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Proceedings of the 18th International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013, volume 6, 2016
the degradation is assigned; and it depends on neither the actual
load characteristics nor the number of cycles.
Rakotonindriana (2009) demonstrated that whenever the data
held are sufficient (i.e. several cyclic tests at various loading
levels), a network of P-y curves can be defined for each depth,
corresponding to a given number of cycles. These curves, which
may truly be qualified as "cyclic P-y", represent the degradation
of the static P-y curves that needs to be assumed in order to
identify global pile behavior after N cycles.
In relying on the substantial database of centrifuge tests
conducted at the IFSTTAR Laboratory, both prior to and as part
of the SOLCYP Project, it could be shown that quantifying the
influence of cycles on P-y curve "degradation" was possible
through introducing a coefficient of reduction rc that depends on:
number of cycles N, maximum applied load Hmax, and cycle
amplitude H c. Expressions for rc have been developed for both
clays and sands (Khemakhem, 2012; Rosquoët, 2013; Garnier,
2013).
The approach proposed by SOLCYP constitutes a decisive
breakthrough by incorporating the effect of cyclic loadings on
pile behavior in the presence of lateral forces.
8.3 Conclusion
The SOLCYP Project was assigned the objective of offering a
better understanding of pile behavior when subjected to cyclic
loadings and moreover developing innovative pile design
methods for handling axial and lateral loads. The response of
bored and driven piles in sands and clays was studied using
various approaches, both experimental (in the laboratory, on
models and in situ) and theoretical. The majority of experimental
data are now available, yet the tasks of data interpretation and
methodological advances still require further work.
For the design of piles subjected to cyclic axial loads, a
gradual approach has been proposed. Its first step, intended to
evaluate the potential need for conducting a detailed cyclic
study, is based on a comparison between the characteristics of
cyclic loads and the pile stability diagram. A critical contribution
of the SOLCYP Project has been to present stability diagrams
for bored and driven piles, in various types of soils (sands and
clays) with all loading modes (compression, tension, alternated).
A thorough, high-quality analysis of the experimental results
obtained will, in time, provide the designer with three types of
approaches: global, local by cyclic transfer curves, and
numerical by finite elements.
For pile design in the presence of cyclic lateral loads, an
extensive database of centrifuge findings was compiled on sands
and clays. Degradation laws could be proposed in order to
describe, in a comprehensive manner, the evolutions in pile head
displacement and maximum bending moment vs. number of
cycles and their severity. An equivalent mission is underway to
produce local transfer laws that take into account the number of
cycles and their characteristics. This effort offers a major
breakthrough compared to the available comprehensive methods.
An initial summary presentation of SOLCYP project findings
will be published in the proceedings of the ISSMGE's TC 209
workshop at the time of the 18th ICSMGE symposium. A book
of professional recommendations on pile computations under
cyclic loadings is to be published upon completion of this
project.
9 GENERAL CONCLUSION
The innovation produced during France's set of national research
projects is not solely the outcome of the fact that a majority of
financing is provided by project partners. In reality, for such a
project to be undertaken, it is also necessary to combine a
sufficient number of partners, which in turn requires a topic that
meets the expectations of the entire profession in the
corresponding civil engineering field, e.g. geotechnical
engineering. Thanks to the input of IREX, the entity assigned to
manage these National Projects, and its skills centers, topics of
broad interest like these have been identified and proposed.
Moreover, the experimental resources (full-scale
experiments, operating facilities made available by partners,
centrifuge experiments, etc.) constitute a project's critical
component, with numerical capacities coming in second. Such is
one of the specificities of France's National Projects program.
Lastly, mention must be made, with regard to geotechnical
engineering in particular, that these National Projects have made
it possible to rally, around a given topic, researchers from all
sectors in France (i.e. State agencies, public corporations,
universities and professional schools, contractors, design
consultants) as well as from abroad in order to work together
and, in so doing, create new ties.
The five National Projects in geotechnical engineering
selected herein as examples (i.e. Clouterre I and II - soil nailing;
Forever - micropiles; Vibrofonçage – vibrodriving ; ASIRI -
reinforcement by rigid inclusions; and Solcyp - piles subjected to
cyclic loadings) all effectively display the innovation, specificity
and experimental nature of France's NP projects and the
dissemination of their results.
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isolés sous chargements cycliques axiaux. Thèse. Université de
Paris-Est, A paraître.
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sur des pieux forés dans des sables denses. Proceedings 18th
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