After focusing on aggregates in this workshop turned its attention in to embankments and natural hazards Such a topic could

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Niveau: Supérieur, Doctorat, Bac+8
contents S p e c i a l I s s u e - M a r c h 2 0 0 9 S p e c i a l I s s u e G e o t e c h n i c a l E n g i n e e r i n g After focusing on aggregates in 2007, this workshop turned its attention in 2008 to embankments and natural hazards. Such a topic could not be of more current interest given the recent events causing damage in the south of France. Embankments and dykes represent for many regional laboratories a field of longstanding expertise, particularly the Blois Laboratory, which I would like to congratulate here for their flawless organisation of these plenary sessions and for the very insightful assessment shared concerning the unique Middle Loire context. Both the maintenance and monitoring approaches towards these facilities adhere to strict risk prevention guidelines. These annual sessions have once again provided the ideal occasion to highlight the noteworthy studies and actual projects, along with recent methodological achievements involving Ponts et Chaussées network contributions and the research leading to such innovative approaches.

  • hydraulic risks

  • geotechnical engineering

  • infiltration monitoring

  • monitoring

  • saar river

  • lcpc

  • methods employed

  • identifying higher-risk embankment

  • regional laboratory


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Spotlight on
embankments at the
editorial LCPC's Plenary Session
Jean-Pierre Magnan
LCPC T echnical Director, devoted to Geotechnical
Geotechnical Engineering
Engineering
After focusing on
aggregates in 2007,
this workshop turned its
attention in 2008 to
embankments and natural
hazards. Such a topic could
not be of more current interest given the recent
events causing damage in the south of France.
Embankments and dykes represent for many
regional laboratories a field of longstanding
expertise, particularly the Blois Laboratory,
which I would like to congratulate here for their
flawless organisation of these plenary sessions
and for the very insightful assessment shared
concerning the unique Middle Loire context.
Both the maintenance and monitoring
approaches towards these facilities adhere to
strict risk prevention guidelines. These annual
sessions have once again provided the ideal
occasion to highlight the noteworthy studies
and actual projects, along with recent Middle Loire embankments: A key to protecting people and property.
methodological achievements involving Ponts
et Chaussées network contributions and the days concentrated on rockfall risks, landslide risks andThe entire geotechnical engineering
research leading to such innovative several site visits. The incidents of major floodingcommunity within the Ministry'sapproaches. regularly reported in the news stress the importance
The workshop programme also underscored scientific and technical network of this category of infrastructure, whose maintenance
the close collaboration enjoyed with gathered during the three days of remains crucial to efficiently preventing risks and
organisations like the local offices of Public
protecting facilities that in some cases date back toNovember 18 through 20, 2008 inWorks and Agriculture Ministries and the
the Middle Ages. These considerations become evenCemagref and Cetmef institutes. Moreover, Seillac (south-western France) for
more pressing in a zone like the Middle Loire, wherethe event set the stage for formal and informal the year's Plenary Session on
the State owns approximately 1,200 km ofexchanges, which are both necessary and Geotechnical Engineering topics.critical to generating a cooperative spirit and embankments. The geotechnical-related activities
advancing the state of knowledge. I would like The central topic of this session's undertaken by the Blois Regional Laboratory focus
to personally thank all participants for their heavily on these aspects, by way of performing stabilityagenda was embankments and natural
presence and ask that they mark in their assessments, providing consulting services and technicalhazards.calendars the next edition of this plenary assistance to the local Public Works authorities and
gathering, to be held in Nice from September Organised jointly by LCPC and the Regional Laboratory actors, and establishing expert evaluations within thest29 to October 1 , 2009. in Blois, the event was open to all members of the framework of a technical support group dedicated to
The topic addressed during the upcoming Public Works Ministry's Scientific and Technical network hydraulic facilities. The wide array of presentationssession's opening day will tie into a current (including LCPC, CETE, the regional laboratories, as throughout the day dealt specifically with one of fiveconcern voiced during the 2007 Grenelle well as the Setra, CETU and CERTU research units) overall themes: the perspective of a facility managerEnvironmental Roundtable: seismic risks. working in the geotechnical field. In his welcoming and the Middle Loire context, regulatory changes,
remarks, Michel Labrousse, Director of the Normandy- breakthroughs in the area of diagnostics, monitoring
Centre regional CETE Office, emphasised the massive and measurement methods, and actual field examples.
participation of the network's regional laboratories:
among the 135 attendees, 17 of these labs werecontents represented. Mr. Labrousse also acknowledged the
initiative to have opened this session to external
Regulatory environment: Embankments partners, like Cemagref and Cetmef, in addition to
to receive greater scrutiny p. 2 representatives from local administrative agencies,
including DDE (Public Works), DDAF (Agriculture),
The unique context DIREN (Environment), DRDe) and
of the Middle Loire zone p. 2 DGPR (Risk Prevention).
Diagnostic capabilities: Risk prevention and historical
Making the most of shared experiences p. 3 preservation
Embankments topped the agenda on this first day ofResearch: Improving understanding of the
the workshop programme, while the two subsequentmechanisms that compromise structures p. 4 Capturing the attention of a large audience.




