A development of the ground settlement evaluation chart on tunnel excavation

터널굴착에 따른 지반침하 예측을 위한 침하량 평가도표 개발

Abstract

The main risk factors of tunnel excavation through urban areas are ground settlement and surface sink which caused by ground conditions, excavation method, groundwater condition, excavation length, support method, etc. In the process of ground settlement assessment, the numerical analysis should be conducted considering the displacement and stress due to tunnel excavation. Therefore a technique that can simplify such process and easily evaluate the influence of tunnel excavation is needed. This study focused on the tunnelling-induced ground settlement which is main consideration of underground safety impact assessment. The parametric numerical analyses were performed considering such parameters as ground conditions, tunnel depth, and lateral distance from tunnel center line, etc. A simplified ground settlement evaluation chart was suggested by analyzing tendency of ground subsidence, lateral influence area and character by depth. The applicability of the suggested settlement evaluation chart was verified by comparative numerical analysis of settlement characteristics.

도심지 터널굴착 시 지반침하는 지반조건, 굴착방법, 지하수 상태, 터널 지보방법 등 다양한 조건이 복합적으로 작용하여 발생할 수 있으며 대표적인 위험요인은 크게 터널굴착에 의한 지반침하와 지표면함몰로 나눌 수 있다. 터널굴착에 의한 지반침하를 예측하기 위해서는 대상구간의 현황 및 시공조건 등을 반영하고 응력 및 변위를 고려한 수치해석을 수행하여야 한다. 그러므로 터널 전체 노선 및 인근 지장물 현황을 포함하는 영역에 대해, 터널 심도가 변하는 다양한 조건을 고려해야 하는 수치해석의 복잡한 과정을 단순화하여 터널굴착으로 인한 지표면 및 심도별 지반침하를 간편하게 예측하고 평가할 수 있는 기법이 필요하다. 본 연구에서는 지하안전영향평가 수행 시 주요 평가항목인 터널굴착으로 인한 지반침하를 연구대상으로 선정하고, 지층조건, 지반특성, 토피고(터널심도) 및 터널 중심선으로부터 횡방향 이격거리와 같은 지반침하 영향요소를 고려한 매개변수해석을 수행하여 심도별 지반침하 특성 및 침하 발생경향을 분석하고, 터널굴착으로 인한 지반침하를 간편하게 예측할 수 있는 침하량 평가도표를 도출하였다. 도출된 침하량 평가도표는 수치해석 결과와 비교 분석을 통해 적정성이 검증되었으며 침하량 평가도표를 이용하여 터널굴착 시 지표침하뿐만 아니라 지중 매설물의 위치와 심도에 따른 침하량을 간편하게 예측하고 평가할 수 있다.

Fig. 1. The flowchart for the development of ground settlement evaluation chart

Fig. 2. Trend of ground settlement with tunnel depth (Mair et al., 1993)

Fig. 3. Standard section of urban railway tunnel

Fig. 4. Condition for the parametric numerical analyses

Fig. 6. Condition for the parametric numerical analyses

Fig. 7. The trend of ground settlement with depth, Case 1 (E = 200 MPa)

Fig. 8. The trend of ground settlement normalized by H (overburden) Case 1 (E = 200 MPa)

Fig. 9. The trend of ground settlement normalized by H (overburden) Case 2 (E = 400 MPa)

Fig. 10. The trend of ground settlement normalized by H (overburden) Case 3 (E = 600 MPa)

Fig. 11. The trend of ground settlement normalized by H (overburden) Case 4 (E = 800 MPa)

Fig. 12. The trend of ground settlement normalized by H Case 5 (E = 1,000 MPa)

Fig. 13. Ground settlement estimation chart normalized by H

Fig. 14. Evaluation chart for tunnelling-induced ground settlement

Fig. 15. Condition of verification case for the evaluation of ground settlement

Fig. 16. Result of ground settlement verification

Fig. 17. Analysis result of the trend of ground settlement

Fig. 18. Ground settlement evaluation by simplified settlement evaluation chart

Fig. 19. Analysis of underground pipe settlement by simplified settlement evaluation chart

Table 1. Ground properties for the parametric numerical analyses

Table 2. Case of simplified subsoil layers of tunnel location (0.5D upper area of tunnel crown)

Fig. 5. Methodology of the development of the evaluation chart

Table 3. Verification of settlement evaluation chart