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Reliability based design of offshore pile foundations

Reliability based design of offshore pile foundations - PSB-OWEA

Leitung: Prof. Dr.-Ing. Martin Achmus
Bearbeiter: Dipl.-Ing. Kirill Schmoor
Laufzeit: 12/2009 - 11/2014
Förderung durch: Niedersächsisches Vorab

Fig. 1: Safety of the investigated system as a function of the deterministic determined global safety factor for axially loaded piles in tension

In contrast to the deterministic design of offshore pile foundations within the reliability based design the uncertainties arising from soil inhomogeneity and the determination of them were statically described in terms of the mean, standard deviation and the type of density function. In addition also other sources of uncertainties, like the error arises from applying a specific bearing capacity formulation (model error), can be included within the probabilistic design process.

By including the uncertainty from the impact a limit state function can be evaluated for the system. Finally by executing an integration of the limit state function, e.g. with the so-called Monte-Carlo method, the failure probability can be determined and compared with the target reliability level.

Fig. 2: Sensitivity factors for the internal friction angle, the buoyant unit weight, the lateral force and the overturning moment for a laterally loaded pile

Work package WP 3 deals with the probabilistic description of the expected resistance values from the soil - (foundation) structure interaction. This requires an analysis of the uncertainties that are involved, and thus identify and separately investigate the contributing factors as well as determine their range with varying parameters. On the one hand, inherent uncertainties arise from the soil inhomogeneities, soil exploration methods, and the limited scope of soil samples as well as soil parameter interpretation methods. And on the other hand, the validity of the available calculation methods, in which the determined soil parameters are required input values, also have to be investigated.

Thus, within the framework of WP 3, the influence of the natural soil heterogeneity as well as the reliability of soil exploration/investigation methods will be analyzed and quantified. Moreover, the effect of the range of variation of the soil parameters on the determination of the limit states of the foundation structure will be investigated. The extent to which offshore-specific uncertainties can be meaningfully taken into account in existing calculation methods for the limit states will also be examined.

Regarding the investigated conclusions the reader is referred to the annual reports and the final report, respectively.