Efficiency Formula for Pile Groups

A new formula is proposed to evaluate the efficiency of axially loaded pile groups. The derivation of the formula is based on the premise that the group effect can be taken into consideration only for the load component carried by the pile shafts. Similar to other group efficiency formulas, the proposed formula relates the load capacity of a pile group to the summation of the capacities of the individual piles through a group‐efficiency parameter. However, earlier group‐efficiency formulas consider only the planar geometry of the pile group in determining the group efficiency. In contrast, the proposed formula accounts for the three‐dimensional geometry of the pile group and the strength and type of the embedding soil. The formula is applicable for pile groups in cohesive and cohensionless soils. Time‐dependent changes of the soil strength can be incorporated in computing short‐term and long‐term efficiencies. A set of design charts based on the proposed formula was developed for the analysis of pile groups with different geometries and soil conditions.