Actes du colloque

Proceedings of the 18

International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013, volume 6, 2016

The strain in nailed soil walls, especially displacements at the

top of the wall, has also been the focus of considerable

instrumentation on both experimental walls and structures

currently in service. The horizontal displacement at the top of a

vertical nailed soil wall of height H thus lies between H/1000

and 3H/1000, depending on the chosen safety coefficient value.

4.4

Clouterre 1 publications

This NPs has been the subject of 50 internal reports and

publications both in France and abroad. The most significant

publication was "

Clouterre

1991 Recommendations for

designing, calculating, constructing and inspecting earth support

systems using soil nailing". This book comprises 7 chapters and,

after being translated into English, was produced in 10,000

copies by the American FHWA (Federal Highway

Administration) before a joint publication was released by

FHWA and the

Presses des Ponts et Chaussées

publisher for

worldwide distribution. These Recommendations greatly helped

promote the nailed soil technique for retaining walls and gave

rise to the NF P 94270 AFNOR Standard, which serves as the

French application standard for Eurocode 7 regarding retaining

wall structures, whether built in nailed soil or reinforced soil.

4.5

The Clouterre II National Project

4.5.1 Organization of this NP

Developed subsequent to

Clouterre I

, which took place from

1993 to 1997, the

CLOUTERRE II

National Project assembled

19 partners, including FHWA, thus making it the first example

of a foreign partner participating in a NP. The total cost of this

project amounted to €1,579,190, including a subsidy from the

DRAST Research Directorate in the amount of €281,708, i.e.

17.8% of the total budget, with the balance provided by the

partners (through dues and in-kind contributions).

4.5.2 The Clouterre II NP research topic

Clouterre

II constituted another milestone towards

understanding and designing nailed soil structures, with

emphasis placed on methods for computing displacements,

execution techniques, behavior in the presence of special

loadings (walls subjected to freezing, earthquakes), and the

behavior of a structure other than a wall (reinforced nail facing

in tunnels built in compressible soil).

4.5.2.1

Construction of nailed soil walls: Facing behavior

and justification

The

Clouterre

I database of nail tension test results was updated,

notably the chart (q

, p

) yielding, for the various soil categories,

the limit friction stress values q

of the soil/nail interaction vs.

limit pressure p

of the pressuremeter. The execution of facing

was studied with regard to drainage. Moreover, a chapter was

devoted to the facing behavior and its justification based on

instrumented structures currently in service, notably the A12

motorway walls southwest of Paris.

4.5.2.2

Displacement calculation methods

The

Clouterre

1991 database of displacement measurements on

actual nailed soil walls was finalized and a semi-empirical

method could be devised thanks to these results.

General methods based on both finite elements (i.e. CESAR

and Plaxis software packages) and finite differences (FLAC-2D)

have been developed. These methods rely on two-dimensional

modeling, whereby the nails are modeled by "equivalent plates

with plane interfaces" for finite elements and "equivalent nails

with load transfer functions" for codes based on finite

differences. Such methods were validated by comparing the

results of calculations with measurements on full-scale

structures, built in soils with known properties, instrumented and

monitored over time from construction through service startup

and ultimate failure. In this respect, the

Clouterre

I experimental

walls constitute an exceptional base of reference structures. In

addition to the conventional parameters of soil elasticity and

strength, the angle of dilatancy



must be included as well as

parameters relative to the nails, facing and their interactions with

the soil. Figure 6 indicates the evolution in horizontal

displacement



h at the top of the

Clouterre

No. 1 wall facing,

accompanied by a comparison with measured values. On the

whole and compared to the previous calculations carried out

(Shaffiee, 1986), it is observed that the measured values have

been accurately predicted, yet it is still advised to perform a

sensitivity study relative to the set of mechanical parameters in

order to ensure the validity of these results.

Fig. 6:. Trends in horizontal displacement calculated at the top of the

cladding; comparison with measurements (

Clouterre

No. 1 wall)

4.5.2.3

Other research



Study of the effect of freezing-thawing: Instrumentation

introduced on a nailed soil wall, built in a mountainous zone in

1982 and subjected to significant facing displacements during a

frozen period, has enabled studying the freezing-thawing

mechanisms and finding a means to incorporate freezing effects

in a nailed soil wall.



Earthquake design: Nailed soil walls are, like Reinforced

Earth walls (Kobayashi

et al.

, 1996), flexible structures that

withstand earthquakes fairly well. As a general rule, their

stability during an earthquake is analyzed with a failure

computation by applying the pseudo-static method. The case of

composite structures, in which a nailed soil wall is supported at

the top by prestressed anchors, requires higher seismic

coefficients to be input into the stability calculations.



Nailing (bolting) of the tunnel face in compressible soil:

Practiced since 1985, the bolting technique using sealed rods

stabilizes linings or full-section tunnel facings during

construction. In this latter case, the rods are made of a composite

material made of fiberglass and resin for the purpose of being

easily destroyed at the time of excavation. The stability of this

reinforced facing is calculated by means of analysis conducted at

the limit equilibrium or by applying failure calculation theory.

Strain calculations that incorporate this nailing into both ground

and retaining walls displacements are of three types: 1) modeling

of each rod, with a 3D computation; 2) homogenization-based

approximation of the ground/rod assembly, with 2D

axisymmetric computations; and 3) simulation of the nailing

effect by applying pressure to the tunnel face, with 2D

axisymmetric computations.

4.5.3 Clouterre II publications

The

CLOUTERRE

II National Project research has given rise

to 22 internal reports and a book entitled "

2002 addendum to

the

CLOUTERRE

1991 recommendations

", published by

Volume 6 - Page 79