This report summarizes the findings of a study on the landslide causes and recovery measures for Umyeonsan Mountain conducted by the Korean Geotechnical Society. The study investigated two landslide sites, identified heavy rainfall as the main cause, and proposed stabilization and drainage improvement measures. Key findings include: - Field surveys found the landslides were caused by heavy rainfall exceeding 100mm from July 26-29 that saturated weak soil layers. - Hydrologic analysis confirmed the heavy rain event could generate runoff exceeding the capacity of existing drainage pipes. - Recommendations are made to install subsurface drains, retaining walls, and reinforce unstable slopes to prevent future landsliding during extreme rainfall.

1. Report No.
KGS11-250
우면산 산사태 원인조사 및 복구대책수립 용역
최 종 보 고 서
2011. 11.
사단
법인
KOREAN GEOTECHNICAL SOCIETY

3. 제 출 문
서울특별시 귀중
서울특별시가 의뢰한 “우면산 산사태 원인조사 및 복구대책 수립”에
대한 연구용역을 성실히 수행하고 연구결과를 종합하여 최종 보고서로
제출합니다.
2011년 11월
사단법인 한국지반공학회
회 장 장 연 수

4. 연구진
연구단장 : 정 형 식 (한양대학교 대우교수, 한국지반공학회 고문)
연구부단장 : 최 경 (한국산지환경조사연구회, 이사)
연구위원 : 신 희 순 (한국지질자원연구원, 영년직연구원)
김 재 헌 (특수법인 사방협회, 이사)
배 규 진 (한국건설기술연구원, 선임연구위원)
한 명 식 (태조엔지니어링, 대표이사)
총괄간사 : 이 승 호 (상지대학교, 교수)
연구원 : 송 영 석 (한국지질자원연구원, 선임연구원)
장 선 철 (태조엔지니어링, 이사)
채 병 곤 (한국지질자원연구원, 책임연구원)
황 영 철 (상지대학교, 교수)
안 재 현 (서경대학교, 교수)
유 병 옥 (한국도로공사, 수석연구원)
권 오 일 (한국건설기술연구원, 전임연구원)
자문위원단
김 상 규 (동국대학교 명예교수, 전 한국지반공학회 회장)
강 병 희 (인하대학교 명예교수, 전 한국지반공학회 회장)
이 종 규 (단국대학교 명예교수, 전 한국지반공학회 회장)
박 찬 호 (유구엔지니어링 회장)
김 수 삼 (한양대학교 명예교수, 전 대한토목학회 회장)
장 연 수 (동국대학교 교수, 현 한국지반공학회 회장)
장 범 수 (한국시설안전공단, 유지관리기술그룹장)
김 만 일 (한국시설안전공단, 연구원)

5. 목 차
제1장 서론 ······················································································································· 1
1.1 개 요 ·············································································································································· 1
1.1.1 과 업 명 ······························································································································· 1
1.1.2 과업기간 ······························································································································· 1
1.1.3 수행기관 ······························································································································· 1
1.1.4 과업목적 ······························································································································· 1
1.1.5 과업범위 ······························································································································· 1
1.1.6 과업내용 ······························································································································· 1
1.2 과업구간 산사태 현황 ·················································································································· 2
1.2.1 산사태 발생 위치도 ············································································································· 2
1.2.2 지구별 산사태 현황 ············································································································ 2
1.3 지형 및 지질 ································································································································· 3
1.3.1 지형 ······································································································································ 3
1.3.2 지질 ······································································································································ 4
1.4 식생현황 ········································································································································ 6
1.5 산사태 일반 ·································································································································· 7
1.5.1 산사태의 개요 ······················································································································ 7
1.5.2 산사태의 유형 ····················································································································· 7
1.5.3 산사태의 분류 ····················································································································· 8
제2장 강우특성 및 수문분석 ······················································································· 21
2.1 최근 호우의 변화 경향 ·············································································································· 21
2.1.1 한반도의 기후변화 양상(2011, 기상청) ··········································································· 21
2.1.2 서울시 기후변화 현황 ······································································································ 22
2.1.3 7월 26～29일 서울 집중호우의 특징 ············································································· 23
2.2 수문분석 ····································································································································· 32
2.2.1 강우분석 ···························································································································· 32
2.2.2 유출분석 ···························································································································· 36
2.2.3 결론 ··································································································································· 40
2.3 우면포대 우수관거 조사분석(국방부 제공자료) ······································································· 41
