Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Change in Statistical Characteristics and Spatial Variability of Cone Tip Resistance Due to Ground Improvement

지반개량에 따른 콘 선단저항값의 통계적 특성 및 공간 변동성 변화

  • Bong, Tae-Ho (Dept. of Forest Science, Chungbuk National Univ.) ;
  • Kim, Byoung-Il (Dept. of Civil & Environmental Eng., Myongji Univ.) ;
  • Park, Shin Young (HJ Shipbuilding & Construction Co., Ltd.)
  • 봉태호 (충북대학교 산림학과) ;
  • 김병일 (명지대학교 토목환경공학과) ;
  • 박신영 (HJ중공)
  • Received : 2024.06.03
  • Accepted : 2024.10.04
  • Published : 2024.10.31
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Abstract

Ground improvement techniques through soil densification are widely used to enhance the cyclic resistance and seismic performance of liquefiable soils. However, most studies have primarily focused on the increase in soil strength before and after ground improvement, with limited investigation into changes in spatial statistical characteristics. This study aims to identify the changes in soil strength and spatial variability due to ground improvement by analyzing data from 19 cases where ground improvement was conducted using timber piles, aggregate piers, and dynamic compaction, with a cone penetration test (CPT) performed pre- and post-improvement. The changes in cone tip resistance were evaluated by comparing cone tip resistance profiles before and after ground improvement, while changes in spatial variability were assessed by examining variations in three parameters of the random field: mean (or trend function), variance, and scale of fluctuation. The results indicate that cone tip resistance generally increased, while inherent variability tended to decrease. The scale of fluctuation, representing spatial autocorrelation, generally increased following ground improvement, with higher initial fluctuation parameters correlating with a greater rate of increase. Furthermore, the probabilistic analysis of liquefaction-induced settlement revealed that changes in the scale of fluctuation due to ground improvement significantly influenced the variability of settlement, underscoring the importance of considering this factor.

지반 조밀화에 의한 지반개량 공법은 지반의 반복저항 강도를 증가시켜 액상화 발생을 억제하는 기술로 널리 활용되고 있다. 그러나 지반개량 효과는 지반개량 전, 후 콘 선단저항값의 증가에만 초점이 맞춰져 있으며 이에 대한 공간 통계학적 특성 변화에 대한 규명은 이루어지지 않았다. 본 연구에서는 지반개량에 따른 지반 강도 증가 및 이에 따른 공간 변동성 변화를 규명하기 위하여 지반개량 전, 후 CPT(Cone Penetration Test)가 수행된 나무말뚝, 쇄석말뚝, 동다짐 공법에 의한 지반개량 사례에 대하여 총 19개소에 대한 자료를 수집하고 분석하였다. 지반개량에 따른 콘 선단저항값의 변화는 지반개량 전, 후 콘 선단저항값의 프로파일을 비교하였으며, 공간 변동성 변화는 랜덤필드 이론을 활용하여 평균(또는 추세 함수), 분산, 변동자의 세 가지 매개변수에 대한 변화를 평가하였다. 결과적으로 콘 선단저항값은 평균적으로 증가하였으며 고유한 변동성은 감소하는 경향을 나타내었다. 공간적 자기상관성을 나타내는 변동자는 지반개량 후 평균적으로 증가하였으며 초기 변동자가 낮을수록 증가율은 높게 나타났다. 또한, 액상화에 의해 유발되는 침하량에 대한 확률론적 해석을 수행한 결과, 지반개량에 따른 변동자 변화는 침하량의 변동성에 유의미한 영향을 미치며 이에 대한 고려가 필요한 것으로 나타났다.

Keywords

Acknowledgement

이 성과는 정부(과학기술정보통신부)의 재원으로 한국연구재단의 지원을 받아 수행된 연구임(No. 2022R1A2C4002583).

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