Rock bolts are essential supports in NATM tunnels and underground mines. A conventional mechanical rock bolt is usually a passive support that is activated by rock mass movement, and then stress equilibrium is achieved passively. The expanding type of the new bolt, similar to swellex bolt, was investigated to safely compress the rock mass and result in comfortable and strong interlocking around rock mass as a active mechanical supporter.

In this study, the dynamic expansion rock bolt which is able to install rapidly in the drilled hole and more actively to be pressed around rock mass has been suggested. It also shows the basic structure and mechanical performance of the suggested rock bolt. Laboratory scale pull-out tests of the rock bolt were performed to evaluate the pull-out load bearing capacity of rock bolt. These revealed that the ultimate pull-out load reached around 10 kN and remained constant during a long displacement, even when the rock bolt was installed in a steel pipe instead of a hole drilled in rock. Also, in-situ pullout test in hard rock, the suggested bolt showed the higher loading value than swellex bolt as a kind of fully frictional bolt, and then it was proved that the active mechanical interlocking was really possible.

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