there are issues with large excavation volumes and limited storage space for excavated materials, significantly increasing construction difficulty, investment, and construction time. 2) Extending the cofferdam's seepage control system to the top of the ballast and installing a measuring system there will increase investment and raise the dam's phreatic line, negatively impacting slope stability.

[0006] Furthermore, when seepage stability problems occur in dams, they typically exhibit significant changes in seepage flow rate over a short period. Simultaneously, the sediment content of the seepage water, i.e., turbidity, also changes markedly during the development of seepage failure. However, seepage monitoring for earth-rock dams usually only monitors seepage flow rate at specific times, failing to directly reflect the changing seepage process. Considering that seepage failure generally occurs within a short period, it is crucial to issue timely safety warnings and take remedial measures when signs of seepage failure appear to prevent its occurrence. Conventional seepage flow monitoring may not be sufficient for the timely detection and resolution of seepage stability problems. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a seepage collection and measurement early warning system for earth-rock dams with deep overburden layers that can effectively combine the downstream cofferdam of earth-rock dams with the downstream seepage monitoring structure, thereby significantly reducing investment costs and implementation difficulties.

[0008] The technical solution adopted to solve the above-mentioned technical problems is: a seepage collection and measurement early warning system for earth-rock dams on deep overburden foundations, including an earth-rock dam, a downstream cofferdam, and a construction diversion tunnel or an ecological water supply tunnel during construction. The seepage collection and measurement early warning system also includes at least a dam foundation seepage interception structure, a seepage collection and output structure, and a seepage measurement structure. The dam foundation seepage interception structure, extending along the height direction, is arranged sequentially along the width direction of the river channel at the center of the downstream cofferdam and in the overburden below it. The seepage collection and output structure is arranged between the earth-rock dam and the downstream cofferdam. The seepage measurement structure is arranged in the construction diversion tunnel or the ecological water supply tunnel during construction. The seepage collection and output structure is connected to the seepage measurement structure through a diversion tunnel arranged on the upstream side of the downstream cofferdam. The elevation of the bottom plate of the diversion tunnel is at least 0.5m lower than the lowest water level downstream of the earth-rock dam.

[0009] Furthermore, the seepage interception structure of the dam foundation includes at least a seepage barrier wall and a geomembrane. The vertically extending seepage barrier wall is arranged perpendicular to the water flow direction in the cover layer below the downstream cofferdam, and the vertically extending geomembrane is arranged perpendicular to the water flow direction at the center of the downstream cofferdam. The upper end of the seepage barrier wall is sealed to the lower end of the geomembrane. The preferred embodiment of the above scheme is that the dam foundation seepage interception structure also includes a grouting curtain, which extends along the length of the downstream cofferdam and is vertically arranged in the bedrock on both sides of the downstream cofferdam and below the seepage barrier; the grouting curtain is sealed and connected to the adjacent seepage barrier and the adjacent geomembrane. The grouting curtain extends vertically downwards 5m below the relatively impermeable layer of the bedrock, and the top elevation of the geomembrane is 0.5m higher than the downstream check water level of the dam.

[0010] Furthermore, the seepage collection and output structure also includes a dam foundation filter layer, a dam body transition layer, a dam foundation transition layer, and a rockfill weighted zone. The interconnected dam body transition layer and dam foundation transition layer are pressed onto the dam foundation filter layer. The dam foundation filter layer is pressed onto the overburden layer below the downstream side of the earth-rock dam. The rockfill weighted zone is arranged on the dam foundation transition layer upstream of the downstream cofferdam. The water diversion tunnel is arranged perpendicular to the water flow direction in the bedrock on the bank of the rockfill weighted zone, with one end connected to the rockfill weighted zone. Downstream earth-rock dam bodies are also pressed onto the transition layer of the dam body and the transition layer of the dam foundation. A dam seepage prevention system is also arranged in the earth-rock dam and the overburden layer below it.

[0011] The preferred embodiment of the above scheme is that the water diversion tunnel includes a water diversion tunnel body, a large rock filling section, a free drainage section, and a highly permeable concrete plug section. The large rock filling section, the free drainage section, and the highly permeable concrete plug section are arranged sequentially from the inside to the outside along the length of the water diversion tunnel body. The output end of the water diversion tunnel body is connected to the seepage measurement structure.

[0012] Furthermore, a filter layer is also covered in front of the large rock filling section. The water diversion tunnel body passes through Class IV, Class III and Class II surrounding rock in sequence along the direction perpendicular to the water flow. The large rock filling section is set in the water diversion tunnel body at the Class IV surrounding rock location. The free drainage section and the highly permeable concrete plug section are set in the water diversion tunnel body at the Class III and / or Class II surrounding rock locations. Lining layers are arranged on the tunnel walls at the Class III and Class II surrounding rock locations.