2.3.1 우수관거의 유출해석 ········································································································ 41
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6. 2.3.2 합리식에 의한 유입량 산정 ····························································································· 42
2.3.3 사례현장 조사분석 ··········································································································· 44
2.3.4 우면포대 통수단면 분석 ·································································································· 51
2.3.5 결언 ··································································································································· 59
제3장 산사태 원인 및 대책방안 ·················································································· 61
3.1 래미안APT 지구 ························································································································· 61
3.1.1 일반현황 ····························································································································· 61
3.1.2 조사현황 ···························································································································· 63
3.1.3 원인분석 ···························································································································· 92
3.1.4 추정 붕괴 과정 ··············································································································· 102
3.1.5 대책방안 제안 ················································································································· 104
3.2 신동아APT 지구 ······················································································································· 105
3.2.1 일반현황 ·························································································································· 105
3.2.2 조사현황 ·························································································································· 107
3.2.3 원인분석 ·························································································································· 139
3.2.4 추정 붕괴 과정 ··············································································································· 148
3.2.5 대책방안 제안 ················································································································ 150
3.3 전원마을 지구 ·························································································································· 151
3.3.1 일반현황 ·························································································································· 151
3.3.2 조사현황 ·························································································································· 152
3.3.3 원인분석 ························································································································· 182
3.3.4 대책방안 제안 ················································································································ 185
3.4 형촌마을 지구 ·························································································································· 187
3.4.1 일반현황 ·························································································································· 187
3.4.2 조사현황 ·························································································································· 189
3.4.3 원인분석 ························································································································· 249
3.4.4 대책방안 제안 ················································································································ 255
3.5 산사태 방재를 위한 관리방안 ································································································ 258
3.5.1 방재시스템 구축의 필요성 ···························································································· 258
3.5.2 국내외 기술개발 현황 ··································································································· 258
3.5.3 방재시스템 구축 추진 방안 ·························································································· 260
제4장 결론 ·················································································································· 261
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7. 제1장 서론 ∎∎∎
제1장 서론
1.1 개 요
1.1.1 과 업 명 : 우면산 산사태 원인조사 및 복구대책 수립 용역
1.1.2 과업기간 : 2011. 09 ～ 11(2개월간)
1.1.3 수행기관 : 한국지반공학회
1.1.4 과업목적
- 7월 말 서울을 중심으로 중부지방에 3일간 약 500mm의 국지성 폭우가 내려 수많은 인명피해 및
재산피해가 발생하였다. 산사태가 발생한 우면산 4개소(래미안 APT, 신동아 APT, 형촌마을, 전원마
을)에 대한 현장 조사 및 산사태 원인을 분석하고 복구 대책 방안 수립을 목적으로 한다.
1.1.5 과업범위 :
서울특별시 서초구 우면산 산사태 4개소
- 서울 서초구 방배동 산 92-1번지 우면산 일대(2개소)
(래미안 방배아트힐(이하 래미안 APT), 방배신동아 럭스빌(이하 신동아 APT))
- 서울 서초구 방배동 전원마을 6길 일대(전원마을)
- 서울 서초구 우면동 산 34-1번지 자연생태공원 일대(형촌마을)
1.1.6 과업내용
- 일반현황 및 산사태 피해현황과 피해원인 조사
- 항구 복구대책, 사면관리제도 개선방안 등
- 1 -

8. 1.2 과업구간 산사태 현황
1.2.1 산사태 발생 위치도
<그림 1.2.1-1> 산사태 발생 위치도
1.2.2 지구별 산사태 현황
1) 래미안APT 지구
서울시 서초구 방배3동에 위치한 래미안APT 앞 우면산에서 발생된 산사태 구간이다. 2011년 7월 27일
오전 10시쯤 집중호우로 인하여 우면산에서 토석류 산사태가 발생되었으며, 토사, 전석 등의 사태물질은
남부순환로를 넘어 래미안APT 3층까지 피해를 주었으며, 사망자가 3명 발생하였다.
2) 신동아APT 지구
서울시 서초구 방배동에 위치한 신동아APT 앞 우면산에서 발생된 산사태 구간이다. 2011년 7월 27일
오전 8시 40분쯤 집중호우로 인하여 우면산에서 토석류 산사태가 발생되었으며, 토사, 전석 등의 사태물질은
남부순환로를 넘어 불교TV방송과 신동아APT 1층까지 피해를 주었다. 사망자는 불교TV방송에서 1명, 신동
아APT에서 2명 발생하였다.
