An Optimization Design Method for Sandbag Revetment Structures on Eroding Beaches

Abstract

This invention belongs to the field of water conservancy and marine engineering technology, and specifically relates to an optimized design method for sandbag revetment protection structures on erosive beaches. The method includes: basic data collection, material selection and determination, optimized design of individual sandbag dimensions, and determination of the structural assembly and installation method. To better utilize sandbag protection structures for the protection of erosive sandy beaches, this application, through theoretical derivation, optimizes the stability design formula for beach sandbag structures, improves the design process for beach sandbag revetment structures, and enhances the applicability of the protection structure.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and marine engineering technology, and specifically relates to an optimized design method for sandbag revetment protection structures on erosive beaches. Background Technology

[0002] Under the dual impacts of global climate change and human activities, coastal erosion has become a significant challenge threatening global coastal ecosystems and human settlements. Statistics show that over 70% of the world's sandy coastlines are suffering from varying degrees of erosion, with the rate of coastal retreat accelerating year by year. This not only leads to the loss of coastal land resources but also causes incalculable damage to infrastructure, tourism resources, and the ecological environment of coastal areas.

[0003] As a major maritime nation, my country's long coastline is also plagued by coastal erosion. Among them, the erosion of sandy coastlines is particularly severe.

[0004] Currently, various coastal protection methods have many drawbacks. While "hard engineering" protection can safeguard the coastline, it cannot address the root causes of erosion and can also cause secondary impacts. "Soft engineering" beach maintenance, due to design and construction problems, leads to sand loss and poor restoration results. Existing protection methods often contradict the mechanisms of coastal erosion, exacerbating localized beach erosion.

[0005] Against this backdrop, there is an urgent need for a scientific and effective solution to protect eroded beaches. This is not only a necessary requirement for protecting the ecological environment and sustainable economic development of my country's coastal zone, but also an important measure to address the challenges of global climate change. Summary of the Invention

[0006] To overcome the problems of existing technologies, this invention aims to provide an optimized design method for sandbag revetment protection structures on erosive beaches through innovative design concepts and technical means, in order to address the challenge of coastal erosion.

[0007] The objective of this invention is achieved as follows:

[0008] This application provides an optimized design method for sandbag revetment protection structures on erosive beaches, including the following steps:

[0009] Step 1, Basic Data Collection:

[0010] Comprehensive data was collected on the target beach and surrounding waters, including sediment evolution characteristics, median grain size of the beach, and wave characteristics and water level changes in the surrounding waters over many years.

[0011] Step 2, Material Selection and Determination:

[0012] Taking into account the acid resistance, abrasion resistance, UV resistance and microbial resistance of geotextiles, polypropylene was selected as the material for preparing individual sandbags.

[0013] The filling material in the sandbags is selected from the in-situ median particle size of the beach, d. 50 =0.25~0.5mm of silt and sand.

[0014] Step 3, Optimization design of individual sandbag size:

[0015] The optimal sandbag size for the target beach is determined using the following design formula:

[0016]

[0017] In the formula, H s It is the incident significant wave height; μ is the coefficient of friction between the sandbags; C w It is the stability coefficient; ρ s It is the density of sand, ρ w ξ is the density of seawater; ξ0 is the fragmentation similarity parameter. L0 is the wavelength of the deep-water wave, L0 = gT 2 / 2π, T is the period of the spectral peak wave, g is the gravitational acceleration; α is the facing angle of the sandbag structure; k is the number of sandbag layers that affect a single sandbag; A T It is the area of ​​the bottom surface of the sandbag;

[0018] The above formula comprehensively considers the influence of various factors, including waves, sediment, and structure, on the size design of a single sandbag, ensuring that the designed sandbag has good stability in complex marine environments.

[0019] Step 4, Determining the structural assembly and installation method:

[0020] The design adopts a layered optimization approach, with the cross-section consisting of a fine sand filling layer, an inner layer of sandbags, and an outer layer of sandbags from the inside out.

[0021] For adjacent sandbags, a stacking method is adopted, and a connecting structure including geogrid is set as needed to enhance the overall anti-slip and anti-erosion capacity of the structure.

[0022] The final design yielded a sandbag revetment structure for the eroding beach.

[0023] Furthermore, in step 1, the wave elements include wave height, wave period, and wave direction; the water level changes include high tide, low tide, and tidal range.

