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MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS DO MINH DAT RESEARCH ON WAVE-REDUCING EFFECTIVENESS OF PILE-SUPPORTED INCLINED-PLATE DIKE FOR COASTAL PROTECTION Major: SPECIAL CONSTRUCTION ENGINEERING Code : 958.02.06 SUMMARY OF DOCTORAL THESIS HA NOI – 2023 The Thesis was completed at the University of Transport and Communications Academic Supervisor 1: Assoc Prof Dr Nguyen Viet Thanh Academic Supervisor 2: Assoc Prof.Dr Phung Dang Hieu Reviewer 1: Reviewer 2: Reviewer 3: The Thesis will be defended in front of the University–Graded Committee of the Thesis Evaluation according to Decision No XXXXX/QĐ-ĐHGTVT dated 2023, signed by the University of Transport and Communications The Thesis can be found at: - National Library; - Library of the University of Transport and Communications INTRODUCTION Research background Research and development of other breakwater types are increasingly encouraged to optimize materials' use, providing environmental-friendly solutions for coastal engineering problems Studying and selecting structure types with high durability and economic efficiency is necessary, especially for coastal protection works The pile-supported inclined-plate breakwaters have many outstanding advantages, such as simple structure, little impact on the surrounding environment, increasing water exchange, use of fewer materials, and are suitable for areas with soft soils, deep water, and uncomplicated construction technology This type of structure has great potential for application in coastal and maritime protection works in Vietnam The Thesis aims to empirically study the interaction between waves and the inclined plate breakwater using the physical model in the 2D wave flume The results are a reliable basis for applying inclinedplate breakwater structures in constructing port and coastal protection works in Vietnam Research objective A study of the interaction between the wave and the inclined-plate breakwater structure is necessary to clarify the hydrodynamic characteristics when the waves act on the inclined plate Based on the results, the study proposed the most effective type of pile-supported inclined-plate breakwater, which can be applied for coastal protection, stabilization works, and harbor basins Research object and research scope 3.1 Research object This study's objective is the interaction between the wave and the pile-supported inclinedplate breakwater in the different experimental wave scenarios suitable for site conditions in Vietnam 3.2 Research Scope The interaction between waves and structures is studied using physical model experiments in a 2D wave flume This study does not consider the structure's strength and the pile foundation's influence on the inclined plate Scientific and practical significance 4.1 Scientific significance Studying the interaction between wave and inclined plate breakwaters will contribute to uncovering the mechanisms of wave transmission, wave reflection, and wave energy dissipation of this type of structure 4.2 Practical significance The traditional inclined plate breakwater was improved by adding notches and holes to improve wave energy dissipation and reduce the height of reflected waves in front of the breakwater This structural solution has an economic cross-section and a low environmental impact The new contribution of the Thesis - The influence of some basic input parameters such as water depth; slope of inclined plate, wave period, and wave steepness on the change of hydrodynamic characteristics, including wave transmission, wave reflection, and wave energy dissipation when the wave interacts with the inclined plate breakwater was investigated Some relationships were established between wave steepness and wave transmittion, wave reflection, and wave energy dissipation - The inclined plate breakwater structure with highly effective wave-absorbing notches and holes was proposed in the coastal protection field In addition, the technical characteristics of inclined plate breakwater structures were applied in the coastal protection in Canh Duong commune, Quang Trach district, Quang Binh province Thesis outline In addition to the introduction, conclusion, and recommendations, the Thesis has four chapters, including: Chapter Overview of domestic and international research on pile-supported inclined plate breakwaters Chapter of the Thesis focuses on setting up and installing a physical model by using similarity parameters, discussing some methods measuring reflected waves, and analyzing the basis of experimental wave selection, thereby suggesting a basis for developing the research scenarios Chapter of the Thesis presents the characteristics of wave transmission, wave reflection, and wave energy dissipation of inclined plate breakwaters In addition, the Thesis also discusses the wave pressure distribution on the inclined plate and the maximum velocity distribution caused by the waves at the gap between the breakwater and the sea bottom Chapter of the Thesis applies the research results from Chapter to propose two types of inclined plate breakwater structures on pile foundations for coastal protection The designs are applied to coastal stabilization and protection projects in Canh Duong commune, Quang Trach district, Quang Binh province CHAPTER OVERVIEW OF STRUCTURE AND THE INTERACTION BETWEEN WAVES AND BREAKWATER 1.1 Overview of breakwater research Researching new technologies in coastal protection works in Vietnam conditions is an urgent requirement with high practical significance Solutions for sand prevention and wave reduction often used in coastal protection works include (Figure 1.1): Mangrove forests; Artificial beach nourishment, groin system; Near-shore wave attenuation barrier system (submerged or immersed); Combination of many solutions Structure of coastal protection works Coastal protection structures are classified as follows: a a Sloping structure b b) Upright structure c c Semi-circular breakwater structure d Wave reduction breakwater using centrifuge wall