Method for manually adjusting length of reservoir area and wind area and reducing dam crest superelevation and floating bridge

Abstract

The invention discloses a method for manually adjusting the length of a wind area of a reservoir area and reducing the height of a dam crest and a floating bridge, the floating bridge is arranged on the upstream of a dam of the reservoir area, and the floating bridge is used for shortening the effective length of the wind area so as to reduce the height of the dam crest. Anchoring devices are arranged at the two ends of the floating bridge, and the floating bridge is fixed to bank slopes or islands on the two sides of a reservoir area through the anchoring devices. According to the method, wave conduction in the reservoir area, wave absorption and breaking, manual regulation and control and wind area length reduction can be actively intervened, and the situation that wave conduction in the larger wind area length causes larger wave climbing and wind congestion water surface height is avoided, so that the dam crest superelevation is reduced, and the concrete work amount or earth and stone filling work amount caused by the dam crest superelevation to a larger extent is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of dam crest elevation design for high dams and large reservoirs, and in particular to a method and a floating bridge for manually adjusting the length of a wind zone in a reservoir area and reducing the superelevation of the dam crest. Background Art

[0002] As the most crucial water-retaining structures in water conservancy projects, dams primarily utilize their inherent water-retaining properties to intercept rivers, creating reservoirs with elevated water levels. This in turn contributes to the comprehensive benefits of water conservancy projects, including flood control, irrigation, water supply, power generation, and navigation. Dams can be classified primarily by their structural form: gravity dams, arch dams, and earth-rock dams. Regardless of dam type, to ensure structural stability and flood control safety, the dam crest must exceed the reservoir's design characteristic water level (normal storage level, design flood level, and verification flood level), and a certain amount of crest height must be reserved to mitigate the risk of overtopping and collapse. According to design specifications (Design Specification for Roller-Compacted Earth-Rock Dams (SL274-2020), Design Specification for Concrete Arch Dams (SL282-2018), and Design Specification for Concrete Gravity Dams (SL319-2018)), the dam crest height y primarily considers the reservoir wave run-up R, the wind-induced water level e, and the safety height A, i.e., y = R + e + A.

[0003] The safety height A is only related to the dam level and characteristic working conditions. For example, for a roller-compacted earth-rock dam, the safety height A for a Class 1 dam under normal operating conditions is 1.5m, and the safety height A for a Class 2 dam under normal operating conditions is 1.0m. The wave height R in the reservoir area is related to multiple factors such as wind speed, wind zone length, and water depth, and can be expressed as , m is the water-facing slope coefficient, K Δ is the roughness permeability coefficient of the water-facing slope (related to the material of the water-facing surface of the dam slope, which is a constant), g is the acceleration of gravity, which is a constant, H is the water depth in front of the water-facing slope, W is the calculated wind speed, D is the length of the wind zone, and H m is the average water depth of the water area; the wind-damaged water surface height e is related to factors such as wind speed, wind zone length, and average water depth of the water area, and can be expressed as , K f is the comprehensive friction coefficient, which is a constant.

[0004] For a specific reservoir, its hydrological and meteorological parameters and topographic data are closely related to objective natural factors such as the local altitude and topography, and are basically fixed values that are difficult to change due to human factors. Therefore, once the characteristic water level of the reservoir (normal water level, design flood level and verification flood level) is determined, the water depth H of the dam body upstream and the average water depth H of the water area are determined. m , wind zone length D and calculated wind speed W can be basically determined and are fixed values, while the gravitational acceleration g and the comprehensive friction coefficient K f is a constant, the permeability coefficient of the upstream slope roughness K ΔThe upstream slope coefficient m is the only variable related to the material of the dam slope. For gravity dams and arch dams, the upstream slope is essentially vertical, and the upstream slope coefficient m is 0. For earth-rock dams, the upstream slope ratio m can be designed. Therefore, considering the many influencing factors such as wave run-up R and wind-induced water level e, once the reservoir's geographical location and characteristic water level are determined, the wind speed W, the water depth in front of the upstream slope H, the length of the wind zone D, and the average water depth H of the water area are calculated. m is a constant, and only the material of the dam slope facing the water and the water slope coefficient m can be adjusted artificially, which directly affects the dam crest superheight and thus affects the dam crest design elevation.