[0024] Furthermore, in step 4, the outermost sandbag in the layered optimization design is made of polypropylene woven geotextile with a unit area mass ≥180g / m².2 The fracture strength is ≥35KN / m radially and ≥25KN / m latitudinally, and the permeability coefficient is 10. -4 ~10 -3 cm / s.

[0025] Furthermore, the method also includes:

[0026] Step 5, Determining the geotextile bag filling rate:

[0027] Calculate the fill rate based on the theoretical maximum volume:

[0028]

[0029] In the formula, a and b are the dimensions of the empty sandbag, and V s This represents the maximum volume of the sandbag after it is filled with sand.

[0030] Specifically, it should be ensured that the filling rate of a single sandbag is greater than 75%.

[0031] Step 6, Design wave height calculation:

[0032] Long-term measured wave data for a certain sea area is obtained using equipment including ocean observation buoys and wave monitoring stations;

[0033] Samples were selected using the ANL and POT methods, and the sample data were substituted into the probability distribution function. The least squares method was used to fit the data, and the relevant parameters of each distribution function were calculated. Based on the comparative analysis of indicators such as root mean square error and correlation coefficient, the best-fit distribution function was determined. The design wave height of the target sea area was calculated using the best-fit distribution function, providing key parameters for the design of sandbag revetments.

[0034] Step 7, Optimize sandbag structural design elements:

[0035] Based on the relevant formulas for wave run-up on sandbag structures, and combined with the actual slope and roughness of the target beach, the wave run-up value is calculated. By comparing the wave run-up calculation results considering the sandbag thickness and those not considering the sandbag thickness, a reasonable top elevation of the structure is determined.

[0036] The advantages and beneficial effects of this invention are:

[0037] 1. This invention provides solid data support for subsequent design by comprehensively collecting basic data and deeply analyzing the characteristics of the coastal environment, ensuring that the design scheme meets actual needs and improving the applicability of the protective structure;

[0038] 2. In the sandbag revetment protection structure optimization design method of the present invention, the innovative single sandbag size design formula comprehensively considers multiple factors, which significantly improves the scientificity and rationality of sandbag design, enhances the stability of sandbags in complex marine environments, and reduces the risk of structural instability.

[0039] 3. The unique structural combination and installation method of the sandbag revetment protection structure described in this invention, through layered design and reasonable material selection, effectively prevents the loss of fine sand, enhances the integrity and erosion resistance of the structure, and improves the protective effect and durability of the sandbag revetment.

[0040] 4. The optimized design method for sandbag revetment protection structure described in this invention provides a more accurate assessment of structural stability through optimized stability control equations, offering a more reliable theoretical basis for the design, construction, and maintenance of sandbag revetments, and contributing to improved safety and reliability of coastal protection projects.

[0041] 5. The precise design wave height calculation method in this invention combines multiple sampling and analysis methods to determine the optimal probability distribution function, thereby obtaining a more accurate design wave height. This provides key design parameters for sandbag revetment structure design and ensures the safety of the structure under wave action with different return periods.

[0042] 6. In the sandbag revetment protection structure optimization design method of the present invention, the optimization of sandbag structure design elements, such as reasonably determining the top elevation of the structure and selecting appropriate geotextile materials, further improves the protection performance and durability of sandbag revetment and reduces long-term maintenance costs.

[0043] 7. The sandbag revetment protection structure optimization design method described in this invention improves the protective effectiveness of sandbag revetments, effectively prevents the retreat of erosive coastlines, and has a limited and non-permanent impact on natural coastal processes. It is a new solution for sandy coast protection that is low-cost, easy to construct, and has good protective effects. It has high cost-effectiveness, focuses on the sustainable development of protective measures and nature, and provides a better option for beach restoration and coastal protection. Attached Figure Description

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Figure 1 , Figure 2 The data shows the seasonal mean elevation of 11 profiles of the South Beach of Chudao Island from 2017 to 2019.

[0046] Figure 3 The variation trend of particle size parameters in dunes, beaches, and scour zones is shown (particle size parameters are the average values ​​of all data).

[0047] Figure 4 This is a diagram showing the return period distribution of design wave heights calculated based on the Pearson Type III curve.

