Experimental and Theoretical Studies on (Relative) Permittivity of the Tunnel Lining

In the paper, for two cases of different ages and different depths, the speed of radar wave transmitted in the testing concrete lining is measured by using the ground penetrating radar (GPR), and corresponding data of permittivity of the concrete lining are therefore obtained. An abnormal phenomenon of the permittivity is observed which shows that the value of permittivity will increase linearly with the depth of the concrete lining. Combined with the characteristics of tunnel lining and taken the free water distribution into account, a new dielectric model of the concrete lining is put forward. Results show that this model can be used to explain the experimental results and provide correct reference for the GPR use in measuring the depth of the concrete lining with good accuracy.