2015 년도한국철도학회추계학술대회논문집 KSR2015A129 도시철도인접지반깊은굴착시지하박스구조물삼차원안정성평가 Three-dimensional Stability Analysis of Underground Box Structure in Urban Railway Adjacent to Deep Excavation in the Ground 이성진 *, 박영곤 *, 이상승 **, 김호석 **, 윤경원 **, 전상수 ** Sung-Jin Lee *, Yeong-Kon Park *, Sang-Seung Lee * *, Ho-Seok Kim * *, Kyeong-Won Yoon * * Sang-Soo Jeon * * Abstract Since a lot of people live in urban areas with high population in limited small area, railway structures in underground have been constructed mainly in big cities. Urban railway structures are facing high risks by mobilized stresses of soils induced by newly constructed structures on the ground and/or excavations. In recent days, the construction of deep excavation in soils for high-rise buildings has frequently caused the stability problems of underground structures in urban railway. In this study, a threedimensional finite difference model using the commercial program FLAC3D is adopted to estimate the stability of urban box structures. Soil profiles and properties in the 00 area of Daejeon subway line No.1 is used to model an underground box structure of urban railway adjacent to deep excavation. Displacements and stresses of the structure induced by deep excavations are estimated to examine its stability with respect to the number of struts and various excavation depths and lengths. Keywords : Urban railway, Deep excavation, Underground structure, Stability, Numerical analysis 초록국내도시의특성은한정된공간에많은인구가밀집하여생활하므로지하공간을이용한도시철도구조물이대도시를중심으로건설되고있다. 도시철도지하구조물은인근신규구조물및굴착시공시지반응력변화에따른위험을부담하게된다. 그중최근고층구조물시공으로인한불가피한대규모굴착은지하구조물의안정성문제를야기시키므로본연구에서는삼차원유한차분해석프로그램인 FLAC3D 를이용하여대전도시철도 1 호선 00 구간지역의지층단면및토질의특성을바탕으로도시철도인접지반깊은굴착시굴착깊이및길이와 Strut 설치개수에따른지하박스구조물에발생하는응력및변위를산정하여구조물의안정성평가를수행하였다. 주요어 : 도시철도, 깊은굴착, 지하구조물, 안정성, 수치해석 1. 서론 산업및기술발전과인구증가로인하여새로운교통수단의필요성이제기된 1970년대후반을기점으로수도권, 부산광역시, 대구광역시, 대전광역시, 광주광역시도시철도가활발하게시공되어운영되고있다. 기존에시공된도시철도는운행기간에비례하여여러가지외부위험요인에노출되며안정성문제를야기시켜왔고특히지하구조물인접지반에신규 교신저자 : 인제대학교공과대학건설환경공학부 (ssj@inje.ac.kr) * 한국철도기술연구원 ** 인제대학교공과대학건설환경공학부