e Wave reduction breakwater using Busadco blocks f Wave reduction breakwater using a hollow A-shaped structure with a pyramid Figure 0.1: Prevent sand and reduce wave breakwaters in shore protection works Various coastal protection structures were built in Vietnam with positive initial results However, most have not yet experienced harsh weather conditions, so their long-term effectiveness cannot be evaluated On the other hand, soft soil conditions cause gravity structure solutions to subside unevenly and tilt, inducing cracking of structures and difficulty in coping with the marine environment This result shows a few studies inclined plate breakwater structures on pile foundations in Vietnam Because the inclined plate structure is placed on a pile foundation, the scope of application is widely applied to areas with soft soil geology, such as the coastal areas of Vietnam Therefore, the research direction of the topic is highly practical 1.2 Overview of research related to the direction of the study Overview of international research A total of 13 international researches on the interaction between waves and inclined-plate breakwaters were summarized with the following results: (i) Methods of the studies: Numerical and physical modeling are two main research methods which numerous researchers conduct (ii) Research conditions - The research has only been carried out by experimental wave combinations without studies on in-situ wave applications These studies were not applied in practice to the site Unfortunately, the inclined plate breakwater structure has many advantages, such as economical cross-section, simple construction, and effective wave reduction - Inclined plate breakwater: The authors conducted research under experimental conditions with inclined plates with inclined angles from 0-90 degrees in both directions forward and opposite the direction of the wave approach According to some experimental results, inclined plates with an angle of inclination of 45-60 degrees compared to the vertical have the most effective reduction ability - Most studies have been performed with inclined plates with smooth, flat-sided platforms Only Shirlal's (2013) investigated the wave transmission of a submerged serrated inclined plate breakwater with rectangular and square fixed in zigzag and parallel configurations tested using monochromatic waves (iii) Practical application: Through an overview of research around the world, it can be seen that the inclined plate breakwater structure (smooth-flat plate) was practically applied in Japan, such as in Kimisu, Chiba, and Fujimori, Suruga Bay, Japan Overview of Vietnam research on the interaction between waves and structures In Vietnam, no studies were conducted on pile-supported inclined plate breakwaters The Thesis reviewed studies on the interaction between waves and breakwater structures in our country, as follows: a) Studies related to sloping breakwaters Studies on sloping breakwater using Rakuna IV blocks applied to Nghi Son breakwater were conducted by Thieu Quang Tuan et al (2014) [43], Le Thi Huong Giang (2016) and Nguyen Quang Luong (2020) [7] b) Numerical simulation research In Vietnam, the numerical simulation research, including the model to determine the level of wave reduction through mangrove forests, was conducted by Nghia et al (2010) [1], the 2D model on VOF (volume of fluid) basis for simulating waves overtopping over a porous breakwater structure (simulation results showed high correspondence with experimental data of Hieu et al (2012) [44]) Hieu et al studied the interaction between wind and waves at breakwaters with slopes of m=4 using numerical wave simulation The numerical wave simulation results are compared with experimental data in the case of overtopping waves without the influence of wind [45] Pham Van Lap (2019) applied a numerical wave simulation model and a physical wave model to study the interaction between waves and sea embankments to determine the flow velocity due to waves at the shallow base in the design of the stone embankment [8] c) The research works on semi-circular breakwaters and 1/4 circular breakwaters Typical studies on semi-circular breakwaters for estuary regulation works were conducted by Nguyen Viet Thanh (2014) [2, 3, 9] and Nguyen Viet Thanh et al in 2017 [10, 11] Regarding the studies of Tran Van Thai and Phan Dinh Tuan (2019) [12], Le Thanh Chuong et al [13], and Phan Dinh Tuan (2021) [14] about wave overtopping over semicircular breakwater structures were applied in the Mekong Delta and Nha Trang However, they were not exposed to extreme weather conditions, and the effectiveness of these structures is still unclear d) Research works on submerged breakwaters Nguyen Viet Tien's doctoral Thesis (2015) studied the wave reduction effectiveness of submerged breakwaters [15] e) Other breakwater research Nguyen Van Thin (2014) [16] and Nguyen Van Dung (2017) [17] used a physical model on a wave flume to study wave overtopping and wave pressure acting on the crest wall structure of the embankment Regarding research on estuary and coastal management solutions, Truong Van Bon [18] and Nguyen Thanh Hung [19] studied the effectiveness of preventing sand and wave attenuation of coastal protection solutions Lo estuary - Cua Dai, Quang Ngai and Nhat Le estuary, Quang Binh Vu Minh Tuan and colleagues (2022) studied the interaction between waves, box-shaped floating breakwater structures, and box-shaped floating breakwaters combined with a semicircular arch on top of the box [20] e Comment on domestic research results: - Research works in Vietnam have mainly focused on the interaction between waves and breakwater structures in the form of sloping breakwater or revetment, semi-circular, hollow A-shaped blocks, hollow upright walls, two rows of piles combined with poured rock cores, etc - No research was carried out on the contents related to problems mentioned in this Thesis Therefore, studying the interaction between waves and pile-supported inclined plate breakwaters is a new direction that clarifies