[0005] To minimize wave run-up R and wind-induced water level e, lower the dam crest superelevation, avoid a higher dam crest design elevation, and thus reduce project pouring or filling volumes and project investment, there are currently no effective engineering measures for manually controlling the dam crest superelevation design in water conservancy projects. For example, in earth-rock dams, these measures can only be implemented by increasing the roughness of the dam slope's upstream surface and adjusting the upstream slope coefficient to enhance frictional resistance along the upstream dam slope to break up waves and minimize the continued rise of waves on the upstream dam surface. Examples include planting grass and trees on the upstream dam slope, installing special-shaped prefabricated blocks, or creating a stepped upstream dam slope. The water level on the slope of a headwater dam fluctuates significantly, especially in high dams and large reservoirs. The annual water level drop on the headwater surface of the dam slope can vary significantly, reaching as much as 20 meters in some reservoirs, making it virtually impossible for vegetation to survive. Special-shaped precast blocks on the headwater dam slope offer good wave-breaking performance, but require high-quality installation techniques. Improper installation can easily lead to waves hollowing out the blocks, causing them to fall and erode, thereby eroding the dam slope fill. A stepped headwater dam slope is a conventional inclined dam slope with multiple vertical steps, utilizing collisions along the steps to dissipate energy and break up longitudinally propagating waves. Overall, current water conservancy projects generally employ passive defenses to reduce wave run-up R and wind-induced water level e. This involves waiting for waves to reach the headwater dam slope and then adjusting the dam slope roughness and slope gradient to enhance frictional resistance along the slope and localized collisions, breaking up the longitudinal propagation of waves. However, there are virtually no active control measures within the reservoir area to break up waves, allowing them to propagate unchecked. Especially in reservoir areas with high wind speed and wide water area, the wind zone is long, the waves in the reservoir area fluctuate significantly, and the wave height can reach 3~5m. The above passive defense measures are basically difficult to be effective. Summary of the Invention

[0006] In order to overcome the shortcomings of the above-mentioned technology, the purpose of the present invention is to provide a method and a floating bridge for artificially adjusting the length of the wind zone in the reservoir area and reducing the superelevation of the dam crest, so as to solve the engineering problems such as the increase in the height of the dam crest and the increase in the engineering workload caused by the larger wind zone length in the reservoir in the wide water area, reduce the wave climbing and the height of the wind-blocked water surface, and reduce the superelevation of the dam crest.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for manually adjusting the length of the wind zone in a reservoir area and reducing the superelevation of the dam crest is special in that it includes arranging a floating bridge upstream of the dam in the reservoir area, and the floating bridge is used to shorten the length of the effective wind zone, thereby reducing the superelevation of the dam crest.

[0008] As a preferred solution, a wire mesh is hung at the bottom of the floating bridge and a counterweight is hung at the bottom of the wire mesh to absorb waves.

[0009] As a preferred solution, the floating bridges are arranged in two or more rows, arranged side by side in sequence along the upstream direction of the dam; both ends of the floating bridges are fixed on the bank slope or island; the width of the floating bridges is 1 to 2 times the maximum average wavelength.

[0010] As a preferred solution, when the original wind zone length of the reservoir area is ≥5000m, three rows of floating bridges are arranged; the distance between the upstream water-facing surface of the dam and the adjacent floating bridge is not less than 30 times the maximum average wavelength; the distance between adjacent floating bridges is 0.15~0.2 times the original wind zone length; when the original wind zone length is <5000m, two rows of floating bridges are arranged, and the distance between the upstream water-facing surface of the dam and the adjacent floating bridge is not less than 10 times the maximum average wavelength; the distance between adjacent floating bridges is 0.2~0.3 times the original wind zone length; the original wind zone length is the effective wind zone length of the reservoir before the floating bridges are arranged.

[0011] Furthermore, when 0.1 to 0.15 times the length of the original wind zone is not less than the minimum distance requirement between the upstream waterfront surface of the dam and the adjacent floating bridge, the distance between the upstream waterfront surface of the dam and the adjacent floating bridge is 0.1 to 0.15 times the length of the original wind zone.

[0012] Furthermore, the maximum average wavelength is the maximum value of the average wavelengths calculated under various characteristic water level conditions of the reservoir before the floating bridge is arranged.

[0013] As a preferred embodiment, the above method specifically comprises the following steps: 1) Obtain data on relevant parameters for dam crest superelevation calculation; 2) calculating the wave elements of the reservoir area based on the relevant parameters; 3) arranging a floating bridge upstream of the dam in the reservoir area based on the relevant parameters and wave elements; 4) Calculate the superelevation of the dam crest in the reservoir area after the pontoon bridge is laid.

[0014] Furthermore, in step 1), the relevant parameters for calculating the dam top superelevation include the length of the reservoir's original wind zone, the reservoir's characteristic water level, the reservoir's multi-year average maximum wind speed W0, and the average depth of the water area H. m , water depth of the dam body upstream H, upstream slope coefficient m, upstream slope roughness and permeability coefficient K Δ, the wind speed W is selected and calculated according to the characteristic working conditions; the characteristic water level of the reservoir area includes one or more of the normal water level, the design flood level and the verification flood level; the wave elements include one or more of the average wavelength, the average wave height, the wave run-up and the wind-damaged water surface height.

