Multi-branch ditch terrain pumped storage power station bottom drainage system and construction method thereof

Abstract

The application discloses a multi-branch ditch terrain pumped storage power station reservoir bottom drainage system and a construction method thereof, which comprises a drainage gallery, a gallery cushion and a gravel drainage layer; the drainage gallery is arranged at the bottom of a reservoir bank asphalt concrete panel and located at the joint part of the reservoir bank and the reservoir bottom; the gallery cushion is arranged below the drainage gallery at the branch ditch part and is seated on a weak weathering zone; the gravel drainage layer is arranged on the upstream side and the downstream side of the gallery cushion and is located above the dam foundation excavation line and is in communication with the drainage system of the drainage gallery. The concrete cushion is additionally arranged below the drainage gallery at the branch ditch of the reservoir bottom, so that the bottom of the drainage gallery directly reaches the weak weathering layer, the risk of structural damage of the concrete drainage gallery caused by uneven settlement of the backfilling stone residue at the branch ditch is effectively avoided, and the long-term operation safety of the drainage gallery located in the backfilling stone residue area of the branch ditch dam bottom is obviously ensured.

Description

Technical Field

[0001] This invention relates to the field of water conservancy and hydropower engineering technology, and in particular to a drainage system for the bottom of a pumped storage reservoir with a multi-branch ditch topography and its construction method. Background Technology

[0002] Currently, pumped storage power station construction is experiencing rapid development, with an increasing number of power stations being located in mountainous areas with complex terrain and geological conditions. Among these, multi-tributary gully terrain is a very common primitive landform, characterized by: multiple deeply incised gullies distributed within the reservoir basin, crisscrossing valleys, dramatically undulating bedrock surfaces, narrow ridges between gullies, and fragmented terrain. To obtain sufficient reservoir capacity and a relatively flat reservoir bottom, engineering typically requires extensive excavation and filling of the tributaries. This involves first excavating the overburden and weathered rock within the tributaries, then backfilling and compacting the material using blasted excavated material or spoil from the reservoir perimeter in layers, ultimately forming an artificial reservoir bottom.

[0003] Against this backdrop, the design of the reservoir bottom drainage system has become one of the key technical challenges affecting the safe operation of pumped storage power stations. The seepage prevention system of pumped storage reservoirs typically employs a composite seepage prevention structure of asphalt concrete panels on the reservoir banks and geomembrane at the bottom, or an asphalt concrete panel covering the entire reservoir basin. Regardless of the form used, seepage control beneath the seepage prevention layer is of paramount importance. After the reservoir is impounded, the sources of seepage mainly include: seepage through the seepage prevention layer, groundwater infiltration from the mountain slopes, and rainfall infiltration. If seepage cannot be discharged in a timely and orderly manner, it will accumulate beneath the seepage prevention layer, leading to increased pore water pressure. When the water pressure exceeds the seepage prevention layer's bearing capacity, the geomembrane or asphalt concrete panel will bulge, crack, or even be punctured and destroyed.

[0004] In multi-tributary ditch terrain, the design of reservoir bottom drainage systems faces more severe challenges than in conventional terrain. Existing pumped-storage reservoir bottom drainage systems mostly employ the method of burying crushed stone drainage blind ditches within a backfill layer of stone and gravel, in conjunction with a bank slope drainage cushion. While crushed stone blind ditches rely on pore seepage for drainage, their equivalent permeability coefficient is higher than that of the backfill stone, but their drainage capacity is significantly insufficient when the seepage flow is large, easily leading to backwater. Furthermore, crushed stone blind ditches lack effective backfiltration protection; over long-term operation, fine particles easily enter the ditches with the seepage, causing siltation and a gradual decline in drainage capacity. Once silted up, the blind ditches are almost impossible to clean and repair. On the other hand, in the tributary sections, due to the large thickness of the backfill stone layer and the limited compaction caused by construction conditions, their bearing capacity and deformation modulus are usually much lower than those of the natural foundation. As a reinforced concrete structure, the drainage gallery has certain requirements for the uniformity and bearing capacity of the foundation. If the foundation is not treated, the drainage gallery may experience excessive or differential settlement, thus affecting its structural integrity.

[0005] The sections crossing tributary ditches, being areas of abrupt topographic changes and thickest backfill, are the weakest links in the drainage system, yet there are few integrated designs specifically for enhanced drainage and anti-settlement measures in these areas. Therefore, this application proposes a drainage system for the bottom of a multi-tributary ditch topographic pumped-storage reservoir and its construction method. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a drainage system for the bottom of a pumped storage reservoir with multiple tributary ditches and its construction method. This system at least solves the problem of excessive or differential settlement of drainage corridors when they pass through multiple tributary ditches, which affects their structural integrity. It can effectively avoid the risk of tensile cracking, shearing cracking, misalignment or overall damage to rigid drainage corridors caused by uneven settlement of backfilled stone slag at the tributary ditches, and improve the long-term structural safety of drainage corridors.