3) 전원마을 지구
우면산 서측, 지하철 4호선 남태령역 부근에 위치하며, 행정지명 상으로는 서울시 서초구 방배동에 해당한
다. 본 지역으로 2011년 7월 27일 오전 집중호우로 인하여 우면산 남서측 산지에서 토석류가 발생되어 전원
마을 주택지에 토사가 유입되었고, 이로 인하여 6명의 사망자가 발생했다.
4) 형촌마을 지구
우면산 자연생태공원이 위치하는 서울시 서초구 우면동 형촌마을에 위치하는 지역으로 2011년 7월 27일
집중호우로 인해 토석류에 의한 산사태가 발생되어 120가구 가운데 60가구가 고립되고, 사망자 1명을 포함
10여명의 사상자가 발생했다.
- 2 -

9. 제1장 서론 ∎∎∎
1.3 지형 및 지질
1.3.1 지형
우면산(258m, 牛眠山)은 서울특별시 서초구와 경기도 과천시의 경계에 있는 산이다. 과거 관악산의 줄기
였던 우면산은 남태령 고갯길 확장으로 현재는 관악산과 완전히 분리되었다.
우면산은 삼막사-관악산-우면산으로 이어지는 북북동방향 산계의 끝자락에 위치하며, 화강암으로 이루
어진 높은 산지의 관악산에 비해 지체구조운동 및 풍화작용에 의해 형성된 편마암류의 낮은 구릉성 산지를
형성한다.
우면산은 산꼭대기 부근의 경사가 30∼35도이며, 주로 화강암 지대로 이뤄진 강북지역과 달리 흑운모
호상편마암이 기반암으로 분포하는데, 편마암 지형은 풍화가 심하고 단층이 많아 산사태에 취약한 지형이라
고 할 수 있다.
<그림 1.3.1-1> 우면산의 지형
우면산 주변의 주요 수계로는 우면산 남쪽방향으로 양재천이 위치하며 북쪽에 위치한 예술의전당 부근이
반포천의 발원지로 추정된다. 우면산 내의 수계는 대부분 계곡부를 따라 형성되었다.
- 3 -

10. 1.3.2 지질
우면산에 기반암으로 분포하는 주 암종은 경기편마암복합체 내에서 가장 넓게 분포하는 선캄브리아기의
흑운모 호상편마암으로 호상구조가 특징적이다. 또한 상대적으로 성분대의 분화가 불량한 화강암질 편마암
도 함께 산출되기도 하며, 부분적으로 암맥류가 관입 분포하고 있다.
전반적으로 풍화가 심하게 진행되어 노두가 빈약한 상태이며 엽리구조가 발달하였으나 그 방향성은 수차
례에 걸친 습곡작용 등에 의하여 불규칙하게 발달되어 있다. 흑운모 호상편마암은 엽리방향이 주향은 북동
쪽, 경사는 남동쪽 방향으로 주로 분포하고 있으며 구성광물은 석영, 사장석, 흑운모, 각섬석으로 구성되어
있다.
<그림 1.3.2-1> 우면산 일대 지질도
- 4 -

11. 제1장 서론 ∎∎∎
<표 1.3.2-1> 흑운모 호상편마암 박편 분석결과(출처 : 서울지하철 913공구)
암석박편 현미경 사진 광물분포
분석결과 대부분 석영과 흑운모로 이루어졌으며, 장석은 대부분 사장석으로 albite twinning을 보였고,
흑운모와 백운모가 결합하여 띠를 이루며, 그 주변에서 깃털모양의 규선석이 관찰되었다.
흑녹렴석은 입자의 크기가 작고 소량 관찰되며, 청녹색 또는 녹자색의 화려한 간섭색을 보이고, open
nicol하에서 relief가 높았으며, 녹니석은 흑운모의 변질로 관찰되며, 부분적으로 방해석이 충진되어 나타
났다.
- 5 -

12. 1.4 식생현황
우면산은 온대낙엽활엽수림 지역에 해당되며, 대부분 지역이 생태자연도 1등급으로 나타났고 식물은 88과
262속 427분류군으로 집계되었다.
