Ultimate pullout resistance of groups of vertical anchors

Abstract

A theoretical investigation on the group action of vertical screw anchors installed in sands is presented. An experimentally observed rupture surface for single anchors was employed to establish the shape of the rupture surface for groups of anchors. A theory was developed to predict the uplift capacity of groups of anchors with different configurations utilizing the theoretical model described in a companion paper. To calculate the uplift capacity, weight and shear factors for shallow and deep groups of anchors are established. These factors are presented as functions of the angle of shearing resistance of the sand, relative depth ratio of an individual anchor within the group, and (or) the ratio between the height of embedded failure bulb and anchor diameter. The effect of overconsolidation due to the compaction technique used in placing the sand was incorporated in the theoretical calculations of uplift capacity. Comparison between theoretical and experimental results shows good agreement in the case of loose and medium sands and satisfactory agreement in the case of dense sand. An empirical equation, based on theory and experimental data, is proposed to mathematically quantify the effect of densification-on the angle of shearing resistance of the sand. Key words : anchors, group action, limit equilibrium, overconsolidation ratio, theoretical analysis, uplift capacity.