the hydrodynamic characteristics and is useful for the practice in Vietnam 1.3 Overview of study methods about the interaction between waves and breakwater structures According to general domestic and international studies, mathematical and physical modeling methods mainly studied the interaction between waves and breakwater structures Mathematical models are popular in studying 1D and 2D problems, while physical models are common in 3D problems The use of mathematical or physical models depends on the importance of the project and the research stage, as well as economic and technical considerations Solid physical model provide calibration data for a relatively accurate mathematical model of the velocity field to calculate erosion and deposition characteristics to present difficult and high-cost numerical models 1.4 Existing problems need to be resolved by the study Direction research of the Thesis: - Research hydrodynamic characteristics when waves interact with pile-supported inclined plate breakwaters with notches and holes to reduce waves - Applying the most effective type of pile-supported inclined plate breakwater structure to protect and stabilize the coast of a given area 1.5 Objectives and content of the study Objectives of the study The objective study considers the hydrodynamic interaction characteristics between waves and pile-supported inclined plate breakwaters and proposes the most suitable pilesupported inclined plate breakwater structure for stabilizing and protecting the coast Specifically objectives as below: - Overview of domestic and international research about the structural characteristics of pile-supported inclined plate breakwaters - Setting up the physical model, selecting experimental wave parameters, and proposing experimental scenarios - Clarify the hydrodynamic characteristics when waves interact with the breakwater - Propose solutions to protect and stabilize the coast and harbor basin Content of the study - Overview of domestic and international research on breakwaters and pile-supported inclined plate breakwaters - Scientific background of research on the interaction between waves and pile-supported inclined plate breakwaters using physical models - Setting up, calibration, and verifying physical models - Research the characteristics of wave transmission, wave reflection, and wave energy dissipation when waves interact with inclined plate breakwaters, - Research the maximum velocity distribution in the gap between the breakwater and the bottom caused by interaction between wave and breakwater - Propose pile-supported inclined plate breakwater structures for coastal stabilization and protection works Expected results - The inclined plate breakwater structure with notches and holes is a type of structure with a simple cross-section Using this structure can save materials and apply them for all types of ground, piling construction, and fast-paced assembly of inclined plates With these advantages, clarifying the scientific background when waves interact with breakwaters is necessary, thereby proposing a structure suitable for Vietnam's coastal conditions - The research results are a useful reference for a fairly new type of structure in Vietnam that can help researchers, consulting companies, and managers have additional structural options for comparison with traditional ones 1.6 Methods of the study Depending on the contents, the following methods were used: - Information collection method: Collecting documents, conducting an overview of studies on the interaction between waves and inclined plate breakwaters structures, and techniques for exploiting information from the internet to update information related to the topic - The methods of learning, summarizing experience, and absorbing advanced scientific and technological results from previous research related to the topic - Based on some sample designs of inclined plate breakwater structural solutions, improvement research was conducted to improve the structure's ability to reduce waves, save materials, and ensure the ability to work stably under the effect of design waves The physical modeling method using wave flume was applied to consider the interaction between waves and inclined plate breakwater structures on pile foundations 1.7 Conclusion of Chapter - Research on improving breakwater structures that are highly durable and have great economic efficiency in coastal protection works is an attractive topic for many scientists worldwide - Building wave attenuation works and breakwaters in Vietnam have achieved certain effectiveness However, they did not test with extreme weather conditions, so there are no results to evaluate the lifespan of these types of structures For soft soil areas, using gravity structures will cause large settlements, making it difficult to ensure the long-term stability of the works - There are two main research methods considering the interaction between waves and breakwater, namely mathematical models and physical models The mathematical model was used to provide boundary conditions for the physical model to reduce unnecessary experiments and investment costs - All studies on the interaction between waves and pile-supported inclined plate breakwaters were performed using physical models The research results described hydrodynamic characteristics including wave transmission, wave reflection, and wave energy dispersion There were a few studies on velocity distribution at the base of the breakwater, and no studies were conducted on the wave pressure distribution affecting inclined plate breakwaters CHAPTER SCIENTIFIC BACKGROUND FOR STUDYING THE INTERACTION BETWEEN WAVES AND PILE-SUPPORTED INCLINED PLATE BREAKWATERS 2.1 Research basis for interaction between waves and inclined plate breakwater structures The physical model needs to satisfy the following requirements to ensure it works as in reality 2.1.1 Similarity theory The model theory is established based on similarity theory When the similarity conditions stipulated by the similarity theory are satisfied, the model (M) and the prototype (N) are similar, and we can base on the results from the model to speculate the corresponding results in the original form For the model to be similar to the prototype, all similarity conditions must be met, including geometric similarity, kinematic similarity, dynamic similarity, similarity in flow state, similarity in wave motion, similarity in wave reflection, and similarity in wave breaking 2.2 Building, calibrating, and validating physical models 2.2.1 Selecting Model Scale Based on available equipment in Vietnam, in-situ wave data along the coast, and similarity requirements, the Thesis chose the scale of a physical model of 1:15 2.2.2 Constructing inclined plate breakwater samples Breakwater sample material: use organic glass with roughness equivalent to 0.0097÷0.012 Dimensions of inclined plate breakwater prototype: 30m x 10m x 0.75m Because of the model scale 1:15, the inclined plate breakwater model has dimensions of 2m x 0.67m x 0.05m (Figures 2.1 and 2.2) Figure 2.1: Fabrication of inclined plate breakwaters Figure 2.2: Inclined plate breakwater cross section is completed The inclined plate model has truncated conical notches with a low bottom of x 5cm, a top-bottom of x cm, a height of 5.0 cm, and concave holes with a length of 5.0cm, Width of 3.0cm, small bottom depth of 0.5 cm, large bottom depth of 1.0 cm 2.2.3 Measuring equipment and arrangement on the experimental model 2.2.3.1 Wave flume The experiment was carried out in a wave flume with a length of 37m, a width of 2m, and a depth of 1.5m at the Key Laboratory of River and Coastal Engineering, Vietnam Academy for Water Resources 2.2.3.2 Wave generator The wave generator can generate regular and random waves in a spectrum of Jonswap, Jonswap Par, Moskowitz, Moskowitz Par, and Sin at a maximum water depth of 1.4m in front of the wave generator The maximum wave height generated in the flume is Hmax = 0.4m and the period is from Tp = 0.5s ÷ 5.0s 2.2.3.3 Wave probes: Wave probe type 202 is manufactured by the Danish Hydraulic Institute (DHI) 2.2.3.4 The experimental model (i) To measure wave height, four-wave probes are arranged as follows: Probes G1, G2, and G3 are located in front of the breakwater and about 0.6L to 0.75L away from the breakwater They are moved during the experiment to correspond to wavelength data and evaluate the reflection ability of the incident waves Probe G4 is placed behind the breakwater to measure the wave height behind the breakwater, about 1.5m as a basis for evaluating the wave transmission efficiency of the breakwater (ii) To measure wave pressure, wave pressure probes are arranged on the surface of the inclined plate breakwater at designated positions about 0.135m apart (iii) the DCS 3900 probe (Doppler Current probe) is used to measure the flow velocity The measuring probe is placed in the middle of the gap between the inclined plate and the bottom of the flume During the experiment, the measuring probe are moved vertically to measure the maximum flow velocity a General layout of the experiment b Arrangement diagram of wave pressure probes Figure 2.3: Experiment general layout diagram and arrangement of measuring probes in the wave flume 2.3 Calibration and validation of the model Calibrating and verifying the experimental model ensure the accuracy of the wave propagation process as in the original form according to the manufacturer's instructions 2.4 Developing research scenarios Based on the analysis mentioned above, the 45 scenarios were conducted in the Thesis 14 m=1.5 gives the lowest wave reduction effect - With the same slope, the wave reflection coefficient does not significantly change when changing the wave height It shows that the notches and concave holes cause the reflected wave to dissipate significant energy when it interacts with the inclined plate breakwater Figure 0.11: Relationship between Kr and wave height with different plate slopes corresponding to water level WL1 Figure 0.12: Relationship between Kr and wave height with different plate slopes corresponding to water level WL2 Figure 0.13: Relationship between Kr and wave height with different plate slopes corresponding to water level WL3 3.2.3 Effect of inclined slope on wave reflection The effect of inclined slope on wave reflection in Figures 3.16-3.18 shows that: - With slope m=1: Water level WL1 has the lowest reflection coefficient, and water level WL3 has the highest reflection coefficient because when the wave impacts the breakwater, a part of it overflows the top, so the reflection is smaller - With slope m = 1.33, WL1 reflection initially tends to increase, then decreases with increasing wave height; WL2 reflection coefficient increases with wave height, then Kr decreases The WL3 reflection coefficient is the lowest, and waves are mostly dispersed on the surface of the breakwater, so the reflection is low - With a slope of m=1.5, WL1 slightly decreases reflectivity when the wave height increases With a gentle slope, waves were broken on the roof so the reflection coefficient was is reduced Figure 0.14: Relationship between Kr and wave height corresponding to different water levels when the inclined slope m=1 Figure 0.15: Relationship between Kr and wave height corresponding to different water levels when the inclined slope m=1,33 Figure 0.16: Relationship between Kr and wave height corresponding to different water levels when the inclined slope m=1,5 15 3.2.4 Effect of wave period on wave reflection The results in Figure 3.19 show that the reflection coefficient changes significantly with a wave period of 1.2 seconds It is quite stable with a period of 1.4 seconds, and changes significantly with a period of 2.2 seconds Thus, it shows that the reflection coefficient is less variable for waves with medium periods than for waves with short and long periods Figure 0.17: Relationship between Kr with the wave period Hs = 0,14m 3.2.5 Effect of wave slope on wave reflection 3.2.5.1 Correlation between wave steepness and wave reflection coefficient when slope m=1 The results of