Reverse drainage structure of concrete face rockfill dam

Abstract

This invention relates to the field of drainage structure technology for water conservancy and hydropower projects, specifically to a reverse drainage structure for a concrete-faced rockfill dam, comprising an upstream drainage unit and a downstream drainage unit. The upstream drainage unit includes a drainage well and a horizontal reverse drainage pipe located on the upstream side of the dam body. The downstream drainage unit includes multiple drainage wells located on the upstream and downstream sides of the water-measuring weir anti-seepage wall on the downstream side of the dam body. The outer periphery of the drainage wells is filled with a reverse filter layer. This application adopts a structural form in which drainage wells are arranged in sections on the upstream and downstream sides of the water-measuring weir anti-seepage wall, which can eliminate the seepage blind zone formed by the anti-seepage wall and balance the reverse water pressure inside the dam throughout the entire area. At the same time, with the help of a multi-ring sealing structure, it is beneficial to avoid the disturbance of the water-stopping components by concrete vibration, effectively eliminate the risk of toe slab leakage and panel cracking, and significantly improve the seepage prevention safety of the dam body during construction. It can also cooperate with water level adaptive pumping and phased dynamic control to ensure the continuous effectiveness of the drainage channel throughout the entire construction cycle.

Description

Technical Field

[0001] This invention relates to the field of drainage structure technology for water conservancy and hydropower projects, specifically to a reverse drainage structure for a concrete-faced rockfill dam. Background Technology

[0002] Existing conventional reverse drainage schemes for ultra-high rockfill dams typically involve constructing a weir or cutoff wall downstream to block seepage. However, current methods only include vertical shafts upstream of the cutoff wall, leaving no downstream drainage points and creating a seepage blind zone. Excessive reverse water pressure can lead to high dam moisture content, significant settlement, and panel collapse. Furthermore, the reservoir's fissure water is weakly corrosive, requiring construction across multiple flood seasons. Traditional galvanized steel pipes lack sufficient corrosion resistance, and single-layer filters are easily clogged by silt during floods, resulting in poor long-term drainage stability. The drainage pipes are positioned above copper waterstops, making them susceptible to deformation during concrete vibration, potentially causing toe slab leakage and through-cracks in the panels. Additionally, the existing downstream vertical shafts are located below the dam's weighted area filling elevation, rendering them ineffective after dam construction. Conventional blasting excavation disturbs the dam foundation rock, generating numerous seepage fissures and further exacerbating the reverse seepage problem within the dam.

[0003] In summary, current ultra-high concrete-faced rockfill dam projects lack an integrated reverse drainage system that adapts to the seepage conditions separated by the anti-seepage wall, takes into account long-term anti-siltation and anti-corrosion, avoids damage to the water-stopping structure, and matches the dam body's layered filling sequence. Traditional drainage structures are difficult to balance the reverse water pressure throughout the dam area, and construction leakage, pipeline blockage, and corrosion are frequent occurrences. In view of this, we propose a reverse drainage structure for concrete-faced rockfill dams. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings mentioned in the background section and provide a reverse drainage structure for a concrete-faced rockfill dam.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A reverse drainage structure for a concrete-faced rockfill dam includes an upstream drainage unit and a downstream drainage unit; The upstream drainage unit includes a drainage well and a horizontal reverse drainage pipe installed on the upstream side of the dam body. The drainage well is arranged on the bedrock and its top extends through the dam body to the upstream panel. One end of the horizontal reverse drainage pipe is connected to the drainage well, and the other end extends through the dam foundation and toe plate to the water collection area at the front edge of the toe plate. The horizontal reverse drainage pipe is arranged below the water-stop copper sheet when it passes through the toe plate. The downstream drainage unit includes multiple drainage wells installed on the upstream and downstream sides of the seepage prevention wall on the downstream side of the dam body. The drainage wells located on the upstream side of the seepage prevention wall are arranged on the bedrock and their tops extend to the downstream slope of the dam. The drainage well located downstream of the cutoff wall is arranged on the bedrock, and its top elevation is lower than that of the drainage well upstream of the cutoff wall. The horizontal reverse drain pipe is made of stainless steel and is wrapped with a double layer of stainless steel filter screen. The outer periphery of the drainage well is filled with a reverse filter packing layer.