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pSSpecial Issue Geotechnical Engineering March 2009
■ focus
The unique
context of the
Middle Loire zone
Six hundred kilometres
of levees contain the Loire
between Nevers and
Angers, delimiting a total
of 100,000 hectares ofNicolas Monié presented the series of new regulatory measures.
floodplain.
Regulatory environment: Loire River embankments are responsible for
protecting several large cities, chief among themEmbankments to receive greater
Tours, Orleans and Blois, accounting for a
scrutiny population served of some 300,000, including
120,000 housing units, 14,000 companies andRedefining rolesThe new set of regulations regarding 72,000 jobs. Given these magnitudes, the directThese updated regulations provide a clear distinctionhydraulic structures, which took cost of a major flood occurring on the Loire hasbetween obligations incumbent upon the facilityeffect on January 1, 2008, have been estimated at 10 billion euros.manager and the set of missions assigned to water
served to strengthen embankment supply services. The embankment owner is responsible
Built in some cases during Medieval times, thefor maintaining, overseeing and verifying facility condition.monitoring activities.
majority of Middle Loire levees date back to theThese obligations include conducting in-depth technicalMr. Nicolas Monié, Deputy Head of a unit with technical
16th century. These are highly fragile systemsinspections and submitting evaluation reports, butoversight of electricity supply, large dams and hydraulic
above all assessing the structural hazards. For their that require regular monitoring. Many types offacilities*, presented the newly-adopted regulatory
part, water supply inspectors periodically supervise phenomena are capable of causing levees tomeasures. According to Mr. Monié, "the key to this
the owner's actions, in ensuring compliance withadministrative reform is to generate a sufficient level break: internal erosion, leaks due to the
regulatory obligations and verifying structural safety.of embankment supervision and maintenance in order presence of pits or roots, levee base
to avoid, to the greatest extent possible, their failure Adoption of a new structural destabilisation (resulting from depression of the
prior to overflowing and internal erosion. classification riverbed and in some areas reaching two
The recent decree has classified structures accordingUntil the present time, it had never been requested metres), or perhaps the presence of significant
to their level of hazard, given the introduction offor embankments to undergo the same type of monitoring karst formations (natural underground passagesgraduated obligations. Four structural categories haveas for dams, which often serve as a means of energy
whose appearance would be due to thethereby been defined (A, B, C and D) based onproduction. The December 11, 2007 decree officially
dissolution of rocks carbonated by circulatingembankment height and population within thestandardises regulatory requirements for both
protection zone. The timetable for conducting the groundwater containing carbonic acid), while notembankments and dams; moreover, the revised
hazard study depends on the designated classification:framework imposes that embankment owners submit overlooking the risk of overflow in the event of
2012 for class A, and 2014 for the other three. Instudies and diagnostic evaluations to the competent large-scale flooding.
addition, the new regulations foresee instituting aauthorities.
cooperative agreement among the corresponding An embankment reinforcement programme for
Beyond safety-related improvements, this modification
monitoring agencies to intervene on behalf of facility the Middle Loire was launched in 1960 and, tohas also been intended to enhance knowledge in the
managers. this day, is still far from completion. Severalarea of structural strength and stability.
*This unit is a component of the Natural and Hydraulic Risks techniques are being employed, namely:
Department within the Ministry's Risk Prevention Directorate. reinforcement by means of a grout curtain,■ testimonial consolidation of levee bases, elimination of low
points, and the installation of weirs.
Jean Maurin
Head of Project Operations for the Loire riverbed
and levees Centre Regional Environment Directorate,
Loire-Brittany Basin Division
In the capacity of overall project supervisor, my role is to merge the perspective of
managers, who possess first-hand, day-to-day knowledge of embankment operations,
with ongoing research in the field. These workshop sessions provide an excellent opportunity for
comparing points of view between researchers and field operators. I was especially interested in“
the research performed on diagnostic methods. Embankments are highly heterogeneous structures. Methods employed must
be adapted to this distinction with dams, for which all monitoring-related features were installed at the time of construction.
Initiated in the 1960's, the programme to restore Loire River embankments is now 70% complete. We are facing phenomena
that call heavily upon our technical competence and experience and that definitely necessitate a sustained diagnostic effort.
As regards Loire riverbed subsidence, the Blois Laboratory has assigned specialised in-house expertise, which can be easily
and continuously deployed, placing the lab in an undeniably advantageous position with respect to other geotechnical
The Middle Loire embankments: An effective flood wall.entities.”
2Special Issue Geotechnical Engineering March 2009
The meander in the Loire River at Sandillon, a site of extensive monitoring.
