Evaluating the penetration resistance of spudcan foundations in clay overlying sand

Yifa Wang, Mark Cassidy, Britta Bienen

Research output: Chapter in Book/Conference paperConference paper

1 Citation (Scopus)

Abstract

Safe installation of mobile jack-up platforms requires accurate prediction of the vertical load-penetration curves of their large ~20 m diameter spudcan footings. Difficulties can arise due to a change of soil strength from a soft to a stiff layer. A substantial increase in the ultimate bearing capacity occurs when a spudcan penetrates vertically through a soft clay layer towards a sand layer. This is because the softer soil that is trapped beneath the spudcan base starts to be squeezed horizontally as the vertical load begins to be borne by the stronger underlying sand layer. The theoretical solution of the bearing capacity of a soil layer on a rigid base has conventionally been used to predict the spudcan penetration resistance in soft over strong layers. However, recent centrifuge experimental studies suggested that the design approaches recommended by current industry guidelines ISO (2016) and SNAME (2008) are not adequately accurate in predicting the sharp increase in the resistance prior to penetration into the sand layer. In this paper, large deformation finite element (LDFE) analyses that capture the evolving soil failure mechanisms during spudcan penetration in a clay layer overlying sand, and explore relationships for the penetration resistance, are reported. The Coupled Eulerian-Lagrangian method was used to simulate the continuous penetration of the spudcan foundation. The clay layer was modelled with the elastic perfectly plastic Tresca model, while the sand layer was modelled by the Mohr-Coulomb model using a nonassociated flow rule. The findings show that the increased capacity is associated with the squeezing mechanism, which starts at the depth where the bottom of the soil failure mechanism first touches the underlying sand layer. This is approximately a third of the spudcan diameter above the clay-sand interface. A simplified expression is proposed to predict the spudcan penetration resistance between the depth at which the squeezing prevails and the clay-sand interface.

Original languageEnglish
Title of host publicationProceedings of the 29th International Ocean and Polar Engineering Conference, ISOPE 2019
EditorsJin S. Chung, Odd M. Akselsen, HyunWoo Jin, Hiroyasu Kawai, Yongwon Lee, Dmitri Matskevitch, Suak Ho Van, Decheng Wan, Alan M. Wang, Satoru Yamaguchi
PublisherInternational Society of Offshore and Polar Engineers
Pages2027-2034
Number of pages8
ISBN (Print)9781880653852
Publication statusPublished - 2019
Event29th International Ocean and Polar Engineering Conference, ISOPE 2019 - Honolulu, United States
Duration: 16 Jun 201921 Jun 2019

Publication series

NameProceedings of the International Offshore and Polar Engineering Conference
Volume2
ISSN (Print)1098-6189
ISSN (Electronic)1555-1792

Conference

Conference29th International Ocean and Polar Engineering Conference, ISOPE 2019
CountryUnited States
CityHonolulu
Period16/06/1921/06/19

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