| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 105 === The surface wave method utilized in shear wave velocity profiling of the underground becomes more mature than ever in recent years. Due to its non-intrusive feature and convenient operations, it is now widely used in site investigation and earthquake engineering. Among all the seismic methods, surface wave testing is easiest to perform since surface wave contains most of the energy in the seismograms. Being able to sample a very large volume, surface wave method is suitable for larger-scale site investigation. The data reduction method for dispersion relation in a surface wave testing is conventionally asociated with a certain method of data acquisition. At present, the two-station spectral analysis of surface wave (SASW) and multi-station analysis of surface wave (MASW) are the most popular methods used worldwide. They involved different approachs in dispersion curve analysis. The debates between two methods are still undergoing. Besides, field configuration such as near offset, geophone spacing and source type would influence the performance of testing. Practically, try and error in the field need to be done before an optimum field configuration was determined. These two situations can be confusing to geotechnical engineers as to apply the method in daily work. The purpose of the study is to propose a more definitive guideline for MASW testing and analysis to optimize the effective frequency range of dispersive curves. Firstly, the influences of field
parameters were fully studied based on field data. Then, a framework based
on pseudo-section concept was proposed to minimize the problems. In the framework, to maximize the bandwidth of dispersion curve, multiple sources can be used for each walk-away shot. For each frequency component, the optimal combination of source and offset can be selected to mitigate the near and far field effects as well as maximize the obtainable bandwidth for the dispersion curve. An expansive offset range in the same spatial range by synthesizing seismic records with different nearest source-to-receiver offsets can be generated based on this approach. The dilemmas in the field configuration is solved and the bandwidth of dispersion curve is maximized. Three field examples demonstrated that this new approach provides a more definitive guideline for MASW testing and maximize the obtainable bandwidth for the dispersion curve.
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