Diagnostic capabilities: Making
the most of shared experiences
a bona fide historian was of tremendous value, as wasThe new regulatory context has
the morphodynamic input, which proves vital tomade it mandatory to proceed understanding and predicting how the riverbed will ■ focus
with a diagnostic evaluation of actually evolve. Thanks to this broader approach, the
geotechnical engineer is now required to incorporateall embankments more than
results from other sources and justify conclusions to1 meter high and responsible for
a wider audience." General protecting at least 10 inhabitants.
Sandillon: Benefiting fromNow would seem the ideal time complementarity in stability study to analyse in detail the methods geotechnical-hydraulic
employed by various regional responses of Rhine River
laboratories, with the aim of Located on one of the most pronounced meanders
drawing lessons that serve the of the Middle Loire, the town of Sandillon features a embankments:
series of levees built close to one another in a patternentire network.
that counters the river's natural flow direction, resulting TowardsVizille: Reliance upon a in significant loads being applied on the embankment,
particularly in the zone immediately following themultidisciplinary approach standardisedcurve. A measurement campaign had previously beenIn 2007, the municipality of Vizille commissioned the
conducted in 2005 by the Blois Laboratory (includingCETE Mediterranean Office, with assistance from
riverbed mapping and an examination of immersedCemagref in Aix-en-Provence, to perform the diagnostic calculation
embankment sections by means of both bathymetryand preliminary design work on an embankment road
and core sampling), subsequently completed byto replace the existing earthen structure built to methods
permeability and shear testing in the laboratory. Theprotect some 7,500 population residing on the right
process to synthesise hydraulic and geotechnical databank of the Romanche River. The study covered a Embankments located on the Upper Rhine
has led to establishing a hydraulic model of the river,number of aspects: analysis of the historical context,
are the focus of a Franco-German workingso as to localise inadequacies in reinforcement,a morphodynamic evaluation, designation of
maintenance and monitoring, as well as to designhomogeneous embankment sections, and a failure risk group established in 2004. The group's objective
necessary facility improvements. A number of structuralassessment on each of these sections. "This type of is to compare the general stability calculationstudies (focusing on overall stability, overflow potential,project demands competence in a multiplicity of
internal and external erosion, etc.) have rounded out methods used for embankments that displaydisciplines, explained Patrick Ledoux with the local
this effort.CETE Office in his presentation. The contribution of differences on both sides of the watercourse.
A series of calculations were thus performed
■ testimonial on two right bank profiles of the Iffezheim River.
While no distinctions were observed in its safety
Matthieu Jouvin evaluation for overall embankment stability,
Head of the Office of Design and Construction,
the group still insisted on the need to forgeIndre-et-Loire Public Works
consensus and voted to create a working group
to examine the internal erosion phenomenon
This is my first time attending one of the network's technical workshops. I was pleased in greater depth.
to accept the invitation by David Mathon, with the Blois Laboratory. I found the
central topic very timely given our day-to-day activity, which consists of overseeing embankment
reinforcement work within the scope of the Loire Regional Master Plan. We are only responsible“
for restoring levees owned by the local public authorities, which already constitute 180 km of protection throughout the
Indre-et-Loire department. Our objective is to successfully limit the risk of embankment failure by means of conducting
various types of works, depending on the specific context. I was very interested by discussions on the diagnostic component,
which is an essential step in identifying higher-risk embankment sections. Regulations now requires such a diagnostic
procedure, making it critical to be well-versed in current investigation methods. The session's focus on regulation was also
most helpful: many new facets now need to be integrated (diagnostic, safety review, hazard study, etc.), each at differing
intervals.”
3Special Issue Geotechnical Engineering March 2009
■ focus
Monitoring of karst-
related phenomena
Karsts are characterised by the appearance of
differently-sized orifices at the ground surface.
When occurring in the vicinity of an
embankment, this phenomenon is capable of
causing serious damage. The mapping of karsts
present beneath local authority levees
throughout the Loire River Basin has given rise
to a research study jointly undertaken by the
BRGM Geological Survey and the Regional
Environmental Agency (DIREN). No fewer than
767 karstic zones have been recorded.
Earthen embankment infiltration monitoring by means of electrical resistivity imaging on the Canal de Houillères of the Saar River The Blois laboratory contributed its findings
and knowledge on subsoil via a boreholeResearch: Improving understanding database along with a wide array of studies,
conducted in large part within the frameworkof the mechanisms that compromise of the former parafiscal tax status.
A methodological guide describing thestructures consolidation work underway relative to the
karstic risk will be released shortly.
