Improvement of Rock Bolt Profiles using Analytical and Numerical Methods
The anchorage capacity of fully grouted bolts has been studied for many years, however the bolt rib profile and its effect on bolt shear resistance is poorly understood. A new development in calculating load transfer capacity between two rib profiles of varying geometries is discussed. The derived mathematical equations presented calculate the stress distribution adjacent to the fully grouted bolt and bolt pull out force needed to fail the resin. The Fast Lagrangian Analysis Continua (FLAC) program was used to verify the calculations of stress within the resin. The novel idea of coupling the bolt geometry with the calculated stress provides another powerful tool to investigate the bolt profile configuration and its effects on the load transfer mechanism for the benefit of the mining industry.
Verification of the Analytical Model for Fully Grouted Rock Bolts Based on Pull-out Test (Case Study: Tabas Coal Mine)
Abstract A new analytical approach able to predict the mechanical behavior of rock bolts subjected to pull-out tests was proposed in this paper. Input parameters of such approach are: rib profile shape, height, width, angle of wrap and spacing, axial bolt pull-out force, and material properties. As for the analytical part, the basis of the new analytical solution for the prediction of the load displacement curve was developed. Derived mathematical equations enable calculations of grout displacement in elastic and elasto-plastic behaviour. In the experimental part, four examined bolts in situ pull-out tests were compared with the predictions of the new analytical approach, and this comparison led to the validation of this approach.
New approach to study load transfer mechanisms of fully grouted bolts
The load transfer mechanisms across the rock/resin/bolt interfaces are governed by the surface properties of the bolt. Although there are various bolt surface configurations available in the market, very little work is reported on die bolt/resin interface failure mechanism. This paper examines the behaviour of bolt surface roughness under constant normal stiffness conditions which is considered as being a realistic way of evaluating bolt surface roughness. To study the shear behaviour of bolt/resin interface, laboratory tests were conducted on the bolt surfaces of two most popular types currently in use in Australian coal mines, at an initial normal stress of 0.1 to 7.5 MPa. The study snowed different shearing characteristics of both bolt types under similar loading environment. Field investigations carried out in a local coal mine produced similar results as obtained from the laboratory testing.