[0007] To achieve the above-mentioned technical features, the objective of this invention is as follows: In a first aspect, the present invention proposes a drainage system for the bottom of a pumped-storage reservoir with a multi-branch ditch topography, including a drainage corridor, a corridor cushion and a gravel drainage layer. The drainage corridor is located at the bottom of the asphalt concrete panel on the reservoir bank and at the junction of the reservoir bank and the reservoir bottom. It is used to collect and discharge seepage water that has passed through the seepage prevention structure of the reservoir bottom and the seepage prevention structure of the reservoir bank. The corridor cushion is placed under the drainage corridor at the cross-branch ditch section and sits on the weakly weathered zone; The crushed stone drainage layer is located on the upstream and downstream sides of the corridor seat, above the dam foundation excavation line, and is connected to the drainage system of the drainage corridor.

[0008] The corridor seat cushion is provided with several horizontally penetrating first drainage holes. The inlet and outlet of the first drainage holes are connected to the downstream and upstream gravel drainage layers on both sides of the corridor seat cushion, respectively. The elevation of the inlet and outlet is lower than the upper surface elevation of the downstream and upstream gravel drainage layers, respectively, to form a low-level drainage channel.

[0009] The corridor cushion is provided with several horizontally penetrating second drainage holes. The second drainage holes are higher than the first drainage holes. One end of the second drainage hole is connected to the rockfill area filled on the upper side of the downstream crushed stone drainage layer, and the other end is connected to the backfill stone slag at the bottom of the reservoir filled on the upper side of the upstream crushed stone drainage layer, so as to form a high-level backup drainage channel.

[0010] The inlet and / or outlet of the first drain hole are equipped with a filter screen or a grid.

[0011] A filter bag is provided around the inlet and / or outlet of the second drainage hole. The filter bag includes a gravel or pebbles filter layer and a geotextile covering the outside of the gravel or pebbles filter layer.

[0012] The corridor cushion is equipped with a drainage monitoring and inspection hole, which extends downward from the drainage corridor and is used to inspect, unclog or maintain the first drainage hole and / or the second drainage hole; the drainage corridor is equipped with a sealed manhole cover at the position of the corresponding drainage monitoring and inspection hole.

[0013] The drainage monitoring and inspection hole is a vertical hole or an oblique hole, and is equipped with one or more of the following: a ladder, a maintenance platform, a closed cover, a lighting device, a drainage volume monitoring device, a water level monitoring device, an endoscope interface, a sludge removal interface, a high-pressure water flushing interface, or a chemical agent injection pipe.

[0014] The cross-sectional shape of the corridor cushion is an isosceles trapezoid to limit horizontal displacement or tilting when the backfilled stone slag on both sides undergoes uneven deformation.

[0015] A drainage ditch is installed at the junction of the top of the backfill stone and the mountain behind the reservoir to drain the water accumulated on top of the backfill stone.

[0016] A construction method for a drainage system at the bottom of a pumped-storage reservoir with multi-tributary gully topography, used for constructing the drainage system at the bottom of the pumped-storage reservoir with multi-tributary gully topography, includes the following steps: S1. Excavate to the weakly weathered rock layer at the cross-branch ditch section, and pour the corridor cushion in the area where the stone slag is backfilled at the bottom of the reservoir. S2. When pouring the corridor seat, a first drainage hole and a second drainage hole are provided inside the corridor seat, and a drainage monitoring and inspection hole is reserved. S3. Lay a gravel drainage layer on both sides of the corridor cushion, and make the inlet and outlet of the first drainage hole located inside the gravel drainage layer. S4. On the upstream side of the crushed stone drainage layer, fill the bottom of the reservoir with backfilled stone slag on the crushed stone drainage layer; on the downstream side of the crushed stone drainage layer, fill the upstream rockfill area and the downstream rockfill area; on the downstream rockfill area, fill the reservoir and backfill with stone slag. S5. Construct a drainage corridor above the corridor cushion and connect the drainage corridor with the reservoir bottom transition material, the reservoir bank drainage cushion area and the crushed stone drainage layer for drainage. S6. Construct a drainage ditch at the junction of the top of the backfilled stone slag and the mountain behind the reservoir. S7. Construct the seepage prevention structure at the bottom of the reservoir and the seepage prevention structure on the banks of the reservoir to form a bottom drainage system for pumped storage reservoirs with multi-branch ditch topography.

[0017] Compared with the prior art, the beneficial effects of the present invention include: 1. This invention, by adding a concrete cushion below the drainage gallery at the bottom of the reservoir at the cross-branch ditch, allows the bottom of the drainage gallery to reach the weakly weathered layer, effectively avoiding the risk of structural damage to the concrete drainage gallery caused by uneven settlement of backfilled stone slag at the branch ditch, and significantly ensuring the long-term operational safety of the drainage gallery located in the backfilled stone slag area at the bottom of the branch ditch dam.

[0018] 2. The present invention provides a horizontally penetrating low-level drainage hole at the bottom of the corridor cushion to prevent the corridor cushion from forming a water barrier on the crushed stone drainage layer or the rockfill area on both sides, so that the seepage water can pass through quickly at a low level, thereby reducing the pore water pressure in the backfill stone and rockfill area, and reducing the risk of water pressure damaging the geomembrane at the bottom of the reservoir and the asphalt concrete panel on the bank.

