Development of Testing Methods of Thin Spray-on Liner Shear-Bond Strength

A fibre reinforced polymeric thin spray-on liner (TSL) has been under development to substitute traditional steel mesh to control skin surface in underground excavations. Its application can largely reduce the labor intensity and significantly increase the mining advance rate. In order to better evaluate the shear-bond strength of polymer liner and thereby assess its geotechnical function in strata skin reinforcement, three shear bond testing procedures were trialed. The aim of the tests was to evaluate pure shear bond strength of TSL to the various strata types without the effect of normal stress and to choose the most appropriate test for future routine testing. The first test method utilized the standard double shear testing procedure using three rock cubes of the 40mm side bonded together with 5mm thick polymer layer. The second test method included a polymer ring 5mm thick and 15mm wide coated on the periphery of each cored sample. The polymer ring was then sheared off each rock core with a steel sleeve and shear bond strength determined. The third test method was identical to the second one except that the polymer ring was partitioned into three segments to eliminate the effect of normal stress onto the substrate. The results show that to obtain the expected shear bond from the double-sided shear testing method was difficult due to the bending of the sample. The second test method was not accurate as the polymer shrinkage during curing time induced the normal stress onto the substrate and therefore increased the measured shear bond values. The results from the third test method indicate that the resin shrinkage did not affect the shear bond values significantly as the shrinkage problem was minimised by leaving three gaps between the adjacent polymer segments. The third test method was considered to be the best testing approach.