Axial load testing of helical pile groups in glaciolacustrine clay

Abstract

The behaviour of helical pile groups has not previously been experimentally investigated through field testing. In the present study, field compressive load tests of 2 × 2 helical pile groups and single piles were conducted in a glaciolacustrine clay in Edmonton, Canada. The group pile spacing, interhelix spacing, and soil setup time were varied. Piezometers were used to measure the excess pore pressure (ue) response to pile installation. Selected groups contained a strain gauge instrumented pile that was used to estimate the pile load transfer and failure mechanism. Group performance was evaluated by estimating the group efficiencies and settlement ratios. Results show that the group interaction of small-diameter helical piles was lower than that of conventional pile groups. The short-term performance of groups was significantly reduced by ue, and groups with smaller group pile spacing had a greater reduction in short-term performance. Instrumented grouped piles and one single pile, both having an interhelix spacing ratio of 5, exhibited individual bearing failure. The measured group capacities and load distributions indicated that individual pile failure occurred, as opposed to block failure.