[0006] Preferably, the upstream drainage unit includes at least two drainage wells spaced apart on the upstream side of the dam body, and at least 12 horizontal reverse drainage pipes spaced apart along the dam axis. The downstream drainage unit includes at least two drainage wells respectively arranged on the upstream and downstream sides of the seepage prevention wall of the measuring weir.

[0007] Preferably, the drainage well includes a reinforcing cage and a fill layer constructed outside the reinforcing cage; The reinforcing cage is longitudinally lapped and welded together. The filter filler layer is provided with a graded crushed stone layer and a transition layer in sequence along the outer wall of the reinforcing cage. The inner diameter of the graded crushed stone layer corresponds to the outer diameter of the reinforcing cage. The transition layer covers the outer side of the graded crushed stone layer.

[0008] Preferably, in the downstream drainage unit, the reinforcement ratio of the steel cage of the drainage well located on the upstream side of the water-measuring weir anti-seepage wall is greater than the reinforcement ratio of the steel cage of the drainage well located on the downstream side of the water-measuring weir anti-seepage wall. The reinforcement ratio of the steel cage of the drainage well in the upstream drainage unit is less than that of the steel cage of the drainage well located on the upstream side of the seepage prevention wall of the downstream drainage unit.

[0009] Preferably, the double-layer stainless steel filter screen includes an inner filter screen and an outer filter screen sleeved on the outside of the inner filter screen; The mesh size of the inner filter is smaller than that of the outer filter, and the inner and outer filters are respectively tied and fixed to the outside of the horizontal reverse drain pipe.

[0010] Preferably, the horizontal reverse drainage pipe is provided with a plurality of spaced water-stop rings along its length, and each water-stop ring is respectively provided at the corner of the horizontal reverse drainage pipe and on the pipe section between adjacent corners. The outer surface of the water-stop ring is coated with a sealant layer.

[0011] Preferably, the upstream drainage unit further includes a concrete retaining wall, which is disposed on the upstream side of the toe slab, and a downstream water collection pool is formed between the concrete retaining wall and the toe slab; The outlet end of the horizontal reverse drainage pipe extends into the downstream water collection pool of the retaining wall. An upstream water collection pool is formed on the upstream side of the concrete retaining wall. A submersible pump is installed between the downstream water collection pool and the upstream water collection pool of the retaining wall.

[0012] Preferably, the concrete retaining wall is a gravity-type water-retaining structure with multiple rows of reinforcing bars anchored at its bottom; The lower end of the reinforcing bar is anchored into the bedrock of the riverbed foundation, and the upper end is buried in the concrete retaining wall. The two sides of the concrete retaining wall are respectively connected to the retaining wall on the left bank slope and the outside of the road in the lower foundation pit.

[0013] Preferably, it also includes a centrifugal pump platform located beside the road in the foundation pit below the back slope of the upstream cofferdam, and a concrete masonry retaining wall and underwater burlap concrete protection are provided on the downstream side slope of the centrifugal pump platform. The concrete masonry retaining wall is located above the underwater burlap concrete protection and the two are connected in the slope height direction. The centrifugal pump platform is equipped with a safety guardrail at its edge.

