A stepped drop energy dissipation method with noise reduction function

Abstract

The present application relates to the field of hydraulic engineering in the water conservancy and hydropower industry, and particularly relates to a stepped water-drop energy dissipation method with noise reduction function. The method forms a three-stage collaborative energy dissipation system of "pebble sound attenuation zone-water-drop step-energy dissipation pool" by excavating tooth grooves, laying anti-freezing impermeable geomembrane, pouring pebble sound attenuation zone framework and filling light-colored natural pebbles, combining with the water-drop steps with surface buried pebbles and the end energy dissipation pool. The method is suitable for various scenes such as urban landscape and freezing and thawing in the north, and has ecological compatibility and construction economy, and the service life of the structure is extended to more than 15 years.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering in the water conservancy and hydropower industry, specifically to a stepped waterfall energy dissipation method with noise reduction function. Background Technology

[0002] Water flow drop engineering projects in urban parks, regulating lakes, and landscape greening often employ multi-stage stepped waterfalls to dissipate water flow energy. This is achieved through progressive collisions and turbulence, reducing downstream scouring. However, existing stepped waterfalls have the following technical drawbacks:

[0003] 1. Significant noise pollution: The water flows directly down and hits the concrete steps, producing a high-frequency, sharp "whooshing" sound. Within 30 meters of the residential area, the noise level can reach more than 65dB, exceeding the nighttime limit of 50dB in the "Environmental Quality Standard for Noise" (GB3096-2008), seriously interfering with the lives and environmental comfort of the surrounding residents.

[0004] 2. Limited energy dissipation efficiency: The energy dissipation rate of traditional two-stage cascades is only about 65%. Under high flow conditions, the flow velocity is still too fast, and the downstream riverbed is severely eroded, which can easily lead to bank instability and structural damage.

[0005] 3. Poor structural durability: Water flow directly washes over the concrete surface, which can easily cause cavitation and abrasion, resulting in a structural service life of less than 10 years. At the same time, the lack of foundation anti-seepage measures makes it easy for seepage and frost heave to cause problems such as foundation settlement and structural cracking in northern freeze-thaw regions.

[0006] 4. High construction and maintenance costs: Traditional drop structures are complex and require large equipment for construction. In the limited space of the city, the construction period is often long. Moreover, the energy dissipation components are prone to blockage and erosion, resulting in frequent and costly maintenance. The pebble energy dissipation area is also prone to siltation, which can affect the energy dissipation and noise reduction effect.

[0007] While existing technologies employ individual solutions such as pebble energy dissipation or cascading water features, none have formed a synergistic system of "pebble noise reduction, cascading energy dissipation, and end-of-pipe energy dissipation pools." Furthermore, no systematic solutions have been proposed for noise control in urban landscapes, adaptability to northern freeze-thaw regions, or ease of maintenance. Therefore, there is a significant technological gap. Summary of the Invention

[0008] To address the problems of existing technologies, this invention provides a stepped waterfall energy dissipation method with noise reduction function.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A stepped waterfall energy dissipation method with noise reduction function includes the following steps:

[0011] Step (1): Excavate a toothed groove with a width of 600mm and a depth of 1000mm at the point where the river water falls; form the foundation space of the energy dissipation zone; in northern freeze-thaw regions, the toothed groove can be deepened to 1200mm to enhance the foundation's resistance to frost heave.

[0012] Step (2): Lay an impermeable geomembrane in the toothed groove and at the bottom of the drop foundation to form an impermeable layer;

[0013] Step (3): Pour a concrete base slab and side walls into the tooth groove to form a pebble sound-absorbing zone frame; specifically, pour a C25 concrete base slab and side walls into the tooth groove to form a pebble sound-absorbing zone frame with a height of 1000mm.

[0014] Step (4): Lay light-colored natural pebbles with a particle size of 40mm-60mm in the pebble silencing zone, with a thickness of 600mm. Arrange multiple pebble silencing zones at intervals along the water flow direction to allow the water flow to fully collide and rub against the pebbles.

[0015] Step (5): Pour the main structure of the waterfall concrete and embed pebbles on the surface of the waterfall steps to form an anti-erosion protective layer;

[0016] Step (6): Install an energy dissipation pool at the end of the drop structure to dissipate the energy of the water flow.

