Investigation of bond capacity of fully grouted bars under different boundary conditions

Abstract

To maintain the stability of jointed rock masses in geomechanical projects such as tunnels, foundations and slopes, installation of fully grouted bars (or rock bolts) with Portland cement has proven to be very effective. Load-bearing capacity or bond capacity of such a reinforcing element is a key parameter influencing reinforcement pattern design. The boundary condition controlled by the rock mass quality affects the mobilised bond capacity in the bar. There is abundant evidence where a successful reinforcing system in a good quality rock does not perform successfully in a low quality environment. To study this effect, a modified tri-axial Hoek cell was used to facilitate application of a ‘constant radial confining pressure’ to different types of grouted bolts while pulling it axially. To pull the bolts under ‘constant radial stiffness’ condition, a series of confining pipes (made from steel, aluminium and PVC) was used as a mould to cast grouted bolts in. During tests, axial load and displacement of the bolt was recorded and the radial dilation of the grout in the first series of tests was also measured and stored in a computer using a data acquisition system. In this paper, details of the laboratory test results are presented and discussed.