Earth pressures acting on vertical circular shafts considering arching effects in c-$\phi$ soils : II. Lab. Model Tests

c-$\phi$ 지반에서의 아칭현상을 고려한 원형수직터널 토압 : II. 실내 모형실험

  • 김도훈 (고려대학교 건축사회환경공학부) ;
  • 차민혁 (고려대학교 건축사회환경공학부) ;
  • 이대수 (한국전력공사 전력연구원) ;
  • 김경렬 (한국전력공사 전력연구원) ;
  • 이인모 (고려대학교 건축사회환경공학부)
  • Received : 2009.12.24
  • Accepted : 2010.01.18
  • Published : 2010.03.31

Abstract

The earth pressure acting on the vertical shaft is less than that acting on the retaining wall due to three dimensional arching effect. Thus, it might be essential to estimate the earth pressure actually acting on the shaft when designing the vertical shaft. In this paper, large-sized model tests were conducted as Part II of companion papers to verify the newly suggested earth pressure equation proposed by Kim et al. (2009: Part I of companion papers) that can be used when designing the vertical shaft in cohesionless soils as well as in c-$\phi$ soils and multi-layered soils. The newly developed model test apparatus was designed to be able to simulate staged shaft excavation. Model tests were performed by varying the radius of vertical shaft in dry soil. Moreover, tests on c-$\phi$ soils and on multi-layered soils were also performed; in order to induce apparent cohesion to the cohesionless soil, we add some water to the dry soil to make the soil partially-saturated before depositing by raining method. Experimental results showed a load transfer from excavated ground to non-excavated zone below dredging level due to arching effect when simulating staged excavation. It was also found that measured earth pressure was far smaller than estimated if excavation is done at once; the final earth pressure measured after performing staged excavation was larger and matched with that estimated from the newly proposed equation. Measured results in c-$\phi$ soils and in multi-layered soils showed reduction in earth pressures due to apparent cohesion effect and showed good matches with analytical results.

Acknowledgement

Supported by : 한국전력공사 전력연구원

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