[0017] The impermeable geomembrane is a frost-resistant impermeable geomembrane with a thickness of ≥0.5mm and an overlap width of ≥100mm between membranes, sealed by welding or bonding. It blocks seepage channels and prevents foundation settlement or frost heave damage.

[0018] The pebble silencing zone is arranged at 5m intervals along the water flow direction.

[0019] The bottom of the pebble silting zone is covered with reverse filter geotextile, and inspection holes are reserved on the side walls to prevent silt blockage and facilitate later maintenance.

[0020] The height of each step of the cascading water feature is 150mm–200mm, and the width of each step is 300mm–400mm.

[0021] The cobblestones embedded in the surface of the cascading steps have a particle size of 50mm–80mm and a burial depth of 20mm–40mm, forming an anti-erosion protective layer.

[0022] The energy dissipation method of the stepped waterfall has an energy dissipation pool with a depth of 1.2m–1.5m and a length of 2–3 times the total height of the waterfall. When the design flow rate increases, the pool length can be adjusted to 3–4 times the total height of the waterfall, or the number of pebble sound-absorbing zones can be increased.

[0023] The light-colored natural pebbles include white, light gray, and light yellow pebbles, which are used to convert high-frequency noise from water flow into broadband natural white noise, achieving a noise reduction of ≥15dB.

[0024] The pebble anechoic zone, cascading steps, and energy dissipation pool form a three-level synergistic energy dissipation system with a total energy dissipation rate of ≥90%.

[0025] In northern freeze-thaw regions, the depth of the tooth groove can be increased to 1200mm to enhance the foundation's resistance to frost heave.

[0026] To further quantify the energy dissipation and noise reduction effects of this invention and the design basis of its key parameters, the following formulas are used for scientific expression. It is clarified that the selection of each technical characteristic parameter is not based on conventional empirical values, but rather on a creative design based on the principles of hydraulics and acoustics, as detailed below:

[0027] 1. Formula for calculating total energy dissipation rate

[0028] The three-stage synergistic energy dissipation system of "pebble anechoic zone, cascading steps, and energy dissipation pool" of this invention can be quantitatively calculated for its total energy dissipation rate ε using the following formula, which intuitively demonstrates the superior energy dissipation effect:

[0029]

[0030] In the formula:

[0031] The upstream inlet velocity (unit: m / s) reflects the initial energy of the upstream water flow;

[0032] The outlet velocity of the energy dissipation tank (unit: m / s) reflects the remaining energy of the water after it has passed through three stages of energy dissipation.

[0033] The total energy dissipation rate (unitless) is ε≥90% in this invention, which is much higher than the 65% of the traditional stepped waterfall, demonstrating the creative synergistic effect of the three-stage energy dissipation system.

[0034] 2. Formula for noise reduction in the pebble anechoic zone

[0035] This invention achieves noise optimization through a pebble anechoic zone. The noise reduction amount ΔL can be quantified using the following formula to clarify the verifiability of the noise improvement effect:

[0036]

[0037] In the formula:

[0038] The noise level (in dB) of a traditional stepped waterfall at 30 meters in a residential area is typically ≥65 dB.

[0039] After adopting this invention, the noise level (in dB) at 30 meters in residential areas can be reduced to below 50 dB;

[0040] The noise reduction amount (unit: dB) is ΔL≥15dB in this invention, which proves that the noise reduction effect of the pebble anechoic zone has a scientific basis and is not simply a matter of piling up materials.

[0041] 3. Design formula for energy dissipation pool length

[0042] As the final stage of the three-stage energy dissipation system, the length L of the energy dissipation pool must be designed to match the total height of the cascade and the water flow rate to ensure the final energy dissipation effect. The design formula is as follows:

[0043]

[0044] In the formula:

[0045] coefficient (Unitless), select according to the design flow rate: when the flow rate is small, k is 2 to 3; when the flow rate is large, k is 3 to 4, which can flexibly adapt to different working conditions;

[0046] Total height of the drop (unit: m);

[0047] The formula represents the length of the energy dissipation pool (in meters). This formula demonstrates that the selection of the energy dissipation pool length in this invention is based on hydraulic principles, rather than conventional size adjustments.

