Performance of a New Driven Battered Micropiles System in Sand-Paper

Paper

Pdf Summary

The study evaluates a lightweight, concrete-free footing system made of a steel cap and inclined, driven micropiles. Installed with small jackhammers and minimal soil disturbance, the system is intended for sites where heavy piling equipment or excavation is impractical.<br /><br />Researchers conducted eight static compression and pull-out tests on four footing configurations in medium-dense sand at Fingal, Australia. The configurations varied in cap size, number of micropiles, and embedment depth. A plate load test provided a comparison with a conventional shallow foundation.<br /><br />Ultimate compressive capacities ranged from 51 to 71 kN, while pull-out capacities ranged from 12 to 20 kN. The footings generally gained capacity with greater embedment and more micropiles, although one configuration showed no improvement, suggesting a negative group effect. Pull-out capacity was only about 24–28% of bearing capacity. The micropile footings also carried substantially more load than the equivalent shallow foundation and showed increased stiffness.<br /><br />Conventional design methods based on individual pile shaft friction, toe resistance, and lateral pressure predicted pull-out capacity reasonably well but underestimated bearing capacity. The authors attribute the additional bearing resistance to reinforcement, soil arching, or block action among the battered micropiles—effects not captured by current design approaches. They recommend further instrumented field tests and validated three-dimensional modelling to clarify these mechanisms and quantify group effects.<br /><br />Overall, the tested system appears promising as an alternative to shallow foundations for light structures in sand. However, design methods should account for the reinforcing interaction between the micropiles and enclosed soil, as well as possible reductions in capacity when piles act in groups.

Keywords

micropile footing

steel cap

inclined micropiles

lightweight foundation

pull-out capacity

bearing capacity

medium-dense sand

group effect

soil arching

shallow foundation alternative