Journal of Korean Tunnelling and Underground Space Association (한국터널지하공간학회 논문집)

Korean Tunnelling and Underground Space Association (한국터널지하공간학회)
권호 표지
DOI QR코드

DOI QR Code

Effect of pore-water salinity on freezing rate in application of rapid artificial ground freezing to deep subsea tunnel: concentration of laboratory freezing chamber test

고수압 해저터널에 급속 인공동결공법 적용시 간극수의 염분 농도가 동결속도에 미치는 영향 평가: 실내 동결챔버시험 위주로

  • Oh, Mintaek (Seoul Housing & Communities Corporation) ;
  • Lee, Dongseop (School of Civil, Environmental and Architectural Engineering, Korea University) ;
  • Son, Young-Jin (SK Engineering & Construction) ;
  • Lee, In-Mo (School of Civil, Environmental and Architectural Engineering, Korea University) ;
  • Choi, Hangseok (School of Civil, Environmental and Architectural Engineering, Korea University)
  • 오민택 (서울주택도시공사 토목기술부) ;
  • 이동섭 (고려대학교 건축사회환경공학부) ;
  • 손영진 (SK건설) ;
  • 이인모 (고려대학교 건축사회환경공학부) ;
  • 최항석 (고려대학교 건축사회환경공학부)
  • Received : 2016.08.16
  • Accepted : 2016.09.06
  • Published : 2016.09.30
Download PDF
⟨ Previous Next ⟩

Abstract

It is extremely difficult to apply conventional grouting methods to subsea tunnelling construction in the high water pressure condition. In such a condition, the rapid artificial freezing method can be an alternative to grouting to form a watertight zone around freezing pipes. For a proper design of the artificial freezing method, the influence of salinity on the freezing process has to be considered. However, there are few domestic tunnel construction that adopted the artificial freezing method, and influential factors on the freezing of the soil are not clearly identified. In this paper, a series of laboratory experiments were performed to identify the physical characteristics of frozen soil. Thermal conductivity of the frozen and unfrozen soil samples was measured through the thermal sensor adopting transient hot-wire method. Moreover, a lab-scale freezing chamber was devised to simulate freezing process of silica sand with consideration of the salinity of pore-water. The temperature in the silica sand sample was measured during the freezing process to evaluate the effect of pore-water salinity on the frozen rate that is one of the key parameters in designing the artificial freezing method in subsea tunnelling. In case of unfrozen soil, the soil samples saturated with fresh water (salinity of 0%) and brine water (salinity of 3.5%) showed a similar value of thermal conductivity. However, the frozen soil sample saturated with brine water led to the thermal conductivity notably higher than that of fresh water, which corresponds to the fact that the freezing rate of brine water was greater than that of fresh water in the freezing chamber test.

고수압 조건의 해저터널 공사에 기존의 그라우팅 공법은 제한을 받게 되어 굴착작업이 어려울 수 있으나, 인공동결공법을 적용할 경우 신속한 차수 및 지반보강 효과를 얻을 수 있다. 인공동결공법을 적용할 경우, 동결 조건에 따라 동결토의 거동이 크게 변화하므로 기존의 연구 사례를 바탕으로 해저지반 등 특수한 조건에서 동결토의 역학적 거동을 예측하는 것에는 한계가 있다. 또한, 인공동결공법의 설계를 위해서는 동결체 형성에 필요한 소요시간 및 동결범위를 산정해야 하며, 해저지반의 경우 간극수 내 염분의 영향을 반영해야 한다. 본 논문에서는 동결토의 열적 특성을 파악하기 위해 인조규사 시료에 대한 실내 열전도도 측정시험과 동결챔버시험을 수행하였다. 동결토와 비동결 포화토 간극수의 염도를 조절하여 동결 과정과 염분에 따른 유효 열전도도를 비정상 열선법을 적용하여 측정하였다. 인조규사 간극수의 염도에 의한 동결특성 변화를 파악하기 위해 동결챔버를 설계 및 제작하였고 이를 통하여 동결 조건을 변화시키며 동결챔버시험을 수행하였다. 동결 조건에 따른 시료내 온도 변화를 분석하고 이를 통해 동결 조건이 사질토의 열전달 특성에 미치는 영향을 평가하였다. 비동결 포화토의 경우는 간극수가 담수(염도 0%)인 조건과 염수(염도 3.5%)인 조건 모두 유효 열전도도가 유사하게 평가되었으나, 동결토의 경우는 간극수가 염수인 조건이 보다 큰 유효 열전도도를 보였다. 이는 동결챔버시험에서 간극수가 염수인 조건이 담수인 조건보다 동결속도가 더 빠른 결과와 일치한다.