[0048] Compared with existing technologies, the invention has the following advantages: significant noise reduction. Through the pebble anechoic zone, the high-frequency, harsh sound of flowing water is transformed into broadband white noise like a natural stream. The noise level can be reduced to below 50dB at a distance of 30 meters from residential areas, which meets the nighttime sound environment standards, i.e., it is 40dB lower than the nighttime noise standards for residential and educational areas.

[0049] Three-stage synergistic energy dissipation: The combination of pebble silencing zone, cascading steps and energy dissipation pool dissipates water flow energy step by step, with an energy dissipation rate of ≥90%, and the downstream flow velocity is reduced from 3m / s to 0.5m / s, which greatly reduces downstream scouring.

[0050] The structure boasts excellent durability and regional adaptability: the frost-resistant and impermeable geomembrane, combined with the deepened groove design, is perfectly suited for the freeze-thaw regions of the north, effectively preventing frost heave damage; the pebble protective layer can reduce the cavitation rate by 70%, extending the structure's service life from less than 10 years to more than 15 years.

[0051] Construction and maintenance are very convenient: the structure is simple and easy to understand, the required materials are easy to obtain, and the construction period is shortened by 40% compared with traditional processes; the design of the side wall inspection holes and the filter cloth makes it easy to quickly clean up the silt and effectively reduce maintenance costs.

[0052] The ecology and landscape are perfectly compatible: the natural light-colored pebbles blend naturally with the water, greatly enhancing the visual appeal; the gaps between the pebbles provide habitat for aquatic organisms, which fully conforms to the concept of ecological water conservancy.

[0053] The parameters are adjustable and the adaptability is extremely wide: the length of the energy dissipation pool and the number of pebble silencing zones can be flexibly adjusted according to the flow rate and drop, which can perfectly adapt to different engineering conditions and has a wide range of applications. Attached Figure Description

[0054] Figure 1 This is a schematic diagram of the structure of the present invention.

[0055] 1. Pebble sound-absorbing zone; 2. Impermeable geomembrane; 3. Waterfall tiered subbase; 4. Waterfall steps; 5. Waterfall concrete; 6. Energy dissipation pool Detailed Implementation

[0056] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0057] Example 1: Dongjiang Canal Waterfall Project of Shenzhen Shawan River Interception and Drainage Project (Southern Landscape Scene)

[0058] 1. Project Overview: The total height of the waterfall is 3m, the design flow rate is 1.2m³ / s, the surrounding area is a residential area and a park, and the noise level is required to be controlled below 50dB. The key requirements for this scenario are noise reduction, landscape compatibility and convenient maintenance, and suitability for construction in limited urban spaces.

[0059] 2. Construction steps and the functions of each technical feature:

[0060] Excavation groove: 600mm wide, 1000mm deep, and 8m long; the core function of this groove structure is to fix the subsequently laid gravel sound-absorbing layer, prevent the gravel from being washed away by water flow, and at the same time provide a stable laying space for the impermeable geomembrane, ensuring the stability of the entire energy dissipation zone foundation and avoiding foundation settlement.

[0061] Laying the impermeable layer: When laying the HDPE geomembrane, ensure the membrane thickness reaches 0.5mm, the overlap width is at least 150mm, and the joints are sealed by welding to ensure integrity. For frost-resistant geomembranes (standard frost-resistant specifications can be used in southern regions), the thickness should not be less than 0.5mm, the overlap width should be at least 100mm, and they should also be sealed by welding. These measures effectively block seepage channels, prevent soil erosion, thus avoiding structural settlement and extending the service life of the drop structure.

[0062] C25 concrete was used in the design and pouring of the energy dissipation zone. The base slab is 200mm thick, and the side walls are 300mm thick, with Φ200mm inspection holes pre-installed in the side walls. The concrete base slab and side walls together form a 1000mm high pebble sound-absorbing zone framework, with its top flush with the cascading steps, ensuring the stability of the pebble sound-absorbing layer's installation area. The design of the inspection holes facilitates the later cleaning of silt and sediment through high-pressure water flushing, effectively reducing maintenance difficulty and solving the problem of easy clogging in the pebble sound-absorbing zone.

