TECHNICAL PAPER

Some aspects of research and practice for pile design in France

Roger Frank1

Received: 3 May 2017 / Accepted: 2 June 2017 / Published online: 22 June 2017

� Springer International Publishing AG 2017

Abstract This paper summarises some aspects of the meth-

ods used in France for designing pile foundations under axial

and transverse loadings. These methods mostly use the results

of Menard pressuremeter (MPM) tests and concern the

determination of the bearing capacity, as well as the prediction

of axial and transverse displacements. The prediction of the

bearing capacity from CPT results is also given. After men-

tioning the general context of foundation design in France, the

details of these methods are described and some of their

experimental background is explained. These methods are

now included in the French standard for pile design (published

by AFNOR, Justification of geotechnical work—National

application standards for the implementation of Eurocode 7—

Deep foundations, 206, 2012), fully compatible with Euro-

code 7 on ‘Geotechnical design’.

Keywords Pile � Axial loads � Transverse loads � Bearing

capacity � Settlement � Transverse displacement �t–z curves � p–y curves � Pressuremeter test � Cone

penetration test

Introduction

The Menard pressuremeter is a specific form of prebored

pressuremeters (note that sometimes it can be driven inside

a slotted tube). It was invented and developed by Menard

[27] who also established the first corresponding rules for

the design of foundations: settlement of foundations [31],

behaviour of deep foundations under transverse loading

[28], and axial bearing capacity of foundations—whether

shallow or deep [29]. The evolution of the rules for the

design of shallow and deep foundations was included in a

general document published by Menard [30].

It is clear that the immense advantage of the Menard

pressuremeter test (MPM) is that it provides the geotech-

nical engineer with both a failure parameter (the limit

pressure pl) and a deformation parameter (the pres-

suremeter modulus EM). It enables him/her to tackle with

the same test the problems of bearing capacity of founda-

tions (using pl), as well as the problems of displacements of

foundations (using EM), i.e. the problems of deformation of

the structures to be carried.

The development of the use of MPM for foundation

design was, nevertheless, very often limited by the fact that

it needed a new approach, outside the conventional and

classical framework of soil mechanics (which had been

developed mainly with the use of laboratory tests, like the

triaxial test and the oedometer test)—see, for instance, the

paper by Gambin and Frank [24].

Indeed, the rules for the design of foundations from

MPM are essentially of ‘direct’ type, i.e. they use direct

correlations between the measured parameter (pl or EM)

and the ‘design’ parameter (bearing capacity, settlement or

transverse displacement). They do not require to determine

first a ‘basic’ soil parameter (parameters of shearing

resistance or oedometer modulus) to enter, subsequently,

into the classical bearing capacity formulae or oedometer

or elastic formulae for the settlement.

One of the other advantages of MPM is that it can be

performed in all kinds of grounds, from soft soils, to very

stiff or very dense soils and soft rocks, thanks to the

This paper was selected from GeoMEast 2017—Sustainable Civil

Infrastructures: Innovative Infrastructure Geotechnology.

& Roger Frank

roger.frank@enpc.fr

1 Ecole nationale des ponts et chaussees, Laboratoire Navier-

CERMES, Marne-la-Vallee, France

123

Innov. Infrastruct. Solut. (2017) 2:32

DOI 10.1007/s41062-017-0085-4

preborehole. In the French geological context, this has also

turned out to be a great advantage.

The Laboratoires des Ponts et Chaussees (LPCs, High-

ways Authority Laboratories) were very soon interested by

the pressuremeter tests and their application to the design

of foundations (see, for instance, among their early publi-

cations, [25]). As a matter of fact, the design rules proposed

by Menard constituted the basis for the first document of

recommendations called ‘‘FOND 72’’, published in 1972

by the Ministry in charge of public works of France.

Starting from the early 1970s, the urgent need for

updated specifications for the foundation design in France

was at the origin of an intensive research work. This

activity was carried out mainly by the Laboratoires des

Ponts et Chaussees (LPCs); it consisted essentially of full-

scale testing and, after 1985, of geotechnical centrifuge

testing performed with the LCPC Nantes centrifuge facil-

ities. Interest was focused on:

– the assessment of design rules for foundations valid for

civil engineering public works contracts, expanding

those already existing for buildings;

– extending to the field of foundations design the limit

state approach elaborated since 1979 for the design of

structures;

– making these foundation design rules compatible with

the latest limit state design specifications used by the

Eurocodes for steel, reinforced concrete or pre-stressed

concrete structures.

Thus, after more than 20 years of research effort, cor-

responding to the construction of important infrastructures

in France, such as the motorway network and the TGV

(very fast train) lines, the Code of Practice, replacing the

‘‘FOND 72’’ recommendations, called ‘Fascicule 62—Titre

V’, was completed [26]. The method for designing axially

loaded piles with MPM results, both for bearing capacity

and settlement (axial displacements), given in ‘Fascicule

62—Titre V’ Code are detailed, in particular, in Busta-

mante and Frank [10] and Frank [20].

