Partially decoupling and collar bonding of the encapsulated rebar rockbolts to improve their performance in seismic prone deep underground excavations

Rockbolt is widely employed all over the world as an effective ground reinforcement element in order to secure the underground workplaces. Ordinary encapsulated rebar or rebar rockbolt is most popular and commonly used as reinforcement in a ground support system because of its accessibility, cost effectiveness and easy practicability. Reinforcement elements in a seismic condition such as rock burst have to dissipate the energy release of the dynamic impact via their deformation and ultimate load capacity,knowing that the former is more important. In other words, achieving early stiff behaviour along with large deformation capacity in rockbolts are the goals for new development in rock reinforcement.Yielding rockbolts are expensive while some of them have large deformation capability with low ultimate load capacity. In this paper, modifications were made on encapsulation of rebar rockbolts to utilise it effectively as a yielding reinforcement in seismic conditions. Applying a sufficient decoupled length in the shank of rebar rockbolts which industry has regularly been using to control the bulking of the stress fractured ground, improves the deformation capacity of the bolt. Additionally, leaving a collar bonding underneath of the bearing pad and plate removes the weaknesses of the head anchorage of rockbolt.Therefore the dynamic performance of the bolt is improved by these easily applicable modifications.The behaviour and performance of encapsulated rockbolts have been discussed first, then the effects of modifications are illustrated. The proposed modification of the rebars is not only cost effective but also easy to apply in the field and improves the performance of reinforcements in seismic prone zones.