[0063] Laying a pebble layer: The bottom layer is a reverse filter geotextile, and the top layer is a 600mm thick layer of light-colored natural pebbles with a particle size of 50mm. One layer is laid every 5m along the water flow direction, for a total of 2 layers. The reverse filter geotextile at the bottom can effectively prevent silt from clogging the gaps between the pebbles, ensuring a long-lasting and stable energy dissipation and noise reduction effect. The top layer of light-colored natural pebbles with a particle size of 40mm-60mm (50mm is selected in this embodiment) is the optimal choice within this range. It can allow the water flow to fully collide, divert, and rub against the pebbles, converting high-frequency sharp noise into broadband natural white noise, achieving a noise reduction of ≥15dB. It can also initially dissipate the energy of the water flow and distribute the water evenly, avoiding concentrated impact of the water flow on the cascading steps. One layer is laid every 5m along the water flow direction. This spacing has been verified by hydraulic tests and can balance energy dissipation efficiency and flow capacity, avoiding the problems of upstream backflow due to too small a spacing and insufficient energy dissipation due to too large a spacing.

[0064] Waterfall construction: C30 concrete, single-step height 180mm, width 350mm, 17 steps in total; 60mm cobblestones embedded on the surface, 30mm deep; single-step height of 150mm-200mm (180mm selected in this embodiment), single-step width of 300mm-400mm (350mm selected in this embodiment). This size design can achieve multi-stage drop to dissipate water flow energy step by step. Combined with the cobblestones embedded on the surface with a particle size of 50mm-80mm (60mm selected in this embodiment) and a depth of 20mm-40mm (30mm selected in this embodiment), it can form an anti-erosion protective layer, reduce the cavitation and abrasion of the concrete surface by water flow, extend the structural life by more than 5 years, and further assist in energy dissipation, improving the overall energy dissipation effect.

[0065] An energy dissipation pool is constructed, measuring 6m in length, 8m in width, and 1.3m in depth. The depth of the energy dissipation pool is 1.2m–1.5m (1.3m is selected in this embodiment), and the length of the pool is 2–3 times the total height of the waterfall (in this embodiment, the total height of the waterfall is 3m, and the length of the pool is 6m, which is twice the total height). As the end of the three-stage energy dissipation system, it can ultimately dissipate the remaining energy of the water flow, reduce the downstream flow velocity to below 0.5m / s, and completely eliminate the risk of scouring the downstream riverbed.

[0066] Effect verification:

[0067] Noise test: Traditional waterfall noise level =65dB, noise value after adopting this invention =48dB. According to the noise reduction formula, ΔL=65-48=17dB≥15dB, which verifies the noise reduction effect of the pebble anechoic zone and meets the nighttime sound environment standard.

[0068] Energy dissipation test: upstream inlet velocity =3m / s, energy dissipation pool outlet velocity =0.45m / s. According to the total energy dissipation rate formula, ε=1-(0.45² / 3²)=1-0.0225=97.75%≥90%, which verifies the high efficiency of the three-level synergistic energy dissipation system of "pebble anechoic zone + waterfall steps + energy dissipation pool".

[0069] Maintenance test: After 6 months of operation, the gravel layer was not significantly blocked by high-pressure flushing through the inspection hole, which verified the maintenance function of the reverse filter geotextile and the inspection hole and ensured that the energy dissipation and noise reduction effect remained stable.

[0070] Example 2: Ecological River Channel Project in Northern Freeze-Thaw Regions (Adaptability Validation)

[0071] 1. Project Overview: The total height of the drop structure is 2.5m, with a design flow rate of 0.8m³ / s. It is located in an ecological river in Beijing, where the lowest winter temperature is -15℃. The key requirements for this scenario are freeze-thaw resistance, structural durability, and noise reduction and energy dissipation.

[0072] 2. Construction adjustments and the effects of various technical features (focusing on freeze-thaw adaptability in northern regions):

[0073] The tooth groove is deepened to 1200mm to enhance the resistance to frost heave. Compared with the 1000mm tooth groove in the southern scenario, the 1200mm depth in the northern freeze-thaw region can further enhance the foundation's resistance to frost heave, avoid foundation settlement and structural cracking caused by winter seepage and frost heave, and adapt to the use requirements of the low temperature environment in the north.

[0074] The geomembrane is designed to withstand freezing temperatures of -25℃ to 40℃. With an overlap width of ≥100mm and a welding sealing process, it can effectively block seepage, prevent frost heave damage, solve the technical defect of easy cracking of the geomembrane in the freeze-thaw region of northern China, and ensure the durability of the structure.

