Behavior of Wind Energy Foundation Systems under Cyclic Loading
-Numerical Approach-

Wind energy plants promise to become an important source of energy in the near future. It is expected that within 15 years, wind parks with a total capacity of thousands of Megawatts will be installed in European seas. Three different foundation concepts (Monopile, Gravity foundation and Jacket foundation) will be investigated. Under the wind and waves action, the foundation supporting these structures will be subjected to highly cyclic loading. This lecture focuses on horizontal loading, which is the design-driving effect for monopiles and gravity foundations. However, for jacket piles the governing loading will be the axial cyclic loading. A three dimensional finite element model is used to investigate the deformation of monopile and gravity foundation with under monotonic und cyclic loading. The elasto-plastic material law with Mohr-Coulomb failure criterion was used. This material law was modified to account for stress-dependency of the oedometric modulus of elasticity using a subroutine which was implemented in the finite element program. To account for cyclic loading, a special innovative approach termed Stiffness Degradation Method (SDM) is applied, which makes use of the results of cyclic triaxial test results. With this method, the increase of displacement and rotation of the foundations can be calculated.
The piles used for jacket type foundation for wind turbine are subjected to highly cyclic tension and compressive loading. The pile capacity under cyclic tension loading decreases with number of loading cycles due to the reduction of pile shaft resistance. A two-dimensional numerical model will be developed. A new numerical simulation scheme called Capacity Degradation Method (CDM) is presented, which allows the calculation of pile capacity due to cyclic loading for driven piles. From the first loading and unloading steps, the shear strain amplitude in each element is calculated and the expected volume compaction under the considered number of load cycles is predicted by a mathematical approach derived from cyclic simple shear tests which is applied to the pile-soil system.
The numerical results for these different foundation systems (Monopile, Gravity foundation and Jacket foundation) with different dimensions under cyclic loading are presented and evaluated. Finally, recommendations regarding further investigations are given.

Behavior of Granular Materials in Microgravity Environment: Implication for NASA Future Exploration Missions

The constitutive behavior of soils such as strength, stiffness, and localization of deformations are to a large extent derived from inter-particle friction transmitted between solid particles and particle groups. Inter-particle forces are highly dependent on gravitational body forces. At very low effective confining pressures, the true nature of the Mohr-Coulomb strength envelope, which is the criterion most frequently used, is unclear both with respect to inter-particle friction and cohesion. Because of the impossibility of eliminating gravitational body forces on earth, the weight of soil grains develops inter-particle compressive stresses which mask true soil constitutive behavior even in the smallest samples of models. Therefore, the microgravity environment induced by near-earth orbits of spacecraft provides unique experimental opportunities for testing theories related to the mechanical behavior of soils. Such materials may include cohessionless soils, silt, clay, industrial powders, crushed coal, etc. This presentation discusses the importance of testing soils under very low confining stresses, effects of gravity on the stress-strain behavior of sand, and examples of potential future exploration missions to the moon and to Mars.

Sustainability of Civil Infrastructure using Shape Memory Technology

Civil infrastructure systems are the heart of any nation. The last few decades have clearly demonstrated the vulnerability of our civil infrastructure systems to problems like aging, natural and man-made hazard including earthquakes, hurricanes, blasts, etc. Among the primary reasons for this vulnerability are the limitations and shortcomings of the construction materials used. No doubt, conventional materials such as steel, concrete, and wood have proven to be limited in terms of their ability to withstand the extreme demands imposed on them by modern societies. The limitations in currently used construction materials combined with the consistently growing population worldwide present new challenges and demands for researchers in the field of structural engineering. Hence, there is an urgent need for new materials that are capable of extending the service life of structures with minimal or no need for maintenance or repairs; materials that are capable of increasing the resilience of our structures against natural and man-made hazards. Shape memory alloy (SMA) is a class of "Smart Materials" that have recently emerged as potential construction material with unique thermomechanical properties, namely shape memory effect and superelasticity/pseudo-elasticity. Shape memory effect is the thermally-triggered shape recovery of SMA when the alloy is in the martensite phase; however, superelasticity effect, which is observed at the austenite phase, is the ability of the mechanically stressed alloy to restore its original shape when unloaded even after being strained beyond its linear range. This presentation will provide the audience with basic background on SMAs and their potential applications is structures. Two applications will be discussed in particular. The first application involves the use of SMA in performing seismic rehabilitation of RC bridge columns that lacks flexural ductility. In this application SMA is used in the form of thermaly-prestressed spirals that can apply large active confinement pressure to the columns at their plastic hinge regions to improve their flexural ductility. The experimental results of large scale shake table test performed on two SMA retrofitted/repaired RC columns are discussed. The results demonstrates the great ability of SMA spirals in mitigating the damage even under strong levels of ground shaking. The second application focuses on utilizing superelastic SMA fibers as reinforcement for polymeric composite bars. The newly developed composite material is named SMA-Fiber Reinforced Polymer (SMA-FRP), and is studied as seismic reinforcing bars for moment resisting concrete frames. Nonlinear time history analysis is employed to study the performance of the frames under sequential earthquakes, i.e. main shocks followed by strong aftershocks. The results prove that using SMA-FRP bars at the plastic hinge regions of the frames helps significantly in limiting the residual drifts and enhancing the energy dissipation of the frames.

