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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013, volume 6, 2016
7.4
Lasting benefits from the ASIRI Project
The ASIRI Project has exposed how a granular distribution
mattress topping a network of rigid inclusions manages to
transfer a durable and significant load. The application to slabs is
currently enjoying widespread development and constitutes a
specialty on the international stage.
Interest in this technique has targeted applications for
sensitive structures. Let's cite the ICEDA project regarding
storage of radioactive wastes, subject to stringent nuclear
installation requirements; this project could be initiated and then
become viable subsequent to safety authority approvals, thanks
in part to the wealth of experience gained on this type of
structure through the ASIRI Project.
8
THE “
SOLCYP
” NATIONAL PROJECT
SOLCYP is a French anagram for "Piles subjected to Cyclic
Loadings".
8.1
Overview of the Solcyp Project
8.1.1
Project objectives
The SOLCYP Project is intended to improve knowledge held on
the behavior of foundation piles subjected to cyclic loadings. Its
assigned objective is to develop the procedures that allow taking
into account the effect of cycles in the design of civil
engineering structures or maritime facilities. The final project
phase comprises preliminary groundwork on standards, in the
aim of introducing the proposed procedure and associated
computation methods into national and international regulations.
The project encompasses a variety of aspects, including: driven
and bored piles; sands and clays; vertical and horizontal loads;
one-way and two-way cyclic loadings; and large numbers of
cycles.
8.1.2
Regulatory shortcomings
While the oil and gas industry has adopted procedures that take
into account the effect of strong cyclic loads due to sea swells on
the foundations of offshore platforms, the effect of cyclic
loadings on foundation behavior has for the most part been
ignored in the construction and civil engineering sector.
Naturally, a few notable exceptions can be found, like the study
of soil liquefaction when subjected to seismic loadings or the
fatigue of pavements and rail embankments. In general however,
no document at either the national, European (Eurocodes) or
international (ISO) level specifically addresses the risks related
to cyclic loadings by proposing a methodological approach to
incorporate such risks into foundation design guidelines.
8.1.3
Applicable structures
This shortcoming is even more surprising given the existence of
a wide range of structures subjected to repetitive loads
displaying a certain degree of regularity in both amplitude and
return period. "Cyclic" loads are basically either environmental
(sea swells, wind, water currents, tides) or operational in origin,
including in particular: land-based wind turbines; coastal or port
facilities (e.g. jetties, dykes); lightweight or slender support
structures exposed to wind action like electricity transmission
towers, chimneys and tall columns; civil engineering structures
supporting transport lines (especially rail bridges); crane
foundations; travelling cranes; and hydraulic turbines.
The anchorages of more recent structures dedicated to the
emerging new energies market (land and offshore wind turbines,
marine turbines, large-sized photovoltaic panels) are particularly
sensitive to the repetitiveness and cumulative effect of loadings.
8.1.4
The SOLCYP study program
The SOLCYP project study program was established as part of
the agenda of a working group assembled by IREX's "Soils"
cluster. It took shape upon defining two complementary study
targets: a project labeled "ANR-SOLCYP" that procured
financing from the ANR (Agence Nationale pour la Recherche)
Research Agency; and one known as "SOLCYP NP" organized
as a National Project with the financial support of the MEDDE
(Ministry of Ecology, Sustainable Development and Energy), the
FNTP (National Federation of Public Works) and 14 project
owners or contractors affiliated with the civil engineering and
energy sectors.
The total pre-tax budget of this NP neared €4.5 million,
broken down as €2.6 M for the ANR-SOLCYP piece and €1.9 M
for SOLCYP NP. The share of public-sector financing amounted
to 28%. The balance was covered by both partner dues and in-
kind contributions. The project got underway during the second
half of 2008 and was scheduled to end in 2014.
This two-tiered organization sparked considerable input from
academic organizations and public research laboratories (6
participants in all).
The ANR tier focused on the project's academic component
and included: a study of the cyclic behavior of reference soils
(clays and sands) through laboratory testing (cyclic triaxial,
cyclic DSS); a study of the static and cyclic behavior of
interfaces via a special battery of tests; execution of
instrumented tests on reduced-scale models inside a large
calibration chamber and in a centrifuge; and the development of
numerical models.
The NP tier was more specifically devoted to experimental
studies conducted on full-scale structures: instrumentation of
structures on piles, pile tests run at experimental sites, and the
development of
in situ
testing tools to measure cyclic soil
parameters.
8.2
Contributions of the SOLCYP program
8.2.1
Characterization of cyclic loads
In the construction and civil engineering field, it is commonplace
to assume that applied loads are of either the static or quasi-static
type. In accordance with regulatory prescriptions, critical loads
are defined by the maximum expected value under the various
load cases considered (serviceability limit state-SLS; extreme
environmental (ultimate)-ULS; accidental limit state-ALS).
The response of a soil subjected to cyclic loadings is complex
and depends on several parameters, namely: average stress,
cyclic stress amplitude, loading frequency, loading rate, and
number of cycles. These aspects are quite familiar in the domain
of geotechnical engineering for offshore oil platforms, but the
need for a thorough and accurate characterization of applied
loadings is not fully recognized in the broader field of civil
engineering. The collection of actual load cases and structural
instrumentation provides a better grasp of these various aspects.
Knowledge derived on the response of soils to cyclic loadings
is based on the set of phenomena tied to earthquakes or sea
swells, i.e. phenomena that involve a relatively small number of
cycles (on the order of a few tens to a few thousands) and span
periods shorter than 100 seconds. The need clearly exists to
extend the range of investigation to larger numbers of cycles
(above a million for wind turbines and intense traffic loads)
while building the capacity to handle phenomena associated with
long return periods (e.g. with respect to the effect of tides or to
the loading/unloading cycles of large tanks).
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