Failure mechanism of resin anchored rebar in potash

Abstract

The use of reinforcing bar (rebar) anchored with resin is a common method of rock support in both hard and soft rock mining. The average bond strength, or the load that the support can sustain for a linear length of bond to the rock, is typically determined through a series of pull tests. The average value of bond strength varies widely, since it is dependent on in-situ rock properties and environment. It is an important value because it allows mine engineers to select the appropriate length and pattern spacing of installation for the support. When a stiff support, like resin-anchored rebar, is placed in a weak, soft material, such as potash, the average bond strength tends to be lower in magnitude than for a typical hard rock installation.

This research was primarily aimed at determining the failure mechanism, in soft rock applications, by which the support loses adhesion and begins to fail by sliding. Results of field pull testing determined that the resin-rock bond strength was the limiting factor controlling when adhesion loss occurred. This study investigated how the bond strength may vary given a number of variables typically found in a potash mine environment. Results reported from testing did not indicate variation in the bond strength of resin anchored rebar, significant for mining applications, given changes in resin cure time, vicinity to active mining areas, or the rock type to which the resin was adjacent.

Using the results of laboratory and field testing, an equation was developed to estimate load on in-situ resin anchored rebar given deformation measurements taken from the field. This equation will help determine safe limits for fracture separations opening in the backs of potash drifts. Investigating the behaviour of resin anchored rebar in potash may lead to methods to improve bond strength and calculation of factors of safety for patterned ground support.