구조물시공시깊은굴착으로인한지하수및지반응력변화는주변지하구조물에영향을미치므로굴착작업을진행할경우인접지하구조물의안정성을고려한설계및시공을통하여기존지하구조물붕괴로인한대규모인명피해를방지하여야한다. 따라서본연구에서는도시철도인접지반에깊은굴착이이루어진경우에지하박스구조물의안정성을평가하기위하여대전도시철도 1호선운영구간의지층단면및토질의특성그리고최근굴착공사현장에서많이사용하고있는지보재인토류벽 (H-Pile(300*200*9*14)), 현장타설말뚝 (C.I.P (Φ400)), Strut(H-Pile(300*300*10*15)) 를적용하여굴착깊이와길이및 Strut 설치개수에따른굴착단계별지하박스구조물에발생하는응력및변위를삼차원유한차분해석프로그램인 FLAC3D를이용하여산정하였다. 2. 지반및구조물특성 2.1 지반특성 본연구에서는대전도시철도 1호선 00구간지역의지층단면과현장시료를채취한후실내시험을통하여얻어진지반특성을 [1] 이용하여수치해석을수행하였으며지반특성은 Table 1과같다. 2.2 구조물특성 Table 1 Physical properties of soils Unit weight (t/m 3 ) Elastic modulus Poison s ratio ( ) Friction angle ( ) Cohesion Land fill 1.7 3000 0.35 25 0.5 Silt clayed 1.7 2000 0.35 25 0.5 Weathered sand 1.9 7500 0.33 34 1.0 Weathered rock 2.0 11000 0.31 40 6.0 Soft rock 2.0 70000 0.30 42 8.0 지중에시공된박스구조물은대전도시철도에시공된박스구조물과동일한구조물을사용하였으며토류벽, C.I.P, Strut는최근공사현장에서많이사용하고있는부재를선정하였으며 [2] Table 2는이들부재의특성을나타낸다. 3.1 수치해석조건 3. 수치해석 Table 2 Physical properties of structures Unit weight (t/m 3 ) Elastic modulus Area (m 2 ) Moment of Inertia (m 4 ) Earth retaining wall 7.80 2.10 10 7 8.36 10-3 1.33 10-4 C.I.P 2.50 2.00 10 6 1.26 10-1 1.26 10-3 Strut 7.80 2.10 10 7 1.20 10-2 2.04 10-4 Box side wall 2.30 2.32 10 6 3.00 10-1 2.25 10-3 Box top slab 2.30 2.32 10 6 1.00 10-1 8.33 10-4 Box bottom slab 2.30 2.32 10 6 6.75 10-1 2.56 10-3
깊은굴착에의한도시철도박스구조물의안정성을평가하기위해상용프로그램인유한차분해석프로그램 FLAC3D를이용하였으며 Mohr-Coulomb 파괴모델을 [3] 적용하였다. 원지반의크기는깊은굴착영향을고려하여깊이 70m, 폭 210m, 길이 50m로하였으며굴착최대깊이 41m, 폭 32m, 굴착우측면과박스구조물좌측벽체의이격거리는 14m이며박스구조물상부슬래브와지표면까지의거리는 11m이고박스구조물은폭 4m, 높이 6m이다. 깊은굴착은전굴착 ( 굴착길이 50m), 반굴착 ( 굴착길이 25m) 의두가지형태로설정하였다. 각각굴착형태별로 Strut 설치개수를달리하여총 4개모델의수치해석을수행하였으며전굴착모식도를 Fig. 1에나타내었으며반굴착모식도를 Fig. 2에나타내었다. 전굴착시 Strut 6개설치 (Model #1) 와 Strut 12개설치 (Model #2) 그리고반굴착시 Strut 6개설치 (Model #3) 와 Strut 12 개설치 (Model #4) 하여수치해석모델링을수행하였다. Fig. 3(a) 와 Fig. 4(a) 는각각전굴착과반굴착시수평방향지반변위를나타내며 Fig. 3(b), Fig. 3(c), Fig. 4(b), Fig. 4(c) 는 6단계굴착시사용된 Strut 6개및 12개설치와지하박스구조물을나타낸다. Fig. 1 Configuration of 50-m length excavation Fig. 2 Configuration of 25-m length excavation (Model #1 & Model #2) (Model #3 & Model #4) (b) Installation of 6 struts (Model #1) (a) Horizontal displacement of the ground (Model #1) (c) Installation of 12 struts (Model #2) Fig. 3 Three-dimensional view of 50-m length excavation, the installation of struts, and underground box structure