The ERINOH projectModelling flows through the
Riprap and geotextileAnother phenomenon drawing considerable attentionembankment body, testing campaigns
from researchers is internal erosion. This subject has controlson erosion mechanisms and infiltration been the focus of a dedicated project called "ERINOH"
The introduction of riprap or geotextiles monitoring through electrical resistivity (French acronym for Internal Erosion in Hydraulic
is a common process during embankmentStructures), launched in 2005 with the participationimaging: this plenary gathering consolidation works. The Blois laboratory wasof teams from LCPC, Cemagref based in Aix-en-
provided the occasion to assess the commissioned to control several project sitesProvence, the Saint-Nazaire Civil and Mechanical
Engineering Institute and the Grenoble-based LTHE within the region and provide feedback. latest in research breakthroughs.
laboratory specialised in studying hydrological and "As regards geotextiles, it is easy to getThe presence of animal pits, tree roots or pipes can
environmental transfers. ERINOH's stated objective tangled up in the myriad of testing standardsinduce water to flow through the body of an embankment.
calls for the laboratory reproduction of basic internal and complicated recommendations issued byThis flow is then capable of leading to internal erosion
erosion mechanisms (unbinding, transport, binding), producers. Geotextiles need to be designed and ultimate embankment failure. Such a so-called
with the goal of deriving an appropriate model. This
"hydraulic fox" phenomenon serves as one of the most on a case-by-case basis, depending on both the
research should help define erosion abacuses for the
frequent causes of failure. Based on data generated soil and site, according to Yasmina Boussafir,purpose of evaluating structural strength.
from geotechnical studies on the embankments of who managed the study with the Blois lab.
The ERINOH project also investigates the internalSaint-Père-sur-Loire, Onzain and Nevers (all located As for riprap, the applicable standards are very
erosion detection methods applicable to embankments.in the central part of France), the Clermont-Ferrand clear-cut and restrictive. Besides the supplyAs part of this component, an infiltration monitoringregional laboratory devised a model that determines constraints inherent in this regional geologicalmethod designed for earthen embankments, usingthe level of structural risk and prioritises the various
context, verifying the characteristics andelectrical resistivity imaging, was experimentally testedforeseeable reinforcement solutions (sheet piling, non-
material dimensions of riprap delivered proveson the Canal de Houillères along the Saar River. Thisporous fill material, geomembrane, etc.).
method was subsequently implemented with success difficult to perform in the field. Certain
on the Saint-Clément-les-Levées site by the Angers adaptations became mandatory in order
regional laboratory. to account for such constraints and project
designer specifications; the end result turned■ testimonial
out to be entirely satisfactory."
Emmanuel Manier
Head of the Line Design Department, SNCF (Railway)
Engineering Division
The choice of embankments and natural hazards as the central topic for this year's Upon completion of these
Geotechnical Engineering workshop attests to the RST Network's marked change in sessions, Jean-Pierre Magnan
approaching problems of this type. This new orientation addresses problems from a more global accompanied by Yasmina
perspective and seeks to assemble the range of skills necessary to develop a response. For the Boussafir and David Mathon“first time, I am able to offer an outsider's view of session proceedings, and let me say how announced the upcoming
impressed I am by the calibre of proposals, experience and overall competence on display. 2009 plenary gathering.
At present, the SNCF Engineering Division only relies to a minimal extent on collaboration with the regional laboratories;
I remain however entirely convinced of the potential benefit and utility generated by pursuing closer relations between us, Next Plenary Session ongiven that we share the same set of values. Embankments are a major concern for both the RFF and SNCF (national railway
owner and operator, respectively) for obvious safety reasons. Naturally, we possess in-house competence on the topic, Geotechnical Engineering
yet our interests would be very well-served through engaging in collaboration with RST's wealth of expertise.” This gathering will be organised around the topic:
"Seismic risks and earthquake-
resistant construction"
and is to be held in Nice from September 29
Publication Director: Hélène Jacquot-Guimbal • Editor-in-Chief: Béatrice Revol • Deputy Editor-in-Chief: Séverine Bienassis • With
the collaboration of: Yasmina Boussafir, Matthieu Jouvin, Jean-Pierre Magnan, Françoise Maillet, Emmanuel Manier, David Mathon, Jean through October 1, 2009.
Maurin, Nicolas Monié. Contact : communication@lcpc.fr Coordination efforts have been assigned to the
LCPC Head Office - 58, boulevard Lefèbvre - 75732 Paris cedex 15 - France - Phone: +33 (0)1 40 43 50 15 - Fax: +33 (0)1 40 43 54 98
Nice Regional Laboratory, in conjunction with
LCPC Centre de Nantes - BP 4129 - 44341 Bouguenais cedex - France - Phone: +33 (0)2 40 84 59 06 - Fax: +33 (0)2 40 84 57 08
the LCPC Geotechnical Engineering Division.
Design, texts, production: www.rougevif.fr - This newsletter is printed on FSC-certified paper in an "Imprim'vert"-certified printing company.
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