The linning concrete of Nikkureyama Tunnel at Jo-Shin-Etsu Highway has been reinforced by steel fiber concrete or carbon fiber sheets because of deformations of the tunnel at 400m of expanded mud stone area. However, many cracks were found at surfaces of steel fiber lining concrete near the carbon fiber sheets area. In this paper, the result of the investigation of cracks inside the lining concrete blinded by the carbon fiber sheets by the ultrasonic reflection sounding system are described.
