In recent years, NATM(New Austrian Tunneling Method) has been increasingly used for shallow tunnels and poor ground in JAPAN.
Friction anchored bolts using normal steel pipes are used in areas where there is a large amount of water inflow, and when it is desirable to obtain reinforcement effects of support quickly after excavation. However, it is difficult to obtain sufficient bond strength between the bolts and the ground due to factors such as rough borehole walls.
In order to improve this situation, the authors developed high-friction anchored bolts using checkered steel pipes. This new method adds protruding striations to the surface of steel pipes to improve the bond effect of the pipes.
This paper describes the overview of newly developed bolts, and the results of pull-out tests conducted in the laboratory and at the actual tunnel site, the verification results of the reinforcement mechanism using 3D finite different method, and examples of application in the field.