Installing Jackups in Punch-Through-Sensitive Clays

Brennan, R.; Diana, H.; Stonor, R.W.P.; Hoyle, Mike; Cheng, Charlene; Roper, Richard.

doi:10.4043/18268-ms

Cited by 38 publications

(32 citation statements)

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“…11(c). In assessing spudcan response after a punch-through, and for safe re-installation on the same location, Brennan et al (2006) came to a similar conclusion that the potential for severe punchthrough decreased with decreasing thickness of the stronger layer. These effects are also similar to those found in the centrifuge tests.…”

Section: Effect Of Thickness Ratio (T/d)mentioning

confidence: 82%

Deep-penetrating spudcan foundations on layered clays: numerical analysis

Hossain¹,

Randolph²

2010

Géotechnique

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This paper presents results of large deformation finite element (LDFE) analyses that investigate the penetration response of deep-penetrating spudcan foundations in stratified soil comprising a strong clay layer overlying weaker clay. Such strength profiles give rise to potential punchthrough failure, with a local maximum penetration resistance followed by some reduction. The paper is a companion paper to one that presents results from centrifuge model tests of the same problem, with the overall aim being to investigate the potential for punch-through failure and its severity, as a basis for improving design methods for evaluating spudcan penetration. The LDFE analyses have simulated continuous penetration of smooth and rough spudcan foundations from the sea-bed surface. A detailed parametric study has been undertaken, exploring the relevant range of layer thickness (relative to the spudcan diameter), strength ratios and spudcan base roughness. The results have been validated against previously published results and the centrifuge test data presented in a companion paper. Excellent agreement was obtained between the results from LDFE analyses and centrifuge tests. As the ratio of the shear strength of the bottom layer to that of the top layer decreased, upwards soil flow around the spudcan shoulder became less pronounced and the failure mechanism was dominated by a steep-sided plug of soil from the top layer being forced deep into the lower layer. The potential for severe punch-through was demonstrated by a significant reduction in the resistance profile as the spudcan approached the interface between the two layers. A preliminary design chart is proposed to estimate the cavity depth above the penetrating spudcan, which was significantly greater than that for a single layer clay. The penetration responses have been presented in terms of profiles of normalised net bearing pressure for a range of layer geometries and soil properties. Potential punchthrough occurred for all cases where the strength ratio was less than or equal to 0 . 6, with the reduction in resistance being greater the lower the strength ratio of the underlying layer to the upper layer, and the thicker the upper layer, but reducing as the strength gradient in the lower layer increased. The current approach suggested in offshore design guidelines is shown to underestimate the penetration resistance significantly, in most cases, and give poor estimates of the likelihood and severity of spudcan punch-through.KEYWORDS: bearing capacity; clays; failure; footings/foundations; numerical modelling; offshore engineering La présente communication présente les résultats d'analyses de larges déformations en éléments finis (LDEF) examinant la réaction à la pénétration de fondations à forte pénétration dans des sols stratifiés, comportant une couche d'argile résistante recouvrant une couche d'argile plus faible. Ces profils de résistance donnent lieu à un risque de rupture à « punch-through », dans le cadre de laquelle une résistance maximale locale à la pénétr...

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Section: Effect Of Thickness Ratio (T/d)mentioning

confidence: 82%

Deep-penetrating spudcan foundations on layered clays: numerical analysis

Hossain¹,

Randolph²

2010

Géotechnique

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“…Brennan et al [13] and Chan et al [15] also describe the reinstallation of a jack-up damaged during its first installation attempt. Holes of 0.065 D (0.914 m) were drilled on an equilateral triangular grid with a spacing of 0.109 D to 0.131 D. All holes were drilled using a 26-inch (0.66 m) mill tooth tricone bit attached to a 36-inch (0.914 m) mill toothed hole opener (see Fig.…”

Section: Case Record 2: Belida B Sunda Shelfmentioning

confidence: 92%

“…The hypothesis is that by perforating the stiff layer with drill holes (and removing the soil) the peak bearing resistance can be reduced. This technique has been recently used to reinstall jack-ups without incident at several locations in Southeast Asia where severe punch-through failures occurred during the first attempt of preloading through layered clays [12][13][14][15]. These case histories and lessons learnt, which have formed the genesis of the experimental programme, are described.…”

Section: A Review Of Perforation Drillingmentioning

confidence: 98%

Experimental investigation of perforation drilling in stiff-over-soft clay

Hossain

Cassidy

Daley

et al. 2010

Applied Ocean Research

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“…The soil properties at every location at a site, however, cannot be known perfectly because the site investigation is often limited in offshore areas. The lack of understanding on the complex soil conditions was found to be a crucial factor on the failures of platforms (Brennan et al, 2006;Gao et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Bearing capacity of spudcan foundations in a spatially varying clayey seabed

Huang³

et al. 2017

Ocean Engineering

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A B S T R A C TSpudcan foundations are often pushed into a spatially varying non-homogeneous seabed to provide bearing capacity for a mobile jack-up platform. The natural variability of soil properties coupled with the complexity of loading conditions make determining the bearing capacity of spudcan foundations a challenging problem. A random finite element method is established to investigate the bearing capacity of a spudcan foundation embedded in a spatially varying clayey seabed when subjected to vertical, horizontal and moment loadings. A criterion is proposed for determining the characteristic value of the shear strength for the random seabed. Results indicate that the spatial variability in the clayey seabed significantly reduces the bearing capacity of a spudcan foundation. This reduction is more significant in the vertical bearing capacity than in the horizontal and moment bearing capacities. The mean bearing capacity is smaller for the clay with larger coefficient of variation of undrained shear strength. A characteristic value of mean minus a standard deviation of the undrained shear strength is capable to ensure the probability of failure is not greater than 5%. This study provide an evaluation method for the spatial variability effect of a clayey seabed, paving the way for a costeffective design of spudcan foundations.

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Installing Jackups in Punch-Through-Sensitive Clays

Cited by 38 publications

References 0 publications

Deep-penetrating spudcan foundations on layered clays: numerical analysis

Deep-penetrating spudcan foundations on layered clays: numerical analysis

Experimental investigation of perforation drilling in stiff-over-soft clay

Bearing capacity of spudcan foundations in a spatially varying clayey seabed

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