Recently, the need to implement the Eurocode 7 on

‘Geotechnical design’ [16, 17] into French practice led to

the publication of the new French standard for the appli-

cation of Eurocode 7 to deep foundations (standard NF

P 94-262, [2]). Most of the practical aspects of pile design

described below have been introduced into the new

standard.

This new French standard, like ‘Fascicule 62—Titre V’,

deals with all the usual pile foundation problems onshore,

such as foundations of bridges, that is to say foundations

subjected to axial loads, transverse loads, moments, nega-

tive skin friction and lateral thrusts due to soil movements.

The recent paper by Burlon et al. [9] gives a comprehen-

sive summary of the document.

The basic principles of the method for design from the

MPM test results originally set up by Menard in the 1960s

are still used. However, the design charts and other quan-

titative material have been continuously changed and

updated following the experimental research work carried

out mainly by the LPCs. This method leads to a complete

set of rules, providing the foundation engineer with all the

means for designing foundations. It contains precise

equations or formulae for calculating bearing capacities

and displacements of pile foundations. Furthermore, the

method has been adapted to the limit state approach.

Bearing capacity of piles

The work by Bustamante and Gianeselli [13] interpreting

the results of the full-scale tests of piles carried out at that

time by the LPCs was a milestone, because it formed the

basis for the revised MPM rules and CPT rules for the

bearing capacity of piles, both for the code for buildings

[18] and for the code for civil engineering works ‘Fascicule

62—Titre V’ [26].

These MPM rules have been continuously updated, as

the results of more full-scale tests became available. At the

occasion of the drafting of the new French standard on pile

foundations (for buildings and civil engineering works),

compatible with Eurocode 7, Bustamante and Gianeselli

[15] and Bustamante et al. [12] re-analysed the data of the

full-scale tests available in the LCPC database (LCPC, now

called IFSTTAR, is the Central Laboratory of the High-

ways Authority). Their work forms the basis of the new

rules ‘PMT 2012’ finally adopted in the French standard of

AFNOR [2]—see Baguelin et al. [3] and Burlon et al. [8].

The LCPC pile database and the new pressuremeter

model (‘PMT 2012’)

Pile data

The results of 174 full-scale static load tests taken from the

database have been used for the calibration of the model.

Out of 174 piles, 114 piles were instrumented along their

shaft. The 174 piles can be distributed into 8 classes and 20

categories (Table 1). Each class is split into one to four pile

categories. The geometrical properties are the following:

the diameters vary between 0.16 and 1.92 m (with a mean

equal to 0.59 m) and lengths between 3.5 and 80 m (with a

mean equal to 15 m). These classes and categories include

the latest piles technologies commonly used. Classes 1 and

2 are devoted to bored piles, class 3 corresponds to screw

piles, classes 4–7 to driven piles and class 8 to micropiles.

For the micropiles, different categories have been defined

according to the type of grouting process: gravity pressure

32 Page 2 of 15 Innov. Infrastruct. Solut. (2017) 2:32

123

(category 17), low pressure (category 18) or high pressure

without or with the use of ‘‘tubes a manchettes’’ (TAM)

(category 19 and 20, respectively). For driven piles,

methods such as hammering or vibrating are included in

the database.

Soil data

For all the pile locations, as a minimum, a sampling by

drilling, as well as a pressuremeter test profile, and

sometimes a cone penetration test profile were performed.

Five ground types have been identified: clay and silt (soil

1), sand and gravel (soil 2), chalk (soil 3), marl and

calcareous marl (soil 4) and weathered rock (soil 5)—see

Tables 2, 4, 5, 6, 7 and 8. The soil identification is carried

out from the soil cuttings when the hole created specifi-

cally for the pressuremeter test is drilled. These five types

of soils are sufficient to take into account nearly all

ground natures encountered in France. Table 2 presents

the number of piles in each class for the five types of

soils in the database. The type of soil is the one prevailing

at the base of the pile.

About the feasibility of MPM tests compared to other

tests, it is worthwhile to note the figures given by Bus-

tamante et al. [12], obtained on 204 sites where pile loads

tests have been performed in France and abroad. These

figures are given in Table 3. They show that the MPM

tests were or could have been performed on the 204 sites

Table 1 Classes and categories

of piles [8]Pile class Pile category

C1: Bored piles 1: No support

2: With slurry

3: Permanent casing

4: Recoverable casing

5: Dry bored pile/or slurry

Bored pile with grooved

sockets

C2: CFA piles 6: CFA pile

C3: Screw piles 7: Screw cast-in-place pile

8: Screw piles with casing

C4: Closed-ended driven piles 9: Pre-cast or pre-stressed concrete-driven pile

10: Coated driven steel pile (coating: concrete, mortar, grout)

11: Driven cast-in-place pile

12: Driven steel pile, closed ended

C5: Open-ended driven piles 13: Driven steel pile, open ended

C6: Driven H piles 14: Driven H pile

15: Driven grouted H pile

C7: Driven sheet pile walls 16: Driven sheet pile

C8: Micropiles 17: Micropile I (gravity pressure)

18: Micropile II (low pressure)

19: Micropile III (high pressure)

20: Micropile IV (high pressure with TAM)

Table 2 Piles distribution by

class and soil type [8]Soil type Pile class Total

C1 C2 C3 C4 C5 C6 C7 C8

Silt and clay

% CaCO3\30%

10 13 8 18 9 4 8 0 70

Sand and gravel 4 8 14 14 5 1 4 3 53

Chalk 4 0 4 9 1 2 4 0 24

Marl and calcareous marl 8 1 3 0 0 1 3 4 20

Weathered rock 4 0 0 0 0 0 0 3 7

Total 30 22 29 41 15 8 19 10 174

Innov. Infrastruct. Solut. (2017) 2:32 Page 3 of 15 32

123

(for 3 sites, there were simply not enough measurements

taken).