[0019] 3. The present invention provides a horizontally penetrating high-level drainage hole on the upper part of the corridor cushion. When the drainage capacity of the low-level drainage steel pipe decreases due to siltation, sedimentation or other reasons, the water level in the rubble area or crushed stone drainage layer rises to the high-level drainage hole, and a backup drainage channel can be formed through the drainage hole to prevent the formation of a local closed water pocket and the continuous increase of water pressure.

[0020] 4. This invention sets up drainage monitoring and inspection holes inside the corridor cushion, which can be used to regularly inspect, clean and maintain the drainage steel pipes and drainage holes, effectively solving the problem of difficult maintenance of traditional buried drainage facilities, and ensuring the reliable operation of the reservoir bottom drainage system throughout its entire life cycle.

[0021] 5. This invention forms a multi-layered, continuous drainage system consisting of a drainage ditch behind the reservoir, a drainage corridor at the bottom of the reservoir, a gravel drainage layer, a low-level drainage steel pipe, and a high-level drainage hole. This system can collect and quickly remove water seepage from the backfilled stone slag behind the reservoir, the drainage cushion layer area on the reservoir bank, the transition material at the bottom of the reservoir, the rockfill area, and the interior of the mountain. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the cross-sectional structure of the drainage system in this invention. In the picture: 1. Drainage ditch; 2. Drainage corridor; 3. Corridor cushion; 4. First drainage hole; 5. Second drainage hole; 6. Drainage monitoring and inspection hole; 7. Crushed stone drainage layer; 7-1 downstream crushed stone drainage layer; 7-2 upstream crushed stone drainage layer; 8 upstream rockfill area; 9 downstream rockfill area; 10. Backfill stone slag behind the reservoir; 11. Backfill stone slag at the bottom of the reservoir; 12. Geomembrane on top of backfill stone slag behind the reservoir; 13. Geomembrane at the bottom of the reservoir; 14. Mountain; 15. Asphalt concrete panel on the reservoir bank; 16. Drainage cushion layer area on the reservoir bank; 17. Transition area on the reservoir bank; 18. Transition material at the bottom of the reservoir. Detailed Implementation

[0024] To more clearly illustrate the purpose, technical solution, and beneficial effects of this application, a further detailed description of this application is provided below in conjunction with illustrations and specific embodiments. It should be specifically noted that the specific embodiments described below are only for illustrating the technical content of this application and do not constitute a limitation on the scope of protection of this application.

[0025] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0026] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection via an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Example 1: like Figure 1 As shown, this embodiment provides a drainage system for the bottom of a pumped storage reservoir with a multi-branch ditch topography, including a drainage corridor 2, a corridor cushion 3, and a gravel drainage layer 7.

[0028] The drainage corridor 2 is located at the bottom of the asphalt concrete panel 15 on the reservoir bank and at the junction of the reservoir bank and the reservoir bottom. It is used to collect and discharge seepage water that has passed through the seepage prevention structure of the reservoir bottom and the seepage prevention structure of the reservoir bank.

[0029] The corridor cushion 3 is located below the drainage corridor 2 at the cross-branch ditch section and sits on the weakly weathered zone.

[0030] The crushed stone drainage layer 7 is located on the upstream and downstream sides of the corridor cushion 3, above the dam foundation excavation line, and is connected to the drainage system of the drainage corridor 2.

[0031] Drainage gallery 2 is a rigid reinforced concrete structure. It is located at the bottom of the asphalt concrete panel 15 on the reservoir bank, at the junction of the reservoir bank and the reservoir bottom. The bottom drainage gallery 2 extends below the asphalt concrete panel 15. A reservoir bottom transition material 18 is located below the reservoir bottom geomembrane 13, a reservoir bank drainage cushion layer 16 is located below the reservoir bank asphalt concrete panel 15, and a reservoir bank transition zone 17 is located below the reservoir bank drainage cushion layer 16. Seepage water through the reservoir bottom geomembrane 13 can be collected through the reservoir bottom transition material 18, and seepage water through the reservoir bank asphalt concrete panel 15 can be collected through the reservoir bank drainage cushion layer 16. Both then flow into the bottom drainage gallery 2 and are safely discharged outside the reservoir.

[0032] Drainage gallery 2 can adopt a rectangular, archway-shaped, or round arch straight wall cross section. The structural strength and impermeability grade of drainage gallery 2 should meet the requirements of pumped storage reservoir operation head, temperature change, construction load and long-term service.

[0033] The centralized discharge of seepage water through the drainage corridor 2 can prevent water pressure from accumulating under the asphalt concrete panel 15 on the reservoir bank and the geomembrane 13 at the bottom of the reservoir, thereby avoiding the seepage prevention structure from bulging, cracking, delamination or top support damage due to excessive water pressure.

[0034] The corridor cushion 3 is a rigid concrete structure and is located below the drainage corridor 2 at the section crossing the branch ditch. The corridor cushion 3 is located within the backfilled stone slag area 11 at the bottom of the reservoir.

