A pioneer in-situ investigation on the bearing capacity and failure causes of real scale fully grouted rockbolts

The actual study presents a thorough investigation on the bearing capacity and failure causes of fully grouted rockbolts. For this purpose, 144 real scale in-situ rockbolt pull-out tests were conducted on Fan River hydropower plant's power tunnels in Rreshen region, Albania. The pull-out tests were performed on full grouted rockbolts of two types: SN-Stor Norfors and PG-Post Grouted, two different bolt diameters: 22 and 25 mm, three bolt lengths: 3, 4 and 6 m and three inclination groups such as: horizontal, 0-30 degrees and 30-90 degrees. The results showed that, the SN bolts have lower bearing capacity and smaller displacement compared to PG bolts. On the other hand, the rockbolts' bond strength and displacement decrease as the installation angle to the horizontal increases. This is due to the difficulties faced in filling the drilled hole with grout as the inclination opposes the gravitational direction. In their entirety the results indicate that grouting quality is a crucial factor on the bearing capacity of fully grouted rockbolts and the system failure is mainly related to the shear failure along the bolt-grout or grout-rock interfaces.