| Summary: | 碩士 === 逢甲大學 === 土木工程所 === 99 === The major purpose of the thesis was to study the detectability of cavity position in coastal dyke using ground penetrating radar as the nondestructive testing tool. By comparing the on-site situation and nondestructive testing result, an average area difference variable obtained from cases with and without cavities was proposed as a quantitative index for cavity existence using Matlab language in order to locate the cavity and to determine its size. A series of sandbox experiments was conducted to simulate the situation of rectangle and triangle cavity at the height of 0, 3, 6, and 10 cm by using 1600 MHz high-frequency antenna. The major on-site test regions of the study were selected from test results from coastal dyke of Chia-Yi and Yun-Lin Counties by using 400 MHz antenna. The scope of the study was mainly the shallow layer near the surface of coastal dyke.
The results reveal that: (1) for a higher value of cavity height, the width of white GPR signal under the concrete slab has the tendency to expand. (2) At the location of cavity, the wave crests and wave trough of GPR signal might be moved early or delayed, and the average area difference will be influenced by the severity of the cavity. The larger of a cavity, the larger of the average area difference, and vice versa. With the help of the curve of t average area difference, the shallow cavities in the coastal dyke can be effectively located.
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