[0035] In multi-tributary ditch terrain, the tributary sections typically require extensive backfilling with gravel. If the reservoir bottom drainage corridor 2 is directly placed on the backfilled gravel, uneven settlement can easily lead to cracking of the corridor later on. Therefore, in this embodiment, a corridor seat 3 is installed at the tributary section to provide stable support for the reservoir bottom drainage corridor 2.

[0036] The corridor seat 3 is not arranged along the entire length of the drainage corridor 2 at the bottom of the reservoir, but only at the sections crossing branch ditches where the terrain changes abruptly, gullies exist, and a large amount of backfill stone is required. For sections with gentle terrain, stable natural foundations, or small backfill thickness, the corridor seat 3 may not be required. This arrangement ensures the structural safety of critical parts while reducing the amount of concrete work and construction costs.

[0037] The bottom of the corridor seat 3 reaches the weakly weathered rock layer or the stable bearing layer 12. During construction, the loose covering layer, strongly weathered and broken layer and weak interlayer at the bottom of the branch ditch can be removed first, and then the corridor seat 3 can be poured to form a reliable foundation support.

[0038] The cross-section of the corridor cushion 3 is an isosceles trapezoid. The isosceles trapezoidal structure provides good stability and embedding effect, reducing the risk of horizontal slippage or tilting of the cushion when uneven deformation occurs due to backfilling of stone slag on both sides. The width of the upper surface of the corridor cushion 3 should meet the construction and support requirements of the reservoir bottom drainage corridor 2, while the width of the lower base can be determined based on the foundation bearing capacity, valley width, and stability calculations.

[0039] The concrete strength grade of the corridor seat 3 can be lower than that of the reservoir bottom drainage corridor 2. For example, the reservoir bottom drainage corridor 2 can use higher strength reinforced concrete, while the corridor seat 3 can use lower strength plain concrete or lightly reinforced concrete to meet the requirements of load bearing and durability while taking into account economy.

[0040] The gravel drainage layer 7 is installed on both sides of the corridor seating cushion 3. For ease of explanation, in conjunction with... Figure 1 The gravel drainage layer located to the right of the corridor cushion 3 is referred to as the downstream gravel drainage layer 7-1, and the gravel drainage layer located to the left of the corridor cushion 3 is referred to as the upstream gravel drainage layer 7-2. In actual engineering, the upstream and downstream sides can be determined according to the direction of water flow, reservoir layout, and tributary topography.

[0041] The crushed stone drainage layer 7 can be formed by laying clean crushed stone, pebbles or graded gravel, which has a large porosity and good water conductivity.

[0042] The upstream side of the crushed stone drainage layer 7-1 is filled with upstream rockfill area 8 and downstream rockfill area 9. The top of the upstream rockfill area 8 is successively provided with reservoir bank transition area 17, reservoir bank drainage cushion layer area 16, and reservoir bank asphalt concrete panel 15. The downstream rockfill area 9 is filled with backfill stone 10, and the top of the backfill stone 10 is provided with a geomembrane 12. The upstream side of the crushed stone drainage layer 7-2 is filled with reservoir bottom backfill stone 11, and the top of the reservoir bottom backfill stone 11 is successively provided with reservoir bottom transition material 18 and reservoir bottom geomembrane 13.

[0043] In this embodiment, a concrete corridor cushion 3 is set below the drainage corridor 2 at the bottom of the reservoir at the cross-branch ditch, and the bottom of the corridor cushion 3 extends to the weakly weathered rock layer or the stable bearing layer. This can effectively avoid the risk of tensile cracking, shearing cracking, misalignment or overall damage to the rigid drainage corridor caused by uneven settlement of backfilled stone slag at the branch ditch, and improve the long-term structural safety of the drainage corridor 2.

[0044] Example 2: Based on Example 1, combined with Figure 1The corridor cushion 3 is provided with several horizontally penetrating first drainage holes 4. The inlet and outlet of the first drainage holes 4 are connected to the downstream side crushed stone drainage layer 7-1 and the upstream side crushed stone drainage layer 7-2 on both sides of the corridor cushion 3, respectively. The elevation of the inlet and outlet is lower than the upper surface elevation of the downstream side crushed stone drainage layer 7-1 and the upstream side crushed stone drainage layer 7-2, respectively, to form a low-level drainage channel.

[0045] The first drainage hole 4 is located inside the corridor seat 3 and extends horizontally through the corridor seat 3. The first drainage hole 4 can be made of a pre-embedded drainage steel pipe, which can be made of anti-corrosion steel pipe, stainless steel pipe, anti-corrosion lined steel pipe, or other pipe with sufficient strength and durability.

[0046] The inlet of the first drainage hole 4 is connected to the downstream gravel drainage layer 7-1, and the outlet is connected to the upstream gravel drainage layer 7-2. The elevations of both the inlet and outlet of the first drainage hole 4 are lower than the elevation of the upper surface of the gravel drainage layer 7 connected to it, so that the seepage water entering the gravel drainage layer 7 can quickly enter the first drainage hole 4 at a low level.

[0047] To ensure gravity drainage, the first drainage hole 4 is sloped at a rate of not less than 0.5% along the direction of water flow, preferably 0.5% to 1%. When the engineering layout allows, a larger slope can be set according to the head difference, drainage distance and design flow rate.

