Experimental Investigation of Installation and Pullout of Dynamically Penetrating Anchors in Clay and Silt
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 140, Issue 7
Abstract
This paper reports the results from a series of model tests undertaken to provide insight into the behavior of torpedo anchors during dynamic installation and pullout in lightly overconsolidated kaolin clay and calcareous silt. The tests were carried out in a drum centrifuge at 200g, varying the drop height (hence the impact velocity) and the time delay for consolidation before pullout. The pullout angle at the mudline was also varied to encompass various mooring systems, including catenary (0°), taut leg (45°), and tension leg (). Two geometries of torpedo anchors were explored, varying the fin and tip geometry. The results demonstrated that the anchor embedment depth increased as the drop height (and hence the impact velocity) increased and the soil undrained shear strength decreased. In stronger silt, the cavity above the installing anchor remained open, whereas in soft clay, it was fully backfilled and replenished. The corresponding anchor embedment depth was also about 0.63 times compared with that in clay. The anchor holding capacity was found to increase with increasing postinstallation consolidation time, depth of embedment, and soil undrained shear strength and with reducing pullout angle at the mudline. The anchor rotation during pullout, and hence the pullout distance for attaining the maximum capacity, reduced as the load inclination at the mudline increased. The fin geometry (rectangular or elliptical) and tip geometry (conical or ellipsoid) were shown to have remarkable influence on the holding capacity, with rectangular fins and conical tip proving to be more effective. The negligible adherence of silt along the anchor sides and the presence of semiliquid material around the extracting anchor resulted in a significantly (34–47%) lower holding capacity in the calcareous silt, with significantly higher intact undrained shear strength.
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Acknowledgments
The research presented here was undertaken with support from the University of Western Australia through the ECM Research Development Grant (ECM RDG10300048). M. S. Hossain is an ARC Postdoctoral Fellow (APDI) and is supported by the ARC Linkage Project LP110100174. The work forms part of the activities of the Centre for Offshore Foundation Systems (COFS), currently supported as a node of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering, through Centre of Excellence funding from the State Government of Western Australia and in partnership with the Lloyd’s Register Foundation. This support is gratefully acknowledged, as is the assistance of the drum centrifuge technician, Mr. Bart Thompson.
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Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 140 • Issue 7 • July 2014
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Mar 10, 2013
Accepted: Jan 31, 2014
Published online: Mar 20, 2014
Published in print: Jul 1, 2014
Discussion open until: Aug 20, 2014
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