극한 강우 시 침투를 고려한 저수지 사면의 거동특성 및 보강대책에 관한 연구 = A Study on the Behavioral Characteristics and Reinforcement Measures of Reservoir Slopes Considering Rainfall Infiltration under Extreme Rainfall Conditions

다국어 초록 (Multilingual Abstract)

A Study on the Behavioral Characteristics and Reinforcement Measures of Reservoir Slopes Considering Rainfall Infiltration under Extreme Rainfall Conditions Moon, Jaehyu Advisor : Prof. Kim, Daehyeon, Ph. D. Department of Civil Engineering Graduate School of Chosun University This study analyzed the behavioral characteristics of the downstream slope of a reservoir embankment under extreme rainfall conditions associated with climate change, and proposed effective reinforcement measures through a combination of laboratory model experiments and numerical analyses. Among the 16,973 agricultural reservoirs in Korea, approximately 88.4% have been in service for more than 50 years, and most of these aging facilities are homogeneous fill dams without a clearly defined impermeable core zone. In addition to this structural vulnerability, the frequency of extreme rainfall events exceeding existing design standards （100- to 200-year return periods） has increased in recent years, leading to a growing number of slope failure cases under the combined condition of flood water level and direct rainfall infiltration into the slope surface. However, conventional slope stability analyses have primarily focused on steady-state water level conditions and have not adequately accounted for the mechanical behavior of unsaturated soil resulting from rainfall infiltration. To address this limitation, an agricultural reservoir in Jeollanam-do, where an actual slope failure occurred in 2020, was selected as the study site. A 1/35-scale rainfall-reproduction model test, designed based on similarity laws, was conducted to measure the pore water pressure distribution and failure behavior within the slope under 200-year return period rainfall and extreme rainfall conditions. In addition, coupled seepage–slope stability analyses using SEEP/W and SLOPE/W were performed to quantitatively evaluate the seepage and slope stability behavior under steady-state conditions （full water level and flood water level） and transient conditions incorporating 200-year, 500-year, and extreme rainfall events. The laboratory model test results showed that pore water pressure within the slope increased with rainfall infiltration, leading to surficial sliding, and the converted failure depth showed a similar trend to the observed failure depth of the actual reservoir, confirming the applicability of the experimental results. The numerical analysis results indicated that, under the unreinforced condition, the factor of safety exceeded the reference value （1.20） when only water level conditions （full and flood water levels） were considered; however, it decreased to approximately 0.99 under transient conditions incorporating extreme rainfall infiltration, falling below the reference value. These results suggest that conventional stability assessments based solely on water level conditions may not adequately reflect the reduction in stability caused by extreme rainfall. Analytical evaluation of four reinforcement methods—berm installation, partial and full riprap reinforcement, and toe drain installation—showed that the factor of safety under extreme rainfall conditions ranked in the order of toe drain （1.31）, full riprap reinforcement （1.28）, partial riprap reinforcement （1.24）, and berm installation （1.01）. In particular, the toe drain exhibited the most effective stability improvement by suppressing the rise in pore water pressure through efficient drainage of infiltrated water, while riprap reinforcement contributed to stability through increased resisting force from added self-weight, and berm installation contributed through improved slope geometry. Each method was found to enhance slope stability through a distinct mechanism. The findings of this study indicate that the stability assessment of downstream slopes of aging agricultural reservoirs should consider not only steady-state water level conditions but also transient conditions associated with rainfall infiltration. The results are expected to serve as basic data for establishing slope stability assessment procedures and selecting appropriate reinforcement methods under extreme rainfall conditions.

목차 (Table of Contents)

• 제 1 장 서 론 1
• 1.1 연구배경 및 목적 1
• 1.2 국내·외 연구동향 3
• 1.3 연구내용 및 방법 6
• 제 2 장 이론적 배경 8
• 2.1 기후변화에 따른 수문순환 변화와 저수지 사면 취약성 8
• 2.1.1 저수지 사면파괴의 영향요인 8
• 2.1.2 강우특성과 사면파괴의 상관성 9
• 2.1.3 우리나라의 강우특성 10
• 2.2 불포화토의 특성 13
• 2.2.1 불포화토의 구성 14
• 2.2.2 모관흡수력 18
• 2.2.3 흙-함수특성곡선 20
• 2.2.4 함수특성곡선 이력현상 22
• 2.2.5 불포화토의 투수특성 24
• 2.2.6 SWCC와 경험식 27
• 2.2.7 SWCC 이력현상과 토질특성 28
• 2.3 불포화토의 역학적 특성 및 전단강도 30
• 2.4 강우침투와 간극수압 및 포화영역 거동 33
• 2.4.1 강우침투 이론과 침투모델 33
• 2.4.2 대표 강우침투 모델 35
• 2.4.3 포화영역의 확산과 간극수압 변화 37
• 2.4.4 강우사상·강우강도에 따른 침투·안정성 변화 38
• 2.5 사면안정해석 이론 39
• 2.5.1 사면안정해석의 개념 및 안전율 정의 39
• 2.5.2 한계평형해석법 40
• 2.5.3 마찰원법 42
• 2.5.4 절편법 44
• 2.6 상사법칙 및 강우 재현 모형실험 48
• 2.6.1 상사법칙의 개념과 종류 48
• 2.6.2 강우에 대한 상사법칙 및 모형 강우 규모 결정 50
• 제 3 장 실험방법 및 결과 53
• 3.1 개요 53
• 3.1.1 연구대상지역 53
• 3.1.2 실내모형실험에 사용된 지반 시료 55
• 3.2 실내모형실험 장치 및 실험방법 57
• 3.2.1 강우재현 실험장치 57
• 3.2.2 데이터 로거 59
• 3.2.3 간극수압계 60
• 3.2.4 상사비 산정 61
• 3.2.5 모형강우 규모의 결정 62
• 3.2.6 실험 수행 모델 63
• 3.2.7 실내모형실험 조성 방법 65
• 3.3 실험 결과 68
• 3.3.1 실내모형실험 결과 68
• 3.3.2 강우강도에 따른 간극수압 측정 결과 69
• 제 4 장 수치해석 검토 71
• 4.1 개요 71
• 4.2 안정성 검토 72
• 4.2.1 모델링 72
• 4.2.2 저수지 안정성 검토 기준 75
• 4.2.3 입력정수 산정 76
• 4.2.4 해석방법에 따른 원지반의 안정성 검토 결과 80
• 4.3 보강대책 별 검토 결과 89
• 4.3.1 간극수압 분포 검토 89
• 4.3.2 사면안정해석 검토 결과 96
• 4.4 결과 및 토의 101
• 제 5 장 결 론 103
• 참고문헌 105