Seismically-induced displacements of a suction caisson in soft clay

Abstract Suction piles are a form of foundation widely adopted in the offshore energy industry. Efforts to enhance the combined Vertical-Horizontal (V-H) performance of piles with the addition of fins, attracted interest from the engineering community in the beginning of the 21st century. Design of this enhancement was surfaced whilst examining foundation solutions for renewable energy projects. Studies to date have primarly considered relatively shallow waters comprising sandy soils, with the behaviour of fin-enhanced piles in very soft to soft clay soils, receiving less attention. The present study emphasis is on typical deep-water deposits of soft clay and attempts to evaluate the impact of varying fin length, shape, orientation and location, on the combined capacity of suction piles by means of three-dimensional finite element analyses. The paper investigates two types of load configuration; in the first instance loading at the pile head and secondly with the load attachment point located at approximately two thirds of the pile embedded length. These two configurations cover different foundation solutions, such as support for subsea infrastructure and anchoring for floating facilities, respectively. Optimum fin-enhanced suction pile configurations are presented for each application, with the results from this study indicating an increase of the load-carrying capacity in V-H space, whilst reducing the overall suction pile size. The efficiency of various configurations is presented with composite plots of increase in holding capacity, plotted against the increase in steel surface area. Preliminary recommendations on fin length, location, shape and orientation for typical suction pile applications are presented with intent to demonstrate the potential for cost savings and reduction in both operational and schedule risk.

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Bearing Capacity of Suction Caisson for Offshore Floating Wind Turbine

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.243-249.4718 ◽

2011 ◽

Vol 243-249 ◽

pp. 4718-4722

Author(s):

Xiu Bin Gong ◽

Qing Lai Fan ◽

Ke Wu

Keyword(s):

Bearing Capacity ◽

Wind Turbine ◽

Soft Clay ◽

Combined Loading ◽

Failure Envelope ◽

Suction Caisson ◽

Floating Wind Turbine ◽

Failure Envelopes ◽

Offshore Floating Wind Turbine ◽

Suction Caisson Foundation

Presented in this paper are the three-dimensional nonlinear finite element analyses of the failure envelopes of suction caisson under torsion, vertical and lateral pullout combined load in soft clay. The soft clay under undrained condition is simulated by perfectly elasto-plastic Tresca model. Through the numerical analyses, the failure envelopes for combined loading (V-T、H-T、V-H-T) of suction caisson is reviewed. And the mathematical expression of failure envelope is deduced. It is shown that (1) the circular plastic failure area is outward-extending. (2) The bearing capacity of suction caisson foundation in V-T、H-T load spaces is increasing with the aspect ratio L/D. (3) The equation of failure envelope can be used to evaluate the stability of suction caisson foundation for offshore floating wind turbine.

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Field Trial and Numerical Back-Analysis of Suction Caisson Extraction in Hong Kong

Volume 7: Offshore Geotechnics; Petroleum Technology ◽

10.1115/omae2009-79313 ◽

2009 ◽

Author(s):

Leon S. D. Lorenti ◽

Dora Y. N. Shum ◽

Barry M. Lehane

Keyword(s):

Hong Kong ◽

Soft Clay ◽

Back Analysis ◽

High Rate ◽

Uplift Capacity ◽

Suction Caisson ◽

Ground Conditions ◽

Shaft Friction ◽

Push Out

An in-situ push-out test was carried out on a 3.4m diameter, 12m high trial suction caisson to determine the ultimate uplift capacity and, in particular, the shaft friction that could be generated along the walls of the caisson. The test was performed in the south-eastern waters of Hong Kong in ground conditions comprising soft clay with alluvial sand at the caisson tip. Numerical back-analysis of test reveal that considerable suction was generated at the caisson base due to a combination of the relatively high rate of loading adopted in the test and the silty nature of the alluvium. Inferred friction values generated on the outside wall of the caisson are found to be in line with existing data reported in the literature.

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Centrifuge modelling of uplift response of suction caisson groups in soft clay

Canadian Geotechnical Journal ◽

10.1139/cgj-2018-0838 ◽

2020 ◽

Vol 57 (9) ◽

pp. 1294-1303 ◽

Cited By ~ 1

Author(s):

Bin Zhu ◽

Jia-lin Dai ◽

De-qiong Kong ◽

Ling-yun Feng ◽

Yun-min Chen

Keyword(s):

Soft Clay ◽

Soil Surface ◽

Displacement Curve ◽

Soil Plug ◽

Suction Caisson ◽

Vertical Displacements ◽

Caisson Foundations ◽

Shadowing Effect ◽

Uplift Resistance ◽

Centrifuge Model Tests

This paper describes a program of centrifuge model tests on the uplift behaviour of suction caisson foundations. The parameters considered were the loading rate, caisson diameter (D), soil strength profile, and type of footing (i.e., mono-caisson and tetra-caissons group). The loading responses were examined in terms of total uplift resistance, suction beneath the caisson lid, and the vertical displacements of the caisson and at the soil surface. There exists a critical uplift displacement, approximately 0.02D and 0.01D for the mono-caisson and the tetra-caissons groups, respectively, at which a turning point can be identified in the load–displacement curve. This was found to be attributed to the adhesion on the caisson–soil interface reaching a peak response and then dropping. Of interest is that the tetra-caissons group exhibits much greater normalized uplift resistance than the mono-caisson group before reaching an uplift displacement of about 0.02D, suggesting superiority of the former in term of serviceability. However, a reversed trend was observed at greater displacement, and accordingly an empirical model was derived to quantify the shadowing effect of caisson groups. Regarding the cyclic response, several cycles of large-amplitude loading are sufficient to reduce the ultimate bearing capacity of caisson(s) to below the self-weight of the inner soil plug(s), indicating a transition of failure mechanism.

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Response of suction caissons for tidal current turbine applications in soft clay to monotonic and cyclic vertical loading

Canadian Geotechnical Journal ◽

10.1139/cgj-2016-0133 ◽

2018 ◽

Vol 55 (4) ◽

pp. 551-562 ◽

Cited By ~ 1

Author(s):

Jeff F. Wallace ◽

Cassandra J. Rutherford

Keyword(s):

Cyclic Loading ◽

Tidal Current ◽

Soft Clay ◽

Design Standards ◽

Suction Caisson ◽

Vertical Loading ◽

Aspect Ratios ◽

Tidal Current Turbine ◽

Current Turbine ◽

Suction Caissons

In soft marine clays, suction caissons provide a foundation system for tidal current turbines that further promote the sustainable nature of the system by allowing for their removal at the end of the structure’s design life. When configured as a multipod, the moment loads resulting from the horizontal flow of water will be transferred to the suction caissons as compression–uplift loads on opposing foundation legs. The behavior of a suction caisson in soft clay was investigated at aspect ratios of 1 and 2 under monotonic and cyclic vertical loading applicable to multipod-supported tidal current turbine design. Installation and solely monotonic vertical load tests indicated lower back-calculated adhesion factor, α, values and higher back-calculated bearing capacity factor, Nc, values than design standards recommend. The capacity and stiffness response of the foundation after undergoing cyclic loading was found to be largely dependent on the magnitude of displacement the foundation underwent during cyclic loading. Additionally, a threshold of elastic foundation response was observed during cyclic loading defined by a cyclic displacement amplitude. These results indicate serviceability constraints will be critical in the design of suction caisson foundations for tidal current turbine applications.

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