[0015] Furthermore, the relevant parameters for calculating the dam crest superelevation are obtained by consulting the reservoir's hydrological and topographic parameters and conducting on-site investigations of the reservoir's hydrological and meteorological data and reservoir area topographic data.

[0016] Furthermore, the method for obtaining the original wind zone length of the reservoir includes: selecting the midpoint of the dam axis as the reference point, and measuring the straight-line distance from the reference point to the reservoir shoreline along the upstream upwind direction, which is the original wind zone length of the reservoir.

[0017] Furthermore, step 2) includes calculating the average wavelength and average wave height at each characteristic water level in the reservoir area, and obtaining the maximum average wavelength and maximum average wave height.

[0018] Furthermore, step 3) includes determining the number of floating bridges to be arranged based on the original wind zone length; determining the floating bridge arrangement distance based on the maximum average wavelength and the original wind zone length; and determining the draft depth of the wire mesh based on the maximum average wave height.

[0019] Furthermore, step 4) includes: Obtain the new wind zone length after the floating bridge is laid in the reservoir area; Calculate the new average wavelength, average wave height and dam crest superelevation under various characteristic water level conditions after the floating bridge is laid in the reservoir area; The maximum value of the dam crest superelevation under various characteristic water level conditions after laying the floating bridge is selected as the dam crest superelevation after laying the floating bridge.

[0020] Furthermore, the length of the new wind zone is 1 to 1.5 times the distance between the upstream waterfront surface of the dam and the adjacent floating bridge.

[0021] The present invention also provides a floating bridge, which is used to adjust the length of the wind zone in the reservoir area and reduce the superheight of the dam top. It is assembled and spliced by pontoons. Its special feature is that: anchoring devices are provided at both ends of the floating bridge, and the floating bridge is fixed to the bank slopes or islands on both sides of the reservoir area through the anchoring devices.

[0022] As a preferred solution, the buoys are connected in series via waterproof ropes.

[0023] As a preferred solution, the buoy has an internal sealed space, and the internal sealed space is partially filled with fine-grained sand and gravel.

[0024] As a preferred solution, vertical lifting ears are provided at the bottom of the buoy along the axis in the longitudinal direction of the floating bridge, a wire mesh is hung on the vertical lifting ears, and a counterweight is hung at the bottom of the wire mesh.

[0025] Furthermore, the draft of the wire mesh reaches 1 to 2 times of the maximum average wave height; and the counterweight ratio is 3 to 5 kg for every 10 m length of the wire mesh.

[0026] Furthermore, the buoy is a rectangular parallelepiped structure with a square top surface, and the height of the buoy is 1 to 2 times the length of a side of the square.

[0027] Currently, there are basically no wave-smoothing engineering measures in the wide water reservoir area, resulting in the wind zone length being basically the distance from the calculation point to the opposite bank. The effective wind zone length is large, and the wave height and wind-damaged water surface height are large. Compared with the existing technology, the beneficial effects of the present invention are: The present invention aims to solve the engineering problems of wave run-up and wind-impeded water surface height increase caused by the larger wind zone length in wide water reservoirs, resulting in superelevation of dam crest and increased engineering workload. The present invention proposes a dam crest superelevation design method and a floating bridge for manually adjusting the wind zone length and reducing wave run-up. That is, by laying a floating bridge in the reservoir area, the wave conduction and wave breaking in the reservoir area are actively intervened, the wind zone length is manually regulated and shortened, and the larger wave run-up and wind-impeded water surface height caused by wave conduction in a larger wind zone length are avoided, thereby reducing the superelevation of dam crest and avoiding the concrete engineering workload or earthwork filling engineering workload caused by a larger degree of superelevation of dam crest.

[0028] (1) The present invention combines the needs of the reservoir project and uses a floating bridge to significantly reduce the wave surge on the downstream side of the floating bridge. The length of the wind zone is artificially designed to reduce the wave climb and the dam crest superelevation, thereby reducing the dam crest design elevation and avoiding the filling engineering volume caused by a larger dam crest elevation.