[0048] The first drainage hole 4 can be set in one or two rows. When the catchment area of ​​the tributary ditch is large, the water inflow from the mountain is large, or the seepage at the bottom of the reservoir is large, two or more rows of parallel first drainage holes 4 can be used; when the catchment volume is small, one row of first drainage holes 4 can be used. The range of the first drainage hole 4 arranged longitudinally along the corridor cushion 3 should preferably not exceed the height of the bottom gravel drainage layer 7 to ensure effective connection between it and the gravel drainage layer 7.

[0049] The inlet and outlet of the first drainage hole 4 can be equipped with a filter screen or grille 19. The filter screen or grille 19 is used to prevent gravel, larger particles or construction debris from entering the interior of the drainage steel pipe 4. In this embodiment, the first drainage hole 4 has the following function: Firstly, as a low-level rapid drainage channel, after the upstream rockfill area 8, the downstream rockfill area 9, or the seepage water from the mountain enters the downstream side gravel drainage layer 7-1, the seepage water enters the first drainage hole 4 under the action of gravity because the inlet of the first drainage hole 4 is located at a low position in the gravel drainage layer, and is discharged to the upstream side gravel drainage layer 7-2, and then discharged outside the reservoir.

[0050] Secondly, it reduces pore water pressure. Organized drainage through the first drainage hole 4 can prevent seepage water from stagnating on both sides of the corridor cushion 3, reduce pore water pressure in the backfill area, and prevent water pressure from causing top-support damage to the geomembrane 13 at the bottom of the reservoir or the asphalt concrete panel 15 on the bank.

[0051] Thirdly, it serves as the main drainage channel under normal operating conditions. The first drainage hole 4 has a large diameter, stable flow, and high drainage efficiency. It is not easily blocked by fine particles, making it suitable as the main drainage path in areas crossing tributary ditches.

[0052] Example 3: Based on Example 2, combined with Figure 1 Several horizontally penetrating second drainage holes 5 are provided in the corridor cushion 3. The second drainage holes 5 are higher than the first drainage holes 4. One end of the second drainage hole 5 is connected to the rockfill area filled on the upper side of the downstream crushed stone drainage layer 7-1, and the other end is connected to the backfill stone slag 11 filled on the upper side of the upstream crushed stone drainage layer 7-2, so as to form a high-level backup drainage channel.

[0053] The second drainage hole 5 is located inside the corridor cushion 3 and is higher than the first drainage hole 4. The second drainage hole 5 can be an inclined channel pre-reserved in the cushion concrete or formed by a pre-embedded steel pipe.

[0054] The inlet of the second drainage hole 5 can be connected to the upstream rockfill area 8, and the outlet can be connected to the backfilled stone slag 11 at the bottom of the reservoir or the upstream side crushed stone drainage layer 7-2.

[0055] The elevations of the inlet and outlet of the second drainage hole 5 are both higher than those of the first drainage hole 4. The second drainage holes 5 are located in the upper part of the corridor cushion 3, and one or more sets can be set at regular intervals along the longitudinal direction of the corridor cushion 3. Each set of second drainage holes 5 may include one or more channels.

[0056] The main functions of the second drainage hole 5 are as follows: Firstly, as a high-level backup drainage channel, during normal operation, seepage water is mainly discharged through the low-level first drainage hole 4. When the first drainage hole 4 becomes partially blocked or its drainage capacity is insufficient due to long-term operation, the water level in the rockfill area gradually rises. When the water level reaches the inlet elevation of the second drainage hole 5, the accumulated water flows through the second drainage hole 5 into the backfilled stone slag 11 at the bottom of the reservoir or the upstream crushed stone drainage layer 7-2, and is then discharged through the bottom drainage system.

[0057] Secondly, it prevents water accumulation and pressure buildup in the rockfill area. Without the elevated second drainage hole 5, leakage from the blocked first drainage hole 4 could create a locally enclosed water body in the upstream rockfill area 8 or downstream rockfill area 9, causing a continuous increase in water pressure and potentially damaging the asphalt concrete panel 15 on the reservoir bank or the geomembrane 13 at the bottom of the reservoir. This embodiment provides an elevated drainage channel through the second drainage hole 5, preventing the continuous accumulation of water pressure.

[0058] Third, it improves long-term reliability. Because the second drain hole 5 is higher than the first drain hole 4, its inlet is less likely to be blocked by settled silt or low-level fine particles, and it can still perform its drainage function when the first drain hole 4 at the lower level is not operating smoothly.

[0059] To prevent fine particles, debris, or construction residues in the rockfill area from entering the second drainage hole 5 with seepage water, and to prevent the outlet from being blocked by backfilled stone debris, a filter bag is installed around the inlet and / or outlet of the second drainage hole 5.

[0060] The filter bag includes a crushed stone or gravel filter layer and a non-woven geotextile covering the outside. The crushed stone or gravel filter layer can be composed of materials with multiple particle sizes. Preferably, the side closer to the drainage hole 5 uses a smaller particle size material, and the side farther away from the drainage hole 5 uses a larger particle size material to form a stable gradation structure. The non-woven geotextile covering the outside of the filter layer is used to prevent fine particles from entering the interior of the filter layer and to prevent the crushed stone from moving.