Principles of the pressuremeter method

The design of foundations with MPM results consists in

correlating the base resistance qb and the shaft resistance qs to

the limit pressure pl. It does not use fundamental soil

parameters as do many other capacity calculation methods.

The correlation between pl and qb is supported by the

analogy between the expansion of a cylindrical cavity

and the mobilisation of the base resistance. Nicholson

et al. [32], for instance, give an excellent example

showing that the Menard limit pressure is the appropriate

parameter to capture the variation of the base resistance

of piles in London Thanet Sand. The relationship

between pl and qs is much more empirical and merely

reflects the fact that the shaft friction increases with the

density for sandy soils or with the consistency for clayey

soils, and thus with the ground resistance, for a given

pile technology.

The new pressuremeter model ‘PMT 2012’ [8]

The unit base resistance qb is given by Eq. (1):

qb ¼ kp ple � poð Þ; ð1Þ

where po is the total initial horizontal stress at the level of

the pile base, ple is the equivalent limit pressure from the

MPM results at the base and kp is the bearing factor. kp is a

function of soil type and pile class (Table 4). It varies

between 1.0 and 3.2.

The unit shaft resistance qs is given by Eq. (2):

qs ¼ a � fsol with the condition qs � qsmax: ð2Þ

The function fsol depends only on the type of soil

(Fig. 1). a is a sort of installation factor; it varies according

to soil type and pile category (Table 5). It varies between

0.4 and 3.8, as can be seen from Table 5. qsmax also

depends on the soil type and pile category (Table 6).

The new penetrometer ‘CPT 2012’ model

The first model for the bearing capacity of piles from CPT

results from the database of the LPCs was established by

Bustamante and Gianeselli [13, 14]. At the occasion of the

drafting of the new French standard for pile design

according to Eurocode 7, a revised ‘CPT 2012’ model was

implemented [2, 9]. There are far less full-scale load tests

available with CPT results than with MPM tests results.

The results of 42 full-scale static load tests in the database

have been used for the establishment of the ‘CPT 2012’

model. Note that only the cone resistance qc is used; the

sleeve friction fs is not used for assessing the bearing

capacity of piles in French practice.

The unit base resistance qb is given by Eq. (3):

qb ¼ kc qce; ð3Þ

where qce is the equivalent cone resistance from the CPT

results at the base and kc the bearing factor. kc is a function

of soil type and pile class (Table 7). It varies between 0.15

and 0.5.

The unit shaft resistance qs is given by Eq. (4)—iden-

tical to Eq. (2):

qs ¼ a � fsol with the condition qs � qsmax: ð4Þ

The function fsol depends only on the type of soil

(Fig. 2). a varies between 0.13 and 2.9 according to soil

type and pile category (Table 8). qsmax is the same as for

the ‘PMT 2012’ model; it depends on the soil type and pile

category (Table 6).

Model factors and calculated value of the pile

resistance [2]

From the ‘PMT 2012’ and ‘CPT 2012’ models described

above, the total pile resistance in compression (bearing

capacity) is then derived in the usual manner:

Rc ¼ qbAb þ RqsiAsi; ð5Þ

and the total pile resistance in tension is:

Table 3 Field and laboratory test feasibility [12]

Test Carried out to full design lengtha Incomplete testb Not carried outc Not applicabled

MPM (pl) 155 3 46 0

CPT (qc) 60 79 23 42

Laboratory tests (cu, c0, u0) 21 67 69 47

SPT (N) 26 54 72 52

a Including the full length of pile ? additional metres below the pile tipb Due to premature refusal for CPT; sampling not possible for laboratory tests; soil strength too high for SPTc Feasible but not planned when the investigation campaign was decidedd Considered from the beginning as inadequate with respect to soil nature or strength

32 Page 4 of 15 Innov. Infrastruct. Solut. (2017) 2:32

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Rt ¼ RqsiAsi; ð6Þ

where Ab is the area of the base of the pile and Asi is the

area of the pile in layer ‘i’ for which the unit shaft friction

is qsi. Note that in the French pile design practice, the unit

shaft friction for piles in tension is the same as for piles in

compression.

