Erosion mechanism assessment of Japanese offshore seabed soil using Erosion Function Apparatus (EFA)
세굴률 측정장치를 이용한 일본 연안 해저 토양의 침식 메커니즘 평가
- 주제(키워드) Erosion , Scour , EFA , Biopolymer , Xanthan gum , BPST
- 주제(DDC) 690
- 발행기관 아주대학교 일반대학원
- 지도교수 장일한
- 발행년도 2025
- 학위수여년월 2025. 2
- 학위명 석사
- 학과 및 전공 일반대학원 건설시스템공학과
- 실제URI http://www.dcollection.net/handler/ajou/000000034363
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
Recently, due to climate change and global warming, there has been an increasing interest in alternative energy. Among alternative energy, wind power is rapidly increasing in demand, and people prefer offshore wind power due to problems such as landscape damage and noise. The foundation shape of offshore wind power is mostly monopile, Scour accidents caused by vortices around the monopile have become a problem. If the piers of wind power or bridges are scoured, it can lead to collapse due to ground settlement. To overcome these problems, in this study, erosion behavior evaluation and scour depth prediction of offshore seabed soils were performed using Erosion Function Apparatus (EFA) and SRICOS-EFA. Biopolymer-based soil treatment (BPST) was introduced as a method of scour mitigation. Erosion parameters (i.e., critical shear stress and erodibility) are determined using Erosion Function Apparatus (EFA), and scour rate is calculated through linear regression graphs. Non disturbed samples obtained from boreholes drilled from Site 1 to Site 3 in Japan are used, and one site is divided into four layers. In the case of Site 1, the critical shear stress of Site 1 layer 4 (S1L4) hard assumption was 53.20 Pa, the highest among the layers, and the erodibility coefficient of Site 1 layer 2 (S1L2) hard assumption was 4.58 mm/hr/Pa, the lowest among the layers, which was the most effectiveness for resisting erosion. On the contrary, the critical shear stress and erodibility coefficient of Site 1 layer 3 (S1L3) were 0.05 Pa and 71.69 mm/hr/Pa, respectively, which were the most vulnerable to erosion, and methods for erosion reduction were explored in the discussion. As for Site 2 and Site 3, they are overconsolidated silty soils and did not show any erosion even at flow velocities up to 7.7 m/s. The soil classification of Briaud (2008) was conducted through the results of the EFA experiment. The erodibility classification was categorized from very low erodibility [V] to very high erodibility [I], which varies from sandy with poor particle size distribution to highly organic clay according to the USCS. SRICOS-EFA numerical analysis was performed using the scour rate obtained from the experiment and 1) geometry information 2) soil information 3) water information. Discharge data was determined for a 17-year period from 2002 to 2018. The results of the analysis showed that the max scour depth of Site 1 was 1.560 m. For Site 2 and Site 3, the max scour depth was 0 m because there was no erosion at all. Xanthan gum biopolymer was treated to reinforce the most vulnerable layer, S1L3. The discharge data was extended to assume a 30-year period, which is the actual wind power usage period. The EFA test confirmed that the erodibility decreased as the concentration of the biopolymer increased. SRICOS-EFA analysis showed that the biopolymer-treated layer was not eroded when treated with 2% xanthan gum, and the maximum scour depth was 2.69 m, which was significantly reduced compared to 7.97 m without treatment. In the case of Site 1, it means that long-term (up to 30 years) structural stability can be achieved by treating the most vulnerable S1L3 with more than 2% of biopolymer-Xanthan treatment.
more목차
CHAPTER I INTRODUCTION 1
1.1 Background 1
1.2 Scope – Organization 5
CHAPTER II SOIL EROSION MECHANISM AND SCOUR RATE ESTIMATION 7
2.1 Introduction 7
2.2 Fundamentals of soil erosion and scour 7
2.2.1 Shear stress and critical shear stress at soil surface 7
2.2.2 Erosion rate and shear stress in water channel 10
2.2.3 Correlation between shear stress and erosion rate 11
2.3 Erosion mechanism in EFA test 13
2.4 Summary and conclusions 15
CHAPTER III METHODOLOGY 16
3.1 Introduction 16
3.2 Erosion Function Apparatus (EFA) for erosion assessment of soil 16
3.3 Soil properties of offshore seabed in Chiba prefecture 21
3.4 Erosion test methods 25
3.5 Summary and conclusions 26
CHAPTER IV EXPERIMENTAL RESULTS 27
4.1 Introduction 27
4.2 Site 1_Layer 1 (S1L1) 27
4.3 Site 1_Layer 2 (S1L2) 32
4.4 Site 1_Layer 3 (S1L3) 38
4.5 Site 1_Layer 4 (S1L4) 43
4.6 Site 2_Layer 1 (S2L1) 50
4.7 Site 2_Layer 2 (S2L2) 54
4.8 Site 2_Layer 3 (S2L3) 57
4.9 Site 2_Layer 4 (S2L4) 62
4.10 Site 3_Layer 1 (S3L1) 65
4.11 Site 3_Layer 2 (S3L2) 69
4.12 Site 3_Layer 3 (S3L3) 72
4.13 Site 3_Layer 4 (S3L4) 76
4.14 Summary and conclusions 79
CHAPTER V SOIL CLASSIFICATION VIA EFA TEST 83
5.1 Introduction 83
5.2 Soil classification by Briaud 84
5.2.1 Erosion classification: Site 1 84
5.2.2 Erosion classification: Site 2 86
5.2.3 Erosion classification: Site 3 87
5.3 Summary and conclusions 88
CHAPTER VI SCOUR RATE PREDICTION USING SRICOS-EFA 89
6.1 Introduction 89
6.2 General input data 90
6.3 Geometry information 91
6.4 Soil data 92
6.4.1 Site 1(S1) data 96
6.4.2 Site 2(S2) data 98
6.4.3 Site 3(S3) data 99
6.5 Water and current data 101
6.6 Estimation curve of scour rate 103
6.6.1 Scour rate prediction: Site 1 103
6.6.2 Scour rate prediction: Site 2 104
6.6.3 Scour rate prediction: Site 3 104
6.7 Summary and conclusions 106
CHAPTER VII FEASIBILITY EVALUATION OF BIO-BASED SOIL TREATMENT FOR EROSION MITIGATION 107
7.1 Introduction 107
7.2 Erosion mitigation effect of bio-based soil treatment 109
7.3 Summary and conclusions 111
CHAPTER VIII CONCLUSIONS 112
REFERENCES 114
ABSTRACT (IN KOREAN) 122
CURRICULUM VITAE 124
