Field behaviour of granular pile-anchors in expansive soils

Different innovative foundation techniques have been suggested for controlling the detrimental volume change behaviour of expansive soils. The efficacy of a recent innovation in the form of granular pile-anchors in controlling heave of expansive clay beds and improving the engineering behaviour of the ambient soil has also been reported, based on results obtained from laboratory model tests. Before suggesting granular pile-anchor foundations for installation in field practices, however, an in situ study of the behaviour of granular pile-anchors is also required as a support to the laboratory study. This paper describes an extensive field study of the behaviour of granular pile-anchor foundations of expansive clay beds. The field study was performed to study the rate of heave, reduction of heave and variation of heave with radial distance and with depth. Heave was found to be reduced by about 90% upon installation of granular pile-anchors. Final heave was reached in just about half the time required for final heave in the case of an unreinforced expansive clay bed. Improvement in the engineering behaviour of the ambient clay was studied through Proctor needle penetration tests and unconfined compression tests. It was found that a maximum increase of about 120% was observed in penetration resistance in the case of expansive clay beds reinforced with granular pile-anchors.