[0061] The filter bag can ensure that leaked water can smoothly enter the drain hole 5, and reduce the risk of the drain hole 5 being blocked by fine particles.

[0062] Example 4: Based on Example 2 or 3, combined with Figure 1 In this embodiment, a drainage monitoring and inspection hole 6 is provided inside the corridor cushion 3. The drainage monitoring and inspection hole 6 extends downward from the drainage corridor 2 and is used to inspect, unclog or maintain the first drainage hole 4 and / or the second drainage hole 5. A sealing manhole cover is provided at the position corresponding to the drainage monitoring and inspection hole 6 in the drainage corridor 2.

[0063] The drainage monitoring and inspection hole 6 is a vertical or oblique hole. The drainage monitoring and inspection hole 6 is equipped with one or more of the following: a ladder, a maintenance platform, a closed cover, a lighting device, a drainage volume monitoring device, a water level monitoring device, an endoscope interface, a sludge removal interface, a high-pressure water flushing interface, or a chemical agent injection pipe.

[0064] The drainage monitoring and inspection hole 6 is located inside the corridor cushion 3 and extends downward from the bottom of the drainage corridor 2. The drainage monitoring and inspection hole 6 can be a vertical hole or a slightly inclined slanted hole.

[0065] A ladder 20 is installed inside the drainage monitoring inspection port 6 to allow personnel or maintenance equipment to enter. A sealed cover is installed at the top of the drainage monitoring inspection port 6 to prevent debris from entering and ensure operational safety. Lighting devices, ventilation devices, water level gauges, flow meters, cameras, or endoscope interfaces may also be installed inside the drainage monitoring inspection port 6.

[0066] During operation and maintenance, the drainage steel pipe 4 and drainage hole 5 can be observed through the drainage monitoring inspection hole 6 to check whether the drainage is smooth. If a partial blockage is found in the drainage steel pipe 4 or drainage hole 5, tools such as a cleaning rod, high-pressure water gun, or rotary pipe cleaner can be inserted through the drainage monitoring inspection hole 6 for cleaning. For calcium deposits or hard blockages that cannot be removed mechanically, scale inhibitors, descaling agents, or other suitable agents can be injected through the reserved chemical agent injection pipe 22 for treatment.

[0067] By setting up drainage monitoring and inspection holes 6, this embodiment enables the drainage steel pipe 4 and drainage holes 5 embedded inside the corridor cushion 3 to be monitored, inspected, maintained, and repaired.

[0068] Example 5: Based on embodiment 1, 2, 3 or 4, this embodiment provides a drainage ditch 1 at the junction of the top of the backfill stone slag 10 behind the reservoir and the mountain 14 to drain the accumulated water on the top of the backfill stone slag 10 behind the reservoir.

[0069] Drainage ditch 1 is a concrete structure. Drainage ditch 1 is located at the junction of the top 10 of the backfilled stone slag behind the reservoir and the hillside 14. Drainage ditch 1 can be arranged continuously along the boundary line between the hillside 14 and the top 10 of the backfilled stone slag behind the reservoir, or it can be arranged in sections according to the water collection path of the hillside.

[0070] Drainage ditch 1 is used to promptly drain runoff from the mountain slope, rainwater runoff, and water accumulated on the top of the backfilled stone slag 10 behind the reservoir. By setting up drainage ditch 1, rainwater or mountain water can be prevented from lingering on the surface of the backfilled stone slag and seeping downwards for a long time, thereby reducing the amount of water entering the backfilled stone slag 10 behind the reservoir, the rockfill area, and the downstream crushed stone drainage layer 7-1 from the source, and reducing the operating pressure on the subsequent drainage system.

[0071] The cross-section of drainage ditch 1 can be determined based on the catchment area, hydrological calculation flow rate, and construction conditions. For example, a rectangular, trapezoidal, or U-shaped concrete ditch can be used. Expansion joints, settlement joints, and erosion-resistant linings can be installed in drainage ditch 1 to adapt to changes in mountainous terrain.

[0072] Example 6: This embodiment proposes a construction method for a drainage system at the bottom of a pumped-storage reservoir in a multi-tributary ditch terrain, used in the construction of the drainage system at the bottom of the pumped-storage reservoir in Embodiment 5, including the following steps: S1. Excavate to the weakly weathered rock layer at the cross-branch ditch section, and pour the corridor cushion 3 in the area of ​​backfilled stone slag at the bottom of the reservoir.

[0073] Specifically, at the section crossing the tributary, excavation is carried out down to the weakly weathered rock layer, removing loose overburden, weak interlayers, silt, strongly weathered and fractured rock, and other unsuitable foundation materials. If necessary, the foundation surface is roughened, cleaned, drained, and consolidated. Afterwards, the gallery seat 3 is cast on the treated foundation using formwork.

[0074] S2. When pouring the corridor cushion 3, a first drainage hole 4 and a second drainage hole 5 are provided inside the corridor cushion 3, and a drainage monitoring and inspection hole 6 is reserved.

