The influence of a single pile on its vertical uplift is tested, and a numerical calculation is conducted through a graded loading method. This study is aimed at investigating the influence of the pile side resistance on soil mass and analyzing the influence of the sensitivity of the soil and pile parameters to lateral resistance. Results show that the influence of the lateral resistance of the pile to the soil in forming silt clay is the first linear attenuation with horizontal distance trend. On the basis of the experiment, the concept of effect radius is presented. The change in pile body and soil parameters is beneficial to increasing the effect radius, thereby increasing the resistance of the pile side and influencing the mobilization range of the micropiles to the surrounding soil. Poisson’s ratio is the most sensitive to the change in the effect radius, followed by the change in the length of the pile. The sensitivity of the remaining parameters to the effect radius is from large to small.