Laboratory studies of the response of shallow foundations have previously considered only planar loading. This paper describes experimental work carried out using a loading device that applies general loading onto model shallow foundations. The loading, involving all six degrees of freedom [vertical (V), horizontal (H2, H3), torsion (Q) and overturning moment (M2, M3)], has been applied to a 150 mm diameter circular flat rough foundation on a loose dry silica sand. Aspects of the loading rig design are briefly described, but the main focus is the presentation of the experimental results. These provide evidence for the generalisation of existing work-hardening plasticity models from planar loading to general loading conditions. This evidence is used to extend an existing numerical model to the six-degree-of-freedom case, and the simulation results are compared with the experimental results.

Investigating six-degree-of-freedom loading of shallow foundations on sand - Discussion

Effect of monopile foundation modeling on the structural response of a 5-MW offshore wind turbine tower

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The engineering of foundations / Rodrigo Salgado

Bearing capacity of composite bucket foundations for offshore wind turbines in silty sand

This paper performed centrifuge load tests of a tripod bucket foundation preliminarily designed as a supporting system of wind turbines and compared the results to those obtained from a test of a monopod bucket foundation. The tripod foundation prototype studied in this study has three bucket caissons, each of which is 6.5 m in diameter and 8.0 m in length. The center-to-center distance between the buckets was 26.9 m. The site is composed of an 11-m thick layer of dense silty sand overlying a thick sandy silt layer. The horizontal load was applied at a height of 33 m from the seabed floor according to the design load condition, and the vertical load was simulated by the self-weight of the model. The moment-rotation angle curves for the tripod foundations were compared with that of the monopod bucket foundation. The moment-rotation curve of the tripod was nearly bilinear, whereas that of the monopod showed a gradual decrease in slope. The yield moment for the tripod foundation was half that of the monopod, but the rotation angle for the yield moment was only 20% that of the monopod. The behavior of the tripod foundation under a cyclic load with respect to the accumulated plastic deformation has also been examined in this study. When the resultant moment of cyclic loading was smaller than the monotonic yield moment, negligible accumulated plastic deformation was observed for both one-way and two-way loading. However, when the resultant moment was higher than the monotonic yield moment, significant cumulated deformation resulted.

Investigation of Monotonic and Cyclic Behavior of Tripod Suction Bucket Foundations for Offshore Wind Towers Using Centrifuge Modeling

Bearing capacity factor Nγ and shape factor were studied for rigid strip and circular footings with a rough base on sand by numerical modelling considering the effect of dilation angle. The numerical model was developed with an explicit finite difference code. Loading procedures and interpretation methods were devised in order to shorten the running time while eliminating the exaggeration of the reaction caused by the explicit scheme. Using the Mohr-Coulomb plasticity model with associated ( ) and nonassociated ( ) flow-rules, the bearing capacity factor  was evaluated for various combinations of internal friction angles and dilation angles. Bearing capacity factor decreased as the dilation angle was reduced from the associated condition. An equation applicable to typical sands was proposed to evaluate the relative bearing capacity for the nonassociated condition compared to the associated condition on which most bearing capacity factor equations are based. The shape factor for the circular footing varied substantially when the plane-strain effect was taken into account for the strip footing. The numerical results of this study showed closer trends with the previous experimental results when the internal friction angle was increased for the strip footing. Discussions are made on the reason that previous equations for the shape factor give different results and recommendations are made for the appropriate design shape factor.

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Numerical Studies on Bearing Capacity Factor N γ and Shape Factor of Strip and Circular Footings on Sand According to Dilatancy Angle

Penetration resistance of bucket foundations with skirt wall in the silty sand of the western coast of Korea was analyzed by centrifuge modelling. The penetration resistance is induced when the bucket foundations are jacked into the soil without suction, and is directly related to the self-weight penetration depth. The procedure by Houlsby and Byrne (2005), which takes into account the effect of stress increase by frictional resistance of skirt wall, was utilized to generate the penetration resistance similar to the experimental results. This paper describes the methods by which major parameters such as lateral earth pressure coefficient and friction angle between the skirt wall and the soil are evaluated. The effect of changes in these parameters on the predictions is analyzed. Also, observed soil behaviour during jacking penetration is investigated.

Jacking Penetration Resistance of Bucket Foundations in Silty Sand Using Centrifuge Modelling

Numerical analyses were performed to study the cluster suction bucket foundation performance in comparison with the monopod suction bucket foundation. The possibility of improving the resistance performance of suction bucket foundations by using cluster configuration was studied. Clustered foundations are formed by arranging multiple bucket foundations in relatively short distances among them. A model cluster foundation composed of three individual buckets was configured such that it has the same cross sectional area, length and total bucket weight to a monopod foundation. Results of numerical modeling are presented in the form of load-displacement curves. Vertical, horizontal and horizontal combined with moment load conditions were considered. The results show that the cluster type configuration improved the resistance performance of the foundations under typical loading conditions.Copyright © 2013 by ASME

Numerical Analysis of Cluster and Monopod Suction Bucket Foundation

In this study, the behavior of suction anchor installed in cohesionless soil was investigated when the anchor was subjected to mainly horizontal load. In order to study the behavior of suction anchor, numerical analysis model was developed. The soil parameters in the model were adopted from the laboratory tests for cohesionless soils sampled from the western coast in Korea. Horizontal load was applied on the head of the suction anchor model. The load and displacement of the suction anchor was monitored. The distribution of the normal and shear stresses along the anchor surface induced by the surrounding seabed soil was analyzed. The soil reaction forces were analyzed based on the stress results to understand the behavior of the suction anchor under a horizontal loading condition.

Dong-Joon Kim

Papers

Investigation of Monotonic and Cyclic Behavior of Tripod Suction Bucket Foundations for Offshore Wind Towers Using Centrifuge Modeling

Numerical Studies on Bearing Capacity Factor N γ and Shape Factor of Strip and Circular Footings on Sand According to Dilatancy Angle

Jacking Penetration Resistance of Bucket Foundations in Silty Sand Using Centrifuge Modelling

Numerical Analysis of Cluster and Monopod Suction Bucket Foundation

Behavior of Suction Anchor For Horizontal Load From Catenary Line In Cohesionless Soils