Dynamic inflating characteristics of steel tube rockbolts combined with blasting ignition system

Rockbolts have been widely applied as permanent and temporary support systems to stabilize openings in tunneling and mining engineering. The presence of rockbolts improves the rock mass behavior by increasing bond strength between the rockbolt and drill hole. A friction rockbolt system, referred to as Starbolt, has been suggested to achieve instant bond strength and rapid installation of multiple rockbolts. The Starbolt system consists of a star-shaped, cold drawn steel tube and blast ignition system. The blast ignition system is able to use the thermite reaction of metal powder and detonation cords to inflate the drawn tube rapidly. In order to successfully install the star-shaped steel tube into drill holes, it is necessary to avoid the burst of the steel tube during inflation by vapor-gas production or detonation of the explosive cord. This study suggested an approach for selecting the materials of the steel tube, which is suitable for the frictional steel tube rockbolts. Dynamic direct tensile tests of five steel tube specimens were conducted using a modified split Hopkinson tension bar to investigate the dynamic failure strengths and deformation. The Johnson-Cook model was used to analyze the dynamic inflating characteristic of steel materials. It was concluded that the STKM11A material, along with the other steel materials, is selected for the material of the steel tube rockbolt. The STKM11A steel tube rockbolts were installed in the thick steel tube to perform the pullout tests. The obtained load and displacement curves of the bolts were analyzed through commercial software, which was able to incorporate the rockbolt models in order to compare with the other types of rockbolts, such as Swellex and anchor bolts.