[0048] Figure 5 Top view and cross-sectional views of sections 1-3 for three design schemes of sandbag bank protection test;

[0049] Figure 6 The protective effectiveness of the sandbag structure under long-term field conditions is shown; (a) and (b) are the observation results of the structure under severe cold conditions; (c) and (d) are the observation results of the sandbag structure of S2 and S3 in the field environment for more than two years.

[0050] Figure 7 These are cross-sectional and sectional views of the second experiment;

[0051] Figure 8 The changes of test sections S4 to S8 before and after the storm waves are shown; among them, (ab) section S4 failed during Typhoon "Fireworks" in 2021; (cd) shows the damage to the grass seed bags and vegetation in section S6 under the impact of the storm waves; and (ef) shows the gravel and seaweed accumulated in front of section S8.

[0052] Figure 9 The effects of sandbag filling rate on design dimensions and structural stability are shown; (a) the effect of sandbag filling rate on design dimensions; and (b) the critical values ​​for structural stability of sandbags with the same dimensions but different filling rates.

[0053] Figure 10 The trend of the best fit criteria for the probability distribution function is shown under different sample sizes; where (a) root mean square error, (b) correlation coefficient, (c) scale parameter, and (d) shape parameter.

[0054] Figure 11 The debris line in segment S2 after the typhoon and the scour line in segment S3 (yellow dashed line) are shown to measure the level of wave rise. Detailed Implementation

[0055] The preferred embodiments of the present invention will be described in detail below with reference to examples. It should be understood that the following embodiments are given for illustrative purposes only and are not intended to limit the scope of the present invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and intent. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0056] Example:

[0057] This embodiment is based on field experimental research on sandbag revetment protection for erosive beaches, and provides an optimized design method for sandbag revetment protection structures for erosive beaches, including the following steps:

[0058] Step 1, Basic Data Collection:

[0059] Comprehensive data was collected on the target beach and surrounding waters, including sediment evolution characteristics, median grain size of the beach, and wave characteristics and water level changes over many years. The wave characteristics included wave height, wave period, and wave direction; the water level changes included high tide, low tide, and tidal range.

[0060] Specifically, this embodiment analyzes measured data from 11 fixed beach profiles on the south beach of Chudao Island from September 2017 to November 2019 to obtain data on sediment evolution characteristics, analyze the seasonal changes in beach profile morphology and slope, and analyze sediment grain size characteristics. It clarifies the erosion and restoration processes of the beach on an interannual scale under the influence of typhoon waves. For example, by statistically analyzing the average elevation of profiles in different seasons, it was found that the beach profile transforms between a normal wave type and a storm type profile throughout the year with the seasonal changes of hydrological wave elements; winter siltation corresponds to a normal wave type profile, while summer erosion corresponds to a storm type profile. Figure 1 , Figure 2 The data shows the seasonal average elevation of 11 sections of the South Beach of Chudao Island from 2017 to 2019.

[0061] Table 1. Seasonal sand transport rate of the beach

[0062]

[0063] Note: "+" indicates that sediment transport is mainly along the coast, "-" indicates that sediment transport is mainly offshore (towards the shore), and "±" indicates that both offshore (towards the shore) sediment transport and coastal sediment transport exist simultaneously.

[0064] By analyzing the area changes of adjacent beach profiles, the main forms of sediment transport were determined, and the beach sediment transport rate was estimated, as shown in Table 1 above, which illustrates the seasonal sediment transport rate. The median grain size of the beach was determined, and its variation patterns in dunes, shoulders, and erosion zones were understood based on multi-year data. Figure 3 The variation trends of parameters such as average grain size of sediments in the sand dunes, beaches, and scour zones were statistically analyzed. Wave data from the surrounding sea area over many years were collected, including wave height, wave period, wave direction, and water level changes such as high tide, low tide, and tidal range. Wave data was obtained using buoy observations. This buoy was located 2.74 km from the test site and began collecting wave meteorological data such as wind speed, wind direction, air pressure, air temperature, wave height, wave period, and wave direction in June 2010. Water level data was obtained through long-term monitoring stations, providing a basis for subsequent design.