When designing piles from ground test results, Eurocode

7 advocates the introduction of an explicit ‘model factor’

cRd (applied to the calculation model), to derive a value of

the calculated total resistance Rcal (in compression or in

tension) with a given confidence level (in other words, it

requires to have a knowledge of the scatter of the calcu-

lation model)—Eq. 7:

Rcal ¼ Rc=cRd or Rcal ¼ Rt=cRd: ð7Þ

Respectively, for the ‘PMT 2012’ model and for the

‘CPT 2012’ model, the factors cRd proposed by the new

French standard are given in Tables 9 and 10 [2]. The

establishment of the model factor cRd for the ‘PMT 2012’

model is the subject of the paper by Burlon et al. [8].

Figure 3 gives the distribution function Rcal/Rmeasured for all

the piles in the database, except injected piles and piles

embedded in chalk (134 piles). This figure shows that the

selected value cRd = 1.15 gives the same confidence level

(88%) as in the case of the former Code of Practice for

bridges ‘Fascicule 65–V’ for which the model factor was

implicitly taken equal to 1.27.

Design value of the pile resistance

For obtaining the so-called ‘characteristic value’ of the

total pile resistance Rk (in compression or in tension) from

the calculated values, Eurocode 7 offers two alternative

procedures (see [21]):

– The ‘model pile’ procedure, which consists in calcu-

lating the values of the pile resistance Rcal for each

profile of ground test results and applying correlations

factors n to the mean and minimum values of Rcal:

Rk ¼ min fRcal;mean=n3; Rcal;min=n4Þ: ð8Þ

Table 11 gives the values of n3 and n4 proposed by

Eurocode 7, where N is the number of ground test profiles.

In the French standard [2], the values of n3 and n4 also

depend on the size of the investigation area, as well as on

the distance to the piles of the project. The values of

Table 11 are thus the maximum possible values for the

AFNOR standard (see [9], for more details).

– The ‘alternative’ procedure or ‘ground model’ proce-

dure where the ground is divided into different layers

with representative values of their properties. Then,

the values of the base resistance qb and of the shaft

friction qsi in each layer ‘i’ are obtained from the

calculation model. Note that in this procedure, the

determination of the representative values is left to

engineering judgment, which can be another source of

dispersion. When using this procedure, the French

standard introduces a second model factor cgm equal

to 1.1 to be applied to the total calculated resistance

(Eq. 9):

0

25

50

75

100

125

150

175

200

0 1 2 3 4 5 6 7pl* [MPa]

f sol [k

Pa]

Clay and SiltSand and GravelChalkMarl and Calcareous MarlWeathered Rock

Fig. 1 Functions fsol for the ‘PMT 2012’ model [8]

Table 4 Bearing resistance

factor kp for the ‘PMT 2012’

model [8]

Pile class Soil type

Silt and clay

% CaCO3\30%

Sand and gravel Chalk Marl and calcareous marl Weathered rock

1 1.15 1.1 1.45 1.45 1.45

2 1.3 1.65 1.6 1.6 2

3 1.55 3.2 2.35 2.1 2.1

4 1.35 3.1 2.3 2.3 2.3

5 1 1.9 1.4 1.4 1.2

6 1.2 3.1 1.7 2.2 1.5

7 1 1 1 1 1.2

8 1.15 1.1 1.45 1.45 1.45

Innov. Infrastruct. Solut. (2017) 2:32 Page 5 of 15 32

123

Rk ¼ Rc=cRdcgm or Rk ¼ Rt=cRdcgm with cgm ¼ 1:1:

ð9Þ

According to Eurocode 7, the design value of the pile

resistance Rd is then obtained by applying a resistance

factor ct to the total characteristic resistance Rk, or resis-

tances factors cb and cs to the total characteristic base and

shaft resistances, Rbk and Rsk, respectively (Eqs. 10, 11):

Rd ¼ Rk=ct ð10Þ

or

Rd ¼ Rbk=cb þ Rsk=cs for piles in compression

and Rd ¼ Rsk=cs in tensionð Þ:ð11Þ

In French practice, for the verification of the ultimate

limit states (ULS) in persistent and transient situations,

design approach 2 of Eurocode 7 is used. In this

approach, one set of combination of the actions coming

from the structure is checked against the design value of

the resistance of the pile foundation, obtained with the

resistance factor ct on the total characteristic resistance Rk

(Eq. 12):

Fd �Rd ¼ Rk=ct; ð12Þ

where ct = 1.1 for piles in compression and ct = 1.15 for

piles in tension (values recommended by Eurocode 7) for

persistent and transient design situations.

