Full scale lab testing for the determination of rock bolt contribution to reinforced joint shear strength

Full scale lab testing for the determination of rock bolt contribution to reinforced joint shear strength

S. Maiolino¹, F.L. Pellet²

¹ CEREMA/DTERCE/DLL-ERA29, Bron, France ([e-mail])

² INSA – University of Lyon, Villeurbanne, France ([e-mail])

ABSTRACT:

The determination of rock bolt contribution to reinforced joint shear strength is still a challenge, especially for assessing reinforced rock mass stability. For this purpose, several experimental studies have been performed during the last decades mostly on reduced scale rock joint and bolt specimens. However, to accurately assess the rock bolt contribution, scale effect has to be accounted for. For this reason full scale lab tests have been performed as an alternative to in situ test for which boundary conditions are more difficult to control.

30 shear tests were carried out with a large scale shear box (1.5 m x 1.0 m). The actuators capacity is 5 MN for the shearing force and 4.0 MN for the normal force applied to the joint. Horizontal and vertical displacements are measured with 6 LVDT sensors set up in different locations of the specimen. Different rock bolt diameters and various rock bolts inclination with respect to the shear plane were tested. In some case several bolts were installed on the same joint with different inclinations. Rock bolts were also instrumented with strain gauges in order to know the stress distribution along the bolt axis.

Experimental results were satisfactorily compared with an analytical model which is able to compute the contribution of the rock bolt to the shear strength of the joint as well the associated displacement of the joint. These conclusions allows us to establish some guidelines to help the designer of reinforced rock engineering structures, such as slope or underground openings, to precise the optimum installation of rock bolts.

KEY WORDS: rock mass reinforcement, rock slope stability,

References:

F.L. Pellet, M. Keshavarz, M. Boulon (2013), Influence of humidity conditions on shear strength of clay rock discontinuities, Engineering Geology, vol 157, pp 33-38.

F. Vallier, Y. Mitani, M. Boulon, T. Esaki, F. Pellet (2010), A new shear model for accounting scale effect in rock joints behaviour, Rock Mechanics and Rock Engineering, vol. 43, no 5, pp 581-595.

F. Pellet, P. Egger (1996), Analytical model for the mechanical behavior of bolted rock joints subjected to shearing, Rock Mechanics and Rock Engineering, vol. 29, no 2, pp 73-97.

F. Pellet, P. Egger, F. Descoeudres (1995), A method for the design of a bolting system for rock slopes, Proceedings of the 8th International Congress on Rock Mechanics, Tokyo - Japan, pp 409 – 412.



Figure - Large scale shear box



Figure Bolt contribution, C, versus shear displacements for different bolt's diameter, d: Comparison of experimental data to analytical results.