| Summary: | 碩士 === 逢甲大學 === 土木工程所 === 93 === ABSTRACT
In the current geological analyses of engineering applications, borehole drilling and sampling tests are generally conducted to investigate material properties and the thicknesses of each geological profile. The defect of the aforementioned technique is that it is limited to a ‘point’ sampling instead of a ‘surface’ detection. It results further in some disadvantages such as questionable representative from borehole drilling, higher rates in error, lack of proper simulation of in-situ stresses, relatively high costs, and low proceeding speeds. Spectral Analysis of Surface Waves Method (SASW) incorporates an impulsive source and two vertical velocity transducers to detect surface wave propagation so that in-situ dispersion curve can be obtained. Both the distance between the source and the first velocity transducer and that between two velocity transducers are 6 meters. Upon finishing the current testing point, the whole array is transferred to the next testing point with the interval of 2 meters. Therefore, this study incorporates a dense and multiple testing-point method so that a ‘surface’ detection can be conducted and a two-dimensional diagram of dispersion curves can be used to show the distribution of underground wave velocity.
The testing site in the study is the A12 Lot in the HsinYi Special District of Taipei City. Two individual test dates are conducted. The in-situ experimental results showed that: 1. The coherence coefficients among these testing points are high, mainly ranging from 0.9 to 0.95 for frequencies of 10~100 Hz, while for some coefficients range from 0.95 and 1.00. 2. Background noise has significant effect on the coherence coefficient which results in irregular oscillation in the low frequency section of the dispersion curve. It is suggested to conduct the SASW test with low background noise. 3. The trend of solum transition can be observed from the dispersion curve in the range of 0-3 meter which is the depth of surface backfill soils, whereas the same soil properties can be recognized from the dispersion curve in the range of 3-20 meters which is about the thickness of low-plasticity clay.
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