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Optimal Inclined Bearing Capacity of Shallow Foundations

IP.com Disclosure Number: IPCOM000217704D
Publication Date: 2012-May-10
Document File: 7 page(s) / 439K

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Optimal Inclined Bearing Capacity of Shallow Foundations

   Majid Hesar Technical Adviser- KBR I~ondon, lJK

ABSTRACT

Tbe current "standard" code methods of analysis of mudmats (e.g. API, DnV) use the concept of stability envelopes to determine the required size of shallow Ibundations. This Paper reports on the recent experience of using advanced finite element techniques to opthnize the bearing capacity of two diverse examples of shallow foundations. One example is a conventional large offsbore jacket unskirtcd mudmat made of GRP matcriall The second is a relatively small skirted caisson-shaped thundation. Nonlinear 3D finite element models utilizing both explicit and implicit time integration schemes in ABAQUS were used. Special features of the models include: ALE formulation for adaptively rcmeshing and remapping the deforming soil mediuna, large sliding frictional contact definitions on soil-structure interfaces mad 3D infinite elements. These features allow the influence of all the important parameters of the problem to be taken into account, such as the interface friction behaviour, m~d progressive global inclination of the structure. The use of these FE models not only achieves economy (up
to 17%), but also provides numerous other pieces of information that are vital for assessing the installation and operational criteria for structures supported by sballow foundations.

KfiY WORDS: shallow foundation; mudmat; caisson; bearing capacity; geotechnical; non-linear finite element; ALE; infinite element

INTRODUCTION

Shallow foundations are utilized in a variety of applications both on land and offshore. In offshore practice the on bottom stability of steel jacket platforms during the temporary condition prior to installation of foundation piles depends entirely on their mudmats. Minimizing the size of mudmats has great benefits in terms of savings in materials and fabrication time, reduction of wind forces during barge transportation, and improving weight distribution for lift.installation offshore. In recent state-of-the-art practice novel hybrid foundation concepts are utilized to develop removable multiple-use caisson type foundations for special deepwater operations.

The current "standard" code methods of analysis of mudmals (e.g. API, DnV) use the concept of stability envelopes, together with partial and global safety factors, to determine the required plan area of mudmat foundalions. This Paper reports on the recent experience of using non- linear finite element (FE) techniques to oplimizc the bearing capacily of two diverse examples of shallow foundations. One example is a conventional large offshore jacket unskirted mudmat made of GRP for weigbt saving. The second is a relatively small skirted caisson foundation with a special base lining for ease of removah Nonlinear 3D

FE analyses utilizing both explicit and implicit time integration schemes in ABAQUS were used. Special features of the ataalyses included: Arbitrary Lagrangi...