한국지반환경공학회 논문집 (Journal of the Korean GEO-environmental Society)

  • 제18권3호
  • /
  • Pages.5-14
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  • 2017
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  • 1598-0820(pISSN)
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  • 2714-1233(eISSN)
한국지반환경공학회 (Korean Geo-Environmental Society)
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직접전단상자 시스템에 따른 동결토의 강도 평가에 관한 실험적 연구

An Experimental Study of Strength Evaluation in Frozen Soils according to Direct Shear Box Systems

  • Kim, Sang Yeob (School of Civil, Environmental, and Architectural Engineering, Korea University) ;
  • Kim, YoungSeok (Geotechnical Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology) ;
  • Lee, Jangguen (Geotechnical Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology) ;
  • Lee, Jong-Sub (School of Civil, Environmental, and Architectural Engineering, Korea University)
  • 투고 : 2016.11.08
  • 심사 : 2017.02.24
  • 발행 : 2017.03.01
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초록

극한지 동결 지반에서 구조물의 설계 및 시공이 진행됨에 따라, 안정성 평가를 위해 동결토의 강도 특성에 대한 실험적 연구가 필수적이다. 본 연구의 목적은 전단 상자 시스템에 따른 동결토의 강도를 평가하는 것으로, 이를 위하여 보편적으로 사용되는 기존 직접전단 시스템(Type-1), 상부 전단 상자 위쪽에 롤러를 설치한 시스템(Type-2), 그리고 상부 전단 상자를 하부 전단 상자와 분리되도록 기둥으로 고정한 시스템(Type-3)을 제작하였다. 모든 시스템에는 모래, 실트, 그리고 증류수를 동일한 비율로 혼합한 시료를 이용하여 조성하였으며, 냉동 챔버 내에서 $-5^{\circ}C$까지 동결된 후 연직 응력 5, 10, 25 그리고 50kPa을 가하며 직접전단실험을 수행하였다. 실험 결과, Type-1은 전단 이동에 따라 상부 전단 상자가 회전(rotation)하여 하부 전단 상자와 접촉하는 문제가 발생했다. 상부 전단 상자의 회전을 롤러로 방지한 Type-2의 경우, 회전을 막는 힘이 전단강도에 추가되어 강도가 과대 평가되었다. Type-3의 경우, 동결 시료만의 전단강도가 평가되었으며, 최대전단강도 발현 시점과 수직변위가 증가하기 시작하는 시점이 유사하게 나타났다. 또한, Type-3의 최대전단강도와 잔류전단강도의 내부마찰각과 점착력은 롤러의 영향이 제거되어 Type-2보다 작게 나타났다. 본 연구는 동결토와 같이 강도가 큰 시료의 경우 Type-3과 같이 개선된 전단 상자 시스템을 이용하여 동결토만의 강도를 평가할 수 있음을 보여준다.

Experimental study on strength characteristics of frozen soils is necessary for the safety evaluation of design and construction in cold region. The objective of this study is to evaluate the direct shear strength of frozen soils obtained from traditional system (Type-1), system with roller on the upper shear box (Type-2), and system with fixed upper shear box separated from bottom shear box (Type-3). Specimens mixed with sand, silt, and water are frozen to $-5^{\circ}C$, and then direct shear tests are conducted under the normal stress of 5, 10, 25, and 50 kPa. Experimental results show that the upper shear box of Type-1 touches the bottom shear box due to the rotation of the upper shear box. The shear strength obtained from Type-2 is overestimated because the preventing rotation force is added to shear force. Type-3 may acquire the only strength of the specimen, and shear strain at peak shear strength is similar to that at the beginning of vertical displacement occurrence. In addition, internal friction angle and cohesion at both peak and residual stresses in Type-3 are smaller than those of Type-2. This study shows that high strength specimens including frozen soils can be effectively evaluated using improved shear box system such as Type-3.

키워드

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