Case Histories in Geotechnical Applications

Rare is the personal experience that combines design and execution and evaluation of a project. Based on over 200 design/build projects done within 10 years, this study summarizes the lessons learned in geotechnical engineering, foundation and shoring projects. It shows how to approach the problem in hand , what design methods to apply, what challenges could be encountered during construction, how to conduct value engineering, what to avoid, and how to learn from each experience by following up, monitoring and comparing measured results to the initial design. Three case histories will be presented as examples of this approach with quantified results. These results show how to take full advantage of a project by making it an efficient learning experience this a successful project.

Modified Clays for Barriers

The aim of this Specialized Lecture is to present the recent advances and issues, as well as original research, on Modified Clays for Barriers. Topics of interest include long-term hydraulic performance of modified clays for GCLs, chemico-osmotic and diffusion efficiency of modified clays, modeling coupled chemical-hydraulic-mechanical behavior of modified clays, wet and dry ageing of modified clays, use of novel bentonites for vertical barrier applications, organoclays for various barrier applications. In addition, the possible reuse of dredged sediments after polymer treatment will also be discussed. Environmental management and handling of dredged sediments is important worldwide because enormous amounts of dredged material emerge from maintenance, construction and remedial works within water systems. Usually these materials after temporary upland disposal in lagoons are disposed in landfills. The aim of this study is to analyse the possible reuse of these sediments as a low-cost alternative material for landfill covers. The mechanisms through which polymers can improve the efficiency of dredged sediments for waste containment low permeable barriers are discussed.

CHADI SAID EL MOHTAR, Ph.D.

THE UNIVERSITY OF TEXAS AT AUSTIN, USA

As a geotechnical scholar researching pore fluid engineering geotechnics, I have developed a research program focused on auto‐adaptive solutions for mitigating geo‐challenges to existing and future infrastructures. My research involves engineering pore fluids and soils for resilient response to adverse and unforeseen loading conditions, with minimal compromise to the performance under normal working loads. Particularly, my work has focused on advancing the fundamental understanding of viscous flow within porous media through relating rheological properties of fluids and suspensions to the mechanical and hydraulic characteristics of geomaterials. Over the course of my research career, I have expanded my work on pore fluid‐soil micro‐mechanics from ground improvement contexts to include mobilization of non‐aqueous fluids within porous media in geo‐environmental and petroleum engineering applications. As such, my research integrates the areas of rheology, deep‐bed filtration, geotechnical, geoenvironmental and petroleum engineering to better understand the progressive temporal and space variations during and post flow of complex fluids in porous media.

