Displacement Pile Group Efficiency Assessment for a Technically and Economically Sustainable Design of Pile Groups in Non-Cohesive Soil-Paper

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The study evaluates how driven displacement piles interact in groups in medium-dense, non-cohesive soil. Researchers tested a 3 × 3 pile group with spacing of three pile diameters (3D) in a calibration chamber and compared it with an isolated pile under equivalent soil and loading conditions. Strain gauges measured shaft and base resistance in center, edge, and corner piles; pile-head forces and settlements were also recorded. Dynamic PANDA soundings assessed soil changes caused by installation.<br /><br />At a settlement of 0.1D, the group’s efficiency was 1.24, meaning its total resistance was 24% greater than that of nine isolated piles. Efficiency was 1.08 at the serviceability settlement of 0.025D. Each group pile outperformed the single pile at the ultimate-limit-state settlement, but responses varied by position: the center pile had the greatest resistance, followed by the corner and edge piles. Increased shaft resistance was the main contributor to the center and corner piles’ performance. For the center pile, shaft and base efficiencies were 1.92 and 1.20, respectively.<br /><br />Installation effects helped explain these results. Driving energy and PANDA soundings indicated that soil densified within the group, particularly in areas influenced by multiple neighboring piles. The soundings showed substantially increased cone resistance inside the group, while measurements farther away remained close to initial values.<br /><br />The findings broadly agree with earlier model studies and suggest that installation-induced densification and pile interaction can enhance the capacity of displacement pile groups. The measured group and individual-pile efficiencies may support more economical and sustainable design. However, further testing is needed to validate the proposed explanation for differences between edge and corner piles.

Keywords

displacement pile group

pile interaction

medium-dense soil

shaft resistance

base resistance

group efficiency

installation effects

soil densification

PANDA soundings

calibration chamber