MatLab's Curve fitting regression calculation using the Trust-region algorithm have given the regression equation form: 𝐾 = 0,0023 × − 0,0411 × + 0,5013 (3-4) With reliability assessment parameters including SSE = 0.0336, RMSE = 0.0529 and R2 = 0,304 as above, it shows that equation (3-4) has acceptable reliability 3.2.5.2 Correlation between wave steepness and wave reflection coefficient when slope m=1.33 The results of MatLab's Curve fitting regression calculation using the Trust-region algorithm have given the regression equation form: 𝐾 = 0,0022 × − 0,0376 × + 0,6983 (3-5) Reliability assessment parameters, including SSE = 0,0161, RMSE = 0,0366, and R2 = 0,4959, show that equation (3-5) has acceptable reliability 16 Figure 0.18: Correlation between K r and wave steepness H/gT2 with slope m=1 Figure 0.19: Correlation between Kr and wave steepness H/gT2 with slope m=1,33 3.2.5.3 Correlation between wave steepness and wave reflection coefficient when slope m=1,5 The results of MatLab's Curve fitting regression calculation using the Trust-region algorithm have given the regression equation form: 𝐾 = 0,0027 × + 0,0563 × + 0,2092 (3-6) With reliability assessment parameters including SSE = 0,019, RMSE = 0,0398, and R = 0,4547, as shown in Figure 3, it shows that equation (3-6) has acceptable reliability The results of the Thesis show that the regression equations (3-4), (3-5), and (3-6) have better reliability than the studies conducted by Shil et al [52] 17 Figure 0.20: Correlation between Kr and wave steepness H/gT2 with slope m=1,5 c 3.3 Characteristics of wave energy dissipation 3.3.1 effect of water level on wave energy dissipation Figures 3.24 to 3.26 show the following two main characteristics: - With the water level at the breakwater crest WL1, the slope m=1.0 has the best wave dissipation ability - With the water level lower than the breakwater crest WL2 and WL3, the slope m=1,5 has the best wave dissipation ability Figure 0.21: Relationship between KL and Hs correspondings to WL1 Figure 0.22: Relationship between KL and Hs correspondings to WL2 Figure 0.23: Relationship between KL and Hs correspondings to WL3 3.3.2 effect of inclined Slope on Wave Energy Dissipation The relationship between the wave energy dissipation coefficient and the wave height corresponding to the slope m=1, m=1.33, and m=1.5 shown in Figures 3.27 to 3.29 gives the following summary results: - The gentler the slope, the better the wave dissipation ability It is obvious because the gentle slope reduces the depth at the base of the breakwater, making it easier to generate breaking waves and climbing waves on the inclined slope - With the water level at the breakwater crest WL1, the wave energy dissipation coefficient is quite small and tends to increase but then decreases This can be explained 18 because the higher the wave height, the higher the wave ability to overtop the breakwater, thus reducing the level of wave energy dissipation Figure 0.24: Relationship between KL and Hs corresponding to m=1 Figure 0.25: Relationship between KL and Hs corresponding to m=1,33 Figure 0.26: Relationship between KL and Hs corresponding m=1,5 - The wave energy dissipation coefficient does not change much with water levels lower than the breakwater crest WL2 This is because the notches and concave holes dissipate wave energy quite evenly - The wave energy dissipation coefficient tends to increase when the water level decreases (corresponding to WL3) This is the result of the waves mostly blocked by the inclined plate breakwater, so the level of wave dissipation increases When the water level reduces, the ability to dissipate wave energy further - When the wave height is low, the possibility of waves breaking on the breakwater roof is quite large, so the wave energy dissipation phenomenon is quite stable When the wave height increases, the wave density decreases because the wave overtopping the breakwater crest is larger, leading to a decrease in the ability to dissipate of wave energy 3.3.3 Effect of wave period on wave energy dissipation - In both cases where the water level is lower than the breakwater crest WL2 and WL3, the KL coefficient does not vary significantly Especially with a gently inclined slope, the KL tends to be stable - These results show that the KL coefficient depends largely on water level but less on wave height and period 3.3.4 effect of wave slope on wave energy dissipation 3.3.4.1 Correlation between wave steepness and wave energy dissipation coefficient when slope m=1 The results of MatLab's Curve fitting regression calculation using the Trust-region algorithm have given the regression equation form: 𝐾 = −0,0244 × + 0,0275 × + 0,2588 (3-7) With reliability assessment parameters including SSE = 0,1247, RMSE = 0,109 and R2 = 0,091 as shown in Figure 3.30, it shows that equation (3-7) has quite low reliability 3.3.4.2 Correlation between wave steepness and wave energy dissipation coefficient when slope m=1,33 With m=1,33, the results of MatLab's Curve fitting regression calculation using the Trustregion algorithm have given the regression equation form: 19 𝐾 = −0,0466 × − 0,0117 × + 0,3217 (3-8) With reliability assessment parameters including SSE = 0,2232, RMSE = 0,1364 and R2 = 0,1819, as shown in Figure 3.31 and the equation (3-8), it shows better results than the case m = However, it is quite small, so the reliability is quite low This is also explained by the fact that on the inclined plate breakwater surface, notches are combined with concave holes to reduce waves Therefore, when waves interact with the breakwater, the nonlinearity is so large that it is difficult to give a general rule Figure 0.27: Relationship between KL and wave steepness with slope m=1 Figure 0.28: Relationship between KL and wave steepness with slope m=1,33 3.3.4.3 Correlation between wave steepness and wave energy dissipation coefficient when slope m=1,5 20 With m=1,5, the results of MatLab's Curve fitting regression calculation using the Trust-region algorithm have given the regression equation form: 𝐾 = −0,0007 × + 