[0014] Preferably, each of the drainage wells is equipped with a deep well pump and a water level monitoring device. The signal output terminal of the water level monitoring device is connected to the control terminal of the deep well pump. The drainage outlet of the deep well pump is connected to a drainage pipeline, which extends upward along the well shaft to the outside of the well opening. The wellhead of the drainage well is covered with a grid-shaped protective cover, and an inspection ladder is fixedly installed on the inner wall of the well shaft.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. The reverse drainage structure of the concrete-faced rockfill dam adopts a structure in which drainage wells are arranged in sections upstream and downstream of the water-measuring weir anti-seepage wall. This can eliminate the seepage blind zone formed by the anti-seepage wall and balance the reverse water pressure in the dam throughout the entire area. At the same time, the horizontal reverse drainage pipe is arranged at a low position below the water-stop copper sheet, and with the multi-water-stop ring sealing structure, it is beneficial to avoid the water-stop components being disturbed by the concrete vibration, effectively eliminate the risk of toe plate leakage and panel cracking, and significantly improve the seepage prevention safety during the dam construction period. 2. This application uses stainless steel pipes combined with a double-layer graded filter screen and a well perimeter graded reverse filter structure, which can combine excellent corrosion resistance and anti-clogging ability, and can adapt to weakly corrosive seepage environments and long-term construction needs across multiple flood seasons; at the same time, the elevation of the drainage well is matched with the dam filling sequence, which can cooperate with water level adaptive pumping and phased dynamic control to ensure the continuous effectiveness of the drainage channel throughout the construction cycle, and improve construction coordination and operation and maintenance economy. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a diagram showing the upstream reverse drainage structure layout of the present invention; Figure 2 This is a cross-sectional layout diagram of the upstream drainage and collection facilities of the present invention; Figure 3 This is a plan view of the downstream drainage wells of the present invention; Figure 4 This is a cross-sectional view of the downstream drainage well of the present invention.

[0017] The meanings of the labels in the diagram are as follows: 1. Centrifugal pump platform; 2. Safety guardrail; 3. Concrete masonry retaining wall; 4. Upstream sump of water for retaining wall; 5. Underwater burlap concrete protection; 6. Concrete retaining wall; 7. Reinforcing bars; 8. Riverbed foundation; 9. Downstream sump of water for retaining wall; 10. Toe slab; 11. Concrete panel; 13. Drainage well. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figures 1-4 The present invention will describe the above technical solution in detail through the following embodiments: This embodiment of the concrete-faced rockfill dam reverse drainage structure takes an ultra-high concrete-faced rockfill dam as the application scenario. It addresses the engineering pain points of high reverse seepage pressure in the dam foundation during the dam filling period and the construction period of the concrete face 11, the obstruction of seepage path by the water measuring weir anti-seepage wall, the easy siltation and corrosion of traditional drainage structures, and the easy damage to the toe slab waterstop structure. It provides a reverse drainage structure with zoned layout, graded drainage, and long-term durability. The overall structure is based on the riverbed foundation 8 and mainly consists of an upstream drainage unit, a downstream zoned drainage unit, a two-stage water collection and pumping system, and a graded reverse filtration protection system. With the water level adaptive control logic, it realizes the orderly drainage and pressure control of reverse seepage in the entire dam section, and avoids the upstream cushion layer being destroyed by seepage and the concrete face 11 being lifted and cracked.

[0020] Specifically, in this embodiment, the upstream drainage unit is located on the upstream side of the dam body, including at least two drainage wells 13 and 12 horizontal reverse drainage pipes. The two drainage wells 13 are located on the left and right banks respectively along the dam axis. The bottom of the drainage well 13 is anchored in the fresh bedrock of the dam foundation, with a bottom elevation of 2471m. The well body extends vertically along the dam body filling height, with a top elevation of 2509m, meeting the requirements for the drainage well opening to be exposed during the panel pouring period and before the dam front cover filling. The drainage well 13 uses a vertical steel cage as the supporting frame for the well body. The steel cage is made of C25@100mm steel bars, prefabricated in sections of 9m length, and connected by double-sided lap welding after on-site hoisting and docking. The weld length is not less than 5 times the steel bar diameter. When single-sided welding is used in parts restricted by construction conditions, the weld length is not less than 10 times the steel bar diameter to ensure the overall structural strength of the well body.

[0021] In this embodiment, the horizontal reverse drainage pipes are made of DN300×8mm stainless steel pipes, arranged at equal intervals along the dam axis, and are embedded in the concrete structure of the toe slab 10. The downstream end of each horizontal reverse drainage pipe is connected to the lower part of the corresponding drainage well 13 and communicates with the water collection space inside the well. The upstream end extends upstream along the dam foundation slope, passes through the upstream end face of the toe slab 10 and extends into the water collection area. In this embodiment, the horizontal reverse drainage pipes are arranged below the water-stop copper sheet inside the toe slab, avoiding the installation and vibration operation space of the water-stop copper sheet, and avoiding squeezing and disturbing the water-stop copper sheet during the concrete pouring and vibration of the toe slab. From the spatial layout, the potential leakage of the toe slab caused by the deformation of the water-stop structure is eliminated.