Combining the equations above shows that the design

value of the total resistance Rd is finally obtained from the

resistances Rc (or Rt) calculated with the ‘PMT 2012’

model or the ‘CPT 2012’ model in the following manner

(Eqs. 13, 14):

– for the ‘model pile’ procedure:

Rd ¼ Rk=ct ¼ Rcal=nct

¼ Rc=cRdnct compressionð Þ or Rt=cRdnct tensionð Þ;ð13Þ

– for the ‘ground model’ procedure:

Rd ¼ Rk=ct ¼ Rcal=cgmct

¼ Rc=cRdcgmct compressionð Þ or Rt=cRdcgmct tensionð Þ:ð14Þ

For serviceability limit states (SLS), the AFNOR code

requires to apply resistance factors cSLS to the charac-

teristic values of the creep or critical resistances Rcr,k,

derived from the characteristic values Rk introduced

Table 5 Values of installation factor a for the ‘PMT 2012’ model [8]

Pile category Soil type

Silt and clay

% CaCO3\30%

Sand and gravel Chalk Marl and calcareous marl Weathered rock

1 1.1 1 1.8 1.5 1.6

2 1.25 1.4 1.8 1.5 1.6

3 0.7 0.6 0.5 0.9 0.9

4 1.25 1.4 1.7 1.4 1.6

5 1.3 1.4 1.8 1.5 1.6

6 1.5 1.8 2.1 1.6 1.6

7 1.9 2.1 1.7 1.7 1.7

8 0.6 0.6 1 0.7 0.7

9 1.1 1.4 1 0.9 0.9

10 2 2.1 1.9 1.6 1.6

11 1.2 1.4 2.1 1 1

12 0.8 1.2 0.4 0.9 0.9

13 1.2 0.7 0.5 1 1

14 1.1 1 0.4 1 0.9

15 2.7 2.9 2.4 2.4 2.4

16 0.9 0.8 0.4 1.2 1.2

17 1.25 1.4 1.8 1.5 1.6

18 1.25 1.4 1.8 1.5 1.6

19 2.7 2.9 2.4 2.4 2.4

20 3.4 3.8 3.1 3.1 3.1

For categories 9–16, the above values are multiplied by 0.75 when the piles are vibro-driven instead of being driven

32 Page 6 of 15 Innov. Infrastruct. Solut. (2017) 2:32

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above (see [9]). The values of the cSLS factors are, of

course, relevant to the various combinations of loads

used for checking the serviceability of the structure. It

should be noted that the way serviceability limit states

are thus treated in the AFNOR code is different from

Eurocode 7. It introduces an additional capacity check

(in terms of loads), as Eurocode 7 relies essentially on

checking the axial displacements (settlements) of the pile

foundation.

Axial displacements

The determination of the load–settlement curve of a single

pile under axial loading is based on the concept of shaft

friction mobilisation curves, also known as t–z curves.

In case a settlement estimate must be made, the use the

s–z curves (unit shaft friction-local displacement curves)

and q–zp curve (base load-base settlement curve) proposed

by Frank and Zhao [23], as shown on Fig. 4, are widely

Table 6 Values of qsmax for design from MPM tests results and from CPT results [2, 9]

Pile category qsmax in kPa

Silt and clay

% CaCO3\30%

Intermediate soil Sand and gravel Chalk Marl and calcareous marl Weathered rock

1 90 90 90 200 170 200

2 90 90 90 200 170 200

3 50 50 50 50 90 –

4 90 90 90 170 170 –

5 90 90 – – – –

6 90 90 170 200 200 200

7 130 130 200 170 170 –

8 50 50 90 90 90 –

9 130 130 130 90 90 –

10 170 170 260 200 200 –

11 90 90 130 260 200 –

12 90 90 90 50 90 –

13 90 90 50 50 90 90

14 90 90 130 50 90 90

15 200 200 380 320 320 320

16 90 90 50 50 90 90

17 – – – – – –

18 – – – – – –

19 200 200 380 320 320 320

20 200 200 440 440 440 500

Table 7 Bearing resistance factor kc for the ‘CPT 2012’ model [2, 9]

Pile class Soil type

Silt and clay

% CaCO3\30%

Intermediate soil Sand and gravel Chalk Marl and calcareous marl Weathered rock

1 0.4 0.3 0.2 0.3 0.3 0.3

2 0.45 0.3 0.25 0.3 0.3 0.3

3 0.5 0.5 0.5 0.4 0.35 0.35

4 0.45 0.4 0.4 0.4 0.4 0.4

5 0.35 0.3 0.25 0.15 0.15 0.15

6 0.4 0.4 0.4 0.35 0.2 0.2

7 0.35 0.25 0.15 0.15 0.15 0.15

8 0.45 0.3 0.2 0.3 0.3 0.25

Innov. Infrastruct. Solut. (2017) 2:32 Page 7 of 15 32

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used in France. The great interest of this method lays in the

fact that the parameters ks and kq can be derived easily

from the pressuremeter modulus EM (Eqs. 15, 16):

ks ¼ 2:0EM=B and kq ¼ 11:0EM=B for fine soils, ð15Þ

ks ¼ 0:8EM=B and kq ¼ 4:8EM=B for granular soils,

ð16Þ

where B is the diameter of the pile. Note that the limit

stresses qs and qb are, respectively, the unit shaft friction

and base resistances derived from the MPM (or CPT)

method(s) described above for the calculation of the

bearing capacity of piles.

Equations 15 and 16 mainly come from empirical corre-

lations, but some theoretical background is also proposed by

Frank [19]. Examples of the use of this MPM method for

predicting load–settlement curves of piles are given in Frank

[19] and Bustamante and Frank [10, 11]. Figures 5 and 6 are

such examples of the use of the Frank and Zhao [23] MPM

method for the analysis of full-scale static load tests.

