Nondestructive detecting thickness of main concrete channel lining in east line project of China South to North Water Diversion using GPR

China South to North Water Diversion project includes the longest water channel in the world now. The length of headwater channel which has been built up by May 2009 is over 700km in Shandong Province. All linings of those headwater channels are made of concrete, which thickness was designed from 5 to 12cm. But at some check position with drilling, the actual thickness of concrete lining was found thinner than design. Consequently, as a nondestructive method, Ground Penetrate Radar (GPR) was used to detect the thickness of concrete lining continuously. Reflection wave method is usual way to measure the thickness of object with GPR. After taking reflection time from measured GPR signal, the thickness of concrete lining could be calculated with penetrating time and velocity of GPR wave. In this method, velocity of GPR wave was a key to calculate the thickness well and truly. In order to conform it truly and quickly, some concrete samples were made according to the same composition of lining concrete. And real dielectric constants of those samples were tested using GPR method. Basing on the experiment results, representative dielectric model of lining concrete, relation between water content and velocity of GPR wave were confirmed. The research results show we could present the CRIM formulae to get velocity of GPR wave when calculating thickness with GPR reflection wave method. Case study approved that could improve precision of measured thickness greatly.