[0029] (2) The floating bridge project adopted by the present invention is low-cost and can be assembled and spliced quickly. Compared with the filling project caused by a larger dam top elevation, the construction period of the floating bridge is short and it can provide a convenient foundation for subsequent tourism development. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a structural schematic diagram of a floating bridge according to the present invention; Figure 2 for Figure 1 Schematic diagram of the top view of a single buoy; Figure 3 for Figure 1 Schematic diagram of the main view of the middle buoy; Figure 4 for Figure 1 A top view of the assembly of the middle buoy; Figure 5 This is a schematic diagram of the arrangement of the floating bridge in the reservoir area in a method of manually adjusting the length of the wind zone and reducing the superelevation of the dam crest according to the present invention; In the figure: A, midpoint of the dam axis; 1, dam; 2, reservoir shoreline; D0, straight-line distance from the midpoint of the dam to the reservoir shore along the upstream upwind direction, i.e., the length of the original wind zone; D1, D2, and D3, from downstream to upstream, are the first-level pontoon spacing, second-level pontoon spacing, and third-level pontoon spacing, respectively; 3, pontoon; 4, anchoring device; 5, waterproof flexible rope; L0, pontoon width; 301, buoy; 302, horizontal lifting lug; L1, buoy width; 303, splicing bolt; 304, vertical lifting lug; 305, sand and gravel; 306, wire mesh; 307, counterweight rope; 308, counterweight; L2, buoy height; L3, wire mesh draft; L m1 , average wavelength; h m1 , average wave height. DETAILED DESCRIPTION

[0031] In order to better explain the present invention, the main contents of the present invention are further illustrated below with reference to the accompanying drawings and specific embodiments, but the contents of the present invention are not limited to the following embodiments.

[0032] Example 1 like Figures 1 to 4 As shown, a floating bridge 3 of the present invention is used to adjust the length of the wind zone in a reservoir and reduce the superelevation of the dam crest. It is assembled and spliced from pontoons 301. Anchoring devices 4 are installed at both ends of the pontoon 3, and the pontoon 3 is fixed to the bank slopes or islands on both sides of the reservoir through the anchoring devices 4. The pontoons 301 have an internal sealed space, which is partially filled with fine-grained sand and gravel 305. Vertical lifting lugs 304 are installed on the bottom of the pontoons 301 along the longitudinal axis of the pontoon 3. Wire mesh 306 is suspended from the vertical lifting lugs 304, and a counterweight 308 is suspended from the bottom of the wire mesh 306.

[0033] Specifically, the floating bridge 3 is composed of a plurality of interlocking, assembled and spliced pontoons 301, each of which has an internal sealed space. The pontoons 301 are rectangular parallelepiped structures with square top surfaces. The side length L1 of the top square of a single pontoon 301 can be selected from 1m to 2m. The height of a single pontoon 301 is denoted as L2, and the height L2 of the pontoon 301 is required to be 1-2 times the side length L1 of the top square of the pontoon 301. To enhance the stability of the pontoons 301, ensure that they can float stably on the water surface, and minimize their swaying caused by wave propagation, the interior of the pontoons 301 is filled with fine-grained gravel 305, one-third of its volume, with an average particle size of 1cm.

[0034] The sides of the buoys 301 are provided with matching grooves and protrusion structures, so that adjacent buoys 301 can be quickly spliced together in a snap-on style, ensuring that each buoy 301 can be snapped together without leaving any gaps. Grooves are provided at the four corners of the buoys 301 to facilitate the installation of splicing bolts 303. Horizontal lifting ears 302 are provided at the four corners of the middle part of the buoys 301. Two or four adjacent horizontal lifting ears 302 are superimposed on each other, so that splicing bolts 303 can be provided at the horizontal lifting ears 302 to fix the four adjacent buoys 301 together, ensuring the overall stability of the spliced buoys. The buoys 301 are connected in series through waterproof flexible ropes 5 and fixedly tied to the bank slopes on both sides to ensure the stability of the floating bridge.

[0035] Vertical lifting lugs 304 are installed at the bottom of pontoons 301. After pontoons 301 are assembled, a single row of wire mesh 306 is vertically suspended from the vertical lifting lugs 304 along the longitudinal axis of the bottom of floating bridge 3. Counterweights 308 are suspended from the bottom of wire mesh 306 via counterweight ropes 307. The counterweights 308 are 3-5 kg per 10 meters of wire mesh 306. The draft L3 of wire mesh 306 is 1-2 times the maximum average wave height. The maximum average wave height is the maximum value of the different average wave heights calculated under various characteristic water level conditions before floating bridge 3 is installed in the reservoir. Based on the actual requirements and the mesh's stability and ability to intercept waves below the water surface, different mesh opening sizes and counterweights 308 are selected. The selection method is as follows: To ensure the mesh's stability and prevent it from being overturned by waves and currents below the surface, mesh opening sizes range from 10×10cm to 20×20cm, and the counterweight ratio at the bottom of mesh 306 is 4–5 kg / 10m. To ensure the mesh's ability to intercept waves below the surface, mesh opening sizes range from 2×2cm to 10×10cm, and the counterweight ratio at the bottom of mesh 306 is 3–4 kg / 10m. Considering the shallow water depth near the banks of the reservoir, the mesh depth can be shortened to just touch the bottom of the bank.

