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🏛️國立陽明交通大學機構典藏

Author: search.filters.author.Chien, Chih-JungHas files: No

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    Quantitative Interpretation of Surface Wave Testing for Assessment of Ground Improvement by Jet Grouting
    (2017-01-01)
    Lin, Chih-Ping
    ;
    Lin, Chun-Hung
    ;
    Chang, Yu-Cheng
    ;
    Chien, Chih-Jung
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    防災與水環境研究中心
    Jet grouting technique is special in that the ground becomes highly heterogeneous after installing the improvement columns. The surface wave method was recently shown to hold good promise to assess the average property of the improved ground and evaluate the area replacement ratio. Even though the improved ground was highly heterogeneous along the seismic survey line, the surface wave method worked well and yielded a homogenized shear wave velocity profile. The increase of shear wave velocity after ground improvement was found to be correlated with the area replacement ratio. This study further examined the quantitative relation between the percentage increase of shear wave velocity and the area replacement ratio. The effect of offline sampling (perpendicular to survey direction) was also investigated. 3D spectral element method was utilized for the numerical investigation. Numerical results show that the offline sampling range is about 75%-85% of the wavelength. Hence, it should be noted when planning survey lines. Furthermore, a positive correlation between replacement ratio and velocity increase exist and the difference caused by the velocity contrast between soils and improved columns could be neglected as the velocity contrast becomes greater than about 5. An empirical predictive model between the velocity increase percentage and area replacement ratio was established based on the numerical simulations.
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    Dispersion analysis of surface wave testing - SASW vs. MASW
    (2017-08-01)
    Lin, Chih-Ping
    ;
    Lin, Chun-Hung
    ;
    Chien, Chih-Jung
    ;
    交大名義發表
    ;
    National Chiao Tung University
    The data reduction method for dispersion relation in surface wave testing is conventionally associated with the certain method of data acquisition, for example, phase shift analysis in the two-station SASW method and 2-D multi-station wavefield transformation of surface wave in the MASW method. The fundamental difference in dispersion analysis between the 2-station and multi-station approach was clarified in this study. Limited to the two channel data, conventional dispersion analysis of SASW suffers from possible phase un-wrapping errors, inefficient data filtering and synthesis, and inability to distinguish multiple modes. The MASW approach, on the other hand, can avoid these problems and provide visualization of dispersion relation through 2D wavefield transformation. As opposed to multiple shots in the SASW testing, the MASW testing typically uses only single shot, limiting the obtainable wavelengths due to near field and far field effects. Combining the merits of these two methods, a multi-shot common receiver configuration survey is proposed to acquire multi-station wavefield for 2D wavefield transformation using as few as two receivers. An additional benefit of the multi-shot common receiver configuration is shown to be better control and higher lateral resolution of the measurement range. (C) 2017 Elsevier B.V. All rights reserved.
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    Application of surface wave method in assessment of ground modification with improvement columns
    (2017-07-01)
    Lin, Chun-Hung
    ;
    Lin, Chih-Ping
    ;
    Dai, Yung-Zheng
    ;
    Chien, Chih-Jung
    ;
    交大名義發表
    Surface wave testing is considered a promising method for assessing average property and actual area replacement ratio of ground modification with improvement columns, owing to its non-destructive nature and large sampling range. However, the surface wave method is essentially a 1-D method assuming horizontally-layered medium. What it measures in highly heterogeneous improved ground remains to be investigated. This study aimed at evaluating the feasibility of surface wave method in the heterogeneous ground with improved columns, and investigating the homogenization of shear wave velocity and the lateral sampling range. Field tests on a jet grouted construction site showed that the surface wave method worked well in such heterogeneous grounds and yielded a site-representative shear wave velocity profile regardless of the survey location. This is attributed to the survey condition where the wavelength is greater than the spacing of grout columns. 1-D analytical models and 2-D numerical simulations were conducted to investigate the quantitative relation between construction parameters and the percentage increase of shear wave velocity after ground improvement. A quantitative approach to estimate the area replacement ratio and overall quality of improvement columns by surface wave testing is proposed. (C) 2017 Elsevier B.V. All rights reserved.