The Koekelare pile of Fig. 5 is a cased screw pile /350 mm/650 mm embedded in a Ypresian clay. It can be

seen that the prediction of the load–settlement curve is

excellent.

Figure 6 shows all the results of the prediction exercise

of class A which was organised for the International

Symposium ISP5-PRESSIO 2005, taking place at the

occasion of the ‘50 years of pressuremeters’ [33, 34]. The

pile is a CFA (continuous flight auger bored pile) with a

diameter B = 0.5 m and a length D = 12 m. The pile is

embedded in a 9.6 m-thick clay layer, below a 2.4 m-thick

silt layer. The water table is located 1.8 m below ground

level. It is interesting to note that the predictions made by

Robas and Kuder [35] and by Said et al. [36]—which are

the closest predictions to the whole initial part of the

measured load–settlement curve—both used the Frank–

Zhao MPM method and were established entirely inde-

pendently from the raw MPM readings.

Table 8 Values of installation factor a for the ‘CPT 2012’ model [2, 9]

Pile category Soil type

Silt and clay

% CaCO3\30%

Intermediate soil Sand and gravel Chalk Marl and calcareous marl Weathered rock

1 0.55 0.65 0.70 0.80 1.40 1.50

2 0.65 0.80 1.00 0.80 1.40 1.50

3 0.35 0.40 0.40 0.25 0.85 –

4 0.65 0.80 1.00 0.75 0.13 –

5 0.70 0.85 – – – –

6 0.75 0.90 1.25 0.95 1.50 1.50

7 0.95 1.15 1.45 0.75 1.60 –

8 0.30 0.35 0.40 0.45 0.65 –

9 0.55 0.65 1.00 0.45 0.85 –

10 1.00 1.20 1.45 0.85 1.50 –

11 0.60 0.70 1.00 0.95 0.95 –

12 0.40 0.50 0.85 0.20 0.85 –

13 0.60 0.70 0.50 0.25 0.95 0.95

14 0.55 0.65 0.70 0.20 0.95 0.85

15 1.35 1.60 2.00 1.10 2.25 2.25

16 0.45 0.55 0.55 0.20 1.25 1.15

17 – – – – – –

18 – – – – – –

19 1.35 1.60 2.00 1.10 2.25 2.25

20 1.70 2.05 2.65 1.40 2.90 2.90

For categories 9–16, the above values are multiplied by 0.75 when the piles are vibro-driven instead of being driven

Fig. 2 Functions fsol for the ‘CPT 2012’ model [2, 9]

32 Page 8 of 15 Innov. Infrastruct. Solut. (2017) 2:32

123

Research on the use of t–z curves for the assessment of

the settlements of piles using the full-scale results of the

LCPC pile database has been developed further by Abchir

et al. [1] and Bohn et al. [7].

Transverse displacements

The methods using the subgrade reaction modulus (or p–

y reaction curves, p—reaction pressure, y—transverse

displacement) are now well known for the design of piles

under lateral loads. These methods, which consider the pile

as a beam on linear or non-linear elastic springs, are very

much used in France, precisely because of the development

of the MPM test which provides the soil engineer with both

strength and deformation information about the soil,

respectively, through the limit pressure pl and the pres-

suremeter modulus EM.

Experimental background

The research carried out by the LPCs have concerned

not only overturning loads at the head, but also trans-

verse thrusts due to lateral soil movements along the pile

shaft (at the toe of an embankment, for instance). In this

latter case, the pile soil lateral displacement y is replaced

by the ‘relative’ displacement Dy = y-g, where g is the

horizontal displacement of the soil in the absence of the

pile.

It must be admitted that there are not as many cases of

comparison of the prediction of the MPM method with full-

scale test results for piles under transverse loadings, as in

Table 9 Values of the model

factor cRd for the ‘PMT 2012’

model [2]

cRd compression cRd tension

All piles, except coated and injected piles and piles embedded in chalk 1.15 1.4

Piles embedded in chalk, except coated and injected piles 1.4 1.7

Coated and injected piles 2.0 2.0

Table 10 Values of the model

factor cRd for the ‘CPT 2012’

model [2]

cRd compression cRd tension

All piles, except coated and injected piles and piles embedded in chalk 1.18 1.45

Piles embedded in chalk, except coated and injected piles 1.45 1.75

Coated and injected piles 2.0 2.0

Table 11 Values of correlation factors n3 and n4 according to

Eurocode 7

N 1 2 3 4 5 7 10

n3 1.4 1.35 1.33 1.31 1.29 1.27 1.25

n4 1.40 1.27 1.23 1.20 1.15 1.12 1.08

N: number of ground test profiles [16]

Fig. 3 Distribution function of

Rcal/Rmeasured for 134 piles (no

injected piles; no chalk), ‘PMT

2012’ model [8]

Innov. Infrastruct. Solut. (2017) 2:32 Page 9 of 15 32

123

the case of the bearing capacity of piles under axial load-

ing. However, a certain number of such comparisons are

available, in particular some experiments carried out by the

LPCs in the 1970s (see [5]).