[0013] Furthermore, the seepage collection and measurement early warning system also includes a seepage flow meter and a safety early warning component. The seepage flow meter is arranged in the measuring weir inside the water-blocking mechanism, and the safety early warning component is arranged in the remote central monitoring room. The data line of the seepage flow meter is connected to the safety early warning component. During the seepage flow monitoring process, the safety early warning component issues a corresponding early warning signal based on the data obtained by the seepage flow meter and the set flow threshold.

[0014] The preferred method of the above scheme is, The seepage flow meter is a weir gauge. The flow threshold for issuing an early warning signal and the corresponding early warning signal type are calculated and set according to the following formulas. Q 黄 =Q 正 ×(1+10%), issue a yellow warning signal; Q 橙 =Q 正 ×(1+30%), issue an orange alert signal; Q 红 =Q 正 ×(1+80%), a red alert signal is issued; Among them, Q 正 This is the upper limit value set under normal seepage flow conditions.

[0015] Furthermore, the seepage collection and measurement early warning system also includes a high-definition monitoring camera. The high-definition monitoring camera is arranged on the wall of the construction diversion tunnel or the construction period ecological water supply tunnel above the water measuring weir, in accordance with the location of the water measuring weir. The data cable of the high-definition monitoring camera is connected to the display equipment in the remote central monitoring room at least. When the safety early warning component issues a yellow or higher alarm signal, the turbidity of the seepage obtained by the high-definition monitoring camera is used to determine the type of seepage stability risk with human intervention. The permeability coefficient of the highly permeable concrete plug section is 1×10⁻⁶. -1 cm / s, the end face of the large stone filling section adjacent to the free drainage section is an inclined slope with a slope ratio of 1:2. During the construction period, the elevation of the bottom plate of the ecological water supply tunnel is 20cm to 50cm lower than the elevation of the bottom plate of the water measurement tunnel.

[0016] The beneficial effects of this invention are as follows: The technical solution provided in this application comprehensively considers the seepage and measurement system of earth-rock dams. Based on existing earth-rock dams, downstream cofferdams, and construction diversion tunnels or construction-period ecological water supply tunnels, this application's seepage collection and measurement early warning system is constructed by adding a dam foundation seepage interception structure, a seepage collection and output structure, and a seepage measurement structure. The dam foundation seepage interception structure, extending along the height direction, is sequentially arranged along the width direction of the river channel at the center of the downstream cofferdam and in the overburden layer below it. The seepage collection and output structure is arranged between the earth-rock dam and the downstream cofferdam, and the seepage measurement structure is arranged in the construction diversion tunnel or construction-period ecological water supply tunnel. Then, the seepage collection and output structure is connected to the seepage measurement structure through a diversion tunnel arranged on the upstream side of the downstream cofferdam. At the same time, the elevation of the bottom plate of the diversion tunnel is at least 0.5m lower than the lowest water level downstream of the earth-rock dam. This effectively achieves the goal of rationally arranging the earth-rock dam seepage monitoring structure with the downstream construction cofferdam, construction diversion tunnel, or construction-period ecological water supply tunnel during its construction period. The seepage collection, measurement, and early warning system provided in this application, systematically planned during the early stages of engineering research or construction, integrates the construction of cofferdams, diversion tunnels, or ecological water supply tunnels in earth-rock dams to achieve seepage interception, collection, diversion, and measurement. This solves the problems of difficulty, time-consuming, and high investment associated with separately setting up downstream cofferdams and water measurement systems for earth-rock dams with thick overburden layers. It also addresses the challenges of modifying downstream cofferdams for water measurement, including high construction difficulty, high risk, and impact on the filling of counterweight bodies. Furthermore, the downstream cofferdam foundation seepage prevention system, combined with the dam's seepage interception system, improves the seepage prevention standard and enhances the seepage prevention effect of the cofferdam. Further improvements can link seepage monitoring with seepage safety early warning in earth-rock dams, enabling intelligent monitoring, facilitating timely detection of engineering problems, better monitoring of dam operation, and aiding in engineering management decisions. Attached Figure Description

[0017] Figure 1 This is a plan view of the seepage collection and measurement system for earth-rock dams with thick overburden layers according to the present invention. Figure 2 for Figure 1 AA section view; Figure 3 for Figure 1 BB cross-sectional view.

