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Grabe J.,University of Management and Technology | Pucker T.,IMS Ingenieurgesellschaft MbH
Frontiers in Offshore Geotechnics III - Proceedings of the 3rd International Symposium on Frontiers in Offshore Geotechnics, ISFOG 2015 | Year: 2015

Pile foundations for multilegged support structures for offshore wind energy plants are commonly installed by pile driving. Vibratory driving for offshore foundation piles is unusual, because of its installation effects. During the installation the soil inside and outside of the pile is compacted and the stresses are reduced. Therefore the bearing capacity of vibratory driven piles is reduced compared to driven piles. A new method is presented to increase the vertical bearing capacity of vibratory driven piles. After the pile installation the soil at the pile toe is braced, such that a soil plug develops. The brace can be caused by geotechnical foams aswell as by mechanical displacement. The potential of this newmethod is drawnup by the use of numerical simulations. A case study is performed to estimate the increase of the bearing capacity depending on the achieved stress increase at the pile toe. Using this new method, the advantages of vibratory driven piles such as its fast and noise reduced installation are combined with increased bearing capacity. The bearing capacity is fully mobilised at very low settlements. Therefore the settlements of this improved pile are expected to be smaller than the settlement of traditional jacked piles under service loads. © 2015 Taylor & Francis Group, London. Source


Duhrkop J.,IMS Ingenieurgesellschaft MbH | Augustesen A.H.,Cowi A/S | Barbosa P.,Iberdrola
Frontiers in Offshore Geotechnics III - Proceedings of the 3rd International Symposium on Frontiers in Offshore Geotechnics, ISFOG 2015 | Year: 2015

A review of current design methods of axially loaded open ended driven steel piles in chalk is presented. Iberdrola pile testing campaign in Kent, United Kingdom, in low density chalk is described and selected results are presented. These include static axial uplift and compressive tests and a two-way cyclic load test on two 0.76m diameter test piles. A comparison between actual and predicted pile behaviour with RATZ (load-transfer) computer program calibrated with direct simple shear Constant Normal Stiffness (CNS) cyclic laboratory tests is presented. © 2015 Taylor & Francis Group, London. Source


Lohning T.,Cowi A/S | Vobbeck M.,IMS Ingenieurgesellschaft MbH | Kelm M.,Cowi A/S
Proceedings of Institution of Civil Engineers: Energy | Year: 2013

In offshore wind turbines grouted connections are generally used to install a transition piece between the steel tower and the monopile foundation. The transition piece is plugged on to the monopile, aligned vertically and the annulus in between is filled with high-strength grout. During service operations unexpected settlement of the transition piece has been observed at several wind turbines. The serious findings have called for additional, extensive numerical analyses for the detailed design of the London Array offshore wind farm. The advanced non-linear finite-element analyses provide a more detailed insight into the structural behaviour of grouted connections. Important effects and a possible mechanism for the settlement at existing wind turbines are detected. The previous practice of designing separately for bending moment and transverse force on the one hand and axial force and torsion on the other hand leads, among other things, to the overestimation of capacity. The interaction has to be taken into account. Source


Rudolph C.,TU Hamburg - Harburg | Mardfeldt B.,Hamburg Port Authority AoR | Duhrkop J.,IMS Ingenieurgesellschaft MbH
Geotechnik | Year: 2011

In Germany dolphins are commonly designed using a procedure after Blum, 1932, proposed in the EAU 2004. However, internationally the p-y-method is applied more widely for dolphin design. In future, legislature in Germany will change towards allowing the p-y-method besides the Blum-method. For the practioning engineer this raises the question of advantages and disadvantages of both methods. This paper contrasts the underlying principles and presents examples for design calculations to allow for comparison of the two methods. © 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source


Barbosa P.,Iberdrola | Geduhn M.,IMS Ingenieurgesellschaft MbH | Jardine R.,Imperial College London | Schroeder F.,Geotechnical Consulting Group LLP | Horn M.,Bilfinger Construction GmbH
Frontiers in Offshore Geotechnics III - Proceedings of the 3rd International Symposium on Frontiers in Offshore Geotechnics, ISFOG 2015 | Year: 2015

Iberdrola is developing the Wikinger offshore windfarm in the German Baltic Sea. The wind turbines will be supported by four legged jackets founded on driven open ended steel piles. Loading will be predominantly axial with shaft resistance governing design. Ground conditions over much of the project area comprise of thick Chalk layers. A review of current pile design methods for Chalk and related onshore pile test campaigns highlighted significant design uncertainties and led to a decision to conduct dynamic and static offshore pile tests at the site. This paper summarizes the aims and rationale of the tests carried out in late 2014, describes the design of the remotely operated testing arrangements and reports on an associated research project that is advancing in conjunction with Imperial College London and Geotechnical Consulting Group. © 2015 Taylor & Francis Group, London. Source

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