Evaluation of an Active Control, Constant Normal Stiffness Apparatus for Improved Evaluation of Shaft Friction in Micropiles in the Offshore Environment

Document Type

Conference Proceeding

Date of Original Version

1-1-2025

Abstract

There is increasing interest in using micropiles as a foundation type for floating offshore wind farms in deep water. Contrary to onshore projects, proof load testing of micropiles in the offshore environment is extremely difficult if even feasible, and as a result, better capacity prediction approaches are required. A key improvement would be incorporation of constant normal stiffness boundary conditions in the evaluation of shaft resistance of small-diameter grouted micropiles. The objective of this study is to present the results of a newly developed, active control system for performing constant normal stiffness tests on sand. A laboratory testing program of monotonic CNS tests on Monterey sand was performed in which relative density, soil spring stiffness, and initial normal effective stress were varied. The ability of the control system to maintain constant normal stiffness during shear was found to be excellent, and test results on both dilative and contractive samples demonstrated consistent trends of shear strength and changes in both shear band thickness and normal effective stress.

Publication Title, e.g., Journal

Geotechnical Special Publication

Volume

2025-March

Issue

GSP 367

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