[0065] Step 2, Material Selection and Determination:

[0066] Based on the beach sandbag structure design process, and utilizing years of wave dynamics and sediment particle size data from Chudao Island, a long-term field test was conducted on the severely eroded coastal section on the north side of Chudao Island. The main design content covered the stability of the structure under hydrodynamic conditions and the durability of the geotextile materials, focusing on design elements such as the top elevation of the structure, the size of individual sandbags, and the type of sandbag material. Taking into account the acid resistance, abrasion resistance, UV resistance, and microbial resistance of the geotextile materials, polypropylene was selected as the geotextile material to prepare individual sandbags.

[0067] The outer sandbags are made of woven high-strength geotextile (polypropylene) material (Geotextile-Type I), with a unit area mass ≥280g / m². 2 Radial tensile strength ≥70KN / m, latitudinal tensile strength ≥56KN / m, permeability coefficient 10 -4 -10 -3 cm / s; the outer sandbag inner layer (filter layer) is made of polyester needle-punched geotextile (Geotextile-II type), with a unit area mass ≥230g / m². 2 The tensile strength is ≥12KN / m; the inner sandbag material is made of polypropylene woven geotextile (Geotextile-III type), with a unit area mass ≥135g / m³. 2 Meridian fracture strength ≥30KN / m, zonal fracture strength ≥22KN / m, permeability coefficient 10 -2 -10 -3 cm / s. All types of materials undergo anti-aging treatment (Table 2 shows the material properties of geotextile sandbags). The filling material inside the sandbags is selected from the in-situ median particle size of the beach with a particle size of d. 50 =0.25~0.5mm of silt, to ensure that it is compatible with the local silt characteristics.

[0068] Table 2. Material Properties of Geotextile Sandbags

[0069]

[0070] Step 3, Optimization design of individual sandbag size:

[0071] The optimal sandbag size for the south beach of Chudao Island is determined using the following design formula:

[0072]

[0073] In the formula, H s It is the incident significant wave height; μ is the coefficient of friction between the sandbags; C w It is the stability coefficient; ρ s It is the density of sand, ρ w ξ is the density of seawater; ξ0 is the fragmentation similarity parameter. L0 is the wavelength of the deep-water wave, L0 = gT 2 / 2π, T is the period of the spectral peak wave, g is the gravitational acceleration; α is the facing angle of the sandbag structure; k is the number of sandbag layers that affect a single sandbag; A T It is the area of ​​the bottom surface of the sandbag.

[0074] The above formula comprehensively considers the influence of various factors, including waves, sediment, and structure, on the size design of a single sandbag, ensuring that the designed sandbag has good stability in complex marine environments.

[0075] Specifically, in this embodiment, based on multi-year water level data of the sea area near the test area, the estimated design high water level at the study site is 1.42m. Using ERA-5 reanalysis data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), statistical analysis was performed on the annual maximum wave height of the 35-year ERA-5 reanalysis wave data of the Chudao sea area. The results showed that the significant wave height for a 25-year return period at the calculation point (within finite water depth) was 4.4m, and the significant wave height for a 50-year return period was 4.6m. Figure 4 ).

[0076] Considering that the bottom elevation of the test section is greater than the high water level and the cost of the test, the size of the sandbag was adjusted to 1.4m long and 0.85m wide (empty sandbag). After being filled with sand, the size of the sandbag is 1.3×0.8×0.2m.

[0077] Step 4, Determining the structural assembly and installation method:

[0078] The specific sandbag revetment test plan is as follows:

[0079] The test section of the eroded coastline on the north side of Chudao Island is 74 meters long and is located in the middle section of the northern coastline of Chudao Island. For example... Figure 5As shown, the first test consisted of three test sections, each designed with the same slope, height, and trench excavation depth, but with different types of sandbags (Table 3 lists the geotextile models of sandbags used in each section of the test): Test section I (S1), 20m long, consisted of fine sand filling, multiple layers of inner sandbags, and one outer sandbag from the inside out; Test section II (S2), 24m long, consisted of fine sand filling, a geotextile filter layer, and one outer sandbag from the inside out, with geogrids used to wrap the outer sandbags into a whole to improve the overall stability of the sandbag protection structure; Test section III (S3), 30m long, consisted of fine sand filling, a geotextile filter layer, one inner sandbag, and one outer sandbag from the inside out, with the geotextile filter layer preventing the loss of fine sand from the inner layer. All test sections were designed with a slope angle of 50°. The top elevation of the revetment structure was designed to be equal to the sum of the extreme high water level and wave run-up, 3.7 m (MSL). A 0.1 m thick layer of undisturbed soil, totaling 3.8 m, was laid on the top of the revetment. The three trenches were excavated from the beach surface to a bedrock layer approximately 1 m deep. The trench widths were 2 m, 2.5 m, and 4 m, respectively. Sandbags were used for backfilling the trenches, and the gaps between the sandbags were filled with fine sand and compacted. The outer sandbags (¥25) of the beach sandbag protection structure had better tensile strength and durability compared to the inner layer (¥5). The filling material inside the sandbags was selected with a particle size of d. 50 =0.25~0.5mm of silt and sand.

