| Summary: | 碩士 === 逢甲大學 === 土木工程所 === 98 === Gravel formation distributes a vast area in the island of Taiwan, and the major soil in Taichung metropolitan area is mainly gravel soil. The characteristic of Taichung Metropolitan Area gravel formation includes large thickness over 100 m, good engineering properties, large stratigraphic variability, high strength, but difficulties to perform material test. Up to now, undisturbed thin-walled samples have not been easily obtained in order to perform some mechanical tests, due to difficulties in drilling operation on site for gravel formation. The purpose of the thesis was to utilize the non-destructive characteristic of Array Testing SASW Method to gravel formation and to study the feasibility of the method for determination of its underground structural profile.
Field experiment of this study was performed at some site near Zonta Road, Tanzih Township in Taichung County, which is made of gravel by deposition. One test line was selected which crosses boreholes at their top. A 6 kg hammer was used to generate vibration and 4 receivers to capture wave propagation, the receiver spacing is 4 meters, and the distance between two measuring points is 2 meters. After the testing was done for one test point, the whole array including the hammer and 4 receivers were moved together to the next test point. Totally 27 test points were conducted. The test results were then compared with the geological borehole data.
The study results show that (1) Maximum amplitude from the time domain represents only the maximum amplitude in the time window but can not be used to relate the amplitudes of main signal and the noise for each frequency; frequency domain amplitude ratio analysis agrees well with the SNR analysis. (2) The existence of gravel formation will cause "strong oscillation phenomenon” in dispersion curve. (3) The inversion program used in this study was designed mainly for horizontal stratum, and the existence of gravel in the field test may cause large the calculation error during the inversion process which results in unsatisfactory inversion result. (4) Results from numerical simulation show that the existence of gravel will affect the apparent wave velocity of surface waves, especially for high frequencies above 40Hz and this may cause low wave velocity in the shallow depth and strong oscillation in dispersion curve as well.
Keyword: Gravel Formation, Array Testing of Spectral Analysis of Surface Waves Method (SASW)
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