0,0285 × + 0,0891 (3-9) Reliability assessment parameters include SSE = 0,1046, RMSE = 0,0933 and R2 = 5694 It shows that equation (3-9) has quite good reliability Thus, it can be seen that the gentler the slope, the clearer the relationship between KL and the wave steepness Figure 0.29: Relationship between KL and wave steepness with slope m=1,5 d 3.4 Wave pressure distribution on the inclined plate 3.4.1 The issues Determine the wave pressure distributed on the breakwater slope The pressure value P for each wave probe in each experiment was calculated and compared with the theory 3.4.2 Wave pressure distribution on pile-supported inclined plate breakwater Figure 3.33 shows the results of measuring and calculating theoretical wave pressure from Appendix F - TCVN 9901:2014 and TCVN 12261:2018, drawing some comments below: - The wave pressure distribution acting on the inclined plate breakwater (m=1.33 and m=1.5) has a similar trend to the wave pressure distribution on the sloping embankment The difference is that the maximum pressure is higher than the experimental results At the same time, the higher the depth, the larger the measured wave pressure distribution than the calculated wave pressure of the sloping embankment - Wave pressure increases when wave height and wave period increase The maximum pressure value appears at the same position P2 The calculated maximum wave pressure is 56 to 97% greater than the experiment - The lowest wave pressure occurs at the bottom of the inclined plate (point P6) This can be explained because part of the wave pressure passes through the gap between the inclined slopes and the flume bottom On the other hand, the higher the depth, the weaker the wave interaction, so the wave pressure is significantly reduced This result shows that, 21 in the absence of experiments on physical models to determine wave pressure, the Method of calculating wave pressure on sloping embankments can be applied as instructed in TCVN 12261:2018 and TCVN 9901:2014 Figure 0.30: Distribution of wave pressure on inclined plate breakwaters on pile foundations with different slopes 3.5 Distribution of maximum wave velocity at the base of the inclined breakwater 3.5.1 Introduction During the experiment, a velocity measuring probe was used to monitor the velocity caused by the waves to evaluate the maximum velocity in front of the base of the pilesupported inclined breakwater The results filtered out the maximum velocity value and the corresponding velocity direction 3.5.2 Maximum velocity distribution due to waves in the gap between the base of the inclined plate breakwater and the bottom Based on experimental data, it is possible to extract the maximum flow velocity and direction corresponding to the original shape The results shown in Figure 3.34 show that: - The maximum flow velocity corresponding to the slope of the inclined plate m = and m = 1.33 tends to be similar and less than the theoretical maximum velocity - With a slope of m = 1.5, the measured maximum velocity tends to be larger than the theoretical maximum velocity It can be explained similarly to the study of Yagci et al because when the slope is gentle, the possibility of waves breaking on the inclined plate appears, increasing the maximum velocity 8,0 Vmax Tinh toán (m/s) Vmax đo đạc (m/s) 7,0 V (m/s) 6,0 5,0 m=1 m=1,33 m=1,5 T thay đổi 4,0 3,0 2,0 1,0 0,0 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Phương án thí nghiệm Figure 0.31: Distribution of maximum velocity due to waves in the gap between the inclined plate breakwater on the pile foundation and the flume bottom 22 - With the constant wave height and changing the wave period, the results show that the maximum velocity appears corresponding to experimental plan PA44 with H=0.14m and T=1.4 seconds corresponding to the original wave is Hnh = 2,1 and Tnh = 5,42 s with inclined slope m = 1,5 This shows that it is difficult to determine the law of variation of the maximum velocity caused by waves when impacting on inclined plate breakwaters on pile foundations - The maximum velocity caused by waves at the gap between the inclined plate and the flume bottom with a large inclined slope is similar to the theoretical formula However, the wave-breaking phenomenon occurs when the slope is gently inclined, causing the maximum velocity to increase significantly The Thesis recommends that experiments be conducted on physical models to determine the maximum velocity caused by waves 3.6 Conclusion of Chapter - The wave transmission coefficient can be determined through the relationship with the wave steepness corresponding to each specific slope The correlation equations (3-1), (3-2), and (3-3) have been built with acceptable reliability The Correlation becomes more obvious when the slope of the inclined plate is gentler - Inclined plate breakwaters on pile foundations with notches combined with waveabsorbing concave holes have a wave reflection coefficient equivalent to inclined slope breakwaters with covered blocks and can be determined through the relationship with the wave steepness corresponding to each specific slope The correlation equations (3-4), (3-5) and (3-6) are built with acceptable reliability - The process of wave energy dissipation is a complex and highly nonlinear process Experimental results show that building a relationship between the wave energy dissipation coefficient and the wave steepness is very difficult when the breakwater has a large slope When the slope is gentle, the nonlinearity is reduced, so the relationship according to equation (3-9) can be used to determine the wave energy dissipation process through the wave steepness - Experimental results show that wave pressure tends to concentrate near the water's edge and is distributed similarly to theory according to TCVN 9901:2014 - The maximum velocity induced by waves at the gap between the inclined plate and the flume bottom with a large inclined slope is similar to the theoretical formula However, the wave breaking phenomenon occurs when the slope is gently inclined, causing