Zur Berechnung der Beanspruchungen und Verschiebungen erdverlegter Fernwaermeleitungen

Eine fuer Fernwaermeleitungen charakteristische Eigenschaft ist die durch die wechselnden Temperaturbelastungen bedingte intensive Wechselwirkung mit dem umgebenden Boden. Mangels ausreichender Erkenntnisse zur Groesse der auftretenden Bodenreaktionskraefte kann diese Wechselwirkung aber bei der Bemessung bisher nicht in zufriedenstellender Weise beruecksichtigt werden. Dies ist jedoch fuer die Ausnutzung moeglicherweise vorhandener statischer Reserven und damit von Kostensekungspotentialen unbedingt erforderlich. Mit der vorliegenden Arbeit wird das Ziel verfolgt, anhand theoretischer Untersuchungen grundlegende Zusammenhaenge bezueglich der Bodenreaktionskraefte aufzuzeigen. Damit soll zu einem besseren Verstaendnis des Tragverhaltens von Fernwaermeleistungen beigetragen und eine zuverlaessige Beurteilung und Interpretation von Messergebnissen ermoeglicht werden. (orig./GL)One characteristic of buried district heating pipelines is their intensive interaction with the surrounding soil, which results from the changing temperature stresses. So far, this interaction could not be taken into account with sufficient accuracy in pipeline dimensioning, owing to a lack of data on the extent of the soil reaction forces to be expected. However, this knowledge is absolutely necessary for making use of potentially available static reserves and the resulting potential cost savings. The investigation attempts to point out fundamental mechanisms of the soil reaction forces on the basis of theoretical investigations. This would contribute to a better understanding of the strength of district heating pipelines and enable a reliable assessment and interpretation of measured findings. (orig./GL)SIGLEAvailable from TIB Hannover: RA 2774(41) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Load-bearing behavior of suction bucket foundations in sand

Suction buckets are a promising foundation solution for offshore wind energy systems. The bearing behavior of monopod buckets under drained monotonic loading in very dense and medium dense sand is investigated in this study by means of numerical simulation with the finite element method. Special focus is given to the ultimate capacity and the initial stiffness of the bucket-soil foundation system. The numerical model is validated by comparison with field test results. The bearing behavior of the structure is explained through an evaluation of a reference system. It is shown that the bucket experiences a heave during horizontal loading. which leads to the formation of a gap between the bucket lid and the soil with increasing load. At large loads and rotations close to failure of the system there is no contact between lid and soil, and the whole load is transferred to the soil via the bucket skirt. A parametric study shows how the ultimate capacity and initial stiffness of the system depend on the bucket dimensions and loading conditions, i.e. load eccentricity. Normalized equations for ultimate capacity and initial stiffness are derived from the numerical simulation results, which can be used in the scope of a preliminary design for buckets in sand. (C) 2013 Elsevier Ltd. All rights reserved

Numerical investigation of spudcan footing penetration in layered soil

Spudcans are a type of foundation for mobile jack-up rigs and are connected to each of the three or four independent legs of a rig. These rigs are widely operating in the offshore industries such as oil and gas exploration and offshore wind park constructions. The diameter of a spudcan is typically between 10 and 16 m, but has steadily increased in recent years with some exceeding 20 m. An accurate prediction of the leg or spudcan penetration is required to assess the minimum leg length of a jack-up rig and to predict any hazards such as risk of rapid leg penetration that can destabilize the rig and lead to catastrophic accidents. Rapid and sudden leg penetration can occur in layered soils where a strong layer overlies a weak layer. This type of failure mechanism in soil is called “punch through”. The current state-of-practice to assess the penetration depth of a spudcan is to evaluate the bearing capacity of the footing applying analytical methods at discrete depths. Analytical bearing capacity methods strongly simplify the penetration process and rely on empirical factors. Continued investigation of the spudcan penetration process by means of physical or numerical models can reduce the amount of empiricism in applied methods in practice, thereby increase accuracy in penetration predictions and reduce risk of rig instability. The results of a finite element numerical model to investigate the spudcan penetration process in layered soils are presented in this paper. The numerical model combines conventional Lagrangian elements, which represent the spudcan, with Eulerian elements that idealize the soil. The utilization of this so-called Coupled Eulerian-Lagrangian finite element method enables the numerical simulation of large deformation processes such as the spudcan footing penetration. Preliminary results are presented and compared with state-of-practice analytical solutions

Verbau und Wiederverfuellung von Leitungsgraeben Grundlagen, Hinweise, Empfehlungen

Available from TIB Hannover: RO 9741(12) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Load bearing behavior of bucket foundations in sand

© 2013 Computational Geomechanics, COMGEO III - Proceedings of the 3nd International Symposium on Computational Geomechanics. All rights reserved.The suction bucket foundation is a relatively new concept for the foundation of offshore wind energy converters. If only one bucket is installed (monopod), the structure is loaded by large horizontal forces and overturning moments. Besides the failure load and the initial stiffness, also the accumulation of head rotations of the foundation structure under cyclic loads has to be considered in the design. The behavior of buckets in sand under monotonic and cyclic horizontal loading is investigated in the paper by means of 3D finite element simulations. An elasto-plastic material law with stress-dependent stiffness approach is used herein. To investigate the behavior of a bucket under cyclic loading, a special numerical scheme originally developed for pile foundations (stiffness degradation method) is applied to the bucket system. The results of a parametric study show that the rate of accumulation of the bucket lid rotation depends on the relative skirt length of the bucket, on the relative density of the sand and also to a certain extent on the load level, i.e. the relative magnitude of the applied load

Advanced incorporation of soil-structure interaction into integrated load simulation

The optimization of monopiles for offshore wind turbines is closely linked to improved foundation models, particularly for large diameter structures. During the last years significant progress on geotechnical level has been made to assess foundation models of monopiles based on high fidelity finite element models. In contrast, integrated load simulation models for offshore wind turbines commonly incorporate soil-structure interaction on a simplified level. This paper presents an efficient coupling approach, suggesting a practical interface between the offshore wind turbine substructure and sophisticated foundation models on mudline level. The approach is applied for load simulations on fatigue load level. The monopile load spectrum has to be defined in advance. Then, a limited number of static foundation pre-simulations are performed to predict the response on interface level by use of loaddisplacement curves. The integration of these curves into the load simulation model is achieved by an extension to spatial loaddisplacement surfaces. For this purpose an interpolation technique has been particularly developed which works efficient and accurate. The test simulations conducted for this paper are limited to co-directional wind and wave direction and a pre-dominant lateral loaded foundation, but the method offers the flexibility to be evolved to spatially loaded pile or bucket foundations