<그림 1.4-1> 우면산 일대 임상도
우면산의 식생현황은 임상도상 활엽수림, 잣나무림, 포푸라림, 활엽수 인공림 등으로 구성되어 있으며,
대부분의 구간에서 활렵수림이 분포하고 있다.
주요 수종으로는 신갈나무, 아까시나무, 상수리나무, 물박달나무 등 활엽수와 소나무가 혼생하며, 전형적
인 한반도 중부지역 야산의 식생형으로 구성되어 있다.
<표 1.4-1> 우면산에서 서식하는 주요 식물
분류 종명세
특산종 병꽃나무, 토현삼
졸참나무, 신갈나무, 굴참나무, 소나무, 노간주나무, 상수리나무, 팥배나무, 오리
잠재 자연지표종
나무, 신나무, 버드나무, 귀룽나무, 참회나무, 산시나무, 갯버들, 꼬리조팝나무
낙엽송, 잣나무, 아까시나무, 현사시, 리기다소나무, 독일가문비, 가중나무, 복사
인공 식재종 나무, 무궁화, 개나리, 족제비싸리, 느티나무, 밤나무, 부들, 애기부들, 노랑꽃창
포, 연꽃
돼지풀, 망초, 개망초, 달맞이꽃, 미국가막살이, 서양등골나무, 털별꽃아재비, 왕
귀화식물종 고들빼기, 서양민들레, 토끼풀, 콩다닥냉이, 미국자리공, 애기수영, 소리쟁이, 호
밀풀
- 6 -

13. 제1장 서론 ∎∎∎
1.5 산사태 일반
1.5.1 산사태의 개요
산사태란, 자연사면 또는 자연사면의 특성을 지닌 인공사면의 붕괴현상으로 암석이나 흙 또는 이들의 혼합
물이 중력에 의해 경사면 아래로 천천히 포행(Creep)하거나 빠르게 떨어지는 현상(Falls) 또는 파괴면을
따라 미끄러지는 상태(Slides & Flows), 그리고 이들이 복합적으로 나타나는 현상을 말한다.
경계면을 따라 지반이 하부로 움직이는 산사태는 전 세계적으로 심각한 자연재해를 유발하며, 지진이나
화산폭발 같은 다른 재해와 연계되어 발생되기도 한다. 대부분의 산사태는 소규모이거나 천천히 발생하지만
때로는 빠른 속도로 대규모로 발생한다. 양상은 다르지만 우리사회에 심각한 피해를 유발하며 특히, 도심지
에서는 그 영향은 더 심각할 수 있다.
우리나라의 경우 국토의 2/3이상이 산지로 이루어져 여름철 장마, 태풍, 집중호우 시 사면파괴, 산사태,
토석류에 의한 토사유출로 인명과 재산피해가 자주 발생한다. 특히 강원지역은 산지면적이 89%를 차지하는
데 2002년 태풍 ‘루사’와 2003년 ‘매미’, 그리고 2006년 7월의 ‘집중호우’에 의에 전국에서 가장 큰 인명
및 재산피해가 발생하였다.
특히, 계곡부와 소하천을 따라 다량의 토사가 유출되는 토석류는 강우에 기인한 산사태 피해의 대부분을
차지할 정도로 발생빈도가 높고 큰 피해를 유발한다는 점에서 특별히 관심을 가질 필요가 있다.
1.5.2 산사태의 유형
형태에 따라 낙하(falls), 전도(topples), 활동(slides), 측방유동(lateral spreads), 흐름(flows)으로 분류
(UNESCO Working Party, 1990, EPOCH, 1993)하고, 파괴면 모양에 따라, 평면(planar), 쐐기(wedge),
단계(stepped), 원호(circular), 준원호(semi-circular) 등으로 분류할 수 있다.
또한 이들의 생성이 복합적인 작용에 의한 것인가 아닌가에 따라 단일(single) 또는 복합(multiple) 이라는
용어를 사용하기도 한다(Brunsden, 1985, Hutchinson, 1988).
지반재료와 활동특징 사이의 정확한 구분이 어려울 수 있으며 하부로 운동하면서 다른 형태로 변화 할
수도 있다.
우리나라에서는 대체로 토석류(debris flow), 암석낙하(rock fall), 암석과 토양 슬라이드(planar slide),
암반포행(rock creep) 및 회전형 슬라이드(rotational slide) 등 5가지 형태의 산사태가 주로 발생한다.