[0018] The markings in the diagram are as follows: 1. Earth-rock dam, 2. Construction diversion tunnel or construction period ecological water supply tunnel, 3. Downstream cofferdam, 4. Cover layer, 5. Water diversion tunnel, 6. Water retaining mechanism, 7. Water measuring weir, 8. Anti-seepage wall, 9. Geomembrane, 10. Dam foundation filter layer, 11. Dam body transition layer, 12. Dam foundation transition layer, 13. Rockfill weighted area, 14. Downstream side earth-rock dam body, 15. Large rockfill section, 16. Free drainage section, 17. Highly permeable concrete plug section, 18. Filter layer, 19. Class IV surrounding rock, 20. Class III surrounding rock, 21. Class II surrounding rock, 22. Lining layer, 23. Inclined slope. Detailed Implementation

[0019] like Figure 1 , Figure 2 as well as Figure 3This invention illustrates a seepage collection and measurement early warning system for earth-rock dams with deep overburden layers, which effectively combines the downstream cofferdam with a downstream seepage monitoring structure, thereby significantly reducing investment costs and implementation difficulty. The seepage collection and measurement early warning system includes an earth-rock dam 1, a downstream cofferdam 3, and a construction diversion tunnel or construction-period ecological water supply tunnel 2. The system further includes at least a dam foundation seepage interception structure, a seepage collection and output structure, and a seepage measurement structure. The dam foundation seepage interception structure, extending along the height direction, is sequentially arranged along the river width direction at the center of the downstream cofferdam 3 and in the overburden layer 4 below it. The seepage collection and output structure is arranged between the earth-rock dam 1 and the downstream cofferdam 3. The seepage measurement structure is arranged in the construction diversion tunnel or construction-period ecological water supply tunnel 2. The seepage collection and output structure is connected to the seepage measurement structure through a diversion tunnel 5 located upstream of the downstream cofferdam. The elevation of the bottom plate of the diversion tunnel is 0.5m lower than the lowest water level downstream of the earth-rock dam. The technical solution provided in this application comprehensively considers the seepage and measurement system of earth-rock dams. Based on the existing earth-rock dam, downstream cofferdam, and construction diversion tunnel or construction-period ecological water supply tunnel, it constructs the seepage collection and measurement early warning system by adding a seepage interception structure, a seepage collection and output structure, and a seepage measurement structure. The seepage interception structure extending along the height direction is sequentially arranged along the width direction of the river channel at the center of the downstream cofferdam and in the overburden layer below it. The seepage collection and output structure is arranged between the earth-rock dam and the downstream cofferdam, and the seepage measurement structure is arranged in the construction diversion tunnel or construction-period ecological water supply tunnel. Then, the seepage collection and output structure is connected to the seepage measurement structure through a diversion tunnel arranged on the upstream side of the downstream cofferdam. At the same time, the elevation of the bottom plate of the diversion tunnel is at least 0.5m lower than the lowest water level downstream of the earth-rock dam. This effectively achieves the goal of rationally arranging the seepage monitoring structure of the earth-rock dam with the downstream construction cofferdam, construction diversion tunnel, or construction-period ecological water supply tunnel during its construction period. The seepage collection and measurement early warning system provided in this application, in the early research or initial planning of the project, combines the use of cofferdams, diversion tunnels or ecological water supply tunnels in earth-rock dam construction to achieve seepage interception, collection, diversion and measurement of earth-rock dams. It solves the problems of difficulty, time-consuming and high investment in setting up and arranging the downstream cofferdam and water measurement system separately for earth-rock dams with thick overburden layers. It also solves the problems of high difficulty, high risk and impact on the filling of counterweight body when using downstream cofferdams to set up water measurement weirs. At the same time, the downstream cofferdam foundation seepage prevention system improves the seepage prevention standard by combining with the dam seepage interception system, and can also improve the seepage prevention effect of the cofferdam.

[0020] Accordingly, in order to adapt to the existing construction diversion tunnel or construction period ecological water supply tunnel 2 and downstream cofferdam 3 layout structure, the seepage measurement structure of this application includes a water-blocking mechanism 6 and a measuring weir 7. The water-blocking mechanism 6 is arranged sequentially along the water flow direction on the bottom plate of the construction diversion tunnel or construction period ecological water supply tunnel 2 on the side adjacent to the seepage collection and output structure. The measuring weir 7 is arranged in a place where the water flow is gentle downstream of the water conveyance channel formed by the water-blocking mechanism 6. In combination with the design concept of the measurement layout structure of this application, which integrates the existing temporarily constructed downstream cofferdam as part of the permanent structure, and in order to maximize the interception of seepage, the seepage interception structure of the dam foundation of this application includes at least a seepage barrier wall 8 and a geomembrane 9. The vertically extending seepage barrier wall 8 is arranged perpendicular to the water flow direction in the cover layer 4 below the downstream cofferdam 3, and the vertically extending geomembrane 9 is arranged perpendicular to the water flow direction at the center of the downstream cofferdam 3. The upper end of the seepage barrier wall 8 is sealed to the lower end of the geomembrane 9. The dam foundation seepage interception structure also includes a grouting curtain. The grouting curtain, which extends along the length of the downstream cofferdam 3, is vertically arranged in the bedrock on both sides of the downstream cofferdam 3 and below the seepage barrier wall 8. The grouting curtain is sealed and connected to the adjacent seepage barrier wall 8 and the adjacent geomembrane 9. The grouting curtain extends vertically downwards into the relatively impermeable layer of the bedrock by 5m. The top elevation of the geomembrane 9 is 0.5m higher than the downstream check water level of the dam.

