서해안 해상 교량의 세굴 심도를 고려한 말뚝기초의 거동 특성 분석 = Analysis of the Behavior Characteristics of Pile Foundations Considering the Scour Depth of the Yellow Sea Bridge

다국어 초록 (Multilingual Abstract)

ABSTRACT

Sea bridges, as core infrastructure for road and rail transportation networks, play a vital role in national economic and social development. With the recent increase in demand for sea bridges, construction technology and methods have also rapidly advanced. However, various technical issues and challenges still exist. One of these issues is the stability of pile foundations. Especially in the case of offshore bridges, the effects of sea currents and waves can cause localized ground erosion, or scour, around the piers. This scour phenomenon reduces the load-carrying capacity of bridge pile foundations and, in the worst case, can lead to structural collapse.
Scour depth issues in pile foundations account for a significant proportion of the causes of many marine bridge collapses worldwide, necessitating thorough research and technical solutions. Indeed, numerous bridge collapses both domestically and internationally have revealed that damage to pile foundations due to scour was the primary cause.
In areas with large tidal ranges and soft seabeds, such as the west coast, there is a high risk that the bearing capacity of bridge foundations will decrease and the stability of the structure will rapidly decrease due to changes in tidal flow and riverbed scour. This scour causes local degradation of the riverbed around piers and piles, which in turn increases the exposed length of the piles, thus acting as a major factor in weakening their ability to resist horizontal and vertical loads.
However, current bridge design standards and foundation design methods either consider scour depth as a simple correction factor or only employ limited, empirically-based approaches, failing to quantitatively reflect the impact of scour in actual marine environments. This lack of a clear assessment and analytical basis for the impact of scour on the structural behavior of bridge foundations limits the reliability of future designs for large-scale marine bridges.
In this study, we aimed to quantitatively evaluate the behavioral characteristics of a sea bridge on the west coast according to changes in scour depth and directly reflect this in the structural behavior analysis of pile foundations to elucidate the structural impact of scour. Using rainfall and tidal current data measured at the actual site, two- and three-dimensional hydraulic analyses were performed to estimate scour depth. The numerical analysis results were compared with theoretical results to determine the scour depth. The scour depths were then used in a three-dimensional finite element analysis to analyze the displacement, moment, axial force, and ground reaction of the pile foundation in a stepwise manner as scour depth varied. This allowed for a quantitative assessment of the impact of varying scour depth on the behavior of the pile foundation. The analysis results showed that as the scour depth increased, the bearing capacity of the pile foundation decreased and the displacement increased, and the stress acting on the pile also increased.
As scour depth increases, the contact area with the ground decreases, shortening the effective support span of the pile. This, in turn, tends to concentrate structural stresses even under identical load conditions. These results demonstrate that existing design approaches that simply reflect scour depth as a correction factor do not adequately reflect changes in actual structural behavior.
This study presents a practical analysis procedure that quantitatively considers the impact of scour depth on the foundation design of offshore bridges, thereby providing a clear overview of the necessary review process during the design phase. However, the analysis conducted in this study was limited and reliant on numerical analysis. Therefore, future research utilizing measurement data from actual construction phases is warranted.

목차 (Table of Contents)

• 제 1 장 서 론· 1
• 1.1 연구의 배경 및 필요성 1
• 1.2 연구동향 2
• 1.3 연구의 내용 및 방법 5
• 제 2 장 이론적 배경 7
• 2.1 세굴 발생의 이론적 배경 7
• 2.1.1 일반 세굴 7
• 2.1.2 국부 세굴 10
• 2.1.3 연합 세굴 16
• 2.1.4 세굴심도 산정의 통합 접근법· 21
• 2.2 말뚝기초의 지지력 산정 이론적 배경 24
• 2.2.1 정역학적 방법에 의한 말뚝의 지지력 24
• 2.2.2 현장시험에 의한 말뚝의 지지력 28
• 2.2.3 재하시험에 의한 말뚝의 지지력 산정방법 32
• 2.2.4 말뚝의 수평지지력 산정방법 36
• 제 3 장 수치해석 40
• 3.1 개요 40
• 3.2 수치해석 대상지역 40
• 3.3 2차원 및 3차원 수리분석 41
• 3.3.1 수리분석을 위한 기초자료 분석 41
• 3.3.2 2차원 수치해석 방법 및 절차· 43
• 3.3.3 2차원 수치해석 범위 및 경계조건 설정 44
• 3.3.4 2차원 수치해석 결과 45
• 3.3.5 3차원 수치해석 방법 및 절차· 48
• 3.3.6 3차원 수치해석 범위 및 경계조건 설정 50
• 3.3.7 3차원 수치해석 결과 51
• 3.4 교량기초 거동분석을 위한 3차원 유한요소해석 55
• 3.4.1 수치해석 개요 55
• 3.4.2 수치해석 범위 및 방법· 58
• 3.4.3 수치해석 적용 지반강도정수 60
• 3.4.4 수치해석 조건 60
• 3.4.5 3차원 유한요소 수치해석 결과 61
• 제 4 장 분석 및 고찰 107
• 4.1 이론식과 수치해석에 의한 세굴심도 분석 107
• 4.2 해상 교량 기초의 세굴영향성 검토 109
• 4.2.1 세굴영향에 의한 말뚝기초의 변형 109
• 4.2.2 세굴영향에 의한 말뚝기초의 작용응력· 111
• 4.3 세굴깊이에 따른 말뚝기초의 거동특성 분석 114
• 4.3.1 세굴심도에 따른 말뚝의 연직방향 지지력 영향 검토 114
• 4.3.2 세굴심도에 따른 말뚝기초의 침하량 영향 검토 116
• 4.3.3 세굴심도에 따른 말뚝의 수평방향 지지력 영향 검토 118
• 제 5 장 결론 및 제언 121
• 참고문헌 124
• Abstract 127