Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Mechanism of Dilatory Dissipation during Piezocone Tests in Lightly Overconsolidated Cohesive Soil

약간 과압밀된 점성토에서 발생하는 피에조콘 지연소산 메커니즘

  • Ha, Tae-Gyun (School of Civil and Environ. Engrg., Seoul National Univ.) ;
  • Jung, Jong-Hong (Expressway and Transportation Technology Institute, Korea Expressway Corporation) ;
  • Kim, Hong-Jong (Expressway and Transportation Technology Institute, Korea Expressway Corporation) ;
  • Park, Lae-Seon (Executive Managing Director for Construction, Korea Expressway Corporation) ;
  • Chung, Choong-Ki (School of Civil and Environ, Engrg., Seoul National Univ.)
  • 하태균 (서울대학교 건설환경공학부) ;
  • 정종홍 (한국도로공사 도로교통기술원 연구개발실) ;
  • 김홍종 (한국도로공사 도로교통기술원 연구개발실) ;
  • 박래선 (한국도로공사 건설본부) ;
  • 정충기 (서울대학교 건설환경공학부)
  • Published : 2007.10.31
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Abstract

For standard piezocones with shoulder filter elements immediately behind the cone tip, general dissipation curves show monotonically decreasing pore pressure from the initial value. However, dilatory dissipation behavior, showing a temporary increase in pore pressure followed by a decrease in the hydrostatic pressure, has been observed in lightly overconsolidated cohesive soils $(1. This unusual dissipation behavior was reported mostly in heavily overconsolidated ground and previous researches were limited to such cases. In this study, the mechanism of dilatory dissipation in lightly overconsolidated cohesive soils was investigated. The relativities of the ground properties evaluated from the CPTu data to the dilatory dissipation were analyzed. And, finite difference analyses on dissipation after cone penetration were performed. It was found that dilatory dissipation occurs in lightly overconsolidated soils since the higher excess pore pressure at the cone face propagates upward to the shoulder filter. Also, it was shown that the ratio of initial excess pore pressure at the cone face to that of the shoulder filter $({\Delta}u_{1i}/{\Delta}u_{2i})$, which is related to overconsolidation ratio (OCR) and hydrostatic pressure $(u_0)$, affects the dilatory dissipation.

원추 후면에서 간극수압이 측정되는 표준 피에조콘의 경우, 일반적인 소산곡선은 간극수압이 초기값에서부터 단조적으로 감소하는 경향을 보인다. 그러나, 간극수압이 일시적으로 증가한 후에 감소하는 지연소산 거동이 과압밀비 4 이하의 약간 과압밀된 점성토 지반에서 확인되었다. 이와 같은 비정규적인 소산 거동은 주로 매우 과압밀된 지반에서 발생하는 것으로 보고되었으며, 기존의 연구도 이러한 경우로 한정되어 진행되었다. 본 연구에서는 약간 과압밀된 점성토 지반에서 발생하는 지연소산의 메커니즘을 규명하였다. 피에조콘 시험으로부터 산정된 지반의 특성과 지연소산의 상관성을 분석하였으며, 콘 관입 이후의 소산거동에 대하여 유한차분해석을 수행하였다. 연구 결과, 약간 과압밀된 점성토에서는 원추 선단에서 발생하는 큰 과잉간극수압이 원추 후면 필터로 상향 전파되어 지연소산이 유발되고, 과압밀비(OCR) 및 정수일$(u_0)$과 관련된 원추 선단과 원추 후면의 초기 과잉간극수압비$({\Delta}u_{1i}/{\Delta}u_{2i})$가 지연소산에 영향을 미치는 것이 확인되었다.

Keywords

References

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