[0080] Table 3 First Test Section Plan

[0081]

[0082] First test of sandbag bank protection effectiveness observation:

[0083] The inherent limitations of geotextile materials are a significant issue in the field application of beach sandbag protection structures. Compared to most other geotextile application environments (such as drainage and inland waterway use), GSS is exposed to strong ultraviolet radiation, frigid conditions, and the cyclical effects of waves over extended periods. This means that damage to geotextile sandbags is difficult to avoid, a key factor limiting the lifespan of geotextile sandbag structures. The types of damage observed in the field can be divided into two main categories: accidental damage (from sharp materials such as pebbles / shells and driftwood) and material aging caused by strong ultraviolet radiation. These damages are easily punctured and abraded by vandals and debris, and their expected lifespan after prolonged exposure to ultraviolet radiation is unclear, making it difficult to construct accurate aging profiles. Figure 6 (a) and (b) show the observation results of the test section under severe cold conditions, with no obvious structural changes; the S2 test section two years later, due to being wrapped with geogrid, is relatively stable overall, but the geotextile has aged and lost strength. Figure 6(c)); The outer layer of sandbag geotextile material in section S3 was completely damaged, and the uppermost damaged material formed a wave-like scour line, but the inner layer of sandbags still played a protective role. Figure 6 In the middle (d), there are many steel wire fishing nets washed in from the sea on the beach.

[0084] The second experiment was modified from the first. Except for the outermost sandbag from the first experiment, the original structural features were retained. In the second experiment, geogrids were used to reinforce the structure, so the sandbag dimensions were reduced to 0.85m long and 0.55m wide (empty sandbags; inflated sandbags are 0.7×0.4×0.2m). Polypropylene woven geotextile was selected as the main material (Table 4). Five comparative test sections were designed, each reinforced with a "reinforced MacPad" to prevent damage to the sandbags caused by repeated erosion from gravel. Test Section IV (S4): 12.5m long, with a sandbag structure slope of 45°. Since the original internal sandbags were not destroyed, they were retained. Only the outer layer design needed to be upgraded, mainly by adding geogrids and stacking them from the outside. The outer sandbags were made of geotextile-IV type. Test Section V (S5): Approximately 9.20m long, with a sandbag structure slope of 60°. Test Section VI (S6): 24m long, with a bank slope of 60°. This test section was divided into two parts. Needle-punched geotextile grass seed bags were placed at elevations exceeding 2.75m (MSL). Test Section VII (S7): 5m long, with a bank slope of 60°. In this test section, the sandbags were placed with their short sides perpendicular to the shoreline. In the other test sections, they were placed parallel to the shoreline. Test Section VIII (S8): 15m long, with only 2 layers of sandbags laid.

[0085] Figure 7 These are cross-sectional and section views from the second experiment. The second experiment included comparisons of the revetment slope, sandbag size, sandbag stacking method, and the feasibility of using ecological grass seed geotextile bags.

[0086] Table 4. Scheme for the Second Test Section

[0087]

[0088] Second test of sandbag bank protection effectiveness observation:

