Zur Tragfähigkeit von Stahlpfählen mit offenen Profilen in nicht-bindigen Böden unter Berücksichtigung des Herstellungsvorganges

Motivation

Monopiles, or open steel pipe piles in general, are increasingly important for offshore structures, especially as foundation for offshore wind power plants. Especially in Europe there are already many offshore wind power parks realized and more are planned. Monopiles can be installed in various ways, e.g. impact-driven or vibratory-driven. The installation method has an import influence on the final bearing behaviour of the pile, the duration of the pile installation and the noise emissions during installation. Aim of this research is to investigate the bearing behaviour of monopiles with regard to their installation method.

Among others, Hartung (1994), Wienholz (1998) and Lammertz (2008) have already investigated the bearing behaviour of impact- and vibratory-driven piles by small scale, full scale and field tests. The research at IGS is utilizing numerical simulations coupled with sophisticated field tests, as the VIBRO project. The VIBRO project is a project under lead of RWE Innogy to investigate the bearing behaviour of vibratory-driven monopiles in comparison the impact-driven monopiles. Within this project, six monopiles have been installed: three vibratory-driven and three impact-driven.

Numerische Simulation

Investigating the bearing behaviour of monopiles requires knowledge about the development of stress and strains around the pile during and after installation. To gain a better understanding of the processes the soil is undergoing during installation, the complete installation of the pile is simulated numerically. These numerical simulations involve advanced modelling techniques to overcome numerical problems with the calculation of large deformations, such as the Coupled Eulerian-Lagrangian (CEL) method and the Arbitrary Lagrangian-Eulerian (ALE) method. The soil is described by a hypoplastic constitutive model (cf. von Wolffersdorff 1996) with the small strain extension by Niemunis & Herle (1997).

 In Fig. 1 results of a numerical simulation are presented. An open steel pipe pile with a diameter of 0.76 m was jacked with a constant velocity into medium dense sand. In the figure the distribution of void ratio after 3 m of driving is shown. The simulation was conducted using the CEL method together with a hypoplastic constitutive law.

Ausblick

Within this research project, a numerical case study will be carried out to investigate the influence of different properties (e.g. installation method) on the bearing behaviour of the piles. The results of this case study will be put in relation to results of sophisticated field tests as the VIBRO project to further investigate the axial and lateral bearing behaviour of monopiles subjected static and dynamic loadings.

Figure 1. Distribution of void ratio e0.


Literatur

Hartung, M. (1994). “Einflüsse der Herstellung auf die Pfahltragfähigkeit in Sand.” Heft 45, Institut für Grundbau und Bodenmechanik, Technische Universität Braunschweig.

Lammertz, P. (2008). “Ermittlung der Tragfähigkeit vibrierter Stahlrohrpfähle in nichtbindigem Boden.” Heft 35, Fachgebiet Grundbau und Bodenmechanik, Universität Duisburg-Essen.

Wienholz, B. (1998). “Tragfähigkeit von Verdrängungspfählen in Sand in Abhängigkeit von der Einbringung.” Heft 57, Institut für Grundbau und Bodenmechanik, Technische Universität Braunschweig.

Niemunis, A., and Herle, I. (1997). “Hypoplastic model for cohesionless soils with elastic strain range.” Mechanics of Cohesive-Frictional Materials, 2, 279–299.

von Wolffersdorff, P. A. (1996). “A hypoplastic relation for granular materials with a predefined limit state surface.” Mechanics of Cohesive-Frictional Materials, 1, 251–271.

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 Kontakt: Johannes Labenski