[0022] Three water-stop rings are installed along the length of each horizontal reverse drainage pipe, and are fixed at the two corners of the pipe and the middle of the inclined pipe section respectively. The water-stop rings are fully welded to the outer wall of the pipe, and the weld is full and free of air holes. After welding, sealant is evenly applied to the outer surface of the water-stop rings to effectively extend the seepage path at the toe plate and greatly improve the anti-seepage and sealing performance of the toe plate at the pipe penetration position.

[0023] like Figure 1 , Figure 2 As shown, a concrete retaining wall 6 is installed on the upstream side of the toe slab 10. The concrete retaining wall 6 is a gravity-type water-retaining structure, cast with C20 concrete, with a top elevation of 2478m, a top width of 0.3m, and a back slope ratio of 1:0.2. Two rows of reinforcing bars 7 are installed at the bottom of the concrete retaining wall 6. The lower end of the reinforcing bars 7 is anchored into the bedrock of the riverbed foundation 8 to a depth of 1.0m, and the upper end is buried inside the weir body of the concrete retaining wall 6. The rows are arranged at a spacing of 0.5m × 0.5m to achieve reliable anchoring between the weir body and the bedrock. The left and right sides of the concrete retaining wall 6 are connected to the left bank slope and the outer retaining wall of the road in the lower foundation pit, respectively, forming a closed water-retaining boundary.

[0024] The area between the upstream end face of the concrete retaining wall 6 and the toe slab 10 forms the downstream collection pool 9. The bedrock at the bottom of the downstream collection pool 9 is trimmed to an elevation of 2473m using a rock-breaking head to create a smooth water collection space. The upstream outlets of all horizontal reverse drainage pipes extend into the downstream collection pool 9. Reverse seepage water from inside the dam flows by gravity through the horizontal drainage pipes into this collection pool for temporary storage. The upstream area of ​​the concrete retaining wall 6 utilizes the natural topography of the left bank to form the upstream collection pool 4. Submersible pump sets are installed in the downstream collection pool 9 to pump the collected water into the upstream collection pool 4 for transfer, achieving the first-stage pumping and lifting.

[0025] like Figure 2 As shown, a centrifugal pump platform 1 is set up at the bank slope platform with an elevation of 2483m on the left bank of the dam site. The centrifugal pump platform 1 is made of C25 concrete with a hardening thickness of 30cm, serving as the installation and operation platform for the upstream secondary pumping equipment. Safety guardrails 2 are installed around the edge of the free side of the centrifugal pump platform 1 to provide safety protection for operation and maintenance personnel working near the edge. The slope downstream of the centrifugal pump platform 1 adopts a stepped protection structure: the slope surface above the elevation of 2478m is built with a concrete masonry retaining wall 3, and the slope surface below the elevation of 2478m is laid with underwater burlap concrete protection 5. The concrete masonry retaining wall 3 and the underwater burlap concrete protection 5 are connected and arranged along the slope height direction to jointly protect the slope soil from water erosion and prevent slope collapse from causing siltation in the collection pool and damage to drainage facilities.

[0026] The water accumulated in the upstream collection pool 4 of the retaining wall is pumped to the secondary pumping station behind the upstream cofferdam by the centrifugal pump group on the centrifugal pump platform 1, and finally discharged into the water area, forming a four-level gradient pumping path of "horizontal pipe gravity flow - downstream collection pool transfer - upstream collection pool lifting - centrifugal pump discharge", which is adapted to the seepage field distribution formed by the elevation difference between the upstream and downstream of the dam foundation.

[0027] The downstream drainage unit is arranged on both sides of the anti-seepage wall of the downstream weir corresponding to the dam. Drainage wells 13 are set on the upstream and downstream sides of the anti-seepage wall to eliminate the downstream seepage blind zone formed by the anti-seepage wall. Among them, two drainage wells 13 are arranged along the 0+355 section of the dam on the upstream side of the anti-seepage wall. The bottom elevation of the well is 2478m and the top elevation of the well is 2557m, which is higher than the filling elevation of the downstream pressure zone of the dam body. This avoids the dam filling operation from burying the well opening and ensures that the drainage channel remains unobstructed throughout the entire construction period. The steel cage of the drainage well 13 on this side is made of C32@100mm steel bars, and the reinforcement ratio is higher than that of the upstream drainage well, which is suitable for the greater soil lateral pressure and seepage pressure on the upstream side of the anti-seepage wall.