[0089] During 2022, three typhoons significantly impacted the waters off the Shandong Peninsula, with Typhoon "Hana" (2106) having the most severe impact. Typhoon "Hana" moved slowly and remained over land for the longest period since 1949, causing direct economic losses totaling approximately 800 million yuan, accounting for 33% of the total storm surge disaster losses for the year (Ministry of Natural Resources, 2019 and 2021, "China Marine Disaster Bulletin"). In the second test, section S4, located in the same position, was 12.5m long with a sandbag structure slope of 45°. Since the original inner sandbags were intact, they were retained; only the outer layer design needed upgrading. Every four layers of sandbags were reinforced with reinforced MacPad mats, and the outer sandbags used geotextile-IV type. On July 30, 2021, under the influence of typhoon waves generated by Typhoon "Hana," the entire structure lost its protective function. Figure 8 (a) and (b)). The first test results showed that wrapping sandbags with geogrids significantly improved the stability of sandbag revetments; therefore, the second test section reduced the size of the sandbags and used micromats with denser pore sizes. Figure 8 The paper presents a comparison of the changes in test sections S5–S8 before and after the action of storm waves. Section S5 is approximately 9.20m long, with a sandbag structure slope of 60° and multiple layers of sandbags laid horizontally, located on an arc-shaped shoreline. Section S6 is 24m long, with a revetment slope of 60°. This test section is divided into two parts: needle-punched geotextile grass seed bags are placed where the elevation exceeds 2.75m (MSL), while geotextile-IV type sandbags are used in other locations and wrapped with inverted Mack mats. Section S7 is 5m long, with a revetment slope of 60°. In this test section, the sandbags are placed with their short sides perpendicular to the shoreline, while in other test sections they are placed parallel to the shoreline. Section S8 is 15m long, with only two layers of sandbags laid vertically and wrapped with inverted Mack mats. Figure 8 (a), (c), and (e)). Under repeated scouring by waves from multiple storms and Typhoon "Fireworks," the outermost layer of the sandbag mat was damaged; under the influence of storm surge and wave rise, test section S6 experienced wave overtopping, and two sandbags were removed, but the overall structure remained stable. The damage to the grass seed bags and vegetation in section S6 under the impact of storm waves was also noted. Figure 8 (d) The large amount of gravel, seaweed, and other debris piled up in front of sections S7 and S8 not only damaged the beach but also severely damaged the landscape. It is worth noting that the geotextile material - Type IV material used in this project has not yet shown any signs of aging.

[0090] The final design adopted a layered optimization design, with the cross-section consisting of a fine sand filling layer, an inner layer of sandbags, and an outer layer of sandbags from the inside out. Adjacent sandbags are stacked and connected by a geogrid as needed.

[0091] Step 5, Determining the geotextile bag filling rate:

[0092] Calculate the fill rate based on the theoretical maximum volume:

[0093]

[0094] In the formula, a and b are the dimensions of the empty sandbag, and V s This represents the maximum volume of the sandbag after it is filled with sand.

[0095] In actual construction, by controlling the sand filling height and measuring the weight of the sandbags, the filling rate of the sandbags used in the test sections S1-S3 was ensured to be between 75% and 85%, and the filling rate of sections S4-S8 was 90%-95%, ensuring that the filling rate of a single sandbag was >75%, in order to meet the stability requirements of the structure under storm conditions. Figure 9 (This demonstrates the impact of sandbag fill rate on design dimensions and structural stability).

[0096] Step 6, Design wave height calculation:

[0097] Long-term measured wave data for the Chudao sea area from 2010 to 2019 were obtained using the 3-meter diameter buoy No. 07 deployed by the Institute of Oceanology, Chinese Academy of Sciences. Samples were selected using the ANL and POT methods, and the sample data were substituted into probability distribution functions. The least squares method was used for fitting, and the relevant parameters of each distribution function were calculated.

[0098] Specifically, the RMSE, correlation coefficient, scale parameter, and shape parameter of the eight probability distribution functions were compared and analyzed using the ANL method. The results showed that FT-III had the smallest RMSE and R... 2 The maximum value represents the best-fit distribution function for the study area. Figure 10 This demonstrates the changing trend of the best-fit criterion for the probability distribution function under different sample sizes.

[0099] The design wave height of the target sea area is calculated using the best-fit distribution function, providing key parameters for the design of sandbag revetments.

[0100] Step 7, Optimize sandbag structural design elements:

[0101] Based on the relevant formula for wave run-up on the sandbag structure, and combined with the actual slope and roughness of the target beach, the wave run-up value is calculated. In this embodiment, the wave run-up calculation results considering the sandbag thickness and not considering the sandbag thickness are compared to determine a reasonable top elevation of the structure.

