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Geot 2005 55 9 679 Hossain M S Hu Y Randolph M F White D J Ge ?otechnique No ?? Limiting cavity depth for spudcan foundations penetrating clay M S H O S S A I N Y H U ?? M F R A N D O L P H a n d D J W H I T E ?? Centrifuge model tests

Hossain M S Hu Y Randolph M F White D J Ge ?otechnique No ?? Limiting cavity depth for spudcan foundations penetrating clay M S H O S S A I N Y H U ?? M F R A N D O L P H a n d D J W H I T E ?? Centrifuge model tests and ?nite element FE analysis have been conducted to study the penetration of spudcan foundations in uniform clay with nominally constant strength with depth In particular the transition between shallow penetration with soil heaving to the ground surface and deep penetration with a localised ow-round mechanism has been investigated This transition governs the onset of back- ow and hence the depth of soil lying on the installed spudcan which in turn in uences the bearing capacity and also the potential for suction to develop and hence the uplift capacity and moment resistance of the foundation The maximum cavity depth above the spudcan prior to any back- ow is therefore a critical issue for spudcan assessment in clay In the centrifuge model tests a half-spudcan model penetrating against a transparent window has been used to visualise the soil ow mechanisms around the spudcan during penetration The formation of a cavity above the spudcan is revealed by both centrifuge modelling and FE analysis It is found that there are three distinct penetration mechanisms during spudcan installation during initial penetration an open cavity is formed with vertical walls with further penetration soil ows partially around the spudcan into the cavity during deep penetration the spudcan is fully embedded and the soil ow mechanism is entirely localised Over the wide range of normalised soil strengths explored the soil back- ow in the second stage was shown to be due to a ow failure that was triggered by the spudcan penetration and not by wall failure that is the collapse of the vertical sides of the soil cavity This observation is supported by FE analysis The cavity depth due to ow failure is much shallower than the criterion for wall failure that is incorporated in current design guidelines Instead a new design chart and expression is suggested with the normalised cavity depth expressed as a function of the soil shear strength normalised by the e ?ective unit weight of the soil and the spudcan diameter KEYWORDS clays footings foundations model tests numerical modelling o ?shore engineering plasticity Des essais de modele centrifuge et des analyses d ? e ?le ?ments ?nis FE ont e ?te ? effectue ?s pour e ?tudier la pe ?ne ?tration de fondations ? spudcan ? dans une argile uniforme avec une force nominale correspondant a la profondeur En particulier nous avons e ?tudie ? la transition entre pe ?ne ?tration peu profonde - avec soulevement de sol a la surface - et pe ?ne ?tration profonde avec un me ?canisme ow- round localise ? Cette transition gouverne le de ?but du refoulement et de la la profondeur du sol sur