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Effect of Sand Contents on Plastic and Liquid Limits and Shear Strength of Clays

모래 함유량이 점토의 액소성한계 및 전단강도에 미치는 영향

  • 박성식 (경북대학교 공과대학 건축토목공학부 토목공학전공) ;
  • 농쩐쩐 (경북대학교 공과대학 건축토목공학부 토목공학전공)
  • Received : 2013.12.04
  • Accepted : 2014.01.06
  • Published : 2014.02.28

Abstract

For soil improvement, sand mats or sand compaction piles are often constructed on soft marine clays. In such cases, some amounts of sand and clay are inevitably mixed. Sand or gravel often exists in the weathered soils near the slope surface. This research investigates the effect of mixing sand content on consistency limits and shear strength of clays. Firstly, sand was mixed with kaolinite or bentonite at 0, 9, 17, 23, 29, 33, 50% and then liquid and plastic limits were measured. Both plastic and liquid limits decreased as a sand content increased. The water content of clay-sand mixtures with different sand content increased by 10% or 20% step by step and then their undrained shear strength was measured using a portable vane shear device called Torvane. For all cases, undrained shear strength of clay-sand mixtures decreased rapidly until reaching a certain value. Their state changed from undrained to drained state gradually as the sand content increased, which caused their undrained shear strength to decrease. On the other hand, a series of direct shear tests were also conducted on such clay-sand mixtures to investigate the effect of sand content on cohesion and angle of internal friction. It was found from clay-sand mixtures that their cohesion decreased but angle of internal friction increased as the sand content increased.

해안지역의 연약지반을 개량하기 위하여 연약지반 위에 모래를 포설하거나 모래다짐말뚝을 시공할 경우 점토와 모래가 서로 섞이는 경우가 많으며, 풍화된 사면의 표층에도 모래나 자갈 섞인 세립토가 많이 존재한다. 본 연구에서는 이와 같은 혼합토에 포함된 모래 함유량의 증가에 따른 점토의 액소성한계 및 전단강도 변화에 대해 연구하였다. 먼저 카올리나이트와 벤토나이트에 모래 함유량을 0, 9, 17, 23, 29, 33, 또는 50%까지 증가시키면서 액소성한계시험을 실시하였으며, 모래 함유량이 증가함에 따라 액소성한계는 감소하는 경향을 보였다. 다양한 모래 함유량을 가진 카올리나이트와 벤토나이트에 함수비를 10% 또는 20%씩 단계적으로 증가시키면서 토베인시험기를 이용하여 비배수전단강도를 측정하였다. 동일한 모래 함유량을 가진 공시체의 경우 특정 함수비에서 비배수전단강도가 급격히 감소하였으며, 공시체 내 모래 함유량이 증가할수록 배수가 발생하면서 비배수전단강도는 감소하였다. 한편 동일한 조건의 혼합토에 대한 직접전단시험을 실시하여 모래 함유량의 증가에 따른 점토-모래 혼합토의 점착력 및 내부마찰각을 측정하였다. 점토 내 모래 함유량이 증가함에 따라 점착력은 감소하였으며, 내부마찰각은 증가하는 경향을 보였다.

Keywords

References

  1. Bera, K. A. (2011), "Effect of Sand Content on Engineering Properties of Fine-Grained Soil Mixed with Sand", Electronic Journal of Geotechnical Engineering, Vol.16, pp.1275-1286.
  2. Dafalla, M. A. (2013), "Effect of Clay and Moisture Content on Direct Shear Tests for Clay-Sand Mixtures", Advances in Materials Science and Engineering, Vol.2013, pp.1-8.
  3. Dumbleton, M. J. and West, G. (1966), "The influence of the coarse fraction on the plastic properties of clay soils", Report 36. Road Research Laboratory, Crowthorne.
  4. Holtz, W. G. and Ellis, W. (1961), "Triaxial shear characteristics of clayey gravel soils", Proc. 5th Int. Conf. Soil Mech. Found Engng, Paris, Vol.1, pp.143-149.
  5. Kim, U.-G., Ahn, T.-B., Hyodo, M., and Beak, W.-J. (2007), "Effects of fine content on the monotonic shear behavior of sand-clay mixtures", Journal of the Korean Geotechnical Society, Vol.23, No.4, pp.91-100.
  6. Kim, U.-G., Kim, D.-W., Lee, J.-Y., and Kim, J.-H. (2012), "Evaluation of cyclic shear strength characteristics of sands containing fines", Journal of the Korean Geotechnical Society, Vol.28, No.7, pp.31-40. https://doi.org/10.7843/kgs.2012.28.7.31
  7. Korean Geotechnical Society (2012), Final report on Landslides at Umyeonsan, KGS, KGS11-250.
  8. Nagaraj, T. S., Murthy, B. R. S., and Bindumadhava (1987), "Liquid Limit determination further simplified", Geotech. Test. J., Vol.12, No.4, pp.302-307.
  9. Park, S.-S. and Choi, S.-G. (2013), "A study on sand cementation and its early-strength using blast furnace slag and alkaline activators", Journal of the Korean Geotechnical Society, Vol.29, No.4, pp. 45-56. https://doi.org/10.7843/kgs.2013.29.4.45
  10. Park, S.-S. and Nong, Zhenzhen (2013), "A proposal of flow limit for soils at zero undrained shear strength", Journal of the Korean Geotechnical Society, Vol.29, No.11, pp.73-84. https://doi.org/10.7843/kgs.2013.29.11.73
  11. Seed, H. B., Woodward, R. J., Jr., and Lundgren, R. (1964a), "Clay Mineralogical Aspects of the Atterberg Limits", Journal of the Soil Mechanics and Foundation Division, Vol.90, No.SM4, pp.107-131.
  12. Seed, H. B., Woodward, R. J., Jr., and Lundgren, R. (1964b), "Fundamental aspects of the Atterberg limits", Journal of the Soil Mechanics and Foundation Division, Vol.9, No.SM6, pp.75-105.
  13. Sivapulliah, P. V. and Sridharan, A. (1985), "Liquid Limit of Soil Mixtures", Geotechnical Testing Journal, Vol.8, No.3, pp.111-116. https://doi.org/10.1520/GTJ10521J
  14. Tan, T. S., Goh, T. C., Karunaratne, G. P., and Lee, S. L. (1994), "Shear strength of very soft clay- sand mixtures", Geotech. Test. J., Vol.17, No.1, pp.27-34. https://doi.org/10.1520/GTJ10069J
  15. Yamamuro, J.A. and Lade, P.V. (1998), "Steady State Concepts and Static Liquefaction of Silty Sands", Journal of Geotechnical and Geoenvironmental Engineering, Vol.124, No.9, pp.868-877. https://doi.org/10.1061/(ASCE)1090-0241(1998)124:9(868)
  16. Yamamuro, J.A. and Covert, K.M. (2001), "Monotonic and Cyclic Liquefaction of Very Loose Sands with High Silt Content", Journal of Geotechnical and Geoenvironmental Engineering, Vol.127, No.4, pp.314-324. https://doi.org/10.1061/(ASCE)1090-0241(2001)127:4(314)