Reducing monopile rotation under lateral loading in sandy soils

ABSTRACT

Many structures (including transmission-line towers, bridges, tall buildings and coastal structures) are founded on piles, which are designed to transmit both vertical and horizontal forces, and resulting moments, to the load bearing strata. The design of such foundations for large lateral repeating loads (e.g. caused by wind, wave action, earthquake) and lateral earth pressures is a challenging task. This paper presents an experimental study that investigates the use of concentric rings (CRs) of small diameter (displacement) piles (SDPs) surrounding a monopile installed in dry sand, with the intention of limiting its rotation (lateral displacement) under repeated lateral loading. The test results showed that the rotation of the monopile, investigated for a range of different repeated lateral loading schemes, was reduced by 35‒75% on account of the densification of the sand achieved during installation of the SDPs and also the lateral confinement they provided to the sand located within the CRs. Significant increases to both the cyclic stiffness and load carrying resistance of the monopile under lateral loading are documented with the inclusion of the SDPs. Further experimental as well as numerical studies are necessary to validate this novel technique and to optimise the geometrical size and network pattern of the SDPs and the CRs.

KEYWORDS:

• Lateral loading
• physical modelling
• monopile
• sand
• soil reinforcement

Acknowledgements

The authors would like to thank the reviewers for many helpful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The first author gratefully acknowledges a Postgraduate Research Award from Trinity College Dublin.