Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Relationship between Flow Limit and Compression Index for Clayey Soils

점성토의 흐름한계와 압축지수의 상관관계에 관한 연구

  • Moon, Hong Duk (Dept. of Civil & Infrastructure Eng., Gyeongsang National Univ.) ;
  • Hwang, Keum-Bee (Dept. of Civil Eng, Kyungpook National Univ.) ;
  • Woo, Seung-Wook (Dept. of Civil Eng, Kyungpook National Univ.) ;
  • Kim, Do-Hyop (Dept. of Civil Eng, Kyungpook National Univ.) ;
  • Kim, Tae-heon (Dept. of Civil Eng, Kyungpook National Univ.) ;
  • Park, Sung-Sik (Dept. of Civil Eng., Kyungpook National Univ.)
  • 문홍득 (경상국립대학교 건설환경공과대학 건설시스템공학과) ;
  • 황금비 (경북대학교 공과대학 건설환경에너지공학부) ;
  • 우승욱 (경북대학교 공과대학 건설환경에너지공학부) ;
  • 김도협 (경북대학교 공과대학 건설환경에너지공학부) ;
  • 김태헌 (경북대학교 공과대학 건설환경에너지공학부) ;
  • 박성식 (경북대학교 공과대학 토목공학과)
  • Received : 2024.08.26
  • Accepted : 2024.10.13
  • Published : 2024.10.31
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Abstract

Obtaining the compression index directly from consolidation tests is time-consuming; thus, it is often estimated using an empirical equation based on the liquid limit. However, the liquid limit measurement can introduce significant errors depending on the instrument or the experimenter. Therefore, this study proposes a new empirical equation for the compression index, utilizing the flow limit, which corresponds to the water content when the undrained shear strength of the clayey soil is zero. To achieve this, clayey soils of various compositions were prepared by mixing sand at proportions of 10, 20, and 30% with calcium-based and sodium-based bentonite. Liquid limit, flow limit, and consolidation tests were subsequently conducted. The results showed that the liquid and flow limits of sodium-based bentonite were 4-7 times higher than those of calcium-based bentonite. Additionally, the compression index differed significantly, ranging from 0.31-4.91. Conversely, regardless of bentonite type, the differences in liquid limit, flow limit, and compression index between the two clayey soils diminished as the sand content increased. The current linear empirical equation for the compression index was found unsuitable for sodium-based bentonite with high liquid limits; hence, a new exponential correlation was proposed. Consequently, the coefficient of determination for the exponential compression index equation based on the liquid limit was 0.81, while the equation using the flow limit achieved a coefficient of determination of 0.98, demonstrating a higher correlation compared to the liquid limit-based equation.

압밀시험으로부터 직접 압축지수를 구하는 것은 상당한 시간이 소요되므로 액성한계를 사용한 경험식으로 간편하게 구할 수 있다. 하지만 액성한계 측정시험은 측정기구나 실험자에 따라 상당한 오차가 발생할 수 있다. 이에 본 연구에서는 점성토의 비배수전단강도가 0일 때 함수비인 흐름한계를 이용하여 새로운 압축지수 경험식을 제안하였다. 이를 위해 칼슘계 및 소디움계 벤토나이트에 모래 함유량을 10, 20, 30%까지 섞어 다양한 점성토를 재성형한 다음, 액성한계, 흐름한계 및 압밀시험을 실시하였다. 칼슘계 벤토나이트보다 소디움계 벤토나이트의 액성한계와 흐름한계가 4~7배 정도 높게 나타났으며, 압축지수는 0.31과 4.91로 더 큰 차이를 보였다. 한편, 벤토나이트 종류에 관계없이 모래 함유량이 증가함에 따라 두 점성토의 액성한계, 흐름한계 및 압축지수의 차이는 감소하는 경향을 보였다. 기존 선형관계의 압축지수 경험식은 액성한계가 높은 소디움계 벤토나이트에는 적용이 어려웠으며, 새로운 지수형 압축지수 상관관계를 제안하였다. 그 결과 액성한계를 사용한 지수형 압축지수 경험식의 결정계수는 0.81이며, 흐름한계를 사용한 지수형 경험식의 경우 결정계수가 0.98로 액성한계 기반 경험식보다 더 높은 상관성을 보였다.

Keywords

Acknowledgement

본 연구는 정부(교육부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업입니다(NRF-2021R1I1A3059731).

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