특히, 토석류(debris flow)는 토석의 흐름을 나타내며, 구체적으로 토석 및 부유물 등이 중력에 의해 경사
면을 따라 흐르면서 형태와 규모가 바뀌는 동적인 현상을 말한다. 토석류라는 용어는 오스트리아의 지질학자
인 Stiny(1910)가 처음으로 언급하였는데, 그는 부유물과 유사를 다량으로 운반하는 산지의 홍수유출을 토석
류로 정의한 바 있다.
- 7 -

14. 1.5.3 산사태의 분류
1) 비탈면 운동형상에 따른 분류
Varnes(1954, 1978)는 산사태에 포함되는 재료와 운동 형태에 따라 산사태를 분류한 바 있는데, 토석류의
경우 흐름운동(Flow)으로 분류하고 재료에 따라 암석류(Rock flow), 토석류(Debris flow), 토사류(Earth
flow)로 구분하였다. 암석류(Rock flow)는 불연속면을 따라 암괴가 비교적 서서히 움직이는 현상으로 크립
현상과 유사한 흐름을 일컫고, 토석류(Debris flow)는 집중강우나 융설에 의한 급류에 다량의 토석이 섞여
흐르는 현상으로 정의하였으며, 토사류(Earth flow)는 세립질의 실트, 점토, 점토질 모래에서 발생하는 파괴
와 더불어 토체 전체가 액상화 되면서 흐르는 현상으로 정의하였다. Varnes는 기존의 토석류와 유사한 토사
운동 현상을 표현하기 위해 사용하는 용어의 차이도 설명하였는데 토석활동(Debris slide)은 비교적 물의
함량이 적고 운동형태가 느린 현상이고, 토석사태(Debris avalanche)는 토석활동(Debris slide)과는 달리
운동형태가 빠른 현상으로 설명하였다. 이외에도 물이 없는 건조상태에서의 토사흐름을 나타내기 위해 Dry
sand flow, Dry silt flow 라는 용어를 사용하기도 하였다.
<표 1.5.3-1> 비탈면의 운동현상 분류(Varnes, 1978)
Type of material
Types of Movement Engineering Soils
Bed rock
Predominant coarse Predominantly file
Falls Rock fall Debris fall Earth fall
Topples Rock topple Debris topple Earth topple
Rotational Rock slump Debris slump Earth slump
Few unit
Slides Rock block slide Debris block slide Earth block slide
Translational
Many unit Rock slide Debris slide Earth slide
Lateral Spreads Rock spread Debris spread Earth spread
Rock flow Debris flow Earth flow
Flows
(deep creep) (Soil creep)
Complex Combination of two or more principal types of movement
- 8 -

15. 제1장 서론 ∎∎∎
<표 1.5.3-2> 비탈면 운동의 개요도
종류 개요도 설명
낙하 • 비탈면으로부터 암석이나 바위가 분리
(Falls) 되어 떼어지는 현상
• 경사면의 끝에서부터 불연속면의 내부
전도
의 수압 및 중력에 의해 암석이 넘어
(Topples)
지는 현상
• 아래로 오목한 활동토체의 파괴면이 회
전하며 이동하는 현상
활동 [회전(rotational)]
(Slides)
• 활동토체가 거의 평면으로 이동하며 소
규모의 회전활동도 같이 발생됨
[병진(translational)]
측방 유동 • 전단 혹은 인장균열에 의해 토체가 측
(Lateral 면으로 확장되는 현상으로 액상화 등에
spreads) 의해 발생
• 포화된 물질이 흘러내리는 현상
• Debris flow
흐름
Debris avalanche
(Flows)
Earth, Mud flow
Creep 등 포함
이번 우면산 산사태의 경우 전체적으로 우리나라에서 주로 발생되는 활동 및 흐름(토석류) 등이 혼합된
복합적인(Complex) 산사태로 판단된다.
- 9 -

16. 2) 흐름(Flow)의 형태를 보이는 산사태의 분류
Hungr 등(2001)은 흐름형태의 산사태를 구성물질, 함수비, 주요특징 및 흐름 속도를 기준으로 분류하였는
데, 이 분류방법은 Varnes가 제시한 산사태의 분류방법을 더 세분화 시킨 것으로, 북미지역과 유럽에서
토석류 현상의 정의를 위해 사용한 명칭 및 토석구성재료를 고려하여 토석류의 분류명칭을 결정하였다.
