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2026 Vol.42, Issue 4 Preview Page
Correlation of RMR Subfactors and Overbreak in a Gneissic NATM Tunnel Based on Face Mapping Data

편마암 지대 NATM 터널 막장면 관찰 자료를 활용한 RMR 세부 분류인자와 여굴 특성의 상관성 분석

Geun-Bae Park1
,
Geon-Woong Lee2
,
Tae-Min Oh3
,
Hyung-Ik Cho4*
박 근배1
,
이 건웅2
,
오 태민3
,
조 형익4*
1Member, Ph.D. Student, Dept. of Civil & Environ. Eng., Gyeongkuk National Univ.
2Manager, Construction Division, Plant EPC Business Group, Doosan Enerbility
3Member, Associate Prof., Dept. of Civil & Environ. Eng., Pusan National Univ.
4Member, Assistant Prof., School of Civil, Environ., & Arch. Eng., Gyeongkuk National Univ.
1정회원, 국립경국대학교 토목환경공학과 박사과정
2비회원, 두산에너빌리티 Plant EPC/건설사업부 팀장
3정회원, 부산대학교 사회환경시스템공학과 부교수
4정회원, 국립경국대학교 건설환경건축공학부 조교수
*Corresponding Author
31 August 2026. pp. 129-143
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Abstract

This study quantitatively analyzed the relationships between rock mass rating (RMR) classification factors and overbreak by linking face mapping records with actual overbreak in a New Austrian Tunneling Method (NATM) tunnel excavated through gneiss. After outlier removal, principal component analysis (PCA), Pearson correlation analysis, and multiple regression were applied to 3,273 field records collected from the up- and down-line tunnels, and the design overbreak volume was compared with the actual overbreak volume and construction cost. The PCA results showed that the first principal component (PC1), representing structural quality through rock quality designation, joint spacing, joint condition, and uniaxial compressive strength, and the second (PC2), representing groundwater conditions, together explained ~76% (up-line) and 75% (down-line) of the total variance. In the correlation and regression analyses, joint and groundwater conditions exhibited relatively strong and consistently significant associations with overbreak, whereas uniaxial compressive strength was significant for many excavation types but showed inconsistent sign patterns across types, indicating limited interpretive reliability. The actual overbreak volume exceeded the design volume by approximately 119% for the up-line and 115% for the down-line. When normalized by excavation length, the excavation types showing the largest overbreak increases per unit length differed from those with the largest absolute overbreak volumes. The largest unit-length increases occurred in ERP-3, corresponding to a widening section on the up-line, and in RP-2, corresponding to a main tunnel–adit junction section on the down-line. This suggests that, in addition to rock mass conditions, excavation geometry, including widening sections and junctions, may influence overbreak. Correspondingly, the associated shotcrete placement cost exceeded the design estimate by ~117%. These findings identify joint and groundwater conditions as key factors influencing overbreak occurrence and support face-mapping-based site management utilizing both the total RMR score and its detailed structural factors to help mitigate overbreak and reduce construction costs.

Keywords
Correlation analysis
Face mapping
Gneiss formation
Groundwater condition
Joint condition
multiple regression analysis
NATM tunnel
Overbreak
RMR classification factor

본 연구는 편마암 지대 NATM 터널의 막장면 관찰(Face Mapping) 자료와 실제 여굴 데이터를 연계하여 RMR 분류인자와 여굴 특성 간의 관계를 정량적으로 분석하였다. 상·하행선에서 수집된 3,273개 현장자료를 대상으로 이상치 제거, 주성분분석, Pearson 상관분석 및 다중회귀분석을 수행하고, 설계 여굴량과 실제 여굴량 및 시공비를 비교하였다. 주성분분석(Principal Component Analysis, PCA) 결과, RQD·절리간격·절리상태·일축압축강도로 구성된 구조적 품질축(PC1)과 지하수상태로 구성된 지하수 영향축(PC2)이 전체 분산의 약 76%(상행선), 75%(하행선)를 설명하였다. 상관 및 회귀분석에서는 절리상태와 지하수상태가 상대적으로 높고 일관된 유의성을 보였으며, 일축압축강도는 다수 유형에서 유의하였으나 부호가 유형에 따라 상반되어 해석의 일관성이 낮았다. 실제 여굴량은 설계 대비 상행선 약 119%, 하행선 약 115% 초과하여 설계기준을 크게 상회하였다. 굴착 연장으로 정규화한 결과, 절대량이 가장 큰 유형과 달리 단위 길이당 여굴 증가량은 상행선의 확폭구간인 ERP-3 TYPE과 하행선의 본선–갱도 접속부인 RP-2 TYPE에서 각각 가장 크게 나타났으며, 이는 암반조건뿐만 아니라 확폭 및 접속부와 같은 굴착 형상의 기하학적 특성도 여굴 발생에 영향을 미칠 수 있음을 시사하였다. 이와 함께 시공비 역시 설계 대비 약 117% 증가한 것으로 산정되었다. 본 연구는 절리상태 및 지하수상태가 여굴 발생의 주요한 영향요인임을 확인하였으며, 총 RMR 점수와 세부 구조인자를 함께 활용한 Face Mapping 기반 현장관리체계가 여굴 억제와 시공비 절감에 기여할 수 있음을 시사하였다.

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Information
  • Publisher :The Korean Geotechnical Society
  • Publisher(Ko) :한국지반공학회
  • Journal Title :Journal of the Korean Geotechnical Society
  • Journal Title(Ko) :한국지반공학회 논문집
  • Volume : 42
  • No :4
  • Pages :129-143
  • Received Date : 2026-07-06
  • Revised Date : 2026-08-07
  • Accepted Date : 2026-08-09
  • DOI :https://doi.org/10.7843/kgs.2026.42.4.129
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