An Analysis of Using Ground-Penetrating Radar Refraction/Reflection Methods to Investigate Possible Fractures and Cavities in Concrete Sea Walls

• Main Authors: Min-Rui Wang, 王敏叡
• Other Authors: Ping-Yu Chang
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/99682610145997511031

碩士 === 國立臺灣海洋大學 === 應用地球科學研究所 === 99 === Ground-penetrating radar (GPR) is a non-destructive geophysical tool that is used to investigate subsurface geology and structures. GPR reflection radargrams are commonly utilized to provide the “image” of the interior of the media being probed. However, the ability of the GPR to detect the fractures and cavities is subject to the fracture aperture, the orientation and geometry of the fissures, and the antenna frequencies. In this study, we attempt to use a wide angle refraction/reflection method, as well as the reflection radargrams to help identify the fractures and cavities in the concrete sea walls retaining a reclaimed land near the campus of National Taiwan Ocean University. We have acquired GPR reflection radargrams along 13 lines with three different antenna frequencies, including 38Mhz, 75Mhz, and 150Mhz in the study area. First, dense GPR data were collected along nine 30-m long parallel lines with 1-m apart. GPR data were collected with the common offset method and a spacing of 10-cm. Second, we collected GPR data at the area adjacent to the pervious survey area with four 454-m long parallel lines with 2-m apart. Hence we are able to provide a pseudo 3D model for an area of 454 m x 8 m. We have identified several parabolic structures showing the possible locations of the fractures and cavities. Lastly we conducted wide angle refraction/reflection methods to provide additional information for the existence of the fractures and cavities.