ABSTRACT:
Expansive steel pipe rock bolts, expanded through the application of hydraulic pressure within the steel tube, provide an instantaneous reinforcing effect through frictional grip with the rock. However, corrosion of the steel pipe is of concern to long term design. In addition, their shear strength is inferior to that of conventional massive rock bolts. In this paper, laboratory-based corrosion resistance and shear strength tests are performed and reported. New ZAM (Zn-6%,Al-3%,Mg) plated expansive rock bolts are shown to fulfill their functional requirements for over 20 years, and the shear rigidity of the expansive rock bolt is shown to be as good as any other type of rock bolt, although its shear strength is less than that of massive rock bolts.
1 INTRODUCTION
The full face grouting system for installing rock bolts is one of the more commonly adopted methods for fixing rock bolts in tunnel construction. The full face grouting system bonds the rock bolt to the rock by filling the annulus between the bolt and borehole wall with cement or resin. However, the reinforcing effect of the rock bolt is not fully reached until the grouting material sufficiently sets. Where the tunnel excavation encounters heavy water inflows or very weak ground, and early reinforcement and stiffening of the rock is required, expansive steel pipe rock bolt systems are used. The expansive steel pipe rock bolt achieves its pull out strength through the expansion of the bolt through the application of a hydraulic pressure within the steel pipe, which in turn generates a frictional contact along the entire length of the steel pipe and the borehole. The fixing effect can be expected immediately after installation, because the system does not need a fixing material that requires time to set (e.g. grout).
