Failure Envelopes for Combined Loading of Skirted Foundations in Layered Deposits

The composite bucket foundation of offshore wind turbines is subjected to a variety of loads in the marine environment, such as horizontal load H, vertical load V , bending moment M, and torque T. In addition, due to the characteristics of its connection section, the water flow around the foundation will produce scour pits of various degrees, reducing the depth of the bucket foundation, which has a nonnegligible impact on the overall stability of the bucket foundation. In this paper, the failure envelope characteristics of different combinations of loads on bucket foundations, including V -H-T, V -M-T, conventional V -H-M, and noncoplanar V -H-M, are numerically investigated with considering different scour depths. The numerical results indicate that the V -H-T, V -M-T, conventional V -H-M, and noncongruent V -H-M failure envelopes gradually shrink inwards with increasing scour depth, and the stability of the composite bucket foundation decreases; the conventional V -H-M failure envelope shows an asymmetry of convexity to the right, and the noncongruent V -H-M failure envelope shows an asymmetry of outward convexity to the left and right. The corresponding mathematical expressions for the failure envelope are obtained through the normalized fitting process, which can be used to evaluate the stability of the bucket foundation based on the relative relationship between the failure envelope and the actual load conditions, which can provide practical guidance for engineering design.

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A New Method to Investigate the Failure Envelopes of Offshore Foundations

Volume 1: Offshore Technology; Offshore Geotechnics ◽

10.1115/omae2016-54513 ◽

2016 ◽

Cited By ~ 1

Author(s):

Yinghui Tian ◽

Tianyuan Zheng ◽

Tao Zhou ◽

Mark J. Cassidy

Keyword(s):

Test Method ◽

New Method ◽

Combined Loading ◽

Resistance Force ◽

Flow Conditions ◽

Load Path ◽

Failure Envelope ◽

Load Paths ◽

Failure Envelopes ◽

Probe Test

This paper presents an alternative numerical method in addition to the traditional ‘probe test’ to investigate the combined loading failure envelopes of foundations in soil. In the ‘probe test’ method, the foundation is displaced with a specified displacement path and eventually the soil resistance force reaches a stabilised point sitting on the failure envelope in the load space. While the displacement paths are arbitrarily or empirically set, the positions of the stabilised loads on the failure envelope can not be predetermined or planned. This paper’s new method, however, can specify the load paths, which directly shoot onto the failure envelope. This allows the investigation of the failure envelope can be better achieved with planned load paths. In addition, this new method is advantageous in checking the plastic flow conditions (i.e. normality of the failure envelope) as the load path directions are predetermined.

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Probabilistic combined loading failure envelopes of a strip footing on spatially variable soil

Computers and Geotechnics ◽

10.1016/j.compgeo.2012.10.008 ◽

2013 ◽

Vol 49 ◽

pp. 191-205 ◽

Cited By ~ 44

Author(s):

Mark J. Cassidy ◽

Marco Uzielli ◽

Yinghui Tian

Keyword(s):

Strip Footing ◽

Combined Loading ◽

Failure Envelopes

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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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Evaluation of undrained failure envelopes of caisson foundations under combined loading

Applied Ocean Research ◽

10.1016/j.apor.2016.05.001 ◽

2016 ◽

Vol 59 ◽

pp. 129-137 ◽

Cited By ~ 12

Author(s):

Moura Mehravar ◽

Ouahid Harireche ◽

Asaad Faramarzi

Keyword(s):

Combined Loading ◽

Failure Envelopes ◽

Caisson Foundations

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Transitional Failure of Carbon Nanotube Systems under a Combination of Tension and Torsion

Journal of Nanomaterials ◽

10.1155/2012/847307 ◽

2012 ◽

Vol 2012 ◽

pp. 1-6

Author(s):

Byeong-Woo Jeong

Keyword(s):

Carbon Nanotubes ◽

Failure Modes ◽

Tensile Failure ◽

Combined Loading ◽

Torsional Buckling ◽

Failure Envelopes ◽

Safe Region ◽

Dynamics Simulations ◽

Double Walled Carbon Nanotubes ◽

Walled Carbon Nanotubes

Transitional failure envelopes of single- and double-walled carbon nanotubes under combined tension-torsion are predicted using classical molecular dynamics simulations. The observations reveal that while the tensile failure load decreases with combined torsion, the torsional buckling moment increases with combined tension. As a result, the failure envelopes under combined tension-torsion are definitely different from those under pure tension or torsion. In such combined loading, there is a multitude of failure modes (tensile failure and torsional buckling), and the failure consequently exhibits the feature of transitional failure envelopes. In addition, the safe region of double-walled carbon nanotubes is significantly larger than that of single-walled carbon nanotubes due to the differences in the onset of torsional buckling.

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Evaluation of Undrained Bearing Capacities of Wide-Shallow Bucket Foundation with Honeycomb Bulkheads in Clay

Advances in Civil Engineering ◽

10.1155/2019/9769042 ◽

2019 ◽

Vol 2019 ◽

pp. 1-13

Author(s):

Qingshan Wang ◽

Xun Han ◽

Yunfei Guan ◽

Yongyong Cao ◽

Wenxuan Li

Keyword(s):

Shear Strength ◽

Three Dimensional ◽

Offshore Wind ◽

Combined Loading ◽

Vertical Load ◽

Bucket Foundation ◽

Failure Envelopes ◽

Soil Shear Strength ◽

New Type ◽

The Moment

As a new type of offshore wind foundation, the wide-shallow bucket foundation with honeycomb bulkheads mainly bears vertical, horizontal, and moment loads. As yet, no systematic study has been conducted regarding the effects of honeycomb bulkheads on the undrained bearing capacities of the wide-shallow bucket foundation. In this study, a large number of three-dimensional (3D) finite element (FE) analyses were performed to investigate the undrained bearing capacities of the wide-shallow bucket foundations with and without honeycomb bulkheads, thereby evaluating the influence of honeycomb bulkheads on the bearing capacities under different conditions. The results show that under uniaxial loading, the uniaxial bearing capacities of the wide-shallow bucket foundation are basically unaffected by the honeycomb bulkheads in homogeneous clay. For nonhomogeneous clay, the moment bearing capacity will be considerably enhanced with the increase in soil shear strength heterogeneity. Under combined loading, the honeycomb bulkheads will enhance the combined bearing capacities only in nonhomogeneous clay. The enhancement effects will increase with the increase in soil shear strength heterogeneity but decrease with the increase in vertical load. Besides, the simplified equations for calculating the uniaxial bearing capacities of the wide-shallow bucket foundation with honeycomb bulkheads are also proposed considering the influence of embedment ratio and soil shear strength heterogeneity. At last, the parameters of an approximating expression are fitted to predict the failure envelopes of this foundation under combined loading.

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