[0036] Example 2 The present invention provides a method for manually adjusting the length of the wind zone and reducing the dam crest superelevation, which is applicable to wide-water reservoirs and large reservoirs. The method includes arranging a floating bridge upstream of the dam in the reservoir area to shorten the effective wind zone length, thereby reducing the dam crest superelevation. The method specifically includes the following steps: 1) Select a reservoir as the application object and record the characteristic water levels of the reservoir area: normal water storage level, design flood level and verification flood level.

[0037] Check the reservoir hydrological and topographic parameters, conduct on-site investigation of the reservoir hydrological and meteorological data and reservoir area topographic data, record the average maximum wind speed W0 in the reservoir area over the years, and measure the average depth of the water area H. m And the water depth H of the dam body's upstream surface, the upstream slope coefficient m and the upstream slope roughness permeability coefficient K Δ, the calculation wind speed W is selected according to the characteristic working conditions. The method for selecting the calculation wind speed W refers to the "Code for Design of Roller-Compacted Earth-Rock Dams" (SL274-2020).

[0038] Determine the original wind zone length D0 of the reservoir: Figure 5 As shown in the figure, the midpoint A of the dam axis is selected as the reference point, and the straight-line distance from the reference point A to the reservoir shoreline 2 is measured along the upstream upwind direction, which is the original wind zone length D0 of the reservoir.

[0039] 2) Calculate the wave elements and dam crest superelevation y1 in the reservoir area under natural conditions 2.1) Calculate the average wavelength L under each characteristic water level condition m1 , average wave height h m1 and dam crest super height y1 According to the design specifications, under various characteristic water level conditions, the average depth of the water area H is measured and consulted. m , water depth of the dam body upstream H, upstream slope coefficient m, upstream slope roughness and permeability coefficient K Δ and calculate the wind speed W, and calculate the average wavelength L under each characteristic water level condition m1 and average wave height h m1 Based on the dam level, the wave run-up R1, wind-induced water level e1, and safety height A0 are calculated for each characteristic water level, and the dam crest free height for each characteristic water level is deduced. The maximum dam crest free height value under each characteristic water level is selected as the existing dam crest free height y1.

[0040] 3) Multiple rows of floating bridges from Example 1 are arranged along the bank slopes upstream of the reservoir dam (or on the reservoir islands), starting from the dam and moving upstream. These rows are perpendicular to the incoming water. The floating bridge closest to the dam is the first floating bridge. The floating bridges from downstream to upstream are the first floating bridge, the second floating bridge, the third floating bridge, and so on. The distance between the first floating bridge and the waterfront of the dam is the first floating bridge spacing D1. From downstream to upstream, the distances between adjacent floating bridges are the second floating bridge spacing D2, the third floating bridge spacing D3, the fourth floating bridge spacing D4, and so on. The width of each floating bridge is L0. The floating bridges float on the water surface and are fixed at both ends to the bank slopes or to the bank slope and the central island by anchoring devices.

[0041] To ensure the bridge's wave-breaking effectiveness, the bridge width, L0, should be 1 to 2 times the maximum average wavelength. The maximum average wavelength is the maximum value among the different average wavelengths calculated under various characteristic water level conditions before the bridge is laid.

[0042] To balance dam safety and ensure the wave-breaking effectiveness of floating bridges, when the original wind zone length D0 is ≥5000m, three rows of floating bridges are deployed within the upstream reservoir area. Taking into account the original wind zone length and the average wave wavelength, the spacing between adjacent floating bridges is 0.15-0.2 times the original wind zone length D0, and the spacing D1 between first-level floating bridges is 0.1-0.15 times the original wind zone length D0. To ensure dam safety and prevent floating bridges from impacting the upstream dam slope, D1 is required to be no less than 30 times the maximum average wavelength. If D1 cannot simultaneously meet the requirements of 0.1-0.15 times the original wind zone length and no less than 30 times the maximum average wavelength, dam safety is prioritized, ensuring D1 is no less than 30 times the maximum average wavelength.

[0043] When the original wind zone length is 5000m greater than D0, two rows of floating bridges are deployed within the upstream reservoir area. Taking into account the original wind zone length and the average wave wavelength, the spacing between adjacent floating bridges is 0.2-0.3 times the original wind zone length D0, and the spacing between first-level floating bridges, D1, is 0.1-0.15 times the original wind zone length D0. To ensure dam safety and prevent floating bridges from impacting the upstream dam slope, D1 is required to be no less than 10 times the maximum average wavelength. Similarly, if D1 cannot simultaneously meet the requirements of 0.1-0.15 times the original wind zone length D0 and no less than 10 times the maximum average wavelength, dam safety is prioritized, ensuring D1 is no less than 10 times the maximum average wavelength.

