Study of Detecting of Cavities with Stepped-Frequency Georadar

• Main Authors: Tseng ,Chun Chih, 曾俊智
• Other Authors: Dr.Chiang,Chine Chung
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/98726119430466797920

碩士 === 國立雲林科技大學 === 營建工程系碩士班 === 89 === Georadar detection is a kind of non-destructive techniques, which was put to use in civil engineering extensively in Europe and America. The georadar was also extensively used in our country, and the technique was mature. Because the cavities can damage the structures potentionally, if we can detect the existence of cavities in advance, we will decrease the engineering damage. In this reaserch, the stepped-frequency georadar is mainly used to detect the cavities, and the contents of thesis can be divided into model tests and field tests. The results of model tests show that in the water, the georadar with 50~700MHz frequency can not detect the cavities deeper than 10cm, and smaller than two table-tennis balls（the volume is about 57.5cm3）. When the frequency of 800~3000MHz was used, the distance of antenna to water was not easily controlled, and it is easy for antenna to be shaken during tests to make noise. The energy of radar waves at higher frequency decrease quickly in the water, so the high-frequency antenna is not suitable to be use in deeper water. In sand-box model tests, the tube with 1.9cm diameter was used in the dry sand to simulate the cavity. When the tube was full of water, with radar at frequency of 800~3000MHz, the curve of reflective signal was mild and long, and the tube was easy to be detected. In field tests，the relative dielectric constants of soils could increase with water content，and decrease the penetration depth of georadar. the soil was in the situation of moisture ，it would affect the results when using the georadar to detect the cavities. And we found that the georadar results obtained in the field were similar to the results obtained in the sand-box model tests.