[0021] Furthermore, as two other important improvements in this application, the seepage collection and output structure also includes a dam foundation filter layer 10, a dam body transition layer 11, a dam foundation transition layer 12, and a rockfill ballast zone 13. The interconnected dam body transition layer 11 and dam foundation transition layer 12 are pressed onto the dam foundation filter layer 10. The dam foundation filter layer 10 is pressed onto the overburden layer 4 below the downstream side of the earth-rock dam. The rockfill ballast zone 13 is arranged on the dam foundation transition layer 12 on the upstream side of the downstream cofferdam. The water diversion tunnel 5 is arranged perpendicular to the water flow direction in the bedrock on the bank of the rockfill ballast zone 13, with one end connected to the rockfill ballast zone. The downstream earth-rock dam body 14 is also pressed onto the dam body transition layer 11 and the dam foundation transition layer 12. A dam seepage prevention system is also arranged in the earth-rock dam 1 and the overburden layer 4 below it. More specifically, the water diversion tunnel 5 includes the water diversion tunnel body, the large rock filling section 15, the free drainage section 16, and the highly permeable concrete plug section 17. The large rock filling section 15, the free drainage section 16, and the highly permeable concrete plug section 17 are arranged sequentially from the inside to the outside along the length of the water diversion tunnel body. The output end of the water diversion tunnel body is connected to the seepage measurement structure. At this point, to facilitate the drainage of seepage water from the earth-rock dam, this application also includes a filter layer 18 covering the front of the large rockfill section 15. The water diversion tunnel body passes sequentially through Class IV surrounding rock 19, Class III surrounding rock 20, and Class II surrounding rock 21 along the direction perpendicular to the water flow. The large rockfill section 15 is located within the water diversion tunnel body at the location of Class IV surrounding rock 19. The free drainage section 16 and the highly permeable concrete plug section 17 are located within the water diversion tunnel body at the locations of Class III surrounding rock 20 and / or Class II surrounding rock 21. Lining layers 22 are arranged on the tunnel walls at the locations of Class III surrounding rock 20 and Class II surrounding rock 21. At this point, the permeability coefficient of the highly permeable concrete plug section 17 is 1×10⁻⁶. -1 cm / s, the end face of the large stone filling section 15 adjacent to the free drainage section 16 is an inclined slope 23, the slope ratio of the inclined slope is 1:2, and the elevation of the bottom plate of the ecological water supply tunnel during the construction period is 20cm to 50cm lower than the elevation of the bottom plate of the water measurement tunnel body.

[0022] Meanwhile, to provide early warning and risk assessment for seepage exceeding the specified flow rate, the seepage collection and measurement early warning system described in this application also includes a seepage flow meter and a safety early warning component. The seepage flow meter is located in the measuring weir inside the water-blocking mechanism 6 upstream of the measuring weir 7, and the safety early warning component is located in the remote central monitoring room. The data cable of the seepage flow meter is connected to the safety early warning component. During seepage flow monitoring, the safety early warning component issues a corresponding early warning signal based on the data acquired by the seepage flow meter and according to the set flow threshold. More specifically, the seepage flow meter is a measuring weir meter, and the flow threshold for issuing the early warning signal and the corresponding early warning signal type are calculated and set according to the following formulas. Q 黄 =Q 正 ×(1+10%), issue a yellow warning signal; Q橙 =Q 正 ×(1+30%), issue an orange alert signal; Q 红 =Q 正 ×(1+80%), a red alert signal is issued; Among them, Q 正 This is the upper limit value set under normal seepage flow conditions. When seepage exceeds the specified flow rate and carries a large amount of sediment, it indicates a potential risk of dam damage, such as piping. Therefore, the seepage collection and measurement early warning system described in this application also includes a high-definition monitoring camera. The high-definition monitoring camera is arranged on the wall of the construction diversion tunnel or the construction period ecological water supply tunnel above the water measuring weir 7, in accordance with the location of the water measuring weir. The data cable of the high-definition monitoring camera is connected to the display equipment in the remote central monitoring room at least once. When the safety early warning component issues an orange or higher alarm signal, the turbidity of the seepage obtained by the high-definition monitoring camera is used to determine the type of seepage stability risk with manual intervention.