[0044] 4) Calculate the dam crest superelevation after the pontoon bridge is laid Calculate the new wind zone length D0' after the floating bridge is laid in the reservoir area: Considering that the average wavelength and average wave height of waves are attenuated after passing through the floating bridge, the new wind zone length D0' in front of the dam is significantly reduced compared with the original wind zone length D0. Combined with the experience of wave transmission engineering, D0' can be taken as 1~1.5 times D1.

[0045] Calculate the average wavelength L under each characteristic water level condition after laying the floating bridge in the reservoir area m2 , average wave height h m2 And dam crest super height y2: According to the design specifications, under the conditions of various characteristic water levels, using the measured and consulted average water depth H m , water depth in front of the water-facing slope H, water-facing slope coefficient m, water-facing slope roughness permeability coefficient K Δ and calculated wind speed W, combined with the new wind zone length D0' after laying the floating bridge in the reservoir area to calculate the average wavelength L under each characteristic water level condition m2 and average wave height h m2Based on the dam level, the wave runup R2, wind-induced water level e2, and safety height A0 were calculated for each characteristic water level. The dam crest superelevation was then deduced, and the highest value under each characteristic water level was selected as the dam crest superelevation y2. D0 - D0' represents the reduction in wind zone length, and y1 - y2 represents the reduction in dam crest superelevation after the floating bridge is installed within the reservoir.

[0046] The working principle of the floating bridge is as follows: most of the wave energy is concentrated in the surface layer of the water body, especially in the water body within 2 to 3 times the thickness of the wave height near the free water surface, where 90% to 98% of the wave energy is concentrated. The deep water body is basically relatively still and has no obvious fluctuations. The floating bridge is laid in the wide water reservoir area, and the characteristic of the floating bridge always floating on the water surface is used to intercept the longitudinal propagation of waves on the water surface and within the range of 2 to 3 times the wave height. The characteristics of the collision between the wave surface in the direction of the water flow and the reflected waves after the waves are intercepted by the floating bridge are continuously exerted, which accelerates the conversion of wave energy, enhances the attenuation of wave energy in the reservoir area, artificially destroys the wave propagation in the reservoir area, artificially attenuates the wave height and wavelength, and stabilizes the water surface on the downstream side of the floating bridge as much as possible, avoids the transmission of waves in the long-distance wind zone to the front edge of the dam slope, thereby artificially adjusting the length of the wind zone in the reservoir area, reducing the wave climb on the upstream dam slope and the super-high dam crest, and avoiding the dam filling project caused by the larger super-high dam crest.

[0047] The present invention is further described below through specific cases.

[0048] A certain reservoir is located in the hilly area of the middle and lower reaches of the Yangtze River. Its total storage capacity reaches the scale of a large (1) type project and its engineering grade is Class I. The dam is an earth-rock dam with a crest length of 700m, a crest width of 10m, a maximum dam height of 63.5m, and a crest elevation of 73.5m. The average maximum wind speed W0 over many years is 13.2m / s, and the length of the original wind zone D0 is 7000m. The slope ratio of the upstream dam is 1:2.93, and the slope ratio of the downstream dam is 1:3.5. The average elevation of the riverbed bottom in the reservoir area is 15m. The design flood level of the reservoir is 70.13m, the verification flood level is 73.01m, and the normal water level is 65.00m.

[0049] 1) Obtain data on relevant parameters for dam crest superelevation calculation.

[0050] 2) Based on relevant parameters, calculate the wave elements and dam crest superelevation of the reservoir area.

[0051] (1) Calculation of wave elements According to the Code for Design of Roller-Compacted Earth-Rock Dams (SL274-2020), for reservoirs in hilly and plain areas, when W < 26.5 m / s and D < 7500 m, the wave height and average wavelength can be calculated using the Hedi Reservoir formula:

[0052]

[0053] Where: h 2% ——wave height with cumulative frequency of 2%, in m; W is the calculated wind speed; D is the length of the wind zone; L m This is the average wavelength to be calculated.

[0054] Wave height h under different cumulative frequencies P (%) p It can be obtained by calculating the ratio of the average wave height to the average water depth and the corresponding cumulative frequency according to the coefficients specified in Table A.1.8 of the Code for Design of Roller Compacted Earth-Rock Dams (SL274-2020). During the calculation process, it is necessary to assume and calculate the average wave height h m , as shown in Table 1.

