Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-45721 Beitrag zu einem Tagungsband Kullolli, Borana; Stutz, H. H.; Cuellar, Pablo; Baeßler, Matthias; Rackwitz, F. Cardoso, A. S.; Borges, J. L.; Costa, P. A.; Gomes, A. T.; Marques, J. C.; Vieira, C. S. A generalized plasticity model adapted for shearing interface problems The response of many geotechnical systems, whose structural behavior depends on shearing effect, is closely related to soil structure interaction phenomenon. Experimentally it is found that the localisation of these effect happens at a narrow soil layer next to the structure. Numerically, this behavior can be modelled through inter-face elements and adequate constitutive models. In this work, a constitutive model in the framework of Gen-eralized Plasticity for sandy soils has been chosen to be adapted for the interface zone. From the direct shear experiments a sandy soil at loose and dense states under different normal pressures is considered. The adapted constitutive model is able to reproduce contraction and dilatation of the soil according to its relative density and it shows a good agreement with the experimental data. Porto, Portugal NUMGE Faculty of Engineering, University of Porto, Porto, Portugal 2018 Numerical Methods in Geotechnical Engineering IX 1 978-1-138-33198-3 Conference Porto, Portugal 25.06.2018 27.06.2018 97 102 2018-08-16 OPUS4-48909 Beitrag zu einem Tagungsband Kullolli, Borana; Cuéllar, Pablo; Baeßler, Matthias; Stutz, H. H. Modelling and calibration for cyclic soil-structure interface behaviour The structural performance of many geotechnical systems (e.g. axially-loaded pile foundations), depends on the shearing resistance at the soil interface, which may govern the load bearing capacity of the foundation. Experimental investigations have shown that this interaction is mainly localised within a narrow shear band next to the structure. Under cyclic loading, a contraction of the soil at the interface may arise (net volume loss), possibly leading to a stress relaxation and thus to a reduction of the load bearing capacity (the so-called friction fatigue). Based on the constitutive similarities between soil continua and interfaces, we propose here the adaption of a Generalized Plasticity model for sandy soils for the numerical analysis of interface problems. In this contribution, the results of an experimental campaign for the parameter calibration of the constitutive model are presented. The tests have been conducted with a ring shear device involving different normal stresses, roughness of the steel plates as well as cyclic loading. The new modelling approach shows promising results and has the additional practical advantage that the interface zone and the soil continuum can both be described with the same constitutive model in general boundary value problems. Glasgow, Scotland EDP Sciences 2019 92 Konferenz 7th International Symposium on Deformation Characteristics of Geomaterials Glasgow, Scotland 26.06.2019 28.06.2019 13007 13013 urn:nbn:de:kobv:b43-489096 10.1051/e3sconf/20199213007 https://creativecommons.org/licenses/by/4.0/deed.de 2019-09-11 OPUS4-48444 Beitrag zu einem Tagungsband Kullolli, Borana; Baeßler, Matthias; Cuéllar, Pablo; Rica, S.; Rackwitz, F. An enhanced interface model for friction fatigue problems of axially loaded piles The shaft bearing capacity often plays a dominant role for the overall structural behaviour of axially loaded piles in offshore deep foundations. Under cyclic loading, a narrow zone of soil at the pile-soil interface is subject to cyclic shearing solicitations. Thereby, the soil may densify and lead to a decrease of confining stress around the pile due to microphenomena such as particle crushing, migration and rearrangement. This reduction of radial stress has a direct impact on the shaft capacity, potentially leading in extreme cases to pile failure. An adequate interface model is needed in order to model this behaviour numerically. Different authors have proposed models that take typical Interface phenomena in account such as densification, grain breakage, normal pressure effect and roughness. However, as the models become more complex, a great number of material parameters need to be defined and calibrated. This paper proposes the adoption and transformation of an existing soil bulk model (Pastor- Zienkiewicz) into an interface model. To calibrate the new interface model, the results of an experimental campaign with the ring shear device under cyclic loading conditions are here presented. The constitutive model shows a good capability to reproduce typical features of sand behaviour such as cyclic compaction and dilatancy, which in saturated partially-drained conditions may lead to liquefaction and cyclic mobility phenomena. Glasgow, Scotland ASME 2019 OMAE 2019 2019 Conference: OMAE Glasgow, Scotland, UK 09.06.2019 14.06.2019 Article Number: UNSP V001T10A013 2019-07-15 OPUS4-48445 Vortrag Kullolli, Borana An enhanced interface model for friction fatigue problems of axially loaded piles The shaft bearing capacity often plays a dominant role for the overall structural behaviour of axially loaded piles in offshore deep foundations. Under cyclic loading, a narrow zone of soil at the pile-soil interface is subject to cyclic shearing solicitations. Thereby, the soil may densify and lead to a decrease of confining stress around the pile due to microphenomena such as particle crushing, migration and rearrangement. This reduction of radial stress has a direct impact on the shaft capacity, potentially leading in extreme cases to pile failure. An adequate interface model is needed in order to model this behaviour numerically. Different authors have proposed models that take typical Interface phenomena in account such as densification, grain breakage, normal pressure effect and roughness. However, as the models become more complex, a great number of material parameters need to be defined and calibrated. This paper proposes the adoption and transformation of an existing soil bulk model (Pastor- Zienkiewicz) into an interface model. To calibrate the new interface model, the results of an experimental campaign with the ring shear device under cyclic loading conditions are here presented. The constitutive model shows a good capability to reproduce typical features of sand behaviour such as cyclic compaction and dilatancy, which in saturated partially-drained conditions may lead to liquefaction and cyclic mobility phenomena. 