[0023] In summary, the technical solution provided in this application also has the following advantages: The water diversion tunnel design of this invention makes full use of temporary facilities during dam construction. It forms a closed seepage interception structure downstream of the dam through the downstream cofferdam seepage prevention system and the bank rock mass. A water diversion tunnel is installed within the construction diversion tunnel or the construction-period ecological water supply tunnel to connect to the downstream rockfill ballast body, serving as a concentrated outlet for seepage downstream of the dam. After the water flow in the diversion tunnel is monitored by a measuring weir, it can be discharged downstream of the cofferdam via the construction diversion tunnel or the construction-period ecological water supply tunnel. The design is highly feasible and economical. While ensuring the accuracy of seepage monitoring over a thick overburden layer, it not only saves the investment and construction time required for adding new seepage interception facilities or excavating the downstream ballast body to construct a measuring weir on top of the cofferdam seepage prevention wall, but also reduces construction difficulty and achieves the scientific and rational utilization of resources.

[0024] Example 1 The technical problem to be solved by the present invention is to provide a construction method for a diversion tunnel of a deep overburden earth-rock dam that can fully integrate the downstream cofferdam and the downstream counterweight structure.

[0025] The technical solution adopted to solve the above-mentioned technical problems is: a construction method for a water diversion tunnel of a deep overburden earth-rock dam, including an automatic monitoring system for seepage volume of the earth-rock dam, which consists of a dam foundation seepage interception system, a seepage collection system, and a seepage measurement system.

[0026] The dam foundation seepage interception system utilizes the downstream cofferdam's seepage prevention system, consisting of a cutoff wall within the overburden layer, grouting curtains on both banks, and a geomembrane above the cutoff wall. The cutoff wall and grouting curtains on both banks are constructed first, followed by the connection structure between the geomembrane and the cutoff wall. The geomembrane construction is then completed as the cofferdam is layered and filled. The cofferdam is built on a deep overburden layer, and the bottom of the grouting curtains around the cutoff wall extends 5 meters into the relatively impermeable layer, forming a fully enclosed seepage prevention system. The top elevation of the geomembrane is 0.5 meters higher than the downstream check water level of the dam, ensuring that downstream river water will never backflow to the upstream side of the dam foundation seepage interception system, and will not affect the reliable operation of the seepage measurement system.

[0027] Earth-rock dams built on thick overburden consist of a seepage-proof core wall, a filter layer, a transition layer, a rockfill layer, and a weighting layer on the downstream side of the core wall, with the downstream cofferdam serving as part of the weighting layer.

[0028] The seepage collection system includes a transition layer, a dam foundation filter layer, a dam foundation transition layer, a rockfill weighted zone, and a water diversion tunnel.

[0029] The transition layer is located downstream of the filter layer and is constructed layer by layer, flush with the core wall and filter layer. The dam foundation filter layer is placed on the overburden layer, and the transition layer above it is constructed after the layered construction is completed. The rockfill weighted zone is constructed together with the weighted zone. Through the transition layer, the dam foundation filter layer, and the dam foundation transition layer, any possible seepage water from the dam body is channeled to the rockfill weighted zone.

[0030] A water diversion tunnel is set between the rockfill weighted area and the seepage measurement point. The seepage measurement point can be arranged in a location where there is less external interference and easy maintenance during the later operation of the project, such as a construction diversion tunnel or an ecological water supply tunnel during the construction period. This invention takes a construction diversion tunnel or an ecological water supply tunnel during the construction period as an example.

[0031] The bottom elevation of the diversion tunnel is at least 0.5m lower than the lowest water level downstream of the dam, ensuring that any seepage in the dam body and foundation can be discharged by gravity through the diversion tunnel, thus preventing the dam body's phreatic line from being raised due to the top elevation of the cofferdam seepage prevention system being higher than the downstream water level.

[0032] The diversion tunnel should be located, as far as possible, within the intact rock mass on the downstream bank of the dam's rockfill weighted area.

[0033] The diversion tunnel, heading towards the outlet, consists of a reverse filter layer, a large rock filling area, a free drainage area, and a highly permeable concrete plug section.

