한국지반공학회논문집 (Journal of the Korean Geotechnical Society)

  • 제22권5호
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  • Pages.47-57
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  • 2006
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  • 1229-2427(pISSN)
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  • 2288-646X(eISSN)
한국지반공학회 (Korean Geotechnical Society)
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벤더엘리먼트 시험의 원리와 고려사항

Principles and Considerations of Bender Element Tests

  • 이종섭 (고려대학교 사회환경시스템공학과) ;
  • 이창호 (고려대학교 사회환경시스템공학과)
  • Lee Jong-Sub (Dept. of Civil and Environment Engrg., Korea Univ.) ;
  • Lee Chang-Ho (Dept. of Civil and Environment Engrg., Korea Univ.)
  • 발행 : 2006.05.01
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⟨ 이전 논문 다음 논문 ⟩

초록

전단파는 흙 입자의 강성과 밀도에 연관된다. 흡 입자의 전단 강성은 물의 존재 여부에 영향을 받지 않는다. 벤더 엘리먼트는 흙과 트랜스듀서 간의 뛰어난 결합 효과를 보여 토질 시험 장치에 적용하기에 편리한 전단파 트랜스듀서이다. 본 논문은 전단파의 기본 원리를 살펴본 뒤, 전자기 커플링 방지, 지향성(directivity), 공진주파수, 초동 추정, 근접장 효과 등을 포함하여 벤더 엘리먼트의 설계와 설치에 대하여 다루었다. 전해질 용액 속에서의 전기적 간섭(cross-talk)현상은 병렬 타입의 벤더 엘리먼트를 사용함으로써 최소화할 수 있다. 캔틸레버 보 형식의 벤더 엘리먼트는 전단파의 지향성은 원형에 가깝게 나타났다. 벤더 엘리먼트의 공진주파수는 벤더 엘리먼트 자체의 특성, 흡의강성 및 엥커 특성에 의존적인 것으로 나타났다. 벤더 엘리멘트 시험에서 가장 어려운 부분 중의 하나는 전단파의 도착시간에 영향을 주는 근접장 효과이다. 근접장 내에서 전단파의 도착시간 산정은 다중반사법(multiple reflection method)과 signal matching 기술을 적용하여 해결할 수 있다. 여러 가지 고려사항이 요구되는 벤더 엘리먼트는 전단파를 이용한 지반 동적 특성 파악에 매우 효과적인 방법이 될 수 있을 것이다.

The shear wave velocity is related with the stiffness of granular skeleton and mass density. The shear stiffness of the granular skeleton remains unaffected by the presence of the fluid. Bender elements are convenient shear wave transducers for instrumenting soil cells due to optimal soil-transducer coupling. This study addresses the principles of the shear wave, the design and implementation of bender elements including electromagnetic coupling prevention, directivity, resonant frequency, detection of first arrival, and near field effects. It is shown that electromagnetic coupling effects can be minimized using parallel-type bender elements. Thus, the in-plane S-wave directivity is quasi-circular. The resonant frequency of bender element installations depends on the geometry of the bender element, the anchor efficiency and the soil stiffness. One of the most cumbersome parts in the bender element test is near field effects, which affect the selection of arrival time. The selection of the first arrival within the near field Is effectively solved by the multiple reflection technique and signal matching technique. Bender elements, which requires several considerations, may be effective tools for the subsurface characterization by using S-wave.

키워드

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