Numerical study on failure and instability of slender rock columns: Synergistic effects of lateral pressure, height-to-width ratio, and material strength

Columnar jointed rock mass (CJRM) combines and mosaic of slender rock columns with different height-to-width ( H / W ) ratios. Revealing the correlation of the mechanical behavior of individual rock columns with internal factors ( H / W ratio and material strength) and external factor (lateral pressure) is fundamental to understanding the deterioration of CJRM. We adopt a numerical scheme that combines a statistical meso-damage constitutive model with a finite element formulation based on finite deformation, which can simultaneously consider both material failure and structural instability of the rock columns. Compression tests of rock columns with different H / W ratios and material strengths under varying lateral pressures were conducted to analyze the macro-strength features and failure modes. The numerical results show that increasing the material strength can improve the macro-strength, while the effect of H / W ratio is the opposite. Both increases can promote the conversion of failure modes, and the evolution process is as follows: material failure-induced structural instability → synergy and competition between material failure and structural instability → structural instability-induced material failure. Notably, for the last failure mode, an increase in lateral pressure decreases the macro-strength of the rock column and heightens its instability risk. This finding provides new insights into the response of rocks with different H / W ratios under lateral pressure, extending beyond traditional material-based perspectives. According to the position of the failure mode demarcation line, the failure mode of the rock column can be regulated. • Studying the mechanical behavior of individual rock columns with internal and external factors is fundamental to understanding the deterioration of columnar jointed rock mass. • A unified finite element numerical scheme is adopted based on statistical meso-damage constitutive mode and finite deformation. • The macro-strength and failure modes of slender rock columns under different height-to-width ratios, material strengths, and lateral pressures are investigated. • Increased lateral pressure can decrease macro-strength and heighten instability risk for rock columns of structural instability-dominated mode.