the maximum velocity to increase significantly CHAPTER APPLYING RESEARCH RESULTS TO PROPOSE THE MOST SUITABLE TYPE OF INCLINED PLATE BREAKWATERS ON PILE FOUNDATIONS IN THE CONSTRUCTION OF COASTAL PROTECTION WORKS IN VIETNAM 4.1 The cross-sectional solution of inclined breakwaters in protection coastal works For the goal of protecting the coast with erosion limitation and beach nourishment, it is recommended to choose the solution of arranging an offshore breakwater or a T-shaped groin or a fishtail-shaped groin in which the wing of the T-shaped or fishtail with an inclined plate breakwater structure can be applied Criteria for selecting shore protection structures include 23 (1) Criteria for route planning and (2) criteria for breakwater shape to ensure the best antierosion effectiveness 4.2 Propose cross-section type of inclined breakwaters with coastal protection works Based on the research results, the Thesis proposes two types of cross-sections of inclined plate breakwaters with notches combined with wave-reducing concave holes applied to build coastal protection works as shown in Figures 4.1 and 4.2 The structural parameters are selected as below Inclined plate; Crest wall; Stubby apex; Concave; Pile foundation; Stone cushion; Breakwater base strengthening block; Selective stone riprap for breakwater reinforcement Figure 0.1: Scenario and ross-section of inclined plate breakwater on pile foundation with closed bottom Inclined plate Crest wall Stubby apex Concave Pile foundation Stone cushion Dike base strengthening block Selective stone 0.2: riprap for dike and reinforcement Figure Scenario ross-section of inclined plate breakwater on pile foundation with open bottom 4.2.1.1 Breakwater Crest elevation The crest of the breakwater is determined based on the following: - For flooded breakwaters, the breakwater crest height is equal to the average water level; - For submerged breakwaters, the breakwater crest elevation is lower than 0.3 times the design wave height of the average water level (Hs); 4.2.1.2 Width and height of inclined plate breakwater: - The Width of the inclined plate breakwater is selected to ensure stability during the designed storm waves 24 - To determine the appropriate breakwater width, conducting studies using physical models is recommended - To increase the weight of the breakwater, it is recommended that the length of breakwater segment enough to ensure stability under the designed storm waves 4.3 Design of inclined breakwaters in the Canh Duong coastal protection works, Quang Binh 4.3.1 Introduction to Canh Duong Coast Canh Duong commune is located at downstream of Roon Bridge, bordering the East Sea to the East, Highway to the West, Roon River to the North, and Quang Hung commune to the South The southern coast of the Roon River estuary in Canh Duong commune experienced serious landslides over a large length in the past few decades The shoreline erosion rate in previous years was quite fast, sometimes up to (1÷2)m/day and night In some parts of the coast, seawater rises daily close to people's houses 4.3.2 Design boundary conditions The Thesis collected boundary conditions for design from the literature [26] 4.3.3 Determine the characteristic parameters of the structure 4.3.3.1 Overall layout To protect the Canh Duong coast, there are two layout options including: - Option involves a protective breakwater along the existing coastline with a length of 1950 meters - Option is the selected option, including the following items (Figure 4.7): + A-B-C coastal protection embankment is 258.0m long; + CDEFGHK coastal protection embankment is 1442.0m long; + Groins type T1 T2 with embankment body is 150 m and the embankment wing is 250m long; + Breakwater for sand prevention and wave reduction L1 and L2 with the length of 250m; In this Thesis, wave-reducing sand prevention breakwaters L1 and L2 are taken as the design object with the structure of inclined plate breakwater on pile foundation 4.3.3.2 Determine the basic parameters of the inclined plate breakwater structure on the pile foundation (1) Breakwater crest elevation: Calculation results of breakwater crest elevation = 2.36m, recommended to choose breakwater crest elevation = 2.5m, seabed elevation in the construction area is -3.0m so total construction height is 5.5m (2) Width and slope of inclined plate breakwater: - Select the elevation of the outermost edge of the breakwater as -1.5, the slope of the inclined plate m = 1.50 Thus, the Width of the inclined plate is 6.0m - To prevent erosion at the base of the pile base, design a structure to protect the breakwater base with a mixed rock layer 75cm thick 4.3.3.3 Compare the inclined plate breakwater structure on the pile foundation with the rubble mound breakwater 25 The Thesis evaluated the advantages and disadvantages and analyzed and compared them with the sloping breakwater structure solution using tetrapods-covered blocks that the design consultant chose 4.3.3.4 Compare the effectiveness of wave reduction The Thesis calculated Kt, Kr, and Kl coefficients and compared them with rubble mound breakwaters with wave-breaking blocks The main results: (i) Wave transmission coefficients in the case of pile-supported inclined plate breakwaters are significantly higher due to the gap between the sea bottom and the breakwater; (ii) Regarding the reflectivity coefficient, it is lower by 20.2%; (iii) Regarding wave energy dissipation coefficient, it is lower 23% than the coefficient of the sloping breakwater with wave breaking block Figure 4.7: Overall layout of coastal protection works A typical cross-sectional shape for a T-shaped groin is shown in Figure 4.8 Figure 0.3: Typical cross-section of inclined plate breakwater protecting Canh Duong coast This result shows that the appropriate structure was chosen depending on the project goals The characteristics of wave transmission, wave reflection, and energy dissipation of the pile-supported inclined plate breakwaters solution are smaller than traditional sloping breakwaters with cover blocks However, it