An enhanced interface model for friction fatigue problems of axially loaded piles

in Proceedings of the ASME 2019 38th, International Conference on Ocean, Offshore and Arctic Engineering, Glasgow 9-14 June 2019 (2019, June 09)

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 ... [more ▼]

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 micro-phenomena 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. [less ▲]

Dutch field tests validating the bearing capacity of Fundex piles

in Proceedings of CPT’18 – International Symposium on Cone Penetration Testing (2018, June)

In 1939, Boonstra was the first to base the tip bearing capacity of foundation piles on the CPT cone resistance. Since then, many engineers and scientists have proposed improved design methods for the ... [more ▼]

In 1939, Boonstra was the first to base the tip bearing capacity of foundation piles on the CPT cone resistance. Since then, many engineers and scientists have proposed improved design methods for the bearing capacity of foundation piles, such as the Dutch Koppejan method. This method holds a mistake in the qc-averaging method. Its tip resistance is based on the cone resistance of an assumed zone between 8D above the tip and 4D below the tip, while several researchers show that this should be in a zone between 2D above the tip and 8D below the tip. In the Netherlands, Belgium and France a field test has been performed indicating that the currently used design method in the Netherlands (the Koppejan Method) was about 30% too high for the tip resistance. This, and also the current qc-averaging method, conflict with the findings of Boonstra, Plantema, Huizinga and White & Bolton. Besides, in the field test, the residual stresses in the piles after installation were completely ignored, in fact, not even measured. Nevertheless, the Dutch Norm Commission Geo-Engineering decided to reduce the bearing capacity of foundation piles in the Netherlands, unless other field tests prove otherwise. Since this reduction is very drastic and since no serious problems due to the use of the unreduced bearing capacity were recorded, the geotechnical contracting company Funderingstechnieken Verstraeten BV has performed field tests on six Fundex piles, and asked the engineering company BMNED to assist with these tests and the design. The aim was to prove that, at least for Fundex piles, a reduction of 30% is too much. The Fundex Pile Tests in Terneuzen show that, especially for the grouted Fundex piles, the pile type factor should not be reduced in combination with the current qc-averaging method. [less ▲]

Historical overview of CPT-based design methods

in Proceedings of the International Conference of Civil Engineering, ICCE 2017, Tirana 12-14 October 2017 (2017, October 12)

The Cone Penetration Test (CPT) is used for many decades in order to evaluate the pile bearing capacity. Pieter Barentsen developed the CPT around 1930 in order to investigate the soil resistance. However ... [more ▼]

The Cone Penetration Test (CPT) is used for many decades in order to evaluate the pile bearing capacity. Pieter Barentsen developed the CPT around 1930 in order to investigate the soil resistance. However, Boonstra was the first, in 1940, to used the cone resistance of the CPT as the unit pile bearing capacity. From this moment, the CPT became very important in the evaluation of the pile bearing capacity. An overview is given about the most common pile design methods, which are based on the in-situ Cone Penetration Test (CPT). This overview will start with the evolution of the CPT, followed by a brief presentation of the methods in use. An important part, in pile design methods, is the averaging procedure of the cone resistance over an influence zone around the pile tip. Since the pile tip is much wider than the tip of the CPT cone, the influence zone of the pile is also much larger, therefore the cone resistance has to be averaged over the influence zone around the pile tip. Unfortunately, the definition of this zone is different for each method in use. Finally, several methods for the pile tip bearing capacity near the interface of a soil layer will be discussed, including related methods from De Beer [1] and White & Bolton [2]. [less ▲]

Développement d'un macroélément pour des calculs sismiques pour des fondations profondes

Bachelor/master dissertation (2015)

The soil-foundation-structure interaction has been always a part of civil engineering where the hypothesis are numerous. These hypothesis can be an acceptance (such as dimensionless efforts ... [more ▼]

The soil-foundation-structure interaction has been always a part of civil engineering where the hypothesis are numerous. These hypothesis can be an acceptance (such as dimensionless efforts / displacements) or neglect ( such as radiation damping on far-field effect, detachment soil-foundation). However, they are used by many researchers in its calculations, thus the soil-foundation interaction its known for particular conditions. This study concerns to the development and programming of a new macro-element taking into account the radiative damping, of course based on previous models ; developed by [Nova and Montrasio, 1991], [Cremer, 2001]...., [Grange et al., 2009] and [Li, 2014]. The last two models will help us during this study. To get some good results we have to find a rheological model that represents on the best way the interaction soil-foundation . The model "Monkey-Tail" [Wolf, 1994] will be chosen. After understanding how the macro-element is going to be introduced in such way that it considers the radiative dumping, FedeasLab (a MATLAB tool, [Filippou and Constandines, 2004]) will check the validation of this model. This will be the second part of the study. [less ▲]