Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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Estimation of Resistance Bias Factors for the Ultimate Limit State of Aggregate Pier Reinforced Soil

쇄석다짐말뚝으로 개량된 지반의 극한한계상태에 대한 저항편향계수 산정

  • Bong, Tae-Ho (Institute of Construction and Environmental Engrg., Seoul National Univ.) ;
  • Kim, Byoung-Il (Dept. of Civil and Environmental Engrg., Myongji Univ.) ;
  • Kim, Sung-Ryul (Dept. of Civil and Environmental Engrg., Seoul National Univ.)
  • 봉태호 (서울대학교 건설환경종합연구소) ;
  • 김병일 (명지대학교 토목환경공학과) ;
  • 김성렬 (서울대학교 건설환경공학부)
  • Received : 2019.03.29
  • Accepted : 2019.05.05
  • Published : 2019.06.30
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Abstract

In this study, the statistical characteristics of the resistance bias factors were analyzed using a high-quality field load test database, and the total resistance bias factors were estimated considering the soil uncertainty and construction errors for the application of the limit state design of aggregate pier foundation. The MLR model by Bong and Kim (2017), which has a higher prediction performance than the previous models was used for estimating the resistance bias factors, and its suitability was evaluated. The chi-square goodness of fit test was performed to estimate the probability distribution of the resistance bias factors, and the normal distribution was found to be most suitable. The total variability in the nominal resistance was estimated including the uncertainty of undrained shear strength and construction errors that can occur during the aggregate pier construction. Finally, the probability distribution of the total resistance bias factors is shown to follow a log-normal distribution. The parameters of the probability distribution according to the coefficient of variation of total resistance bias factors were estimated by Monte Carlo simulation, and their regression equations were proposed for simple application.

이 연구에서는 쇄석말뚝공법의 한계상태설계법 적용을 위하여 양질의 현장재하시험 자료로부터 저항편향계수의 통계적 특성을 분석하고 지반 불확실성 및 시공 오차를 고려한 총 저항편향계수를 산정하였다. 저항편향계수 산정을 위한 예측모델은 기존 모델들에 비하여 높은 예측성능을 보인 Bong and Kim(2017)의 MLR 모형을 활용하였으며 그 적합성을 평가하였다. 저항편향계수의 확률분포를 산정하기 위하여 카이제곱 적합도 검정을 수행하였으며 정규분포가 가장 적합한 것으로 나타났다. 공칭저항의 총 변동성은 점토의 비배수전단강도 및 쇄석말뚝 시공 시 발생할 수 있는 시공 오차에 대한 불확실성을 포함하여 산정하였다. 최종적으로 총 저항편향계수의 확률분포는 로그정규분포를 따르는 것으로 나타났다. 총 저항편향계수의 변동성에 따른 확률분포의 매개변수는 Monte Carlo 시뮬레이션을 통하여 산정하였으며, 간편한 적용을 위하여 이에 대한 회귀식을 제안하였다.

Keywords

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Fig. 1. Probability of failure in reliability-based design

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Fig. 2. Comparison of estimated and observed ultimate bearing capacity

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Fig. 3. Relationship between the predicted ultimate bearing capacity and the resistance bias

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Fig. 4. Cumulative distribution of sample resistance biases and fitted normal distribution

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Fig. 5. P-P plot for diagnosing normal distribution of sample resistance biases

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Fig. 6. Probability density function of total resistance according to COVsu of 10, 20, and 30%

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Fig. 7. Relationships between parameters for probability distribution of ln(λR) and COVTotal

Table 1. Summary statistics for proposed MLR

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Table 2. Performance of MLR model by Bong and Kim (2017)

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Table 3. Summary of results of Chi-square test

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Table 4. Statistic properties of total resistance bias

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