Case Study: Application of GPR to Detection of Hidden Dangers to Underwater Hydraulic Structures

After long-term operation, a variety of hidden defects will occur in hydraulic structures, which will endanger the safety of a water conservancy project. In particular, hidden defects located below the water surface cannot be easily recognized by conventional methods and thus constitute the main reason for occurrence of dangerous situations in such hydraulic structures. It is therefore necessary to carry out periodic checks on the underwater structures. Ground-penetrating radar (GPR) is a highresolution, nondestructive technology for detection of underground objects using a high-frequency electromagnetic pulse, and has been extensively applied to a variety of fields such as engineering/geologic exploration, underground archaeological survey, detection of scour holes around bridge piers, etc. In order to investigate the capability of GPR in detecting hidden dangers to underwater hydraulic structures, the authors have conducted GPR application-related experiments for more than 20 hydraulic projects since 1996, and in order for the GPR application to be successful in narrow spaces such as lock chambers, the authors also designed an antenna that can be directly operated on the waterʹs surface. Experimental results demonstrate that GPR can be used not only to detect hidden dangers with high precision, such as uneven settlement and cracking at impervious blanket or apron water bottoms, but also to detect hidden dangers to underwater hydraulic structures, such as damage of reverse filter below the sloping clay core of a dam, settlement and cracking of the antiseepage geomembrane at the bottom of a reservoir, concentrated seepage channel, etc. The application effect will be demonstrated in this paper based on some practical examples of using the GPR technique for such types of detection.