In this study, rockbolts made of polypropylene random copolymer (PP-R) material were assessed as an alternative to steel split sets in a series of experimental studies that included both laboratory and field-scale tests. PP-R tubes and typical steel split sets were compared by means of static loading (pull and shear), impact loading, corrosion, diametric compression, insertion into drill-holes, and creep tests. Despite the advantages of PP-R; being a noncorrosive material, being shaped by the roughness of drill-hole surfaces, and having ideal support reactions because of high resistance to crack propagation, strain relaxation was found to be a considerable problem with the PP-R tubes inserted into the drill-holes. The results suggest that further work should be undertaken to develop new bolts using PP-R tubes instead of steel split sets.

INTRODUCTION

Split set rockbolts are popular, especially in the mining industry, as a result of their advantages such as practical application, ability to start carrying load without waiting for curing of the grout materials, and good load-bearing capacity despite high deformation. However, underground water can substantially affect steel materials and decrease their load-bearing capacity, especially with long contact times and acidic groundwater conditions (Hoek, 2006; Komurlu and Kesimal, 2015; Hassel and Villaescusa, 2005). The two main factors affecting the frictional load-bearing capacity of the split sets are the normal stress on the drill-hole surface and the coefficient of friction at the contact interface between the bolt and drillhole surfaces (Li, Stjern, and Myrvang, 2014; Heerden 2007; Qingliang et al., 2013; Perras, Diederichs, and Besaw, 2014). Although a rigid rockbolt material is advantageous as the normal stress on the friction surface is supplied due to the decrease in the slit width and diameter of the bolt inserted into the drillhole, a rigid surface prevents the bolt from being shaped by the roughness of the drill-hole surface, which decreases the coefficient of friction. Rockbolt loading mechanisms resulting from rock mass deformation can be divided into axial and shear loading types. The rockbolts are exposed to both axial and shear loading as the rock mass deforms. The frictional load-bearing capacity plays an important role in changing the support reactions under both shear loading and the axial loading conditions (Pellet and Egger, 1996; Srivastava and Singh, 2014; Oreste and Cravero, 2008; Ranjbarnia, Fahimifar, and Oreste, 2016; Garga and Wang 1993).

This content is only available via PDF.
You can access this article if you purchase or spend a download.