Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Unsaturated Shear Strength Characteristics of Nakdong River Silty Sand

낙동강 실트질 모래의 불포화 전단강도 특성

  • Received : 2012.10.22
  • Accepted : 2013.02.18
  • Published : 2013.02.28
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Abstract

There are many technical problems, which can not be resolved by the concept of saturated soil mechanics. Unsaturated soils show an apparent cohesion due to negative pore pressure and relatively lower permeability due to entrapped air compared to saturated soils. The determination of engineering properties of soils with various moisture content is very important to evaluate shear strength and stability of natural and engineered soils. So various researches should be made on unsaturated soils. Especially, sandy soils are widely distributed near Nakdong river, one of the four rivers where Restoration Projects were carried out. Many structures such as dams, flood control facilities, detention facilities and reservoirs have been built in this area. In this study, unsaturated triaxial compressive tests were conducted on sands or silty sands at Nakdong river in order to provide their fundamental characteristics for design and construction of geotechnical structures. As a result of the tests, the maximum deviator stress increased as the confining stress and matric suction increased. The cohesion increased non-linearly as the matric suction increased, but the angle of internal friction was marginally changed.

포화토의 개념과 원리로는 실제 지반에서 발생하는 현상과 거동이 제대로 해석되지 않는 많은 공학적 문제들이 있다. 불포화토는 부간극수압의 영향으로 겉보기점착력을 보임과 동시에 물의 흐름에 있어서 간극 속에 공기의 함입으로 투수성이 저하하는 등 포화토와는 다른 거동특성을 나타내는 것으로 알려져 있다. 따라서 흙 속의 수분 함량에 따른 공학적 특성을 규명하는 것은 지반강도의 산정, 구조물의 안정성 등을 판단하는데 있어서 중요한 자료를 제공하므로 많은 연구와 노력이 필요하다. 특히, 하천복원 프로젝트인 "4대강 살리기"중 한 곳인 낙동강유역에는 모래 지반이 넓은 지역에 걸쳐 분포하고 있으며, 중소규모의 댐, 홍수조절지, 하천변 저류지 및 저수지 재개발 등 많은 토목구조물이 건설되고 있다. 본 연구에서는 낙동강유역 내 불포화상태에 있는 지반구조물의 설계 시공 및 안정성 검토에 기초적 자료를 제공하고자 낙동강 중하류 실트질 모래를 대상으로 불포화 삼축압축시험을 실시하였다. 시험 결과 최대축차응력은 구속압과 흡인력이 증가함에 따라 증가하는 것으로 나타났다. 또한 점착력은 흡인력의 증가에 따라 비선형적으로 증가하였으나, 내부마찰각은 크게 변하지 않는 것으로 나타났다.

Keywords

References

  1. Andrew M. R. and J. B. Burland. (1999), "Use of the Tensil Strength of Water for the Direct Measurement of High Soil Suction". Can. Geotech. J., 36: pp.178-180. https://doi.org/10.1139/t98-080
  2. ASTM D2325-68 (1994) e1, "Standard Test Method for Capillary- Moisture Relationships for Coarse- and Medium-Textured Soils by Porous-Plate Apparatus".
  3. ASTM D4253-00, "Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table".
  4. ASTM D4254-00, "Standard Test Methods for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density".
  5. Bishop, A. W. and Donald, I. B. (1961), "The Experimental Study of partly Saturated Soil in the Triaxial Apparatus", Proceedings 5th ICSMFE, pp.13-21.
  6. Craig. A. B. and C. D. Shackelford (2001), "Soil-Water Characteristic Curves and Dual Porosity of Sand-Diatomaceous Earth Mixtures", J. of Geotech. and Geoenvir. Engrg. ASCE, 127(9): pp.790-800. https://doi.org/10.1061/(ASCE)1090-0241(2001)127:9(790)
  7. Fredlund, D G., Morgenstern, N. R., and Widger, R. A. (1978), "Shear strength of unsaturated soil", Canadian Geotechnical Journal, 15(3): pp.313-321. https://doi.org/10.1139/t78-029
  8. Fredlund, D. G. and Morgenstern, N. R. (1977), "Stress State Variables for Unsaturated Soils", Journal of the Geotechnical Engineering, ASCE, Vol.103, No.GT5, pp.447-466.
  9. Fredlund, D. G. and Rahardjo, H. (1993), "Soil Mechanics for Unsaturated Soils", John Wiley & Sons Inc., pp.64-123.
  10. Jeong, S. S., Yu, N. D., and Kim, J. H. (2004), "Characteristics of unsaturated weathered soils with varying clay contents", Korea Society of Civil Engineers Conference, pp.2487-2492.
  11. Jubert, A. P. and Colmenares, J. E. (2006), "Stress-strain-suction behaviour of two clayey materials under unconfined conditions". Unsatureted Soils. Geotechnical special publication. No.147, ASCE, pp.109-1120.
  12. Kim, Y. S. and Kim, D. M. (2008), "Characteristics of Undrained Cyclic Shear Behavior of Nak-Dong River Sand by Silt Contents", Journal of the Korean Geotechnical Society, Vol.24, No.11, pp.79-89.
  13. Kim. C. K. (2003), "Characteristics of Stress-strain Behaviour for Unsaturated Weathered Granite Soil", Journal of Korea Society of Civil Engineers-C, Vol.23, No.3, pp.177-184.
  14. Krahn, J., Fredlund, D. G., and Klassen, M. J. (1989), " Effect of Soil Suction on Slope Stability at Notch Hill", Canadian Geotechnical Journal, Vol.26, No2, pp.269-278. https://doi.org/10.1139/t89-036
  15. Lee, H. K. and Lee, I. (2009), "A Study for Unsaturated-Character of Weathered Granite Soil in Korea", Journal of Korean Geo-Environmental Society, Vol.10, No.3, pp.13-20.
  16. Lee, S. J., Lee, S. R., and Jang, B. S. (2002), "Unsaturated Shear Strength Characteristics of Weathered Granite Soils", Journal of Korea Society of Civil Engineers-C, Vol.22, No.1, pp.81-88.
  17. Leong E. C. and Rahardjo, H. (1995), "Characteristic Curves for two Residual Soils from Granitic and Sedimentary Formations", Preceeding of the International Conference on Unsaturated Soils, UNSAT'95, Paris. France, pp.519-524.
  18. Lim, S. Y. (2007), "The Shear Characteristics of Unsaturated Sandy Soils", Journal of the Korean Geotechnical Society, Vol.23, No.10, pp.57-64.
  19. Moon, J. B., Kim, S. K., and Jang, Y. S. (1993), "Development and Verification of Negative Pore Pressure Tip for unsaturated Flow Analysis", Korea Society of Civil Engineers Conference, Vol.1993, No.1, pp.385-388.
  20. Song, C. S. and Chang, P. W. (1994), "Development of Constitutive Model for the Prediction of Behaviour of Unsaturated Soil(I) -Study of Characteristics of Unsaturated Soil", Magazine of the Korean Society of Agricultural Engineers, 36(4), pp.87-94.
  21. Song, C. S. and Choi, D. H. (2007), "Characteristics of Shear Strength for an Unsaturated Soil with the Matric Suction", Journal of Korean Env. Res. Tech., Vol.10, No.1, pp.82-83.
  22. Wheeler, S. J. (1988), "A Conceptual Model for Soils Containing Lage gas Bubbles", Geotechnique, 38(3), pp.389-397. https://doi.org/10.1680/geot.1988.38.3.389

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