[0075] The length of the energy dissipation pool is adjusted to three times the height of the waterfall (7.5m). Based on the design formula for the length of the energy dissipation pool, the total height of the waterfall in this embodiment is H=2.5m. The design flow rate is relatively small, so the coefficient k=3 is selected. The calculated length of the energy dissipation pool is L=3×2.5=7.5m, which is consistent with the actual construction dimensions. This can further improve the energy dissipation effect and ensure that the downstream flow velocity is reduced to below 0.5m / s. It is also suitable for the water flow conditions of northern rivers. The other technical features (pebble silencing zone, waterfall steps, etc.) are consistent with those in Embodiment 1. They have the same function, namely, to achieve noise reduction, auxiliary energy dissipation, and convenient maintenance. The light-colored natural pebbles also take into account ecological and landscape compatibility, and the gaps between the pebbles can provide habitat space for aquatic organisms.

[0076] Effect verification:

[0077] Freeze-thaw cycle test: After two winters of operation, the structure showed no cracking or leakage, verifying the freeze-thaw resistance of the deepened groove and the frost-resistant impermeable geomembrane, making it suitable for use in northern freeze-thaw regions;

[0078] Noise test: Traditional waterfall noise level =65dB, noise value after adopting this invention =49dB. According to the noise reduction formula, ΔL=65-49=16dB≥15dB, which verifies that the noise reduction effect of the pebble anechoic zone is stable.

[0079] Energy dissipation test: upstream inlet velocity =2.8m / s, outlet velocity of the energy dissipation pool =0.4m / s. According to the total energy dissipation rate formula, ε=1-(0.4² / 2.8²)=1-0.0204=97.96%≥90%, which verifies the applicability of the three-level collaborative energy dissipation system in northern scenarios and can effectively reduce downstream scouring.

Claims

1. A stepped waterfall energy dissipation method with noise reduction function, characterized in that, Includes the following steps: Step (1): Excavate a toothed groove with a width of 600mm and a depth of 1000mm at the point where the river water falls; Step (2): Lay an impermeable geomembrane (2) inside the toothed groove and at the bottom of the drop foundation to form an impermeable layer; Step (3): Pour concrete base slab and side walls into the tooth groove to form the pebble sound absorption zone (1) frame; Step (4): Lay light-colored natural pebbles with a particle size of 40mm–60mm in the pebble silencing zone (1), and arrange multiple pebble silencing zones (1) at intervals along the water flow direction. Step (5): Pour the main structure of the drop concrete (5), and embed pebbles on the surface of the drop steps (4) to form an anti-erosion protective layer; Step (6): Install an energy dissipation pool (6) at the end of the drop structure to dissipate the energy of the water flow.

2. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The impermeable geomembrane (2) is a frost-resistant impermeable geomembrane (2) with a thickness ≥0.5mm and an overlap width between membranes ≥100mm.

3. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The pebble silencing zone (1) is arranged at 5m intervals along the water flow direction.

4. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The bottom of the pebble silting zone (1) is covered with reverse filter geotextile, and the side wall is reserved with inspection holes to prevent silt blockage and subsequent maintenance.

5. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The height of each step (4) is 150mm–200mm and the width of each step is 300mm–400mm.

6. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The cobblestones embedded on the surface of the cascading steps (4) have a particle size of 50mm–80mm and a burial depth of 20mm–40mm.

7. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The energy dissipation pool (6) has a depth of 1.2m–1.5m and a length of 2–3 times the total height of the waterfall. When the design flow rate increases, the pool length can be adjusted to 3–4 times the total height of the waterfall, or the number of pebble sound-absorbing zones (1) can be increased.

8. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The light-colored natural pebbles include white, light gray, and light yellow pebbles, which are used to convert high-frequency noise from water flow into broadband natural white noise, achieving a noise reduction of ≥15dB.

9. The stepped waterfall energy dissipation method according to claim 1, characterized in that, The pebble anechoic zone (1), the cascading steps (4), and the energy dissipation pool (6) form a three-level synergistic energy dissipation system with a total energy dissipation rate of ≥90%.

10. The stepped waterfall energy dissipation method according to claim 1, characterized in that, In northern freeze-thaw regions, the depth of the tooth groove can be increased to 1200mm to enhance the foundation's resistance to frost heave.

Images