Caisson capacity in undrained soil: Failure envelopes with internal scooping

The bearing capacity of embedded foundations subject to combined horizontal and moment loading in undrained soils is of interest particularly to the offshore geotechnical engineer. These loadings can be experienced by monopod foundations and offshore manifolds and often take the form of a horizontal load applied at a lever arm height above the foundation base. Previous design methods using the failure envelope approach have suggested that peak moment capacity of a foundation is mobilized with positive horizontal loads, but that peak horizontal load is mobilized with no additional moment loading. This paper reports numerical work specifically investigating the effects of the embedment ratio on the horizontal-moment foundation capacity under no vertical load in both uniform strength and "normally consolidated" undrained soil. It is shown that the embedment ratio significantly affects the eccentricity of the M–H failure envelope so that the shape varies when normalized by the pure moment (M0) and pure horizontal load (H0) capacity. The reasons for the eccentricity of the failure envelopes are understood by investigating soil deformation mechanisms calculated during FE analysis and by accompanying upper bound plasticity analysis. This mechanistic understanding is used to suggest load reference point translations that ease curve-fitting of the complex failure envelopes for use in design.Key words: bearing capacity, foundations, numerical modelling and analysis, plasticity.

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Effect of Underlying Sand Layer on Undrained Capacity of Spudcan Foundations in Soft Clay Under Combined Loading

Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics ◽

10.1115/omae2018-78198 ◽

2018 ◽

Author(s):

Yifa Wang ◽

Mark J. Cassidy ◽

Britta Bienen

Keyword(s):

Soft Clay ◽

Three Dimensional ◽

Small Strain ◽

Combined Loading ◽

Sand Layer ◽

Element Analysis ◽

Moment Capacity ◽

Soil Failure ◽

Failure Envelopes ◽

Vertical Bearing

During the operational phase, the spudcan foundations of a mobile jack-up rig are subjected to combined vertical, horizontal and moment loading. Although previous research has indicated a substantial increase in vertical bearing capacity when a spudcan penetrates through a soft clay layer towards a sand layer, the response of spudcan foundations subjected to combined loadings in such stratification has yet to be understood. This study investigates the effect of the underlying stronger sand layer on the undrained VHM capacity of a spudcan foundation using three-dimensional small-strain finite element analysis. Results show the significant increase in vertical and moment capacity, whereas the horizontal capacity is minimally affected. The soil failure mechanisms are identified and changes in the size and shape of failure envelopes, accounting for the sand layer underneath, are quantified. An analytical expression is proposed to predict the combined capacity of a spudcan foundation in clay overlying sand.

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Effect of Pile and Load Inclination on the Pile Resistance In both Compression and Tension

Wasit Journal of Engineering Sciences ◽

10.31185/ejuow.vol2.iss1.21 ◽

2014 ◽

Vol 2 (1) ◽

pp. 11-29

Author(s):

Ahmad Jabber Hussain ◽

Alaa Dawood Salman ◽

. Nazar Hassan Mohammad

Keyword(s):

Bearing Capacity ◽

Inclination Angle ◽

Theoretical Study ◽

Pile Installation ◽

Soil Failure ◽

Inclined Pile ◽

Uplift Resistance ◽

Lift Forces ◽

Batter Piles ◽

Pile Resistance

According to this theoretical study which was about loading of piles under different condition of loading (compression and up-lift forces ) and for deferent pile installation (vertical and inclined pile ) by which it called (positive batter pile ) when the inclination of the load and pile is in the same direction and called (negative batter pile) when the inclination of load is opposite to the pile inclination, and from studying these cases the results of analysis can be summarize in the flowing points: 1-Variation of load inclination on piles effects on the bearing capacity and uplift resistance. It was found that bearing capacity of the piles increase with increasing of load inclination up to the inclination angle (37.5ͦ) which represents the maximum bearing capacity and then the bearing capacity decrease with increasing of load inclination. 2- Variation of batter pile affects the bearing capacity of the pile and up-lift resistance. by which equivalent angle will be used as result between the load and piles inclination and this angle will be used in calculation of piles resistance . 3- It was noticed the shape of soil failure is highly affected by the inclination of pile. The shape of failure for the soil which is in contact with pile and this include (vertical and batter piles) is highly affected by the angle of inclination.

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