As for those with determination of the reaction curves

along the shaft, the experiment on Provins site (which will

be briefly reported below) and different research projects

on Plancoet site on isolated piles, as well as on a group of

two piles and on a group of six piles (see e.g. [4]) must be

mentioned. Also, the measurements taken during 16 years

on a steel pipe driven through an unstable slope at Salledes

(Puy-de-Dome) are very valuable [22]. For the group of

two piles at Plancoet, it is interesting to note that the

reaction measured on the trailing pile is found to be

reduced by a factor of 0.4–0.5 relatively to the leading

(front) pile, with the distance between the two axes being

three times the frontal width.

The basic method from MPM tests [28] is detailed in the

book by Baguelin et al. [5]. It shows how the subgrade

reaction modulus ks = p/y was originally derived by

Menard from his formula for the settlement of shallow

foundations using the pressuremeter modulus EM. Some

theoretical background for the use of EM from the MPM

test is also proposed by Frank [19].

The original Menard method is still in use in the current

French practice with some adaptation [2]. Indeed, from the

various experimental evaluations, Baguelin et al. [5]

conclude that the subgrade reaction modulus ks proposed

by Menard is, in general, pessimistic for quick monotonic

loadings. It tends to overestimate the head displacements

and the maximum bending moment of piles submitted to

loads at their head, and thus is conservative. In reality,

foundations must often sustain cyclic and/or long duration

loads and the soil can be severely damaged by the instal-

lation of the piles, all being parameters very difficult to

quantify in everyday practice. These different facts allow

thinking that the original subgrade reaction modulus pro-

posed by Menard is quite acceptable for long duration and/

or cyclic loads.

p–y method from MPM test results

From the results of the MPM test at the considered depth

(EM, pressuremeter modulus; pc, creep pressure and pl,

limit pressure), the reaction curve (p, y) of a single pile at a

given depth is established as shown in Fig. 7 (where P is

the total reaction P = pB, with B being the diameter or

frontal width of the pile).

In the present state of practice, Menard’s subgrade

modulus is used for the initial stiffness Es = ksB for long

duration loads on the pile (cases a and b of Fig. 7). In

the case of short duration or accidental loads, the initial

stiffness is 2Es (cases c and d of Fig. 7). For seismic

loads, the initial stiffness can even reach much larger

values [2].

settl

emen

tS o

(mm

)

-40

-30

-20

-10

00 500 1000 1500

Load Qo (kN)

calculated

measured

Fig. 5 Comparison of measured and calculated load–settlement

relationship for the Koekelare pile [10]

0

5

10

15

20

25

30

35

40

45

50

0 200 400 600 800 1000 1200 1400Charge en tête / vertical load (kN)

dépl

acem

ent /

set

tlem

ent (

mm

)

Pieu test/pile tested(Bustamante M. et Gianeselli L.)Antoinet et al.

Bahar et al.

Robas et Kuder

Said et al.

Mecsi

Monnet

Fig. 6 Comparison of the experimental curve with the participants’

predictions [33]

kτ

qs

qs2

τ

z

kτ5

kq

qb

qb2

q

zb

5kq

Fig. 4 Model for t–z curves from MPM test results [23]

32 Page 10 of 15 Innov. Infrastruct. Solut. (2017) 2:32

123

Above the creep pressure pf measured with the MPM

(pf & pl/2 can be used as an estimate), the non-linear

effect is taken into account either by reducing the tangent

reaction modulus by one-half (case b and d of Fig. 7) or by

limiting the reaction pressure p to the creep pressure pf (or

the total reaction to Pf = pfB) (cases a and c of Fig. 7).

Finally, the ultimate pressure pu on the pile is taken as

being the limit pressure pl measured with the MPM for

lateral soil thrusts along the shaft of for accidental loads

(case b and d of Fig. 7).

The p–y curve is, in principle, modified for depth values

z lower than a critical depth zc, due to surface effect. For

z = 0, the pressures are divided by 2 for the same dis-

placement y (or y-g) and are then linearly interpolated

until z = zc. For cohesive soils zc is taken equal to 2B (B is

the diameter of the pile) and for granular soils it is taken

equal to 4B.

Design of piles subjected to lateral soil thrusts

along their shaft

The design of piles subjected to lateral soil thrusts along

the shaft of the pile, created by nearby slopes for instance,

is based on the ‘free soil displacement’ concept (Fig. 8). It

is assumed that the lateral reaction p–y curve now links the

lateral reaction pressure p to the ‘relative’ displacement

Dy = y-g, where y is the equilibrium soil-pile lateral

displacement sought, and g is the free lateral soil dis-

placement (or displacement in absence of the pile)—see

e.g. Bigot et al. [6] and Frank [19, 20]. For predicting g(z),

the AFNOR standard (2012) reproduces the method

already existing at the time of the ‘Fascicule 62—Titre V’

(1993) [26]. The displacement g(z) function of depth z de-

pends on the geometry of the slope, the parameters of the

underlying soft soil and the position of the pile.

