Laboratory Tests on Thin Spray-On Liner Penetrated Rock Joints in Direct Shear

Thin spray-on liners (TSLs) are becoming more attractive as an effective mine roadway support medium in underground mines. The benefits of TSLs in stabilising the rock surface for underground mining roadways have been studied by some researchers (Tannant 2001; Stacey and Yu 2004; Mason and Stacey 2008; Ozturk 2012a; Nemcik et al. 2013). The fast setting TSLs can almost immediately support the excavations once applied onto the rock substrate. Stacey (2001) described some support mechanisms of TSLs and proposed the theory of ‘‘promotion of block interlock’’. The aim of this mechanism is mainly to maintain the rock mass in a stable condition by keeping the broken blocks in place and minimising block rotation. Ozturk and Tannant (2011) argued that rather than the mechanical interlocking, chemical reaction between the rock grain matrix and the liner material is more important to get higher adhesive strength. Stacey and Yu (2004) stated that the TSL penetration into the joints and fractures within the rock mass plays an important role in the supporting system. The depth of penetration of a TSL depends on its consistency, the sprayed pressure and the openness and orientation of the blasting-induced joints. For the less viscous TSLs, the penetration into the joints will be much greater. Mason and Stacey (2008) used the analytical method to study the effect of the penetration of TSLs into joints and fractures. The results revealed that the elastic modulus of fractured rock penetrated by liner material is the same as the elastic modulus of the rock without fractures. Fowkes et al. (2008) studied a crack repaired with TSLs and the results indicated that the crack filled with TSL material can prevent crack propagation and consequent failure. Ozturk (2012b) showed that edge crack propagation is the main failure mechanism during pull-off tests, although Fowkes et al. (2008) argued that cavitation being a cohesive failure of TSL resulting from growth and coalescence of micro-voids is likely the rupture mechanism of TSL adhesion tests. To study the shear behaviour of TSL penetrated rock joints, the direct shear test was adopted. The effects of surface roughness, penetrated thickness to asperity height ratio, shear rate, and normal load on the shear behaviour of TSL penetrated rock joints were investigated in this study.