[0034] First, the diversion tunnel will be excavated. Sections in Class IV surrounding rock will not be lined to allow seepage water to enter the diversion tunnel. Large rockfill areas will be constructed within a certain range of the Class IV surrounding rock section and the rockfill weighted area at the tunnel face. These areas will be densely packed with hard, fresh rock blocks. A filter layer will be constructed on the surface of the large rockfill area to allow seepage water within the rockfill weighted area to flow effectively and persistently into the drainage tunnel. The weighting above the filter layer can be added as needed; therefore, the diversion tunnel will not affect the overall project schedule. The slope ratio of the fill outside the diversion tunnel in the large rockfill area will be 1:2.

[0035] For Class II and III surrounding rock sections, the diversion tunnels are free drainage zones and are lined with concrete to prevent leakage from affecting the accuracy of dam seepage monitoring.

[0036] The section near the construction diversion tunnel or the ecological water supply tunnel during construction is a highly permeable concrete end cap. Its length is determined based on the stability requirements of the sidewall during flow through the construction diversion tunnel or the ecological water supply tunnel during construction, and its permeability coefficient is 1×10⁻⁶. -1 The flow rate is cm / s, comparable to that of riprap, and it can serve as a gravity-flow drainage system.

[0037] The slope of the bottom slab of the diversion tunnel toward the construction diversion tunnel or the construction period ecological water supply tunnel shall be 0.5%. The elevation of the bottom slab of the construction diversion tunnel or the construction period ecological water supply tunnel shall be 20cm to 50cm lower than the elevation of the bottom slab of the diversion tunnel, so as to ensure that the seepage water in the diversion tunnel can be discharged to the downstream of the cofferdam through the construction diversion tunnel or the construction period ecological water supply tunnel.

[0038] The seepage measurement system is installed near the sidewall of the construction diversion tunnel or the ecological water supply tunnel during construction. After the construction diversion tunnel or the ecological water supply tunnel ceases to function and the plugs near the dam curtain line are sealed, the corresponding lining sidewalls of the construction diversion tunnel or the ecological water supply tunnel during construction are removed. A water-retaining structure is installed on the bottom slab of the construction diversion tunnel or the ecological water supply tunnel on the side of the diversion tunnel to guide the water flow. Then, a measuring weir is installed slightly downstream where the water flow is smoother. The measuring weir installed in this way is free from external interference, has a good working environment, and can be equipped with an automatic measurement system. It can be integrated into the intelligent management system of the project, enabling real-time monitoring of dam seepage during daily operation.

[0039] The seepage measurement and early warning system comprises a seepage measurement system and a safety early warning system, integrated into the engineering intelligent monitoring system. The measurement items mainly include the seepage flow rate and seepage turbidity status captured by cameras at each monitoring time, as well as changes in monitoring items at adjacent monitoring times. The seepage measurement system feeds the monitoring results back to the monitoring system center in real time and automatically issues corresponding safety early warning signals based on the relationship between the monitored values ​​and the set safety thresholds, providing a reference for engineering management and decision-making.

[0040] The seepage measurement system includes a measuring weir and an image acquisition device. The seepage flow rate is measured by a weir gauge installed in the measuring weir. The measurement is automatic, and the data can be directly transmitted to the safety early warning system of the dam monitoring center. The image acquisition device captures images of the seepage turbidity in real time, and the images are directly transmitted to the dam monitoring center.

[0041] After receiving seepage flow monitoring data, the safety early warning system displays corresponding early warning signals based on manually set flow thresholds. Different early warning signals correspond to different colored indicator lights. The safety early warning system employs three levels of control measures: yellow, orange, and red. No early warning signal indicates that the project is operating normally, meaning no safety risks have been detected. The presence of any level of early warning signal indicates an abnormality in the project's operation, suggesting varying degrees of safety risks.

[0042] Earth-rock dam projects are usually impounded in stages until the water level reaches the normal impoundment level. The seepage flow and its variation patterns of the dam differ significantly between the impoundment process and the water level maintenance stage. Therefore, the thresholds for the above-mentioned safety warnings at each level are set separately for the impoundment stage and the water level maintenance stage.

[0043] Meanwhile, the changes in seepage flow during the water storage stage are more indicative of the operational status of the project and help to identify problems in a timely manner, thus they deserve more attention. However, after the seepage flow stabilizes during the water level maintenance stage, the change is usually very small. Therefore, the monitoring frequencies for seepage flow during the water storage stage and the water level maintenance stage are set separately.

[0044] During the water storage phase, monitoring is conducted twice daily; during the water level maintenance phase, monitoring is conducted once weekly; and the reservoir water level is monitored twice daily, with each monitoring session taking place in the morning or at 8:00 PM. When an early warning signal is issued, the monitoring frequency for yellow, orange, and red warnings increases to once every 30 minutes, once every 20 minutes, and once every 10 minutes, respectively. After the warning is lifted, the monitoring frequency returns to normal.

