Analytical Study of the Behavior of Rock Bolts

ABSTRACT: Three analytical models for rock bolts have been developed: one for bolts subjected to a pull load in pullout tests, one for bolts installed in uniformly deformed rock masses, and one for bolts subjected to the opening of individual rock joints. Development of the models is based on the description of the mechanical coupling at the bolt interface. For rock bolts in pullout tests, the shear stress of the interface attenuates exponentially with increasing distance from the loading point when the deformation is compatible across the interface. Decoupling may start first at the loading point when the applied load is large enough and then propagate towards the far end of the bolt with a further increase in the applied load. For rock bolts installed in uniformly deformed rocks, the loading process of the bolts due to rock deformation has been taken into account in developing the model. Model simulations have confirmed the concept that a bolt in situ has a pick-up length, an anchor length and a neutral point. It is revealed also that the face plate plays a significant role in enhancing the reinforcement effect. In jointed rock masses, several axial stress peaks may occur along the bolt because of the opening of rock joints intersecting the bolt.