Abstract
Nail pullout tests for the application of nail rock reinforcement were simulated using finite element analysis, and boundary conditions were representative of equivalent pullout tests. The numerical models combined a frictional nailrock contact formulation and an elastoplastic constitutive law for the rock. This approach was chosen in order to include both restricted dilation and frictional slip. Key properties were varied in order to assess their impact on pullout resistance. Cox's analytical shear lag model over predicted the apparent nail-rock contact stiffness due to inappropriate boundary conditions. The numerical model managed to capture the qualitative response of the nail during pullout, though absolute values of pull force were somewhat overestimated. The highest pullout forces were obtained when the strength of the rock was fully mobilized before slip occured. Nail-rock friction and initial contact stress were therefore the most important determinants of maximum pullout force. Radial specimen confinement and rock dilation did greatly influence maximum pullout force, but were more important in increasing nail displacement at maximum pullout force due to their effect on contact hardening.