Keywords

References

  1. Kang, J.M., Lee, J.G., Lee, J., Kim, Y. (2013), "Analysis of the Relationship between Unconfined Compression Strength and Shear Strength of Frozen Soils", Journal of the Korean geosynthetics society, Vol. 12, No. 3, pp. 23-29. https://doi.org/10.12814/jkgss.2013.12.3.023
  2. Kim, Y.C. (2003), "Experimental Studies on the Uniaxial Compression Strength Unfrozen Water Content and Ultrasonic Wave Velocity of Frozen Soils", Journal of The Korean Society of Civil Engineers, Vol. 23, No. 5-C, pp. 309-317.
  3. Seo, Y.K., Kang, H.S., Kim, E.S. (2008), "A Study of Cold Room Experiments for Strength Properties of Frozen Soil", Journal of Ocean Engineering and Technology, Vol. 22, No. 2, pp. 42-49.
  4. Andersland, O.B., Ladanyi, B. (2004), Frozen Ground Engineering (Second edition). Chichester: John Willey & Sons., p. 363.
  5. Blackwell, J.K. (1956), "A transient-flow method for determination of thermal constants of insulating material in Bulk", Journal of Applied Physics, Vol. 25, No. 2, pp. 137-144. https://doi.org/10.1063/1.1721592
  6. Carlslaw, H.S., Jaeger, J.C. (1959), "Conduction of heat in soilds", 2nd Edition, Oxford University Press, New York.
  7. Da Re, G., Germaine, J., Ladd, C. (2003), "Triaxial Testing of Frozen Sand: Equipment and Example Results", Journal of Cold Regions Engineering, Vol. 17, pp. 90-118. https://doi.org/10.1061/(ASCE)0887-381X(2003)17:3(90)
  8. De Vries, D.A. (1963), "Thermal properties of soils. In Physics of plant environment", Edited by W.R. Van Wijk. North-Holland Publishing Company, Amsterdam, The Netherlands, pp. 210-235.
  9. Germant, A. (1950), "The thermal conductivity of soil", J. Apll. Phys, pp. 750-752.
  10. Ishikawa, T., Miura, S. (2008), "Numerical modeling for mechanical behavior of granular materials subjected to freeze-thaw action with DEM", 12th International Conference on Computer Methods and Advances in Geomechanics, Vol. 2, pp. 1219-1226.
  11. Johansen, O. (1975), "Thermal conductivity of soils", Ph.D. thesis, University of Trondheim, Trondheim, Norway. CRREL Draft English Translation 637, US Army Corps of Engineers, Cold Regions Research and Engineering Laboratory, Hanover, N.H.
  12. Kersten, M.S. (1949), "Laboratory research for the determination of the thermal properties of soils", Research Laboratory Investigations, Engineering Experiment Station, Technical Report 23, University of Minnesota, Minneapolis, Minn.
  13. Li, S., Lai, Y., Zhang, M., Zhang, S. (2006), "Minimum ground pre-freezing time before excavation of Guangzhou subway tunnel", Cold Regions Science and Technology, Vol. 46, pp. 181-191. https://doi.org/10.1016/j.coldregions.2006.09.001
  14. Mickley, A.S. (1951), "Thermal conductivity of moist soil", American Institute of Electrical Engineers Transactions, 70, pp. 1789-1797. https://doi.org/10.1109/T-AIEE.1951.5060631
  15. Nishimura, S., Gens, A., Olivella, S., Jardine, R.J. (2009), "Thm-coupled finite element analysis of frozen soil: Formulation and application", Geotechnique, Vol. 59, pp. 159-171. https://doi.org/10.1680/geot.2009.59.3.159
  16. Shannon, W.L., Wells, W.A. (1947), "Test for thermal diffusivity of granular materials", Proceedings of ASTM, Vol. 47, pp. 1044-1055.
  17. Xu, X., Lai, Y., Dong, Y., Qi, J. (2011), "Laboratory investigation on strength and deformation characteristics of ice-saturated frozen sandy soil", Cold Regions Science and Technology, Vol. 69, pp. 98-104. https://doi.org/10.1016/j.coldregions.2011.07.005
  18. Yang, Y., Lai, Y., Dong, Y., Li, S. (2010), "The strength criterion and elastoplastic constitutive model of frozen soil under high confining pressures", Cold Regions Science and Technology, Vol. 60, pp. 154-160. https://doi.org/10.1016/j.coldregions.2009.09.001