• 비액상화 흐름(Non-liquified flow) : 일반적인 사면의 파괴현상, 구성물질에 따라 비액상화 모래(실트,
자갈, 토석)흐름으로 명명
• 흐름활동(Flow slide) : 파괴된 토사가 액상으로 변화하면서 흐르는 현상, 구성물질에 따라 모래(실트,
토석, 암석)흐름으로 명명
• 점토흐름활동(Clay flow slide) : 함수비가 액성한계보다 큰 상태로서 예민비가 큰 점토가 액상으로 변화하
여 흐르는 현상
• 토사류(Earth flow) : 주로 점토나 세립질이 많은 토사에서 함수비가 충분할 때 발생하는 느린 흐름 파괴현상
• 토석류(Debris flow) : 물과 비교적 높은 농도로 섞인 암석, 자갈, 모래, 흙 혼합물이 빠르게 흐르는 현상,
수로형 토석류와 사면형 토석류로 분류
• 이류(Mud flow) : 물과 비교적 높은 농도로 섞인 점토, 실트 등의 세립분이 많은 흙 혼합물이 빠르게
흐르는 현상으로 토석류와 유사함
• 토석홍수(Debris flow) : 물과 비교적 높은 농도로 섞인 점토, 실트 등의 세립분이 많은 흙 혼합물이 빠르게
흐르는 현상으로 토석류와 유사함
• 토석사태(Debris avalanche) : 부분적 포화 또는 포화된 암석, 자갈, 모래가 경사가 급한 구간을 따라
빠르게 이동하는 현상으로 사면형 토석류와 유사함
• 암석사태(Rock avalanche) : 비교적 건조한 암석 파쇄물이 빠른 속도로 이동하는 현상
토석류와 같은 흐름운동을 나타내는 현상의 분류를 위한 중요한 구분기준은 재료의 구성물질과 함수비로
볼 수 있으며, 공학적 적용을 위해서는 구성물질과 함수상태를 구분하는 기준이 필요하다.
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17. 제1장 서론 ∎∎∎
<표 1.5.3-3> 흐름(Flow)의 형태를 보이는 산사태 분류(Hungr 등 2001)
명칭 구성물질 함수비 특징 속도
비액상화 흐름
실트, 모래, 자갈, 과잉간극수압 발생하지
(Non-liquified 건조, 습함, 포화 다양함
토석(애추) 않음. 발생부피가 한정됨
flow)
극히 빠름
흐름활동 실트, 모래, 토석, 파괴표면 액상화 가능물질, 일정한
(Extremely
(Flow slide) 연암 에서 포화 함수비
rapid)
점토흐름활동 예민점토 액성한계 원위치 액상화, 일정한
극히 빠름
(Clay flow slide) (Sensitive clay) 보다 큼 함수비
느림에서 매우
토탄(이탄)류 과잉간극수압 빠름
토탄, 이탄(Peat) 포화
(Peat flow) 발생 (Slow to very
rapid)
빠르지 않음
토사류 느린이동
점토나 토사 소성한계 근처 (Less than
(Earth flow) (Plug flow)
rapid)
토석류 기 형성된 수로흐름,
토석(Debris) 포화 극히 빠름
(Debris flow) 함수비 증가
이류 액성한계 혹은
진흙(Mud) 미립자 토석류 매우 빠름 이상
(Mud flow) 그이상
토석홍수
토석(Debris) Free water 존재 홍수 극히 빠름
(Debris flow)
토석사태 수로형성 없음,
부분적으로 또는
(Debris 토석(Debris) 상대적으로 얕고 가파른 극히 빠름
완전히 포화
avalanche) 근원지
암석사태 암편 다양, 대체로 신선암(Intact rock),
극히 빠름
(Rock avalanche) (Fragmented rock) 건조 큰체적
3) 토석류
① 토석류의 정의
가. 기존연구자들의 정의
- A fast moving mass of unconsolidated, saturated debris (WikipediA)
- A flow of sediment and water mixture in a manner as if it was a flow of continuous fluid
driven by gravity. It attains large mobility from the enlarged void space saturated with water
and slurry (Takahashi, 2006)
- A rapid movement of saturated soil, rocks and other debris down a steep mountain channel
(Swanston and Swanson, 1976)
- Gravity-induced rapid mass movement intermediate between landslides and water flooding
(Johnson,1970)
- 토석류(土石流) : 홍수로 산사태가 나서 진흙과 돌이 섞여 흐르는 물 또는 그런 흐름
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18. 나. 토석류 정의
경사가 급한 산지(계곡)에서 물과 토석(흙과 암)이 혼합되어 빠르게 이동하는(흐르는) 현상
• 토석류를 정의하는 주요어(keyword)
- Main Phenomena: flow, mass movement
- Velocity : fast, rapid, large mobility
- Material : water-debris mixture, soil-rock-debris