[0102] In the first test, the combined value of the design high water level and wave run-up was used to calculate the top elevation. No wave overtopping occurred in sections S1-S3, but the wave run-up value was still explored and optimized. In the second test, the wave rise level was measured based on the debris line in section S2 and the scour line in section S3 after the typhoon. The top elevation of the sandbag bank was reduced to 2.75m (the average of the debris line and scour line elevations). At the same time, test sections with different top elevations were set up for comparison to further optimize the design scheme. Figure 11 The level of wave rise is measured by the debris line in segment S2 and the scour line in segment S3 after the typhoon.

[0103] Finally, it should be noted that the above description is only used to illustrate the technical solutions of the present invention and is not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention.

Claims

1. A method for optimizing the design of sandbag revetment protection structures for erosive beaches, characterized in that, The method includes the following steps: Step 1, Basic Data Collection: Comprehensive data on the target beach and surrounding waters were collected, including sediment evolution characteristics, median grain size of the beach, and wave elements and water level changes in the surrounding waters over many years. Step 2, Material Selection and Determination: Taking into account the acid resistance, abrasion resistance, UV resistance and microbial resistance of geotextiles, polypropylene was selected as the material for preparing individual sandbags. The filling material in the sandbags is selected from the in-situ median particle size of the beach, d. 50 =0.25~0.5 mm of silt and sand; Step 3, Optimization design of individual sandbag size: The optimal sandbag size for the target beach is determined using the following design formula: In the formula, It is the height of the incident effective wave; It is the coefficient of friction between the sandbags; It is the stability coefficient; , It is the density of the sand. It is the density of seawater; These are fragmentation similarity parameters. , It is the wavelength of deep-water waves. , It is the periodicity of the spectral peak. It is gravitational acceleration; The facing angle of the sandbag structure; It refers to the number of layers of sandbags; It is the area of ​​the bottom surface of the sandbag; The above formula comprehensively considers the influence of various factors, including waves, sediment, and structure, on the size design of a single sandbag, ensuring that the designed sandbag has good stability in complex marine environments. Step 4, Determining the structural assembly and installation method: The design adopts a layered optimization approach, with the cross-section consisting of a fine sand filling layer, an inner layer of sandbags, and an outer layer of sandbags from the inside out. For adjacent sandbags, a stacking method is adopted, and a connecting structure including geogrid is set as needed to enhance the overall anti-slip and anti-erosion capacity of the structure. The final design yielded a sandbag revetment structure for the eroding beach.

2. The method according to claim 1, characterized in that, In step 1, the wave elements include wave height, wave period, and wave direction; the water level changes include high tide, low tide, and tidal range.

3. The method according to claim 1, characterized in that, In step 4, the outermost sandbag in the layered optimization design is made of polypropylene woven geotextile with a unit area mass ≥ 280g / m². 2 Radial tensile strength ≥ 70 KN / m, latitudinal tensile strength ≥ 56 KN / m, and permeability coefficient 10. -4 ~10 -3 cm / s.

4. The method according to any one of claims 1 to 3, characterized in that, The method further includes: Step 5, Determining the geotextile bag filling rate: Calculate the fill rate based on the theoretical maximum volume: In the formula, a and b are the dimensions of the empty sandbag, and V s This represents the maximum volume of the sandbag after it is filled with sand. Among these measures, it is essential to ensure that the filling rate of a single sandbag is greater than 75%.

5. The method according to any one of claims 1 to 3, characterized in that, The method further includes: Step 6, Design wave height calculation: Long-term measured wave data for a certain sea area is obtained using equipment including ocean observation buoys and wave monitoring stations; Samples were selected using the ANL and POT methods, and the sample data were substituted into the probability distribution function. The least squares method was used to fit the data, and the relevant parameters of each distribution function were calculated. Based on the comparative analysis of the root mean square error and correlation coefficient, the best-fit distribution function was determined. The design wave height of the target sea area was calculated using the best-fit distribution function, providing key parameters for the design of sandbag revetments.

6. The method according to any one of claims 1 to 3, characterized in that, The method further includes: Step 7, Optimize sandbag structural design elements: Based on the relevant formulas for wave run-up on sandbag structures, and combined with the actual slope and roughness of the target beach, the wave run-up value is calculated. By comparing the wave run-up calculation results considering the sandbag thickness and those not considering the sandbag thickness, a reasonable top elevation of the structure is determined.

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