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2026 Vol.36, Issue 3 Preview Page

Research Article

Role of a Fault Zone on Tunnel Floor Heave in an In-Service Tunnel: A Case Study

공용 중인 터널 바닥부 융기에 대한 단층대의 역할: 사례 연구

Woon Sang Yoon1*
,
Byeong Hyun Han2
,
Hangseok Choi3
,
Young-Wan Shin4
,
Jeong-Woo Seok5
,
Hong-Rae Im5
윤 운상1*
,
한 병현2
,
최 항석3
,
신 영완4
,
석 정우5
,
임 홍래5
1Technical Adviser, Earth EnG Co., Ltd.
2Director, Water Resources Department 1, Dohwa Engineering Co., Ltd.
3Professor, School of Civil, Environmental and Architectural Engineering, Korea University
4CEO, Hakyong Engineering Co., Ltd.
5Pro, Global Civil ENG Team, Samsung C&T
1㈜어스이엔지 기술고문
2도화엔지니어링 수자원1부 상무
3고려대학교 건축사회환경공학부 교수
4㈜하경엔지니어링 사장
5삼성물산 건설부문 해외 토목 ENG팀 프로
*Corresponding Author
30 September 2026. pp. 407-421
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Abstract

This study investigated the mechanism of long-term floor heave and the influence of a fault zone in an in-service twin-tube tunnel crossing Mt. Toham in Gyeongju, South Korea, where progressive floor heave has been observed since 2016. To clarify the mechanism of deformation, long-term monitoring records, pavement elevation surveys, tunnel face maps, drillcore observations, seismic tomography, and laboratory soil tests including X-ray diffraction (XRD) were comprehensively analyzed. The results show that the heave-affected section intersects the Oedong Fault, the boundary fault of a Neogene sedimentary basin. The ground was classified into four geological units: clay-rich fault core (ZD), fault damage zone (ZC), weathered rockmass (ZB), and competent jointed rockmass (ZA). Illite, kaolinite, and chlorite were identified within the fault core, whereas no swelling clay minerals were detected. These findings indicate that the long-term floor heave controlled primarily by squeezing behavior rather than clay swelling. A comparison of three squeezing ground assessment methods showed that the fault core was consistently classified as at least severe squeezing ground, with the Hoek-Marinos Method most accurately reproducing the observed spatial distribution and magnitude of floor heave. The heave-affected section progressively expanded from the fault core and damage zone into the adjacent weathered rock over time, but its propagation was constrained where competent jointed rock was encountered. Based on these findings, a new geotechnical concept, the fault influence zone (FIZ), is proposed to describe the time-dependent propagation of deformation beyond the fault zone. Accordingly, the reinforcement design for in-service tunnels should encompass not only the fault zone but also the surrounding FIZ.

Keywords
tunnel floor heave
in-service tunnel
fault zone
squeezing behavior
fault core
fault damage zone
fault influence zone
long-term deformation

본 연구는 경주시 토함산을 횡단하는 쌍굴 도로터널에서 2016년 이후 지속적으로 관측된 터널 바닥부 융기의 발생 메커니즘과 단층대 영향을 규명하였다. 이를 위해 장기 계측자료, 노면 고도 측량, 굴진면 및 시추코어 관찰, 탄성파 토모그래피와 XRD를 포함한 토질시험 결과를 종합적으로 분석하였다. 분석 결과, 바닥부 융기 구간은 신생대 신진기 퇴적분지의 경계단층인 외동단층과 터널이 교차하는 구간으로 확인되었으며, 지반은 점토질 단층핵(ZD), 단층손상대(ZC), 풍화암반(ZB), 양호한 절리암반(ZA)의 지질 단위로 구분되었다. 단층핵에서는 일라이트, 카올리나이트, 녹니석이 확인되었으나, 팽창성 점토광물은 검출되지 않았다. 이는 장기적인 터널 바닥부 융기가 점토광물의 팽창보다는 지반의 압착 거동에 의해 지배됨을 시사한다. 세 가지 압착성 지반 평가법을 비교한 결과, 단층핵은 모든 평가법에서 심한 압착성 지반 이상의 취약한 지반으로 평가되었으며, Hoek-Marinos 방법이 실제 바닥부 융기의 공간적 분포와 변형 규모를 가장 잘 재현하였다. 또한 바닥부 융기 구간은 시간 경과에 따라 단층핵과 단층손상대에서 인접 풍화암반까지 확장되었으나, 양호한 절리암반이 출현하는 구간에서 융기 전파가 제한되는 것으로 나타났다. 이러한 결과를 바탕으로 본 연구에서는 단층대 범위를 넘어 시간 경과에 따라 변형이 확산되는 영역을 설명하기 위하여 새로운 지질공학적 개념인 단층영향구간(fault influence zone, FIZ)을 제안하였다. 이에 따라 공용 중인 터널의 보강 범위는 단층대 뿐 아니라 장기 변형의 영향을 받는 주변 단층영향구간까지 포함하도록 설계되어야 한다.

키워드
터널 바닥부 융기
공용 중 터널
단층대
압착 거동
단층핵
단층손상대
단층영향구간
장기 변형
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Information
  • Publisher :Korean Society of Engineering Geology
  • Publisher(Ko) :대한지질공학회
  • Journal Title :The Journal of Engineering Geology
  • Journal Title(Ko) :지질공학
  • Volume : 36
  • No :3
  • Pages :407-421
  • Received Date : 2026-07-09
  • Revised Date : 2026-08-05
  • Accepted Date : 2026-08-10
  • DOI :https://doi.org/10.9720/kseg.2026.3.407
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