[0075] Specifically, a first drainage hole 4 is pre-set inside the corridor cushion 3, and the position and slope of the inlet and outlet of the first drainage hole 4 are controlled. The slope of the first drainage hole 4 along the water flow direction is not less than 0.5%, preferably 0.5% to 1%.

[0076] Meanwhile, a second drainage hole 5 is reserved in the corridor cushion 3, located above the first drainage hole 4. The second drainage hole 5 can be formed by pre-embedded pipe, pre-reserved core pipe, or other hole-forming methods. The elevation of the inlet and outlet of the second drainage hole 5 should be higher than the elevation of the first drainage hole 4.

[0077] Meanwhile, a drainage monitoring and inspection hole 6 is reserved in the corridor cushion 3, and a ladder is installed.

[0078] S3. Lay a gravel drainage layer 7 on both sides of the corridor cushion 3, and make the inlet and outlet of the first drainage hole 4 located inside the gravel drainage layer 7.

[0079] Specifically, gravel drainage layers 7 are laid on both sides of the corridor cushion 3, including a downstream gravel drainage layer 7-1 and an upstream gravel drainage layer 7-2, so that the inlet and outlet of the first drainage hole 4 are connected to the corresponding gravel drainage layer 7 respectively.

[0080] A filter bag is installed around the inlet and / or outlet of the second drainage hole 5. The filter bag consists of multi-sized crushed stone or gravel wrapped with non-woven geotextile. When installing the filter bag, it should be ensured that it is tightly connected to the drainage hole to prevent fine particles from flowing around and entering the second drainage hole 5.

[0081] S4. On the upstream side of the crushed stone drainage layer 7-2, fill the bottom of the reservoir with backfill stone 11, and on the downstream side of the crushed stone drainage layer 7-1, fill the upstream rockfill area 8 and the downstream rockfill area 9; on the downstream rockfill area 9, fill the reservoir and backfill with stone 10.

[0082] S5. Construct drainage corridor 2 above corridor cushion 3, and connect drainage corridor 2 with reservoir bottom transition material 18, reservoir bank drainage cushion area 16 and gravel drainage layer 7 for drainage.

[0083] Specifically, a reservoir bottom drainage corridor 2 is constructed above the corridor cushion 3. The reservoir bottom drainage corridor 2 can be a cast-in-place reinforced concrete structure. During construction, it should be ensured that the reservoir bottom drainage corridor 2 is connected to the reservoir bottom transition material 18, the reservoir bank drainage cushion layer 16, and the gravel drainage layer 7.

[0084] S6. At the junction of the top of the backfilled stone slag 10 and the mountain 14, pour drainage ditch 1.

[0085] Specifically, at the point where the top of the backfilled stone slag 10 meets the mountain 14 behind the reservoir, the survey line is laid out, a trench is excavated, and a drainage ditch 1 is formed by pouring concrete. The longitudinal slope, cross-sectional dimensions, and outlet location of the drainage ditch 1 are determined based on the catchment area and design flow rate. The outlet of the drainage ditch 1 should connect to a natural ditch, an intercepting drainage system, or an external drainage system.

[0086] S7. Construct the seepage prevention structure at the bottom of the reservoir and the seepage prevention structure on the banks of the reservoir to form a bottom drainage system for pumped storage reservoirs with multi-branch ditch topography.

[0087] Specifically, the following components were constructed according to the design requirements: the bottom transition material 18, the bottom geomembrane 13, the bank drainage cushion layer 16, the bank asphalt concrete panel 15, and the top geomembrane 12 for backfilling with slag behind the reservoir.

[0088] It is understandable that when the length of the corridor seat cushion 3 exceeds 20~30m, an expansion joint should be installed, with a rubber waterstop inside.

[0089] It is understandable that a construction joint should be made between the drainage corridor 2 and the corridor cushion 3, the surface should be roughened, and a water-swellable sealing strip should be installed. If the corridor and the cushion are cast as a whole, then reinforcing steel bars should be installed at the cross-section.

[0090] This invention is applicable to the protection of drainage and seepage prevention structures at the bottom of pumped storage power stations, including upper and lower reservoirs, as well as similar mountain reservoirs, regulating reservoirs, and artificial basin projects, in terrain conditions with multiple tributaries, gullies, or valleys. The system has a clearly defined structure, is feasible to construct, and is easy to operate and maintain. It can improve the structural safety of drainage corridors across tributaries, enhance the capacity to remove seepage water from the reservoir bottom, and ensure long-term operational reliability, thus possessing significant engineering application value.

[0091] 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 its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A drainage system for the bottom of a pumped-storage reservoir with multi-branch ditch topography, characterized in that: Includes drainage corridor (2), corridor cushion (3) and gravel drainage layer (7); The drainage corridor (2) is set at the bottom of the asphalt concrete panel (15) on the reservoir bank and is located at the junction of the reservoir bank and the reservoir bottom. It is used to collect and discharge the seepage water that has passed through the seepage prevention structure of the reservoir bottom and the seepage prevention structure of the reservoir bank. The corridor cushion (3) is placed below the drainage corridor (2) at the cross-branch ditch and sits on the weakly weathered zone; The gravel drainage layer (7) is located on the upstream and downstream sides of the corridor cushion (3), above the dam foundation excavation line, and connected to the drainage system of the drainage corridor (2).

