• Title/Summary/Keyword: SASW

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A Study Using Nondestructive Tests Based on Stress Waves for the Estimation of Concrete Compressive Strength (응력파 기반 비파괴 검사법에 의한 콘크리트 강도 추정에 관한 연구)

  • Joo, Hyun-Jee;Cho, Young-Sang
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.11a
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    • pp.675-678
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    • 2004
  • The importance of predicting concrete compressive strength of in concrete structures is gradually increasing in construction industry. The estimation of concrete compressive strength of is a critical factor of the construction schedule and quality control. This study was performed to examine the relationship between concrete compressive strength and stress wave velocity which was determined by the impact echo method and SASW method.

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NDT Determination of Cement Mortar Compressive Strength Using SASW Technique

  • Cho, Young-Sang
    • KCI Concrete Journal
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    • v.13 no.2
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    • pp.10-18
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    • 2001
  • The spectral analysis of surface waves (SASW) method, which is an in-situ seismic technique, has mainly been developed and used for many years to determine the stiffness profile of layered media (such as asphalt concrete and layered soils) in an infinite half-space. This paper presents a modified experimental technique for nondestructive evaluation of in-place cement mortar compressive strength in single-layer concrete slabs of rather a finite thickness through a correlation to surface wave velocity. This correlation can be used in the quality control of early age cement mortar structures and in evaluating the integrity of structural members where the infinite half space condition is not met. In the proposed SASW field test, the surface of the structural members is subjected to an impact, using a 12 mm steel ball, to generate surface wave energy at various frequencies. Two accelerometer receivers detect the energy transmitted through the medium. By digitizing the analog receiver outputs, and recording the signals for spectral analysis, surface wave velocities can be identified. Modifications to the SASW method includes the reduction of boundary reflections as adopted on the surface waves before the point where the reflected compression waves reach the receivers. In this study, the correlation between the surface wave velocity and the compressive strength of cement mortar is developed using one 36"x36"x4"(91.44$\times$91.44$\times$91.44 cm) cement mortar slab of 2,000 psi (140 kgf/$\textrm{cm}^2$) and two 36"x36"x4"(91.44$\times$91.44$\times$91.44 cm) cement mortar slabs of 3,000 psi (210 kgf/$\textrm{cm}^2$).

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Evaluation Technique of Ground Densification on Sand Deposit using SASW and Resonant Column Tests (표면파시험과 공진주시험을 이용한 사질토지반 개량평가 시스템의 개발)

  • 김동수;박형춘;김성인
    • Journal of the Korean Geotechnical Society
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    • v.15 no.1
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    • pp.41-52
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    • 1999
  • In order to assess the quality and depth of ground densification by compaction, SPT and/or CPT are performed before and after compaction. Both methods are intrusive and one point tests, require a substantial time to evaluate a large area, and their results are quite dependent on the operation technique and soil type. In this paper, the quality and extent of ground densification by compaction was evaluated by using in situ SASW test and laboratory resonant column (RC) test results. SASW test was used to determine the shear wave velocity profiles before and after compaction, and RC test was adopted to determine the correlation between the normalized shear wave velocity and the density of the site, which is almost uniquely independent of confinement. Testing and data reduction procedures of both tests were discussed, and a simplified evaluation procedure of ground densification was proposed. Finally, the feasibility of the proposed method was verified by performing field study at Inchon International Airport Project. Field densities determined by the proposed method matched well with those determined by sand cone tests.

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Inversion of spectral analysis of surface waves with analytic Jacobian (해석적 자코비안을 이용한 표면파 기법의 역산)

  • Ha, Hee-Sang
    • Journal of the Korean Geophysical Society
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    • v.5 no.3
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    • pp.233-245
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    • 2002
  • The spectral-analysis-of-surface-waves (SASW) method is a nondestructive testing method based upon generation and detection of elastic stress waves. SASW is widely used as one of the techniques to determine stiffness profile in engineering geophysics. The essential steps involved are construction of an experimental dispersion curve from data collected in situ, and inversion of the dispersion curve to determine the stiffness profile. The main object of this study is to derive an analytical Jacobian for the inversion. If we set the subsurface to N homogeneous layer, it could save 2N times Jacobian calculation compared to numerical jacobian calculation during inversion. To reconstruct a stiffness profile, constrained damped least square method was applied for the inversion. The algorithm was tested for the numerical data and for the real asphalt and tunnel data, which were able to verify the stiffness profile. The stiffness profile reconstructed by the algorithm showed the possibility to appraise the soundness of tunnel with applications SASW.

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Safety Evaluation of Rock-Fill Dam by Seismic(MASW) Method (사력댐의 안정성평가를 위한 표면파탐사(MASW)의 활용성)

  • 정해상;오영철;방돈석;안상로
    • Proceedings of the Korean Geotechical Society Conference
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    • 2003.03a
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    • pp.359-364
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    • 2003
  • For safety evaluation of a rock-fill dim, it is often necessary to investigate spatial distribution of weak zones such as fracture. Both DC-resistivity survey and seismic(SASW) method are usually used for the purpose. Recently, Multichannel analysis of surface waves(MASW) method which makes up for the weak point of SASW method is developed and the site examination which is simple came to be possible comparatively. In order to obtain 2-D shear-wave velocity(Vs) profile along the dam axis that can be associated with dynamic properties of filled materials, MASW method was adapted. Then, DC-resistivity survey and drilling survey were performed to compare with each results. We confirmed that the MASW method and DC-resistivity survey show complementary result that corresspond with drilling result. Therefore, MASW method is an efficient method for dynamic characterization of dam-filling materials and also the combination of related methods such as DC-resistivity can lead to an effective safety evaluation of rock-fill dam.

