Experimental Study On Detection Of Tunnel Lining With On-board GPR And High Frequency Surface Waves

China is a country that has the most tunnels and underground projects.Although Chinese geological environment is the most complicate among the world,China still develops most quickly.Therefore,tunnel lining quality should be a priority for all.Since tunnel lining is in a closed architecture after it was finished,if we use the traditional way to check tunnel lining quality,it's inevitable to destroy tunnel lining to a certain degree,which results in low efficiency and high economy cost.So non-destructive detecting method becomes the first choice.The present main nondestructive detecting methods include ground penetrating radar(GPR)testing,surface wave inspection and infrared thermal imagery detection.And on-board GPR is gradually applied to general investigation on tunnel disease for its quick speed and succession.High-frequency surface wave has the advantages of convenience,high resolution and not being shiled by ferro-magnetic,thus it is used to tunnel disease,quality testing and mechanical evaluation.And on railway running line,high-frequency surface wave can reduce boreholes or replace boreholes.At the present,the two techniques are at the primary stage of tunnel testing and evaluating,especially on cavities behind tunnel lining and precise measurement of lining thickness.In order to improve the image identifying theory and method that on-board GPR tests tunnel lining,in this paper,I mainly have studies on the following.1)All numerical modeling about ground penetrating radar testing tunnel are based on ground coupling antenna,because at present during almost GPR inspection,antenna must be very close to lining surface.While on-board GPR uses air coupling antenna to do inspection,so there are some distances between antenna and lining surface.Therefore,this paper does numerical modeling of on-board GPR testing tunnel based on air coupling antenna.Based on time finite difference method and under on-board testing condition,I do numerical modeling of cavities that are in different sizes and fillers by using GprMax software,and the results reflect the following.(1)Under the conditions that the antenna height is 1 meter and lining thickness is 0.4 meter,the minimum radius of detectable air cavity is o.4 meter,and the minimum radius of detectable water-filling cavity is 0.15 meter.(2)In numerical modeling of different antenna height,when antenna height is 1.9 meter,the minimum radius of detectable air cavity is o.6 meter.2)The experiments of GPR and High-frequency surface wave indicate that the two methods have good effect,and GPR atlas is more visual.As for extracting thickness,GPR and hig-frequency surface wave both effectively get its relevant thickness,but high-frequency surface wave is more precise.In this paper,through forward modeling of different models,and the actual measurements that on-board GPR and high-frequency surface wave made on physical model,the three testing results can verify and supplement reciprocally,so that the results can offer some references for future tunnel lining testing.