2. The drainage system for a pumped-storage reservoir with multi-branch ditch topography according to claim 1, characterized in that: The corridor seat (3) is provided with several horizontally penetrating first drainage holes (4). The inlet and outlet of the first drainage holes (4) are respectively connected to the downstream side crushed stone drainage layer (7-1) and the upstream side crushed stone drainage layer (7-2) of the crushed stone drainage layer (7) on both sides of the corridor seat (3). The elevation of the inlet and outlet is lower than the elevation of the upper surface of the downstream side crushed stone drainage layer (7-1) and the upstream side crushed stone drainage layer (7-2), respectively, to form a low-level drainage channel.

3. The drainage system for a pumped-storage reservoir with multi-branch ditch topography according to claim 2, characterized in that: The corridor cushion (3) is provided with several transverse second drainage holes (5). The second drainage holes (5) are higher than the first drainage holes (4). One end of the second drainage hole (5) is connected to the rockfill area filled on the upper side of the downstream crushed stone drainage layer (7-1), and the other end is connected to the backfill stone slag (11) filled on the upper side of the upstream crushed stone drainage layer (7-2) to form a high-level backup drainage channel.

4. The drainage system for a pumped-storage reservoir with multi-branch ditch topography according to claim 2, characterized in that: The inlet and / or outlet of the first drain hole (4) are provided with a filter screen or a grid.

5. The drainage system for a pumped-storage reservoir with multi-branch ditch topography according to claim 3, characterized in that: A filter bag is provided around the inlet and / or outlet of the second drainage hole (5). The filter bag includes a gravel or pebbles filter layer and a geotextile covering the outside of the gravel or pebbles filter layer.

6. The drainage system for a pumped-storage reservoir with multi-branch ditch topography according to claim 3, characterized in that: The corridor cushion (3) is provided with a drainage monitoring and inspection hole (6) inside. The drainage monitoring and inspection hole (6) extends downward from the drainage corridor (2) and is used to inspect, dredge or maintain the first drainage hole (4) and / or the second drainage hole (5). The drainage corridor (2) is provided with a sealing well cover at the position corresponding to the drainage monitoring and inspection hole (6).

7. The drainage system for a pumped-storage reservoir with multi-branch ditch topography according to claim 6, characterized in that: The drainage monitoring and inspection hole (6) is a vertical hole or an oblique hole. The drainage monitoring and inspection hole (6) is equipped with one or more of the following: a ladder, a maintenance platform, a closed cover, a lighting device, a drainage volume monitoring device, a water level monitoring device, an endoscope interface, a sludge removal interface, a high-pressure water flushing interface, or a chemical agent injection pipe.

8. The drainage system for a pumped-storage reservoir with multi-branch ditch topography according to claim 1, characterized in that: The cross-sectional shape of the corridor cushion (3) is an isosceles trapezoid to limit the horizontal displacement or tilting of the corridor cushion (3) when uneven deformation occurs due to backfilling of stone slag on both sides.

9. The drainage system for a multi-branched ditch topographic pumped storage reservoir according to claim 4, characterized in that: A drainage ditch (1) is provided at the junction of the top of the backfill stone slag (10) and the mountain (14) to drain the water accumulated on the top of the backfill stone slag (10).

10. A construction method for a drainage system at the bottom of a pumped-storage reservoir in a multi-branch ditch terrain, characterized in that, The drainage system for the bottom of the pumped-storage reservoir with multi-branch ditch topography as described in claim 9 includes the following steps: S1. Excavate to the weakly weathered rock layer at the cross-branch ditch section, and pour the corridor cushion in the area of ​​backfilled stone slag at the bottom of the reservoir (3). S2. When pouring the corridor seat (3), a first drainage hole (4) and a second drainage hole (5) are set inside the corridor seat (3), and a drainage monitoring and inspection hole (6) is reserved. S3. Lay a gravel drainage layer (7) on both sides of the corridor cushion (3) and make the inlet and outlet of the first drainage hole (4) located inside the gravel drainage layer (7); S4. Fill the bottom of the reservoir with stone slag (11) on the upstream side of the crushed stone drainage layer (7-2) and fill the upstream rockfill area (8) and the downstream rockfill area (9) on the downstream side of the crushed stone drainage layer (7-1); fill the reservoir with stone slag (10) on the downstream rockfill area (9). S5. Construct a drainage corridor (2) above the corridor cushion (3) and connect the drainage corridor (2) with the reservoir bottom transition material (18), the reservoir bank drainage cushion area (16) and the gravel drainage layer (7) for drainage. S6. At the junction of the top of the backfilled stone slag (10) and the mountain (14) behind the reservoir, pour a drainage ditch (1). S7. Construct the seepage prevention structure at the bottom of the reservoir and the seepage prevention structure on the banks of the reservoir to form a bottom drainage system for pumped storage reservoirs with multi-branch ditch topography.

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