Helical pile: physical and numerical modeling for marine geotechnical applications
Context and Motivation
With the development of renewable energies and the need to shift construction methods towards low environmental impact solutions (reduced carbon footprint and reuse/dismantling), there is now a booming market for a new type of foundation, e.g. for light structures (solar panel supports), individual houses or developments in protected or tourist/recreation areas (pontoons/bridges/barges) or for temporary structures. There are also other applications that are currently being explored, concerning anchors (operating in traction) in aquatic or marine environments e.g. floating wind turbines or solar panels on barges, or wave energy converters.
In the field of marine geotechnical engineering, the helical pile (HP) consists of a metal shaft on which one or more helices are welded. Because they are easy to install and decommission, most often, these helical piles are of small dimensions (length of a few meters, diameter of the helix of about 30 cm). They are also silent to install, which is an important requirement for installation offshore and onshore. Despite their clear advantages, the design of HP is neither covered by the current Eurocodes nor by the specifications and standards. In addition, the cyclic loads that the HP experiences are likely to cause a "fatigue" issue at the shaft-ground interface and in the vicinity of the helix, which can lead to long-term degradation and performance issues. Therefore, research and development work on the long-term cyclic behaviour of HP is required to provide a thorough understanding of the performance degradation risk and implement design practices for the industry.
Project Objectives
The research project will tackle the following 6 objectives:
- elucidate the most appropriate methods of geotechnical investigation to build semi-empirical design guidelines (we will focus initially on the case of cohesionless soils and then move to the case of cohesive soils),
- understand the possible methods of installation for the HP, and how to characterize the HP response to torque phases of the installation and axial push phases of the
- highlight the consequences of an "imperfect" installation (different from a one-step drive-by-turn) on its subsequent behaviour,
- establish a simple model to predict the bearing capacity of these piles: we will distinguish the function in "anchorage" (traction), from the function in compression, but also the effect of cyclic loading,
- understand the influence of the geometrical configuration (one/two helices, for example) on the bearing capacity,
- devise an experimental test campaign to validate/control the long lift/behaviour (short term/long term)?
The Ph.D. student will work towards these objectives, to propose design guides that are adapted to the field of use of these piles and their associated stresses.
How to apply
To apply, please email:
▪ A CV
▪ A cover letter detailing your suitability and motivation for this position
▪ A copy of your transcript
Email to zheng.li@univ-eiffel.fr and luc.thorel@univ-eiffel.fr. Please, do not hesitate to get in touch for further information.
Further information:
Please, download the PDF below. See also:
https://www.ifsttar.fr/offres-theses/sujet.php?num=3879&num_session=1
https://theses.doctorat-bretagneloire.fr/sis/campagne-2024
Deadline for applications: March 27th 2024