A total of 162 three-dimensional numerical models were simulated to evaluate the stabilization of a two-layer undrained clay slope using a row of micropiles. The slope had an inclination angle of 26.6° (2H:1V), with soft clay (su = 30 kPa) overlying stiff clay (su = 150 kPa). The inclination of the interface at the base of the soft layer (α) varied from 0° to 20°, corresponding to α/θ ratios of 0–0.75. Six dimensionless micropile spacings (s/DMP) ranging from 2 to 12 were considered. The numerical models incorporated the two-layer slope, micropile row, soil–micropile interface, and interlayer interface. Micropile row location, s/DMP, and α/θ were varied to quantify their effects on slope displacement and stabilization performance. The results showed that placing the micropile row at the slope crest with s/DMP = 4.0 provided the most favorable stabilization response, reducing lateral displacement by 20.52%. A three-dimensional polynomial surface was developed to relate s/DMP and α/θ to slope displacement for conditions with and without surface loading at the slope crest. The proposed relationship achieved a coefficient of determination (COD) of 0.98 and provided an accurate representation of the numerical results.