[0045] Whether a safety warning is issued is controlled by the monitoring values ​​of seepage flow and seepage flow change. That is, when the seepage flow or seepage flow change reaches a certain threshold, a corresponding warning will be issued.

[0046] The method for determining the seepage flow warning threshold during the water level maintenance phase is as follows: First, based on the seepage flow obtained from three-dimensional seepage calculation and analysis, and after reasonable correction by combining engineering analogy and engineering experience, determine the upper limit value Q of the normal seepage flow at this water level under normal operating conditions. 正 Secondly, determine the thresholds for each level of warning signal, with the yellow warning threshold Q. 黄 =Q 正 × (1+10%), Orange alert threshold Q 橙 =Q 正 × (1+30%), Red Alert Threshold Q 红 =Q正 × (1+80%). The method for determining the warning threshold for changes in seepage flow is as follows: when the change in seepage flow between two adjacent monitoring times is greater than 15%, 30%, and 50%, the warnings are respectively yellow, orange, and red.

[0047] The method for determining the seepage flow warning threshold during the water storage stage is as follows: First, determine the upper limit value Q of the normal seepage flow corresponding to the initial water level and the target water level during the water storage stage, following the method described above for the water level maintenance stage. 正 Secondly, according to Darcy's law of seepage, when the seepage path is the same, the flow rate is linearly related to the water level difference. Therefore, the seepage flow rate corresponding to each water level during the water storage process is approximately determined by linear interpolation. Finally, the warning thresholds for each water level during the water level rise in the water storage stage are calculated using the method for the water level maintenance stage. The method for determining the warning threshold for seepage flow rate change is as follows: when the seepage flow rate change is greater than 30%, 50%, and 80% at two adjacent monitoring times, it is respectively a yellow warning, an orange warning, and a red warning.

[0048] The turbidity of the seepage water is determined manually, and the overall operational status of the project is assessed in conjunction with safety warnings. Clear seepage water, free of sediment, is the ideal state. During the initial impoundment of the dam to its normal impoundment level, the seepage water is relatively turbid in the early stages, and if significant sediment is being carried out, the frequency of video recording should be increased. If the seepage water remains turbid or the turbidity worsens for more than 1-2 hours, a safety warning should be issued manually as needed. If the seepage water gradually becomes clear and the sediment content gradually decreases, it is considered to be operating normally. During the water level maintenance phase, clear seepage water without sediment, or with a small amount of sediment that gradually decreases, is considered normal. If the seepage water changes from clear to turbid or the sediment content increases, an immediate safety warning should be issued, the frequency of video recording should be increased, and close monitoring of changes in the seepage water status is essential.

Claims

1. A seepage collection and measurement early warning system for earth-rock dams on deep overburden foundations, comprising a rockfill dam (1), a downstream cofferdam (3), and a construction diversion tunnel or an ecological water supply tunnel during construction (2), characterized in that: The seepage collection and measurement early warning system includes at least a dam foundation seepage interception structure, a seepage collection and output structure, and a seepage measurement structure. The dam foundation seepage interception structure, which extends along the height direction, is arranged sequentially along the width direction of the river channel at the center of the downstream cofferdam (3) and in the cover layer (4) below it. The seepage collection and output structure is arranged between the rockfill dam (1) and the downstream cofferdam (3). The seepage measurement structure is arranged in the construction diversion tunnel or the construction period ecological water supply tunnel (2). The seepage collection and output structure is connected to the seepage measurement structure through a water diversion tunnel (5) arranged on the upstream side of the downstream cofferdam. The elevation of the bottom plate of the water diversion tunnel is at least 0.5m lower than the lowest water level downstream of the rockfill dam.

2. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 1, characterized in that: The seepage measurement structure includes a water-blocking mechanism (6) and a water-measuring weir (7). The water-blocking mechanism (6) is arranged sequentially along the water flow direction on the bottom plate of the construction diversion tunnel or the construction period ecological water supply tunnel (2) on the side of the seepage collection and output structure. The water-measuring weir (7) is arranged on the downstream side of the water conveyance channel formed by the water-blocking mechanism (6) where the water flow is gentle.

3. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 2, characterized in that: The seepage interception structure of the dam foundation includes at least a seepage barrier wall (8) and a geomembrane (9). The seepage barrier wall (8), which extends vertically, is arranged perpendicular to the direction of water flow in the cover layer (4) below the downstream cofferdam (3). The geomembrane (9), which extends vertically, is arranged perpendicular to the direction of water flow at the center of the downstream cofferdam (3). The upper end of the seepage barrier wall (8) is sealed to the lower end of the geomembrane (9).

4. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 3, characterized in that: The dam foundation seepage interception structure also includes a grouting curtain. The grouting curtain, which extends along the length of the downstream cofferdam (3), is vertically arranged in the bedrock on both sides of the downstream cofferdam (3) and below the seepage barrier (8). The grouting curtain is sealed to the adjacent seepage barrier (8) and the adjacent geomembrane (9). The grouting curtain extends vertically downwards 5m below the relatively impermeable layer of the bedrock, and the top elevation of the geomembrane (9) is 0.5m higher than the downstream check water level of the dam.

5. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 4, characterized in that: The seepage collection and output structure also includes a dam foundation filter layer (10), a dam body transition layer (11), a dam foundation transition layer (12), and a rockfill weighted zone (13). The interconnected dam body transition layer (11) and dam foundation transition layer (12) are pressed onto the dam foundation filter layer (10). The dam foundation filter layer (10) is pressed onto the overburden layer (4) below the downstream side of the rockfill dam. The rockfill weighted zone (13) is arranged on the dam foundation transition layer (12) on the upstream side of the downstream cofferdam. The water diversion tunnel (5) is arranged perpendicular to the water flow direction in the bedrock on the bank of the rockfill weighted zone (13), with one end connected to the rockfill weighted zone. Downstream rockfill dam body (14) is also pressed onto the transition layer (11) of the dam body and the transition layer (12) of the dam foundation. A dam seepage prevention system is also arranged in the rockfill dam (1) and the overburden layer (4) below it.

6. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 5, characterized in that: The water diversion tunnel (5) includes the water diversion tunnel body, the large rock filling section (15), the free drainage section (16), and the highly permeable concrete plug section (17). The large rock filling section (15), the free drainage section (16), and the highly permeable concrete plug section (17) are arranged sequentially from the inside to the outside along the length of the water diversion tunnel body. The output end of the water diversion tunnel body is connected to the seepage measurement structure.

7. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 6, characterized in that: A filter layer (18) is also covered in front of the large rock filling section (15). The water diversion tunnel body passes through Class IV surrounding rock (19), Class III surrounding rock (20) and Class II surrounding rock (21) in sequence along the vertical direction of water flow. The large rock filling section (15) is set in the water diversion tunnel body at the position of Class IV surrounding rock (19). The free drainage section (16) and the highly permeable concrete plug section (17) are set in the water diversion tunnel body at the positions of Class III surrounding rock (20) and / or Class II surrounding rock (21). Lining layers (22) are arranged on the tunnel walls at the positions of Class III surrounding rock (20) and Class II surrounding rock (21).

8. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 6, characterized in that: The seepage collection and measurement early warning system also includes a seepage flow meter and a safety early warning component. The seepage flow meter is arranged in the water measuring weir (7) inside the water-blocking mechanism (6), and the safety early warning component is arranged in the remote central monitoring room. The data line of the seepage flow meter is connected to the safety early warning component. During the seepage flow monitoring process, the safety early warning component issues a corresponding early warning signal based on the data obtained by the seepage flow meter according to the set flow threshold.

9. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 8, characterized in that: The seepage flow meter is a weir gauge. The flow threshold for issuing an early warning signal and the corresponding early warning signal type are calculated and set according to the following formulas. Q 黄 =Q 正 ×(1+10%), issue a yellow warning signal; Q 橙 =Q 正 ×(1+30%), issue an orange alert signal; Q 红 =Q 正 ×(1+80%), a red alert signal is issued; Among them, Q 正 This is the upper limit value set under normal seepage flow conditions.

10. The seepage collection, measurement, and early warning system for earth-rock dams on deep overburden foundations according to claim 9, characterized in that: The aforementioned seepage collection and measurement early warning system also includes a high-definition monitoring camera. The high-definition monitoring camera is arranged on the construction diversion tunnel wall or the construction period ecological water supply tunnel wall above the water measuring weir (7) in accordance with the location of the water measuring weir. The data line of the high-definition monitoring camera is at least connected to the display equipment in the remote central monitoring room. When the safety early warning component issues a yellow or higher alarm signal, the turbidity of the seepage obtained by the high-definition monitoring camera is used to determine the type of seepage stability risk with the participation of a person. The permeability coefficient of the highly permeable concrete plug section (17) is 1×10⁻⁶. -1 cm / s, the end face of the large stone filling section (15) adjacent to the free drainage section (16) is an inclined slope (23), the slope ratio of the inclined slope is 1:2, and the elevation of the bottom plate of the ecological water supply tunnel during the construction period is 20cm to 50cm lower than the elevation of the bottom plate of the water diversion tunnel body.

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