Study of GPR image characteristics of dams´ hidden weak points

For using GPR as a non-destructive testing to the hidden weak points in dam or seawall, how to reasonably analysis the GPR image and obtain the exact interpretations is still an unsolved problem. Combined with the dam engineering features and detection experiences, geophysical models of typical hidden weak points, such as horizontal non-homogeneous layer, slope non-homogeneous zones bearing coarse-grained or fine-grained material mezzanine and cavities filled with different materials in cohesive soil dam, were set up for numerical simulation. Numerical simulations of radar wave performance in these typical hidden weak point models were conducted by using the finite difference time domain (FDTD) solution over a 2D space, with a perfectly matched layer (PML) absorbing boundary conditions. Simulated results illustrated that spatial distribution of hidden weak points can be interpreted from the GPR image. On the condition of complicated environment, interpretation of local hidden weak point character relies upon careful analysis on dynamic characteristics including phase and frequency features of reflected wave, and diffracted wave character. Based on the wave field characteristics of the typical hidden weak points, some GPR images collected at a reservoir dam and seawall had been interpreted. Engineering applications indicated that appropriate numerical model construction and simulation interpretation could be a helpful guide to real GPR test for hidden weak points.