인공동결공법 적용 후 융해에 따른 해성점토지반의 역학적 특성 평가
Evaluation of mechanical characteristics of marine clay by thawing after artificial ground freezing method
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초록
인공동결공법(artificial ground freezing method)은 연약지반 및 도심지에서의 지하구조물 시공에 적합한 차수 및 지반보강 공법이다. 인공동결공법은 동결관(freezing pipe)을 지중에 매설한 후 냉매(refregerant)를 순환시켜 대상 지반에차수벽 및 지지체의 역할을 수행하는 동결벽체(frozen wall)를 형성한다. 그러나 간극수의 동결에 따른 간극수의 부피팽창은 지반의 변형을 야기시킬 수 있고, 시공완료 후 동결토의 융해에 따른 지반의 소성변형 및 입자의 재배치 등은 지반의 역학적 특성을 변화시킨다. 본 논문에서는 인공동결공법에 따른 해성 점토지반(marine clay)의 동결속도를 평가하기위하여 인공동결공법 현장실증시험을 수행하였다. 현장실증시험은 지중에 3.2 m 깊이로 매설된 동결관 1공 내로 초저온 냉매인 액화질소를 순환시키는 방법으로 수행되었다. 또한, 원지반과 인공동결공법에 의해 동결/융해된 지반에 대한피에조 콘 관입시험(piezo cone penetration test, CPTu) 및 공내재하시험(lateral load test, LLT)을 수행함으로써 동결/ 융해(freezing-thawing)에 따른 해성 점토지반의 강도 및 강성 특성의 변화를 평가하였다. 시험결과, 부피가 약 2.12 m3 인 원기둥 모양의 동결체를 형성하는데 총 3.5일이 동안 약 11.9 ton의 액화질소가 소요되었다. 동결/융해에 따른 지반의강도 및 강성 저하는 각각 48.5%, 22.7%로 산정되었다.
Abstract
The artificial ground freezing (AGF) method is a groundwater cutoff and/or ground reinforcement method suitable for constructing underground structures in soft ground and urban areas. The AGF method conducts a freezing process by employing a refrigerant circulating through a set of embedded freezing pipes to form frozen walls serving as excavation supports and/or cutoff walls. However, thermal expansion of the pore water during freezing may cause excessive deformation of the ground. On the other hand, as the frozen soil is thawed after completion of the construction, mechanical characteristics of the thawed soil are changed due to the plastic deformation of the ground and the rearrangement of soil fabric. This paper performed a field experiment to evaluate the freezing rate of marine clay in the application of the AGF method. The field experiment was carried out by circulating liquid nitrogen, which is a cryogenic refrigerant, through one freezing pipe installed at a depth of 3.2 m in the ground. Also, a piezo-cone penetration test (CPTu) and a lateral load test (LLT) were performed on the marine clay before and after application of the AGF method to evaluate a change in strength and stiffness of it, which was induced by freezing-thawing. The experimental results indicate that about 11.9 tons of liquid nitrogen were consumed for 3.5 days to form a cylindrical frozen body with a volume of about 2.12 m3. In addition, the strength and stiffness of the ground were reduced by 48.5% and 22.7%, respectively, after a freezing-thawing cycle.
참고문헌 (22)
- Angin, I., "Effects of diatomite (DE) application on physical properties of soils subjected to freeze-thaw cycles", Soil and Tillage Research, 160(1), pp.34~41 (2016)
- Arenson, L. U., "The effect of salinity on the freezing of coarse-grained sands", Canadian Geotechnical Journal, 43(3), pp.325~337 (2006)
- Chamberlain, E. J., "Effect of freezing and thawing on the permeability and structure of soils", Engineering Geology, 13(1-4), pp.73~92 (1979)
- Cheng, Y., "Experimental research on the shear strength deterioration between the freezing and thawing surface of melting soil slope in seasonal frozen regions", Proceedings of the Ninth International Conference of Chinese Transportation Professionals, pp.2284~2290 (2009)
- 최찬용, "동결융해 반복에 따른 철도노반재료의 전단강도 변화", 한국지반환경공학회 논문집, 12(7), pp.13~21 (2011), 한국지반환경공학회
- Eigenbrod, K. D., "Effects of cyclic freezing and thawing on volume changes and permeabilities of soft fine-grained soils", Canadian Geotechnical Journal, 33(4), pp.529~537 (1996)
- Han, L., "In situ monitoring of frost heave pressure during cross passage construction using ground-freezing method", Canadian Geotechnical Journal, 53(3), pp.530~539 (2016)
- Jessberger, H. L., "State-of-the-art report-Ground freezing. Mechanical properties, processes and design", Engineering Geology, 18(1), pp.5~30 (1981)
- 강성승, "동결융해시험에 의한 사암 및 안산암의 풍화특성 평가", 터널과 지하공간, 21(2), pp.145~150 (2011), 한국암반공학회
- Kudryavtsev, S. A., "Numerical modeling of the freezing, frost heaving, and thawing of soil", Soil Mechanics and Foundation Engineering, 41(5), pp.177~184 (2004)
- Padilla, F., "Simulation and analysis of frost heaving in subsoils and granular fills of roads", Cold Regions Science and Technology, 25(2), pp.89~99 (1997)
- Papakonstantinou, S., "Evaluation of ground freezing data from the Naples subway", Geotechnical Engineering, 166(3), pp.280~298 (2013)
- Pimentel, E., "Numerical interpretation of temperature distributions from three ground freezing applications in urban tunneling", Tunnelling and Underground Space Technology incorporating Trenchless Technology Research, 28(1), pp.57~69 (2012)
- Qi, J., "A review of the influence of freeze-thaw cycles on soil geotechnical properties", Permafrost and Periglacial Processes, 17(3), pp.245~252 (2006)
- Robertson, P. K., "Soil classification using the cone penetration test", Canadian Geotechnical Journal, 27(1), pp.151~158 (1990)
- Shawn, P. C., "Ground freezing to repair leaks in a slurry wall shaft", World Tunnel Congress 2016, pp.1~10 (2016)
- 신은철, "인공지반동결 시스템을 이용한 동결차수벽의 실험적 연구", 한국지반신소재학회 논문집, 8(3), pp.35~44 (2009), 한국지반신소재학회
- Shin, E. C., "Frost heaving pressure characteristics of frozen soils with frost-susceptibility and degree of saturation", Korean Geotechnical Society Spring Conference 2002, pp.329~336 (2002)
- Song, H., "Finite element analysis on 3D freezing temperature field in metro cross passage construction", Procedia Engineering, 165(1), pp.528~539 (2016)
- Sun, C., "Research on the freezing method applied to tunnel cross passage of the Guangzhou metro", Modern Tunnelling Technology, 49(3), pp.161~165 (2012)
- Yan, Q., "Thermal-solid coupling analysis of the connected of the cross aisle in metro constructed by horizontal freezing in ground", China Railway Science, 33(1), pp.54~59 (2012)
- Yang, P., "Numerical simulation of frost heave with coupled water freezing, temperature and stress fields in tunnel excavation", Computers and Geotechnics, 33(6), pp.330~340 (2006)