[0028] In this embodiment, two drainage wells 13 are arranged along the 0+393 section of the dam on the downstream side of the anti-seepage wall. The bottom elevation of the wells is 2481m and the top elevation is 2548m, which is adapted to the dam filling height and seepage field distribution on the downstream side. The reinforcement cage of the drainage well 13 is made of C25@100mm steel bars. The reinforcement scheme is optimized while meeting the structural strength requirements, achieving differentiated economic design. Each downstream drainage well 13 is equipped with two deep well pumps, arranged in a one-in-use and one-out-of-charge configuration. The flow rate of a single pump is 400m³ / h and the head is 85m, which meets the pumping requirements under high-flow seepage conditions. The downstream drainage pipeline is dynamically relocated according to the filling progress of the dam's ballast zone. After the ballast zone is filled, the drainage pipeline will be finally connected to the drainage ditch on the mountainside of the downstream access road, guiding the seepage to the outside of the downstream cofferdam.

[0029] In this embodiment, all drainage wells 13 and horizontal reverse drainage pipes are equipped with a graded reverse filtration protection system to achieve step-by-step filtration of seepage and prevent the loss of fine particles and pipe blockage. For drainage wells 13, the outer side of the well body is filled with a graded crushed stone layer and a transition layer from the inside to the outside: a 50cm thick layer of graded crushed stone is filled close to the outside of the reinforcing cage. The graded crushed stone is artificially mixed and formed by mixing large, medium and small stones to form a continuous grade. A 1m wide transition layer is filled outside the graded crushed stone. The maximum particle size of the transition material meets the requirements of the dam filling zoning. The filling process uses a small hydraulic plate rammer for static pressure compaction to avoid excessive compaction load causing deformation of the reinforcing cage. A 2m thick reverse filter material layer is pre-laid at the bottom of the well to receive the seepage water flow from the bottom of the well and prevent bedrock weathering particles from entering the well with the water flow.

[0030] For horizontal reverse drainage pipes, the outer wall of the pipe is wrapped with a double layer of stainless steel filter mesh, forming a graded filtration structure: the inner filter mesh has a mesh size of 1mm×1mm, and the outer filter mesh has a mesh size of 5mm×5mm. Both filter meshes are fixed to the outer wall of the pipe with fine lead wire. In the section of the pipe corresponding to the dam cushion layer, a geotextile filter layer is added outside the filter mesh to further intercept fine particles of silt. Through graded filtration from coarse to fine, particulate impurities in the dam filling material are intercepted layer by layer, avoiding clogging of the pipe inlet hole caused by high sand content seepage during the flood season. At the same time, the stainless steel material can resist the erosion of weakly corrosive fissure water in the reservoir area, greatly improving the long-term service life of the drainage structure and meeting the drainage needs of long-term construction across multiple flood seasons.

[0031] Before constructing drainage well 13, pre-splitting blasting and trimming of the dam foundation is required. For the upstream and downstream dam foundations of drainage well 13, down-the-hole drilling is used to drill holes and trim them to the corresponding elevation according to the design slope ratio of 1:1. The blasting operation adopts pre-splitting blasting technology, with pre-splitting holes laid along the designed slope surface at a spacing of 1.0m. Emulsion explosives with decoupled charges are used, and the explosive cartridges are fixed by binding with bamboo strips. Buffer holes and main blasting holes are laid inside the slope, with a row spacing of 2.5m×2.0m between buffer holes and 3.5m×2.5m between main blasting holes, using a continuous charge structure. The blasting is initiated by electronic digital detonators, and the amount of explosives used in each stage is strictly controlled to minimize the disturbance of blasting vibration to the surrounding rock of the dam foundation, avoid secondary seepage fissures caused by conventional blasting, and reduce the amount of reverse seepage replenishment of the dam foundation from the source.

