The elasto-plastic analysis of normal stress increment and stress paths for the bore wall of rock-socketed pile

As the relative displacement of the pile-rock interface increases, the sliding and mutual squeezing between asperities of the pile-rock interface causes the normal stress increases by Δσ_n with the normal displacement. All prevalent theoretical methods use the elastic solution of cylindrical cavity expansion in an infinite medium to calculate the normal stress increment Δσ_n during an increase in the relative displacement of the pile-rock interface. To further optimize the calculation method for the normal stress increment Δσ_n of the bore wall of the rock-socketed pile, this study conducts an elasto-plastic analysis of the stress and displacement fields during expansion using cavity expansion theory and the Hoek-Brown failure criterion. Based on the obtained elasto-plastic solution, some validation cases are represented to illustrate the difference between the results of Δσ_n due to both elastic and elasto-plastic solutions. When the normal displacement is greater than the critical normal displacement and the rock of the bore wall yields, the elastic method overestimates the Δσ_n and shear strength at the pile-rock interface, which renders the design unsafe. Three modifications are then proposed to calculate the shear strength at the pile-rock interface. After that, parametric studies are conducted to examine the effects of geometric and rock-related parameters on the Δσ_n of the bore wall. Finally, the radial and tangential stress paths and possible crack formation of rock of the bore wall during expansion are discussed.