unconsolidated saturated debris
sediment-water mixture
- Location : steep mountain channel
- Driving : gravity-induced
다. Debris Flow에서 “Debris” 의미
- 사전적 의미 : 부스러기, (파괴물의) 파편, (지질), 암석 부스러기
- General : remains of something that has been otherwise destroyed
- Geology : remains of geological activity including landslide, volcanic explosions, avalanche,
or lahars
- Forestry: dead tree, remains of branches on the ground
- Stream : logs, sticks, branches
-토석 : 흙과 돌을 아울러 이르는 말
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19. 제1장 서론 ∎∎∎
<사진출처 : 한국도로공사, 2006, 연합뉴스>
② 토석류재료의 분류
가. By Shroder (1971) in "Landslides of Utah"
- Debris: 20～80% of material are greater than 2mm in size and remainder of the fragments
are less than 2mm.
- Earth : 80% or more of the fragments are smaller than 2mm (range of materials from
non-plastic sand to highly plastic clay)
- Debris Flow & Mud Flow (Varnes, 1978)
Debris flow: Relatively high percentage(>60～70%) of coarse fragments
Mud flow: At least 50% of sand-, silt-, and clay-sized particles
나. 입경에 따른 흙의 분류
- Coarse fragment
Name of Diameter (mm) Name of soil Diameter (mm)
soil separate (USDA classification) separate (Soil Mechanics)
Clay less than 0.002 Silt and clay Less than 0.074 (#200 sieve)
Silt 0.002–0.05 Fine sand 0.075 – 0.42
Very fine sand 0.05–0.10 Medium sand 0.42 – 2.0
Fine sand 0.10–0.25 Coarse sand 2.0 – 4.76 (#4 sieve)
Medium sand 0.25–0.50 Small gravel 4.76 – 19.0
Coarse sand 0.50–1.00 Large gravel 19.0 – 76.2
Very coarse sand 1.00–2.00
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20. 다. 토석류: 물과 흙의 혼합물 (water-debris mixture)
• 혼합비율의 정의
- 용적농도(volumetric concentration) : 토석류 단위부피에 포함되어 있는 토석의 부피( Cd = Vs/V)
로 정의
• 일반적인 토석류 용적농도 : 0.4 ～ 0.8
- 0.4 미만: 물의 함량이 많음 -> 홍수형태(flood), 소류(bedload)
- 0.8 이상: 흙의 함량이 많음 -> 사면파괴, 활동형태(slide)
• 일반적인 조립토의 간극율(n=Vv/V=1-Cd)
- 간극율(n) = 0.15(조밀) ～ 0.60 (느슨)
- 용적농도(Cd = 1-n)
③ 토석류 생성조건
• 시험에 의한 생성조건의 확인 (Takahashi, 2006)
- 토석류를 만드는 힘: 중력 (gravity)
- 위치운동에너지로 빠르게 전환 : 경사
- 토석의 이동가능성 : 충분한 유량
<사진출처 : Takahashi, 2006>
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21. 제1장 서론 ∎∎∎
④ 토석류의 분류
가. 토석류를 부르는 다양한 용어들
- Die Muren (stiny, 1910)
- Debris flow, Debris Torrent, Debris Avalanche, Debris Flood
- Stony debris flow(or Bouldery debris flow), Woody Debris flow
- Mud flow, Lahar, Mud flood
- Hyper-concentrated flow
- Earth flow
- Hillslope debris flow, Channelized debris flow, Apline debris flow
- Debris slide
나. 산사태의 운동형태에 따른 분류
• By Varnes(1978)
- Classified slope movement by type of movement and type of material
Type of material
