Macroelement modeling of shallow foundations

The paper presents a new macroelement model for shallow foundations. The model is defined through a non-linear constitutive law written in terms of some generalized force and displacement parameters. The linear part of this constitutive law comes from the dynamic impedances of the foundation. The non-linear part comprises two mechanisms. One is due to the irreversible elastoplastic soil behavior: it is described with a bounding surface hypoplastic model, adapted for the description of the cyclic soil response. An original feature of the formulation is that the bounding surface is considered independently of the surface of ultimate loads of the system. The second mechanism is the detachment that can take place at the soil-footing interface (foundation uplift). It is totally reversible and non-dissipative and can thus be described by a phenomenological non-linear elastic model. The macroelement is qualitatively validated by application to soil-structure interaction analyses of simple real structures

Undrained sliding resistance of shallow foundations subject to torsion

While the behavior of shallow foundations under vertical load combinations has been the subject of numerous studies, the response of shallow foundations subjected to combined horizontal and torsional loading has received considerably less attention. New offshore applications of shallow foundations for LNG facilities and other subsea structures have underscored the importance of the behavior of shallow embedded foundations subjected to combined in-plane translation and torsion. This study investigates the undrained bearing capacity of rectangular and square shallow foundations under eccentric horizontal loads through comparisons of various limit equilibrium and plastic limit analysis solutions to 3-D finite element solutions. In general, the plastic limit approach considered in this paper agrees well with the finite element solutions, although it has some tendency to over-predict capacity at greater embedment depths. The studies revealed a general insensitivity in the shape of the yield envelope to variations in embedment depth, which permits a simplified analysis suitable for first order estimates of load capacity. The variables considered in this study include footing aspect ratio, embedment depth, and load direction in addition to eccentricity.This is the author's accepted manuscript. The final version can be found published by ASCE in the Journal of Geotechnical and Geoenvironmental Engineering here: http://ascelibrary.org/doi/abs/10.1061/(ASCE)GT.1943-5606.0001138

Investigation of the Size Effect at Different Geometries on Stress Distribution of Sandy Soils

In this study, the induced vertical soil stress values occuring along with horizontal surfaces at predetermined depths of the shallow foundations on sandy soils were investigated by model tests. In the model tests pressure transducer was used to measure the stresses.Circular foundations at different size were used in the model tests and the size effect were investigated. As a result of this study, the size effect at circular foundations wasn't found tobe an important factor on stress distribution of sandy soils

The vertical capacity of grillage foundations

Grillage foundations may provide an economical alternative to offshore ‘mudmat' foundations for seabed infrastructure, owing to their improved hydrodynamic characteristics, which are important during installation. Grillage foundations consist of a mesh of vertical grilles that penetrate the seabed during loading. Offshore loadings on these types of foundation are likely to consist of vertical (mostly dead weight) loading and horizontal ‘in-service' loads. However, to date there is no accepted method of design, as foundation capacity may differ significantly from that of conventional solid shallow foundations. This paper presents an analytical method designed to calculate the variation of vertical bearing capacity with grille penetration in sand. The results show that grillages are able to achieve the same capacity as solid foundations of the same breadth, but this requires significant penetration of the grillage. Consequently, design choices are likely to depend on the amount of settlement the structure can tolerate. Simplified analytical equations have been presented to allow calculation of the load–settlement response, and to calculate how much settlement is required to mobilise the flat-plate capacity of a solid mudmat of the same overall breadth. The methodology has been validated by comparing results with those from model tests. </jats:p

Investigating the changing deformation mechanism beneath shallow foundations

The design of shallow foundations has traditionally used a mixture of plasticity-based solutions to find the ultimate limit state and either a factor of safety on the plasticity solution or a linear elastic solution to attempt to design for the serviceability limit state. The serviceability limit state is intrinsically linked to the deformation mechanism that occurs beneath the shallow foundation in service. A better understanding of these soil movements can pave the way for more rational design approaches. In this paper, small-scale experimental work is used to show that the deformation mechanism beneath strip and circular foundations continuously changes as the footing is displaced. The mechanisms observed at intermediate settlements, noted to be typical design points, are best described by a mixture of solutions. Linear mixes of idealised fields were analysed using an upper bound approach to determine the load–displacement behaviour of each mix. The envelope of lowest upper bounds indicated that the optimal mix of fields changes depending on the footing settlement. At typical design points for shallow foundations mixtures dominated by ellipsoidal cavity expansion mechanisms were found to be optimal for both axisymmetric and plane strain cases. Comparison of theoretical and experimentally measured predictions indicated that using linear mixes of fields gives a good approximation to the true behaviour and may be used for settlement-based design approaches in the future. This is the author accepted manuscript. The final version is available at http://www.icevirtuallibrary.com/content/article/10.1680/geot.14.P.226

AceWiki: A Natural and Expressive Semantic Wiki

We present AceWiki, a prototype of a new kind of semantic wiki using the controlled natural language Attempto Controlled English (ACE) for representing its content. ACE is a subset of English with a restricted grammar and a formal semantics. The use of ACE has two important advantages over existing semantic wikis. First, we can improve the usability and achieve a shallow learning curve. Second, ACE is more expressive than the formal languages of existing semantic wikis. Our evaluation shows that people who are not familiar with the formal foundations of the Semantic Web are able to deal with AceWiki after a very short learning phase and without the help of an expert.Comment: To be published as: Proceedings of Semantic Web User Interaction at CHI 2008: Exploring HCI Challenges, CEUR Workshop Proceeding

Centrifuge testing to evaluate the liquefaction response of air-injected partially saturated soils beneath shallow foundations

Earthquake-induced liquefaction of saturated soils continues to cause severe damage to structures with shallow foundations. In recent years, artificially reducing the degree of saturation and forming partially saturated zones within saturated soils has been proposed as a liquefaction mitigation technique. This study experimentally investigates the liquefaction response of air-injected partially saturated soils beneath shallow foundations. A series of centrifuge tests were conducted on the shallow foundations with different bearing pressures. The results of the tests show that the generation of excess pore pressures and consequent liquefaction-induced settlements of shallow foundations were a strong function of the degree of saturation. Forming spatially distributed partially saturated zones in the liquefiable soils limited the development of high excess pore pressures and liquefaction susceptibility of soils, particularly at the higher confining stresses. The reduction in the degree of saturation of soils decreased the depth of liquefied soil layer, and increased the resistance of soil to the bearing capacity failure. On the other hand, the decrease in the degree of saturation of liquefiable soils led the larger accelerations to be transmitted to the foundations through unliquefied soil zones. It is therefore concluded that use of air-injection as a liquefaction mitigation measure does reduce structural settlements, but will have the consequence of larger structural accelerations.Ministry of National Education (M.E.B.) of TurkeyThis is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s10518-016-9968-