(b) Installation of 6 struts (Model #3) (a) Horizontal displacement of the ground (Model #3) (c) Installation of 12 struts (Model #4) Fig. 4 Three-dimensional view of 25-m length excavation, the installation of struts, and underground box structure 3.2 수치해석결과 본연구에서는내공단면의사용효율이높은개착공법 [4] 으로시공된지하박스구조물을적용하였다. 최종굴착시구조물에발생하는변위를검토하였으며박스구조물의천단, 하부, 좌 우측벽의중앙에서산정된축응력, 휨모멘트, 전단응력값을바탕으로허용응력설계법을적용하여지하박스구조물의안정성검토를실시하였으며네가지모델모두굴착에인접한좌측벽부에서수평변위량이가장크게나타났으며마지막 6단계굴착에서최대변위가발생하였다. 수직변위는굴착심도가어느정도까지깊어질때까지는히빙 (Heaving) 이발생하여구조물의변위가상향으로발생하지만그이상의굴착이이루어진경우에는변위가하향으로발생되었다. 전체적으로수직방향변위는수평방향변위보다약 50% 정도작게나타났다. Strut 설치개수차이에따라발생한수평변위를살펴보면 Model #1이 Model #2보다약 3~4mm, Model #3가 Model #4보다약 2~3mm 더크게발생하였다. 이는 Strut 설치개수가적으면구조물의변위가상대적으로크게발생함을알수있다. 전굴착과반굴착시수평변위를살펴보면 Model #1이 Model #3보다, Model #2가 Model #4보다모두약 2~3mm 더크게발생하여전굴착모델이반굴착모델보다발생변위가큼을알수있다. Table 3는굴착단계중발생한축응력, 인장응력, 전단응력중최대값을산정하여허용응력설계법을통한구조물의안정성검토결과값을나타내었다. 네가지모델모두발생응력이허용응력이내로발생하였으며 Strut 설치개수가많은 Model #2가 Model #1보다 Model #4가 Model #3보다더안전하고전굴착과반굴착의경우를비교해보면 Model #3가 Model #1보다 Model #4가 Model #2보다더안전함을알수있다. Table 3 Mobilized stress and FS of underground box structure Mobilized stress Model #1 Model #2 Model #3 Model #4 FS* FS FS FS Compressive 9.73 9.84 9.78 9.89 Tensile 1.06 1.10 1.07 1.11 Shear 2.54 2.78 2.63 2.88 (allowable compressive stress) = 960t/m 2, (allowable tensile stress) = 65t/m 2, (allowable shear stress) = 39t/m 2, *FS = Factor of safety
3. 결론 본연구에서는도시철도인접지역의깊은굴착으로인한지하박스형구조물의안정성을평가하기위하여대전도시철도의지반특성및구조물의특성을반영한삼차원수치해석을수행하였다. 단계별깊은굴착에따른도시철도지하구조물에발생한변위는전굴착시반굴착한경우보다약 20%, Strut 12 개설치시 Strut 6 개설치한경우보다약 30% 큰수평변위가발생하였고각각의경우에발생한최대응력의차이는미미하여압축, 인장, 전단응력모두허용범위내에있는것으로나타났다. 콘크리트박스구조물에발생된인장응력의안전율 1.0~1.1 은압축응력과전단응력의안전율 2.5~9.8 에비해상대적으로매우작으므로굴착시구조물에발생되는인장응력검토가반드시이루어져야한다. 후기 본연구는미래창조과학부및국가과학기술연구회의융합연구사업의일환으로수행하였음. [ 융합연구단 -14-2-ETRI, 사물인터넷 (IoT) 기반도시지하매설물모니터링및관리시스템기술개발 ] 참고문헌 [1] SunJin Engineering Corporation (1997) Rail Section 7 Geotechnical research report, Daejeon metropolitan express transit corporation, Deajeon, Korea, pp. 45-62. [2] http://kimminseo777.tistory.com/m/post/79 (Accessed 15 April 2015) [3] Itasca Consulting Group, Inc. (2002) FLAC3D Manual: Theory and background, Itasca Consulting Group, Inc., Minnesota, USA. [4] N.-S. Ahn, S.-S. Kim (1998) Design example of structure (civil engineering, architecture), Science and technology book publishing, Seoul, Korea, pp. 156-178.