Type of movement Engineering Soil
Bedrock
Predominantly coarse Predominantly fine
Falls Rock Fall Debris Fall Earth Fall
Topples Rock Topple Debris Topple Earth Topple
Rotational Few unit Rock Slump Debris Slump Earth Slump
Slides
Many Rock Block Slide Debris Block Slide Earth Block Slide
Translational
unit Rock Slide Debris Slide Earth Slide
Lateral Spread Rock Spread Debris Spread Earth Spread
Rock Flow Debris Flow Earth Flow
Flows
(deep creep) (soil creep)
Complex Combination of two or more principal types of movement
다. 흙-물 혼합체 흐름의 분류
• Classification of Flow of Soil-Water Mixture
- Water content, Material Type, Velocity
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22. • Classification of soil-water mixture flow
- Material type & water content
- 16 -

23. 제1장 서론 ∎∎∎
라. 유사 현상과의 구분
• Slide / Flow / Avalanche 의 구분
- 구성재료 : 유사함
- 물의함량 :
Slide (활동) : 부분포화 (soil)
Flow (흐름) : 완전포화 (soil-water mixture)
Avalanche(사태): 건조-부분포화
- Rate of movement
Slide (활동) : very slow ～ slow
Flow (흐름) : very rapid
Avalanche(사태): very rapid ～ extremely rapid
• Debris Flow / Earth Flow의 구분
- Debris flow(토석류) : 다량의 물과 섞인 모래, 자갈, 암석의 흐름 형태상 수로형 토석류에 해당
(Hungr, 2001)
- Earth flow(토사류) : 포화에 가까운 실트, 점토, 모래의 흐름 형태상 사면형 토석류에 해당
<사진출처 : Hungr, 2001>
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24. 마. 토석류의 분류
• 토석류 정의: 경사가 급한 산지(계곡)에서 물과 토석(흙과 암)이 혼합되어 빠르게 이동하는 흐르는 현상
• 재료에 따른 분류:
- Mud flow, debris flow(stony debris flow, woody debris flow)로 구분
• Slide, Avalanche와는 구분
- 이동 속도의 차이, 함수량의 차이
• Earth flow와 Debris Flow의 구분 필요
- 형태적인 차이, 함수량의 차이
- Earth slide는 Debris Flow의 시작의 일부분
⑤ 토석류의 일반적 특징
가. 토석류 발생과정
• 시작-이동-퇴적의 과정을 거침
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25. 제1장 서론 ∎∎∎
나. 토석류 시작메카니즘
(1) 토석류 시작 유형
• 시작유형은 3가지로 구분 (Takahashi, 2006)
– 강우시 자연사면 파괴로 인한 쇄설물의 이동
– 계곡유량으로 인한 계곡 바닥과 측벽의 세굴, 침식물의 이동
– 계곡내 퇴적된 자연 토사댐의 붕괴로 인한 쇄설물의 이동
(2) 시작유형의 구분 방법
• 실제현장조사를 통한 관찰로 구분 가능 / 엄밀한 구분은 어려움
(3) 국내에서의 일반적인 토석류 시작 유형
• 경사가 급한 계곡상부에서 표층파괴 형태로 발생
다. 사면파괴에 기인한 토석류 시작 메커니즘
• 파괴전(pre-failure)
- 강우에 의한 표토층의 포화 진행 : 자중증가
- 간극수압증가로 인한 전단강도 감소 : 강도감도
- 지하수흐름에 의한 침투력의 작용 : 하중증가
하중 > 강도 : 파괴의 시작
• 파괴후(post-failure)
- 파괴시작 후 강도감소, 점착력 상실로 인해 과다 변형 및 표면 균열 발생
- 균열부로 표면수가 침투되고 지속적인 변형 및 파괴 진행
- 변형속도가 빨라지면서 파괴토체가 느슨해지고 액상화 현상 발생
- 파괴토체가 아래로 이동하면서 가속
- 이동하는 토체는 하부표토층에 하중으로 작용하고 연쇄적으로 파괴진행
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26. 라. 사면파괴 유발요인
• 내적요인과 외적요인으로 구분
• 내적요인
- 지질조건 : 지층구분, 암종, 지질구조(절리구조) 등 (지질학)
- 지반조건 : 흙의 종류 및 상태, 강도-변형 특성, 투수특성 등 (토질역학)
- 지형조건 : 경사, 집수지형 (지형학)
- 식생조건 : 수목근계, 식생 또는 노출 등 (임학)
• 외적요인
• 강우조건 : 강우강도, 지속시간, 이전 강우량 (수리,수문학)
- 20 -