Numerical modelling of inflatable steel-tube rock bolt considering nonlinear contact behaviour

Inflatable steel-tube rock bolts are useful as they can introduce a pullout resistance immediately after installation and do not cause a loss of frictional force under groundwater existing environment. The anchoring mechanism and pullout resistance of the inflatable steel-tube has been basically explained through theoretical studies. The contact behaviour between the tube and borehole rock is essentially geometrically nonlinear and elasto-plastic, which cannot be properly considered in theoretical approaches. In this study, the contact behaviour of inflatable steel-tube rock bolts was investigated through a novel modelling based on the contact theory. A validating representative model test for an inflatable steel-tube rock bolts was performed and successfully reproduced through the contract modelling method. It is revealed that the contact behaviour was found to significantly differ from the theoretical assumptions. Parametric analyses were carried out to investigate the effect of influencing factors such as the diameter ratio, the elastic modulus and maximum installation pressure that cannot be considered in the theoretical model. It was found that the state of full inflation is the stress turning point where the general tube behaviour changes from mainly plastic to elastic. The maximum contact stress was obtained immediately before full inflation.