Results of the full-scale experiment of Provins [6]

The experiment on the site of Provins is interesting

because the behaviour of a full-scale instrumented pile

was examined under head loading, and also when being

submitted to lateral thrusts along its shaft due to the

construction of an embankment. The pile is a steel

instrumented pipe, of OD = B = 0.926 m and thickness

e = 0.015 m. The four stages of the experiment (initial

head loading to 120 kN, then embankment construction to

a height of 3.80 m, to a height of 6.80 m and after

3 months of consolidation under this final height) have

been analysed in detail by using the different pres-

suremeter prediction methods [6]. Here, only the main

results concerning the Menard MPM method described

above are discussed for conciseness.

Figure 9 compares the measured values M of bending

moments (left) and displacements (right) (M) for the last

level of applied load at the head (120 kN shear load at

0.20 m from ground level) to the results of three prediction

methods:

– curve A, with the original Menard reaction curve

(Fig. 7, case b)

Fig. 7 Soil reaction P = pB

against lateral displacement

y ([20], after [26]).

a Predominant permanent

actions at the pile head.

b Predominant lateral soil

thrusts along the shaft.

c Predominant short time

actions at the pile head.

d Predominant accidental

actions at the pile head

Innov. Infrastruct. Solut. (2017) 2:32 Page 11 of 15 32

123

– curves B and C, with p–y reaction curves constructed

on the basis of self-boring pressuremeter tests results

(not discussed here).

In the surface layer (silt and clay), the predominant one

for head loading, the use of the MPM method of Fig. 8

yields a mean soil reaction modulus:

Es ¼ ks � B ¼ 2900 kPa curve Að Þ:

It is clear from Fig. 9 that the MPM method (curve A) is

on the safe side for short duration head loadings: the

maximum bending moment is slightly overestimated and

the displacements are overestimated by a factor of 2. This

is consistent with the conclusions of Baguelin et al. [5]. It

also shows that for long duration loadings at the head, the

original Menard reaction modulus is quite acceptable,

given all the uncertainties.

Figure 10 compares the measured values M of bending

moments (left) and displacements (right) (M) after

3 months of consolidation under the final height of the

embankment to the results of the same three prediction

methods (curves A, B and C). Here, the difficulty is the

prediction of the bending moments, as it is a ‘displace-

ment-imposed’ problem. The measured bending moment

(curve M) in the upper part is well predicted by the

present MPM method for long duration lateral thrusts

along the pile shaft (curve A, case b of Fig. 7). In the

lower part, the method overestimates the bending moment

by a factor of around 1.8, which is largely on the safe

side.

The full-scale experiment of Salledes (steel pipe pile

installed through an unstable slope), where the measure-

ments were taken during 16 years, confirmed the great

difficulty in predicting the long duration behaviour of piles

undergoing lateral thrusts along their shafts from a moving

ground; it is clear that the MPM method overestimates the

bending moments of such piles (see [22], for the extensive

analysis of this unique experiment).

Fig. 8 Pile subjected to lateral soil thrusts along the shaft ([20], after

[26])

Fig. 9 Provins pile. Comparison of measured and calculated bending moments and displacements for head loading [6]

32 Page 12 of 15 Innov. Infrastruct. Solut. (2017) 2:32

123

Conclusions

This paper has explained some key aspects of the present

rules used in France for designing pile foundations.

Attention has been focused on the use of Menard pres-

suremeter (MPM) as an efficient tool for designing foun-

dations. The Menard pressuremeter by providing both a

failure parameter (the limit pressure) and a deformation

parameter (the pressuremeter modulus EM) allows to tackle

not only bearing capacity problems, but also all the prob-

lems linked to the displacements of foundations, which are

recommended by Eurocode 7.

In particular, the new French standard for the design of

deep foundations of buildings and civil engineering works

has been mentioned [2]. This new standard includes the

revised pressuremeter method for the bearing capacity of

piles [8, 12]. It is fully compatible with the requirements of

Eurocode 7 [16].

The MPM rules are not only flexible, in the sense that

they can incorporate easily the new experimental findings,

but also because they are a tool for checking all limit states,

whether the ultimate ones or the serviceability ones.

Eurocode 7 is a code which advocates explicitly the ‘dis-

placement design’ of foundations (compared to the ‘ca-

pacity’ or traditional design), especially for serviceability

checks. The MPM-based design models are obviously able

to face this challenge.

In accordance with Eurocode 7, the calculation models

for the bearing capacity of piles, included in the new

French standard, are based on the results of full-scale load

tests on piles.

The new MPM rules for piles (‘PMT 2012’ model) have

been fully calibrated against the database of more than 170

full-scale static load tests on piles. The corresponding CPT

rules have also been calibrated against the results in the

database (‘CPT 2012 model’).

The important role of displacements of foundations of

structures is fully recognised in Eurocode 7 and in the

French standard. A displacement design approach might

prove to be more important than the traditional design

based on the determination of the bearing capacity and

application of a ‘large’ factor of safety.

Are we ready to base our SLS verifications solely on

displacement assessments? … and is the structural engineer

also ready?

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