Self drilling hollow bar is used extensively for the stabilization of tunnel portals. The ability of self drilling hollow bar to accommodate a range of different ground conditions make it to be a popular choice for tunneling works. Self drilling anchor system mainly consists of hollow bar, drill bit, nut, plate, coupler and spacer, which has the characteristic of integrating drilling, grouting and anchoring as a whole. Hollow bar plays an important role in the system. Hollow bar has a hollow structure. Compared with the solid bar, hollow bar has higher stiffness in the same cross section. Hollow bar matched with drill bit can connect with rock drill, drilling holes by rotary drilling or impact rotary drilling. It plays the role of a drill rod. The inner hole of hollow bar can be used for grouting instead of the grouting pipe of solid bar. Hollow bar is left into the hole after drilling and grouting, playing the role of reinforcement and bearing most of the load. Therefore, hollow bar has three functions drill rod, drill pipe and reinforcement bar.
