Nondestructive testing for support quality of tunnel

摘要

A tunnel in Chengde collapsed several times and cracks existed in the second lining. Using non-destructive testing equipment, tunnel support was detected to find out the hidden trouble early. In the section of K16+890～K16+950, the quality of tunnel support was assessed, with GPR and anchor measuring apparatus. In the tunnel, the thickness of composite lining was 25cm, and the second lining was 38cm, both of which met the design requirements. Positive peak method was selected to locate on I beam. The average longitude space of I beam was 127cm, while the design value is 120cm. Many rock bolts was lacked at the right crown. Moreover, the bolts in the haunch did not kept in diamond layout, close to I beam. Through analyzing waveforms of impact-echo, the number of qualified bolts only made up 74 per cent of the total bolts. The large space of I beam led to the lack of holding power. Meanwhile, the disqualified bolts limit the coordination deformation between surrounding rock and support. All the support defects led to tunnel collapse. These tests results demonstrate that NDTcan be used to mitigate the risks of tunnel construction.