2019 Konferenz Glasgow, Scotland, UK 09.06.2019 14.06.2019 2019-07-15 OPUS4-48446 Vortrag Kullolli, Borana Modelling and calibration for cyclic soil-structure interface behavior The structural performance of many geotechnical systems (e.g. axially-loaded pile foundations), depends on the shearing resistance at the soil interface, which may govern the load bearing capacity of the foundation. Experimental investigations have shown that this interaction is mainly localised within a narrow shear band next to the structure. Under cyclic loading, a contraction of the soil at the interface may arise (net volume loss), possibly leading to a stress relaxation and thus to a reduction of the load bearing capacity (the so-called friction fatigue). Based on the constitutive similarities between soil continua and interfaces, we propose here the adaption of a Generalized Plasticity model for sandy soils for the numerical analysis of interface problems. In this contribution, the results of an experimental campaign for the parameter calibration of the constitutive model are presented. The tests have been conducted with a ring shear device involving different normal stresses, roughness of the steel plates as well as cyclic loading. The new modelling approach shows promising results and has the additional practical advantage that the interface zone and the soil continuum can both be described with the same constitutive model in general boundary value problems. 2019 Konferenz :International Symposium of Geomaterials Glasgow, Scotland, UK 26.06.2019 28.06.2019 2019-07-15 OPUS4-49639 Beitrag zu einem Tagungsband Rica, S.; Van Baars, S.; Kullolli, Borana Ülgen, D.; Saygili, A.; Kahyaoglu, M. R.; Durmaz, S.; Toygar, O.; Göcügenci, A. The importance of the horizontal stresses on the bearing capacity of a foundation pile In case one wants to predict or design the bearing capacity of a foundation pile and there are no possibilities to perform an in-situ test, such as a Cone Penetration Test, the pile bearing capacity is in most cases estimated with analytical formulas. The most known and used method is the Meyerhof method published some decades ago. There are also other design methods such as derived from a certain failure mechanism around the pile tip, which is, in most cases, wedge failure mechanism. This failure mechanism was originally developed for a shallow (infinite) strip foundation, though. Therefore, it represents a plane failure mechanism. Numerical simulations on loaded foundation piles performed with the Plaxis software Show however, that the failure mechanism of a foundation pile represents a far more complex threedimensional failure mechanism around the pile tip. In addition, the existing analytical methods for foundation piles are based on the vertical stresses in the soil, as if the failure mechanism is the same as of a shallow foundation. Numerical simulations, performed in Plaxis show that, not the vertical, but the horizontal stresses, play an important role on the pile bearing capacity. Plaxis represents the stresses in the soil by using the procedure. So, different horizontal soil stresses are obtained for different values of the lateral earth pressure coefficient. The results show that the pile tip bearing capacity depends strongly on the horizontal stresses in the soil, but only for. The same results were observed by using a Material Point Method (MPM). Consequently, the analytical methods should estimate the pile bearing. Bodrum, Turkey 1st Mediterranean Young Geotechnical Engineers Conference Turkish Society for ISSMGE (ZMGM) 2019 2019 1st Mediterranean Young Geotechnical Engineers Conference Bodrum, Turkey 23.09.2019 24.09.2019 151 158 2019-11-21 OPUS4-47066 Posterpräsentation Kullolli, Borana Numerical modelling of soil-structure interfaces The governing load bearing mechanism of multi-pile foundations is often the shaft friction. Under cyclic loading the soil particles next to the foundation rearrange and tend to compact leading to a decrease of the surrounding normal stress. The reduction of the normal stress leads to a lower threshold for shear stress (friction fatigue), which results in a degraded shaft bearing capacity. The common interface models used for numerical simulations (e.g. Mohr-Coulomb) are not able to capture such behavior. This work aims to develop an interface material model that incorporates such features of the contact behavior at the soil-structure interface. 2018 Alert Geomaterial Workshop Aussois, France 01/10/2018 06/10/2018 2018-12-19 OPUS4-47068 Vortrag Kullolli, Borana A generalized plasticity model adapted for shearing interface problems The response of many geotechnical systems, whose structural behavior depends on shearing effect, is closely related to soil structure interaction phenomenon. Experimentally it is found that the localisation of these effect happens at a narrow soil layer next to the structure. Numerically, this behavior can be modelled through interface elements and adequate constitutive models. In this work, a constitutive model in the framework of Generalized Plasticity for sandy soils has been chosen to be adapted for the interface zone. From the direct shear experiments a sandy soil at loose and dense states under different normal pressures is considered. The adapted constitutive model is able to reproduce contraction and dilatation of the soil according to its relative density and it shows a good agreement with the experimental data. 2018 Numerical Geotechnics Porto, Portugal 25/06/2018 28/06/2018 2018-12-19 OPUS4-47069 Posterpräsentation Kullolli, Borana Soil-structure interaction of offshore foundations The response of many geotechnical systems, whose structural behavior depends on granular friction and a shearing effect with the ground, is characterized by a complex soil-structure interaction at their interfaces. Experimentally it is found that this interaction is highly non-linear, state-dependent and localized within a narrow layer of soil next to the structure, whereby cyclic loads can play a key role. Numerically, this behavior is often modelled with overly simplified models of interface elements that neglect cyclic effects within the soil. This work introduces a new perspective with an adequate constitutive model in the framework of Generalized Plasticity for sandy soils for an improved consideration of the interface mechanics. 2018 PhD Day BAM Berlin, Germany 31/05/2018 31/05/2018 2018-12-19