[0055] Table 1: Ratio of wave height to mean wave height (h) at different cumulative frequencies P (%) p / h m )

[0056] (2) Calculation of wave run-up The design wave run-up value should be determined according to the project grade. For dams of grades 1, 2 and 3, the design wave run-up value R1% with a cumulative frequency of 1% is used; for dams of grades 4 and 5, the design wave run-up value R5% with a cumulative frequency of 5% is used. When the slope coefficient of the upstream slope is m = 1.5~5.0, the average wave run-up is calculated as follows:

[0057] Where: R m ——mean wave run-up, m; m——slope coefficient of the water-facing slope. If the slope angle is α, it is equal to cotα; K Δ —Roughness and permeability coefficient of the water-facing slope, which can be obtained from the Code for Design of Roller-Compacted Earth-Rock Dams (SL274-2020) based on the type of facing; K w ——Empirical coefficients are obtained according to the "Code for Design of Roller-Compacted Earth-Rock Dams" (SL274-2020), as shown in Tables 2 and 3.

[0058] Table 2: Roughness and permeability coefficient K Δ

[0059] Table 3: Empirical coefficient K w

[0060] Wave height R at different cumulative frequencies pThe average wave height h m The ratio of the water depth H to the water front of the dam body and the corresponding cumulative frequency P (%) are calculated according to the coefficients specified in Table A.1.13 of the "Code for Design of Roller-Compacted Earth-Rock Dams" (SL274-2020), as shown in Table 4.

[0061] Table 4: Ratio of climbing height to average climbing height under different cumulative frequencies (R p / R m )

[0062] (3) Height of water level caused by wind The height of the wind-damaged water surface is calculated as follows:

[0063] Where: e is the height of the wind-damaged water surface at the calculation point, m; K f ——Comprehensive friction coefficient, take 3.6×10 -6 ; W——calculated wind speed, m / s; D——wind zone length, m; g——acceleration due to gravity, take 9.81m / s 2 ; H m ——average water depth, m; β——the angle between the calculated wind direction and the normal of the dam axis, (°).

[0064] (4) Dam crest superelevation The dam crest superelevation under various characteristic water level conditions is calculated through wave run-up, wind-induced water level height and safety heightening, and the highest one is selected as the dam crest superelevation.

[0065] 3) Laying of floating bridge According to the present invention, three floating bridges are laid in the upstream reservoir area at 900m, 2100m and 3300m away from the water surface of the dam. The floating bridges are 40m wide and are spliced by 1m×1m rectangular pontoons. The size of a single pontoon is 1m×1m×2m, and 1 / 3 of the volume of the pontoon is filled with fine-grained sand and gravel. A 2.5m high wire mesh with a mesh size of 3×3cm is hung vertically directly below the floating bridge, and a 4kg counterweight is hung vertically every 10m at the bottom of the wire mesh.

[0066] 4) Calculation of dam crest superelevation after laying the floating bridge Assuming the new wind zone length D0' is 1000m, calculate the new dam crest superelevation y2 according to the formulas in the previous step 2).

[0067] The calculation results of various parameters before and after laying the floating bridge are shown in Table 5.

[0068] Table 5: Calculation results of various parameters under different characteristic water levels, unit / m

[0069] Table 5 shows that for each characteristic water level condition (normal storage level, design flood level, and check flood level), when there is no floating bridge within the reservoir area, the original wind zone length D0 is 7000m, and the maximum calculated dam crest elevation is 73.01 + 2.60 = 75.61m under the check flood level. After the floating bridge is added to the reservoir area, the new wind zone length D0' is 1000m, and the maximum calculated dam crest elevation is 73.01 + 1.71 = 74.72m under the check flood level. Compared to the dam crest free height calculation without the floating bridge within the reservoir area, the maximum dam crest free height can be reduced by 0.89m after the floating bridge is added to the reservoir area. Therefore, adding a floating bridge within the reservoir area can significantly reduce the design dam crest elevation.

[0070] In this embodiment, the dam is an earth-rock dam with a crest length of 700m, a crest width of 10m, a maximum dam height of 63.5m, and a crest elevation of 73.5m. The upstream dam slope ratio is 1:2.93, and the downstream dam slope ratio is 1:3.5. The upstream dam slope is a dry block stone slope protection, and the downstream dam slope is a turf slope protection. According to the calculation of the dam crest superelevation, after adding a floating bridge in the reservoir area, the maximum dam crest superelevation can be reduced by 0.89m. Ignoring the difference in the height of the left and right dam abutments and the height of the middle part of the dam body, the engineering volume is calculated based on the maximum dam height section. The filling volume of the dam crest and upstream and downstream dam slopes can be reduced as shown in Table 6, saving 119,000m of earthwork filling volume on the upstream dam slope. 3 , dam top filling earthwork volume 0.62 thousand m 3 , saving 142,100 m2 of earthwork on the downstream dam slope 3 , greatly reducing the amount of work, saving materials, construction time, costs, and increasing the efficiency of dam construction.

