Effect of Skirt Geometry Variation on Uplift Capacity of Skirted Foundation

摘要

Skirted foundations are an alternative to pile foundations in offshoreand oil and gas facilities. In this paper, a new idea for geometryimprovement for skirted foundations is presented. For this purpose,numerical investigation has been used to explore the load carryingcapacity of skirted foundations with non-vertical walls in respect to thevertical axis. The soil-foundation system is modeled in anaxisymmetric fashion. The material of the circular skirted foundation isassumed to be linear and elastic. The soil is assumed to be fine and softand its failure stage obeys the Drucker-Prager criterion. In this study,the effect of wall stiffness on the bearing capacity is investigated.Results were presented as applied relations and graphs. The results ofstudies show that the bearing capacity of skirted foundations increasesproportionally with increase of the wall face angle with respect to thevertical direction. In addition, it has been found to achieve the greaterpull out bearing capacity, greater displacements are required.Numerical analysis has been performed to investigate the upliftbehavior of skirted foundation with inclined surface. Based on theresults obtained, some of the general findings are as follows:Noticeable bearing capacity is achieved through the optimization of theskirted foundation geometry. The pullout capacity of skirtedfoundations with inclined sides is achieved at greater displacementscompared with the case for vertical sided foundations. With increasingthe soil undrained shear strength (Su), the bearing capacity increasesespecially for foundations with inclined skirt surface. In clay with lowundrained shear strength, the influence of the inclined surface in skirtedfoundations is greater. With increasing length/diameter ratio for skirtedfoundations, the pullout capacity increases due to holding greater soilmass in plug and due to greater soil-foundation contact surfaces. Sincethe increase in skirt length needs greater forces in order to dissipateinduced negative pore pressures, the undrained bearing capacity willgrow up.