has more economic advantages, including material savings, quick construction, and eco-friendliness 26 4.4 Conclusion of Chapter - The Thesis proposed a type of inclined plate breakwater structure on pile foundations for application in the construction of stable and coastal protection works - It proposed the wave reduction breakwater solution to protect the coast of Canh Duong commune, Quang Trach district, Quang Binh province, using an inclined plate breakwater structure on a pile foundation CONCLUSION AND FURTHER RESEARCH DIRECTIONS Results of the Thesis 1.1 General research Research on improving breakwater structures with high durability, great economic efficiency in exploiting coastal works, and coastal protection is an attractive topic of many scientists The solutions for shore protection works built in our country still have certain limitations, especially with soft soil conditions The overall results show that the inclined plate breakwater solution on a pile foundation with notches combined with a wave-reducing concave hole has the advantage of an economical cross-section suitable for soft geology with simple construction technology and being environmentally friendly Physical models were used for common interaction between waves and pile-supported inclined plate breakwaters The research results have described hydrodynamic characteristics, including wave transmission, wave reflection, and wave energy dispersion There are a few studies on velocity distribution at the base of the breakwater and almost no studies on the distribution of wave pressure acting on inclined plate breakwaters 1.2 Physical model research Based on reliable experimental results on wave flumes, the Thesis has researched the effects of some basic input parameters such as water level, inclined slope, wave period, and wave steepness to changes in hydrodynamic characteristics, including wave transmission, wave reflection, and wave energy dissipation when waves interact with the pile-supported inclined plate breakwater structure with notches combined with wave- reducing concave holes The relationships between wave steepness and wave transmission coefficient have also been developed according to formulas (3-1), (3-2), and (3-3); between wave steepness and wave reflection coefficient according to formulas (3-4), (3-5) and (3-6); and between the wave steepness and the wave energy dissipation coefficient according to the formulas (3-7), (3-8), (3-9) 1.3 Research on application to practical works The Thesis proposed two types of inclined plate breakwater structures on pile foundations for application in the construction of coastal protection works (Figures 4.1 and 4.2) This type of project is registered for intellectual property regarding useful solutions and has been accepted by the National Office of Intellectual Property of Vietnam with application number 494w/QD-SHTT dated January 12, 2021 A breakwater solution to reduce incident waves was proposed to stabilize and protect the coast of Canh Duong commune, Quang Trach district, Quang Binh province, using an inclined plate structure on a pile foundation Calculations show that this breakwater structure ensures safe working under designed wave conditions 27 New contribution of the Thesis - The Thesis researched the effects of some basic input parameters such as water level, inclined slope, wave period, and wave steepness on changes in hydrodynamic characteristics, including wave transmission, wave reflection, and wave energy dissipation when waves interact with the inclined plate breakwater structure on a pile foundation with notches combined with wave reduction concave holes - It proposed the possibility of applying inclined plate breakwater structures on pile foundations with notches combined with wave-reducing concave holes in the construction of Vietnam's coastal protection works At the same time, it also proposed the technical characteristics of the structure of coastal protection works in Canh Duong commune, Quang Trach district, Quang Binh province Further research direction - The Thesis has only researched one subject: the inclined plate breakwater on a pile foundation with notches combined with wave-reducing concave holes in which the notches and concave holes are arranged in parallel Therefore, it is necessary to research ways to improve the structural forms and layout of notches and concave holes to find the technically and economically optimal form - Although 45 research scenarios have been proposed, the Thesis still does not cover all actual conditions in exploitation Especially due to the limitations of wave-generating equipment and wave flume models, storm wave scenarios interacting with inclined plate breakwaters have not been implemented Therefore, the research direction on the wave flume model will be more appropriate when evaluating the overall effectiveness of the works LIST OF PUBLISHED WORKS [1] [2] [3] [4] [5] Đỗ Minh Đạt, Nghiên cứu thực nghiệm đặc trưng phản xạ sóng đê nghiêng cọc Tạp chí Giao thơng vận tải, số tháng 3/2018, p 90-92, ISSN 23540818 Nguyen Viet Thanh, Do Minh Dat, Experiment study on the performance of a submerged modified pilesupported inclined plate breakwater Proceedings of the 10th International Conference on Asian and Pacific Coasts, APAC 2019, p 10071011, 2020, DOI:10.1007/978-981-15-0291-0_138 Trần Việt Kiên, Đỗ Minh Đạt, Nguyễn Thị Ly, Nguyễn Viết Thanh, Nghiên cứu ứng dụng kết cấu chống xói chân cơng trình thảm bê tơng cho cơng trình ven biển Tạp chí Biển Bờ, số tháng năm 2018, p 36-41 Viet Thanh Nguyen, Minh Dat Do, Chi Zhang, Effectiveness of Maintenance Dredging in the Navigation Channel of Cua Lo Port, Vietnam Proceedings of the 3rd International Conference on Sustainability in Civil Engineering (ICSCE 2020), November 26-27th, 2020, Hanoi, Vietnam ISBN: 978-604-76-2284-9 Nguyen Viet Thanh, Do Minh Dat, Vu Minh Tuan Back siltation in Bach Dang navigation channel, Nam Trieu Estuary, Vietnam In River Sedimentation – Wieprecht et al (Eds),p 1222-1228, 2016 Taylor & Francis Group, London, ISBN 978-1-138-02945-3