[0071] Table 6: Savings in filling work volume on the dam crest and upstream and downstream dam slopes compared to the original

[0072] In summary, the method of the present invention can effectively reduce the superelevation of the dam crest, thereby saving engineering workload and reducing costs, effectively eliminating waves, reducing wave run-up and wind-induced water level height, and improving the construction efficiency of the dam.

[0073] Other parts not described belong to the prior art.

Claims

1. A method for manually adjusting the length of the wind zone in the reservoir area and reducing the superelevation of the dam top, characterized by: The method comprises arranging a floating bridge upstream of the dam in the reservoir area, wherein the floating bridge is used to shorten the length of the effective wind zone, thereby reducing the super-height of the dam top.

2. The method according to claim 1, wherein: A wire mesh is hung at the bottom of the floating bridge, and a counterweight is hung at the bottom of the wire mesh.

3. The method according to claim 1, wherein: The floating bridges are arranged in two or more rows and are arranged in sequence along the upstream direction of the dam; both ends of the floating bridges are fixed on the bank slope or island; and the width of the floating bridges is 1 to 2 times the maximum average wavelength.

4. The method according to claim 1, wherein: When the original wind zone length of the reservoir area is ≥5000m, three rows of floating bridges are arranged, and the distance between the upstream water-facing surface of the dam and the adjacent floating bridge is not less than 30 times the maximum average wavelength, and the distance between adjacent floating bridges is 0.15~0.2 times the original wind zone length; when the original wind zone length is <5000m, two rows of floating bridges are arranged, and the distance between the upstream water-facing surface of the dam and the adjacent floating bridge is not less than 10 times the maximum average wavelength, and the distance between adjacent floating bridges is 0.2~0.3 times the original wind zone length.

5. The method according to claim 4, characterized in that: When 0.1 to 0.15 times the length of the original wind zone is not less than the minimum distance requirement between the upstream waterfront surface of the dam and the adjacent floating bridge, the distance between the upstream waterfront surface of the dam and the adjacent floating bridge is 0.1 to 0.15 times the length of the original wind zone.

6. The method according to claim 3, 4 or 5, characterized in that: The maximum average wavelength is the maximum value of the average wavelengths calculated under various characteristic water level conditions of the reservoir before the floating bridge is arranged.

7. The method according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Obtain data on relevant parameters for dam crest superelevation calculation; 2) calculating the wave elements of the reservoir area based on the relevant parameters; 3) arranging a floating bridge upstream of the dam in the reservoir area based on the relevant parameters and wave elements; 4) Calculate the superelevation of the dam crest in the reservoir area after the pontoon bridge is laid.

8. The method according to claim 7, wherein: In step 1), the relevant parameters for calculating the dam top superelevation include the length of the original wind zone of the reservoir, the characteristic water level of the reservoir, the average maximum wind speed W0 of the reservoir over many years, the average depth of the water area H m , water depth of the dam body upstream H, upstream slope coefficient m, upstream slope roughness and permeability coefficient K Δ , the wind speed W is selected and calculated according to the characteristic working conditions; the characteristic water level of the reservoir area includes one or more of the normal water level, the design flood level and the verification flood level; the wave elements include one or more of the average wavelength, the average wave height, the wave run-up and the wind-damaged water surface height.

9. The method according to claim 7, wherein: Step 4) includes: Obtain the new wind zone length after the floating bridge is laid in the reservoir area; Calculate the new average wavelength, average wave height and dam crest superelevation under various characteristic water level conditions after the floating bridge is laid in the reservoir area; The maximum value of the dam crest superelevation under various characteristic water level conditions after laying the floating bridge is selected as the dam crest superelevation after laying the floating bridge.

10. The method according to claim 9, characterized in that: The length of the new wind zone is 1 to 1.5 times the distance between the upstream waterfront surface of the dam and the adjacent floating bridge.

11. A floating bridge, used to adjust the length of the wind zone in the reservoir area and reduce the super height of the dam top, is assembled and spliced by pontoons; its characteristics are: Anchoring devices are provided at both ends of the floating bridge, and the floating bridge is fixed to the bank slopes or islands on both sides of the reservoir area through the anchoring devices.

12. The floating bridge according to claim 11, characterized in that: The buoy has an internal sealed space, and the internal sealed space is partially filled with fine-grained sand and gravel.

13. The floating bridge according to claim 11 or 12, characterized in that: A vertical lifting lug is provided at the bottom of the buoy on the axis in the length direction of the floating bridge, a wire mesh is hung on the vertical lifting lug, and a counterweight is hung at the bottom of the wire mesh.

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