Stability and bifurcation in reinforced boreholes

Rock nailing of a borehole is considered as a means to reinforce the rock and increase its borehole failure strength. The technique is modeled using Cox’s original shear-lag method. In the continuum sense, nail reinforcement is viewed as a body force that acts as a confinement. The finite element formulation of the reinforced elastoplastic borehole is presented and results from an elastic analysis with stiff nails are compared against existing analytical solutions for elastic rocks with rigid nails. The formulation couples the mechanical behavior of the rock with the nail-rock contact law equation that must be solved in a coupled manner. The bifurcation condition for borehole failure in a Cosserat elastoplastic rock is subsequently extended to a reinforced borehole for stability analysis.