Transferring Innovative Research into Practical Wisdom: The Case of Grouting

For decades, permeation grouting has been used as a cost-effective low disturbance ground improvement technology that allowed geotechnical engineers to help strengthening the soils and provide proper control of water flow. While permeation grouting can be a very useful solution, the design of an appropriate pre-grouting program can be the difference between a successful job and an expensive on-the-go repair. However, current grout design relies heavily on rules-of-thumb and outdated charts. The geotechnical investigation is rarely targeted towards grouting design and the final grouting decisions are made based on index measurements such as fines content or soil classification at most. The collective "past experience" is more commonly used for final grouting design than any other geotechnical work. Flow of suspensions through porous media is a very complex phenomenon owing to the diversity of possible flow stoppage mechanisms involved. For some cases, rheological blocking occurs due to viscous grouts; however, in most cases, permeation is controlled by filtration. Filtration is the process of particles being pulled out of the suspension and trapped by the soil grains which leads to the simultaneous change in the physical properties of porous media (decrease in void ratio) and the rheological properties of the grout. Recent research on the topic highlights these complexities and the potential to use advanced laboratory testing to properly characterize the grouts and design it for field specific conditions and desired final improved performance. Despite the complexity of the science behind permeation grouting, practitioners often reference insitu heterogeneity and variability to dismiss the need for a more systematic design approach. However, heterogeneity and variability is always part of geotechnical design but that never stopped engineers of performing proper geotechnical design based on measured engineering properties and this should be the case for grouting as well. Particularly, with all the recent advances to grouting materials and its accompanying additives, grouting is now possible with more diluted suspensions (higher w/c ratios) and the grouts are more "flowable" than ever before. These advances are making most of existing charts and common rules of thumb obsolete and therefore, it is the optimal time to implement recent advances in grouting research into common practice.

Geosynthetic-Reinforced Pile-Supported Embankments: Load Transfer Mechanisms

In recent years, piles have been increasingly used to support embankments when they cross soft soils, approach bridges, and are widened and/or elevated. Geosynthetics have been used to bridge over the span of piles to enhance load transfer from soil to piles and reduce total and differential settlements. However, the geosynthetic-reinforced pile-supported embankments have presented a complicated geotechnical problem in terms of soil-geosynthetic-pile interactions and load transfer. This presentation will start with the historical development of pile-supported embankments and focus on the load transfer mechanisms involved in the geosynthetic-reinforced pile-supported embankments under static and dynamic loading, including soil arching, tensioned membrane effect, and stress concentration.

Engineering geology for the conservation of UNESCO heritage sites

Cultural heritage represents the legacy of the human kind on the planet earth. It is evidence of millennia of adaptation of humans to the environment. Cultural heritage can be intangible (e.g. traditional knowledge, customs, ritual practices or beliefs) and tangible, the latter including various categories of places, from cultural landscapes and sacred sites to archaeological complexes, individual architectural or artistic monuments and historic urban centres. The most world wide representative Cultural and Natural Heritages are included within “UNESCO Convention Concerning the Protection of the World Cultural and Natural Heritage”. They are the flagship of a large number of monuments and sites diffused at either national or local level.
The sites and remains are not always in equilibrium with the environment. They are continuously impacted and weathered by several internal and external factors, both natural and human-induced, with rapid and/or slow onset. These include major sudden natural hazards, such as earthquakes or extreme meteorological events, but also slow, cumulative processes such the erosion of rocks, compounded by the effect of climate change, without disregarding the role of humans, especially in conflict situations.
Against this background, engineering geology and earth science in general may play an essential role in the conservation and management of cultural properties. The relevance and potential of these areas of study was not fully appreciated in the past. At present, however, their contribution is increasingly acknowledged as the need for an inter-disciplinary approach, which would bring together art history, science, management and socio-economic concerns, has become more and more apparent.
As a matter of fact, the protection of Cultural Heritages from geotechnical and geological hazards is a border area between Science for Conservation of Cultural Heritages and Earth Science.
The present talk is reporting some examples from the author’s work experience in different part of the world, demonstrating the relevance of geological sciences for the conservation on monuments destroyed by explosions (e.g. Bamiyan, Afghanistan, Herat, Afghanistan), damage by landslides and rock fall (e.g. Machu Picchu, Peru; Petra, Jordan, Vardzia, Georgia; Zohak, Afghanistan, Swayambu, Nepal), affected by rising dumpness (e.g. Lumbini, Nepal; Koguryo, North Korea; Bayannuur, Mongolia), finally by weathering (e.g. Laliblea, Ethiopia; Rapa Nui, Easter Island, Chile) and structural deradation (e.g. Pompei, Italy). This presentation will focus on the relevance of modern technologies for investigation and monitoring, as fundamental step for a safeguarding project that have to enhance, as much as possible, traditional knowledge and local sustainable practices, in conservation techniques.