[0032] Each drainage well 13 is equipped with an automatic water level monitoring device. The signal output terminal of the water level monitoring device is electrically connected to the control unit of the corresponding deep well pump and submersible pump to form a water level adaptive pumping system. The system presets a water level control threshold. When the water level in the well is higher than the upper threshold, the pump will automatically start pumping. When the water level drops to the lower threshold, the pump will automatically stop operating, realizing unattended intelligent drainage management and reducing the energy consumption of the equipment during idling.

[0033] In accordance with the dam construction schedule, this structure implements a phased differentiated water level control strategy: Before the panel pouring, the upstream side uses a combination of gravity flow through horizontal reverse drainage pipes and pumping from drainage well 13 to control the water level inside the dam below the safe elevation, ensuring the stability of the cushion layer and the extruded sidewall structure; from the panel pouring period to the dam front paving and backfilling, the two upstream drainage wells 13 and 12 horizontal drainage pipes operate simultaneously to strictly control water level fluctuations inside the dam, preventing reverse water pressure from lifting the panel pouring body and ensuring the quality of the toe slab waterstop construction; during the dry season, when the horizontal drainage pipes are sealed, the pumping force is increased through drainage well 13 to reduce the sealing pressure. To ensure the quality of the sealing construction, the water level at the working face was controlled. After the dam front cover was filled to the wellhead elevation, the upstream reverse drainage system was shut down, and the upstream water was diverted to temporary open drainage facilities. The downstream side corresponding to the water measuring weir construction progress adjustment and control logic was as follows: before the water measuring weir construction, the water level was controlled according to the principle of "the water level does not overflow the dam axis"; during the water measuring weir construction period, "pumping water as soon as it appears" was implemented to ensure dry working conditions for the anti-seepage wall construction; after the water measuring weir construction was completed, the upstream side drainage well 13 of the anti-seepage wall undertook the main drainage task, and the downstream side well cooperated to control the water level in the pressure zone; after the downstream cofferdam was demolished, the entire reverse drainage system was shut down.

[0034] The working principle of this embodiment is as follows: relying on the characteristics of the dam foundation being high in the middle and low upstream and downstream, a gravity-flow water guiding network covering the entire dam section is formed by the drainage wells 13 arranged differently upstream and downstream of the anti-seepage wall and the upstream horizontal drainage pipe. The reverse seepage water inside the dam body is filtered by the graded reverse filter structure and then flows into the drainage wells and collection pool, and is then discharged through the graded pumping system. At the same time, through the design of low-position arrangement of drainage pipes to avoid water-stopping structures, differentiated reinforcement to adapt to different loads, pre-splitting blasting to reduce seepage water in the surrounding rock, and phased dynamic control of water level, the problems of seepage blind spots, easy siltation and corrosion, easy damage to water-stopping, and poor construction coordination of traditional reverse drainage structures are comprehensively solved. While ensuring the structural safety of the ultra-high panel rockfill dam during construction, the long-term effectiveness and economy of the drainage system are improved.

[0035] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A reverse drainage structure for a concrete-faced rockfill dam, characterized in that: Includes upstream drainage units and downstream drainage units; The upstream drainage unit includes a drainage well (13) and a horizontal reverse drainage pipe located on the upstream side of the dam body. The drainage well (13) is located on the bedrock and its top extends through the dam body to the upstream panel. One end of the horizontal reverse drainage pipe is connected to the drainage well (13), and the other end extends through the dam foundation and toe plate (10) to the water collection area at the front edge of the toe plate. The horizontal reverse drainage pipe is arranged below the water-stop copper sheet when it passes through the toe plate (10). The downstream drainage unit includes multiple drainage wells (13) set on the upstream and downstream sides of the seepage prevention wall of the water measuring weir on the downstream side of the dam body. The drainage wells (13) located on the upstream side of the seepage prevention wall are arranged on the bedrock and their tops extend to the downstream slope of the dam. The drainage well (13) located on the downstream side of the anti-seepage wall is arranged on the bedrock, and its top elevation is lower than the top elevation of the drainage well (13) on the upstream side of the anti-seepage wall; The horizontal reverse drain pipe is made of stainless steel and is wrapped with a double layer of stainless steel filter screen. The outer periphery of the drainage well (13) is filled with a reverse filter packing layer.

2. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 1, characterized in that: The upstream drainage unit includes at least two drainage wells (13) spaced apart on the upstream side of the dam body, and at least 12 horizontal reverse drainage pipes spaced apart along the dam axis. The downstream drainage unit includes at least two drainage wells (13) respectively arranged on the upstream and downstream sides of the water-measuring weir anti-seepage wall.

3. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 1, characterized in that: The drainage well (13) includes a steel cage and a fill material layer filled on the outside of the steel cage; The reinforcing cage is longitudinally lapped and welded together. The filter filler layer is provided with a graded crushed stone layer and a transition layer in sequence along the outer wall of the reinforcing cage. The inner diameter of the graded crushed stone layer corresponds to the outer diameter of the reinforcing cage. The transition layer covers the outer side of the graded crushed stone layer.

4. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 3, characterized in that: In the downstream drainage unit, the reinforcement ratio of the steel cage of the drainage well (13) located on the upstream side of the water-measuring weir anti-seepage wall is greater than that of the steel cage of the drainage well (13) located on the downstream side of the water-measuring weir anti-seepage wall. The reinforcement ratio of the steel cage of the drainage well (13) in the upstream drainage unit is less than that of the steel cage of the drainage well (13) located on the upstream side of the seepage prevention wall of the downstream drainage unit.

5. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 1, characterized in that: The double-layer stainless steel filter screen includes an inner filter screen and an outer filter screen sleeved on the outside of the inner filter screen. The mesh size of the inner filter is smaller than that of the outer filter, and the inner and outer filters are respectively tied and fixed to the outside of the horizontal reverse drain pipe.

6. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 1, characterized in that: The horizontal reverse drainage pipe is provided with a plurality of spaced water-stop rings along its length, and each water-stop ring is respectively provided at the corner of the horizontal reverse drainage pipe and on the pipe section between adjacent corners. The outer surface of the water-stop ring is coated with a sealant layer.

7. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 1, characterized in that: The upstream drainage unit also includes a concrete retaining wall (6), which is located on the upstream side of the toe slab (10), and a downstream water collection pool (9) is formed between the concrete retaining wall (6) and the toe slab (10). The outlet end of the horizontal reverse drainage pipe extends into the downstream water collection pool (9) of the retaining wall. An upstream water collection pool (4) is formed on the upstream side of the concrete retaining wall (6). A submersible pump is installed between the downstream water collection pool (9) and the upstream water collection pool (4).

8. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 7, characterized in that: The concrete retaining wall (6) is a gravity-type water-retaining structure, and its bottom is anchored with multiple rows of reinforcing bars (7). The lower end of the reinforcing bar (7) is anchored into the bedrock of the riverbed foundation (8), and the upper end is buried in the concrete retaining wall (6). The two sides of the concrete retaining wall (6) are connected to the retaining wall on the left bank slope and the outside of the road in the lower foundation pit, respectively.

9. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 1, characterized in that: It also includes a centrifugal pump platform (1) set on the side of the road in the foundation pit below the back slope of the upstream cofferdam. The downstream side slope of the centrifugal pump platform (1) is equipped with a concrete masonry retaining wall (3) and an underwater burlap concrete protection (5). The concrete masonry retaining wall (3) is located above the underwater burlap concrete protection (5) and the two are connected in the slope height direction. The centrifugal pump platform (1) is equipped with a safety guardrail (2) at its edge.

10. The reverse drainage structure of the concrete-faced rockfill dam as described in claim 1, characterized in that: Each of the drainage wells (13) is equipped with a deep well pump and a water level monitoring device. The signal output terminal of the water level monitoring device is connected to the control terminal of the deep well pump. The drainage outlet of the deep well pump is connected to a drainage pipe. The drainage pipe extends upward along the well shaft of the drainage well (13) to the outside of the well opening. The wellhead of the drainage well (13) is covered with a grid-shaped protective cover, and a maintenance ladder is fixedly installed on the inner wall of the well cylinder of the drainage well (13).

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