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2026 Vol.42, Issue 1 Preview Page
Influence of Particle Size Distribution on the Settling Velocity of Sand: An Effective Diameter-based Prediction Model

입도분포가 사질토의 침강속도에 미치는 영향 분석 및 유효 입경을 이용한 예측 모델 연구

Noeul Kim1
,
Hyunwook Choo2*
김 노을1
,
추 현욱2*
1Member, Graduate Student, Dept. of Civil and Environmental Engineering, Hanyang Univ.
2Member, Associate Prof., Dept. of Civil atuind Environmental Engineering, Hanyang Univ.
1정회원, 한양대학교 건설환경공학과 석사과정
2정회원, 한양대학교 건설환경공학과 부교수
*Corresponding Author
28 February 2026. pp. 69-79
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Abstract

Accurate prediction of settling velocity is critical for evaluating the long-term stability of geotechnical structures and for consolidation design. However, conventional studies have simplified natural sediments as uniform, single-sized particles, failing to account for the complex effects of particle size distribution (PSD). This study investigates the influence of PSD on settling behavior through laboratory experiments using silica sand and glass beads with a constant median particle size (D50) of approximately 0.7 mm but varying coefficients of uniformity (Cu). Settling velocities were measured using video tracking for single particles and a load-cell-based cumulative mass method for bulk-settling conditions. The results demonstrate that as the PSD widens, the drag coefficient (CD)–Reynolds number (Re) relationship deviates substantially from established guidelines, exhibiting a distinct settling lag. This behavior is attributed to excess pore water pressure generated by fine particles and to local upward flow induced by larger particles, which collectively hinder the descent of smaller particles. Quantitatively, D50-based predictions of the CD–Re relationship result in a high MAPE of over 130%. By introducing an effective particle diameter (Deff) based on the specific surface area, the MAPE is reduced to approximately 22%. Furthermore, a simplified correlation between Deff and Cu is proposed in this study, providing a practical and computationally efficient framework for predicting the settling velocity of nonuniform geomaterials.

Keywords
Effective particle diameter
Group settling
Particle size distribution
Settling velocity
Uniformity coefficient

흙의 침강속도에 대한 정확한 예측은 지반 구조물의 장기 안정성 평가 및 압밀 설계에 필수적이다. 그러나 기존 연구들은 자연 퇴적물을 단일 입경으로 단순화하여 실제 퇴적물의 비균일한 입도분포 효과를 충분히 반영하지 못하는 한계가 있다. 본 연구는 이를 보완하기 위해 평균 입경(D50)을 0.7 mm로 고정하고 균등계수(Cu)를 변화시킨 silica sand와 glass beads를 대상으로 침강 실험을 수행하였다. 침강속도는 단일 입자의 경우 비디오 추적 기법을, 그룹 침강 조건에서는 로드셀 기반의 누적 질량 측정법을 통해 정밀하게 측정하였다. 실험 결과, 동일한 D50 조건에서도 입도분포가 넓어질수록 또는 시료가 비균일할수록 항력계수(CD)–레이놀즈 수(Re) 관계가 기존 가이드라인에서 크게 이탈하며 침강 속도가 지연되는 현상이 확인되었다. 이러한 현상은 미세 입자에 의한 과잉 간극수압 발현 및 조립 입자 침강 시 발생하는 국부적인 상승류가 미세 입자의 하강을 방해하는 수리학적 상호작용의 결과로 분석되었다. 정량적으로 D50을 대표 입경으로 사용할 경우 CD–Re 관계 예측오차(MAPE)가 130% 이상으로 매우 높게 나타났으나, 비표면적 기반의 유효입경(Deff)을 대표 입경으로 도입한 결과 오차율이 약 22% 수준으로 획기적으로 감소하였다. 최종적으로 본 연구에서는 Deff와 Cu 사이의 상관관계식을 제안함으로써, 비균일 퇴적물의 침강속도 산정에 대한 실무적 효율성과 예측 정확도를 동시에 향상시켰다.

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Information
  • Publisher :The Korean Geotechnical Society
  • Publisher(Ko) :한국지반공학회
  • Journal Title :Journal of the Korean Geotechnical Society
  • Journal Title(Ko) :한국지반공학회 논문집
  • Volume : 42
  • No :1
  • Pages :69-79
  • Received Date : 2026-01-06
  • Revised Date : 2026-01-22
  • Accepted Date : 2026-01-23
  • DOI :https://doi.org/10.7843/kgs.2026.42.1.69
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