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A Study on the Applicability of Numerical Analysis for the SASW Method (SASW 기법에 대한 수치해석 적용성 연구)

  • 김동수;윤종구;이병식;박형춘
    • Journal of the Korean Geotechnical Society
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    • v.17 no.1
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    • pp.67-76
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    • 2001
  • 현장지반의 최대전단탄성계수를 신속하고 합리적으로 구할 수 있는 표면파기법에 대해 유한요소법을 이용하여 시뮬레이션 할 경우 적용할 수 있는 효율적인 해석조건에 대한 연구를 수행하였다. 본 연구결과 파의 전파형상을 효율적으로 묘사하기 위하여는 관심 있는 최소 파장에 대한 유한요소 크기의 비가 매우 중요한 요소임을 확인하였고, 데이터의 측정시간간격도 중요한 요소임을 확인하였다. 또한, 유한요소해석을 이용하여 얻은 반무한체 시스템과 2층 시스템의 분산곡선과 이론적 분산곡선이 비교적 잘 일치함을 볼 수 있었다. 따라서, 유한요소해석을 적절히 적용하는 경우에 표면파기법을 효과적으로 시뮬레이션 할 수 없음을 확인하였다. 현장지반의 최대전단탄성계수를 신속하고 합리적으로 구할 수 있는 표면파기법에 대해 유한요소법을 이용하여 시뮬레이션 할 경우 적용할 수 있는 효율적인 해석조건에 대한 연구를 수행하였다. 본 연구결과 파의 전파형상을 효율적으로 묘사하기 위하여는 관심 있는 최소 파장에 대한 유한요소 크기의 비가 매우 중요한 요소임을 확인하였고, 데이터의 측정시간간격도 중요한 요소임을 확인하였다. 또한, 유한요소해석을 이용하여 얻은 반무한체 시스템과 2층 시스템의 분산곡선과 이론적 분산곡선이 비교적 잘 일치함을 볼 수 있었다. 따라서, 유한요소해석을 적절히 적용하는 경우에 표면파기법을 효과적으로 시뮬레이션 할 수 없음을 확인하였다.

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A Study on the Finite Difference Forward Modeling in SASW Method (차분 전개를 이용한 표면파 기법의 모형 응답 계산)

  • Ha, Hee-Sang;Shin, Chang-Su;Seo, Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.5 no.2
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    • pp.99-107
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    • 2002
  • An analytical forward modeling algorithm was developed for the efficient application to the geotechnical engineering in SASW (Spectral Analysis of Surface Waves) method. for the theoretical dispersion curve, the finite difference method using motion stress vector, which was proposed by Aki and Richards, was employed and verified with two earth models. For the stable and fast calculation, it was found that the model size depending on the frequency range is suitable $1.5\~2$ times bigger than the wavelength.

A Study on the Applicability of the Reinforced Railroad Roadbed Method by Field Test (현장부설시험을 통한 철도 강화노반공법의 적용성에 관한 연구)

  • 황선근;신민호;이성혁;최찬용;이시한
    • Proceedings of the Korean Geotechical Society Conference
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    • 2000.03b
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    • pp.215-222
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    • 2000
  • The reinforced roadbed should have the ability to spread out the load intensity lower than the bearing capacity of the subgrade of track structure as well as to prevent the softening of roadbed by providing appropriate stiffness in the roadbed, thus fully supports the track structures. Full scale reinforced roadbeds with several different types of monotoring sensors was also constructed to evaluate the performance of each reinforced roadbed through the continuous monitoring while the train operation. In this study, Field tests such as PLT, SASW were also carried out at each reinforced roadbed. The results of the field and lab tests, installation and calibration of sensors, as well as construction condition of the reinforced roadbed are presented.

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Evaluation of Seismic Response Characteristics of Hong-Seong Area based on In-Situ and Laboratory Tests (현장 및 실내시험에 기초한 홍성지역 지진응답특성 평가)

  • 박덕근;김교원
    • The Journal of Engineering Geology
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    • v.11 no.1
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    • pp.25-35
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    • 2001
  • For the ground resrxmse analysis, both in-situ and laboratory testing techniques such as downhole, SASW, resonant column and torsional shear tests were perlormed for Hong-Seong area. The grOlmd upper 30m is classified as SD since it has an average shear wave velocity as 209m/s. The response specLrums obtained by site-specific analyses generally satisfied the seismic code, but near the resonance period the motion was evaluated to be higher than the code.

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A Study on Applicability of Numerical Analyses for Stress Wave-Based NDE Techniques (응력파를 이용한 비파괴 탐상기법의 수치해석 적용성에 관한 연구)

  • 이영준;이종세
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2003.04a
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    • pp.504-512
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    • 2003
  • Simulation programs have been developed and used as an attempt to improve the accuracy of Non-Destructive Evaluation(NDE) techniques. The applicability of these programs is very limited, however, because it is difficult to describe the delicacy of the propagation of stress waves. To investigate the applicability of the finite element analysis for stress wave-based NDE techniques numerical simulation for Impact-Echo method and SASW method is performed. The numerical studies are performed to determine the essential parameters such as contact time of impact load, mesh size and time step size. These studies show that the choice of parameter is very important for improving the accuracy and confidence of the numerical procedure and, thereby, the applicability of the numerical analysis for stress wave-based NDE techniques

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