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BULLETIN DES LABORATOIRES DES PONTS ET CHAUSSÉES - 233 - JULY-AUGUST 2001 - RÉF. 4381 - PP. 37-67 37

The unload-reload pressuremeter test

Olivier COMBARIEU

Laboratoire régional des Ponts et Chaussées, Rouen

Yves CANÉPA

Laboratoire régional des Ponts et Chaussées de l’Est Parisien, Melun

Introduction

The standardized testing procedure to perform a Ménard pressuremeter test (AFNOR, 2000) involves astep by step loading of the soil, until the pressuremeter limit pressure p

is reached. About ten loading

increments are generally required to achieve this.The “pressure-volumetric” curve is used to compute the Ménard pressuremeter modulus, denoted by E

M

,which is determined on the quasi-linear part of this curve within an interval defined by two specific pres-sure values (p

1

et p

2

), the first of which is roughly equivalent to the horizontal earth pressure at-rest p

0,

and the second to the pressuremeter creep pressure p

f

.

The modulus E

M

is frequently used to estimate the displacement of geotechnical structures: for verticallyand/or horizontally loaded foundations, flexible earth retaining structures, and even as a first assessmentfor embankment lying on compressible soil.

These calculations, which are specific to the Ménard pressuremeter, combine theoretical and empiricalelements. The main expressions that are proposed (for settlement of footings and piles, etc.) have beencompared with the displacement measured in loading tests conducted on real structures. Among the

works which can be mentioned are researches conducted by Louis Ménard and his associates (Ménardand Rousseau, 1962; Ménard and Lambert, 1966) during the 1960s, and then some years later observa-tions on structures (Bru et al.

, 1973) and trials conducted by the Laboratoire des Ponts et Chaussées(LPC) (Canépa and Depresles, 1990).

Although simpler expressions, i.e. for calculating the settlement of shallow foundations (Canépa, 1990),are able to provide equally good results, the formulae proposed by Ménard have been considered suffi-ciently accurate for the justification of usual structures and have been taken up in the French regulatorytexts (fascicule 62, 1993), the main difficulty being the determination of a relevant modulus for the prob-lem in question.

In this context, it is worth mentioning that the pressuremeter modulus E

M

is very sensitive to the qualityof the boring in which the pressuremeter probe is inserted (as is, to a lesser extent, the limit pressure p).

Originally, boring conducted with a hand auger (in fine soils) with considerable precautions (for exam-ple, injecting slurry into the borehole if necessary in order to support its walls) was considered to be thetechnique that disturbed the soil the least. This boring procedure, which is unusable in many soils andvery limiting in the case of deep investigations, has largely been abandoned in favour of faster equipmentand therefore less costly execution, which is however considered by some to be “destructive” for the soil.The large range of boring tools and machines has encouraged studies of how the boring mode affects thecharacteristics obtained for the main types of soil and the development of recommendations, first of allincorporated in the LPC test procedures and then in the French standard NF P 94-110-1.

However, good practice is not always followed (see Annex 1), and it must be admitted that some of thevalues for the E

M

modulus (and the limit pressures p) that are to be found in geotechnical investigationreports are completely unacceptable and underestimate the properties of the soil. This is a disservice to

the pressuremeter method, which is of great value and whose usefulness in the context of calculating thesettlement of shallow foundations was stated by R. Frank in the general report he presented in Florenceten years ago (Frank 1991).



BULLETIN DES LABORATOIRES DES PONTS ET CHAUSSÉES - 233

- JULY-AUGUST 2001 - RÉF. 4381 - PP. 37-67

38

It is also important to bear in mind that even when the tests are well performed, the measured Ménardmodulus corresponds to an average modulus for the pressure range “p

o – p

f

”. While this is acceptablefor some calculations (for example, estimating the settlement of small foundations under service loads),the Ménard modulus cannot be applied blindly to any problem. In particular, it is clear that in the caseof displacements associated with small soil deformations (typically less than 1%), the Ménard pres-suremeter modulus E

M

cannot be considered to be indicative of the behaviour of the soil.

Finally, we should bear in mind that design methods based on “linearly elastic” soil behaviour modelsare becoming more prevalent, in particular because of increasing use of finite element computationcodes. To the extent that these are used in a reasonable manner, that is to say on condition that a suitable“elastic” modulus is applied, the validity of these techniques has been demonstrated by forecasts andmeasurements on structures, as is the case for the pressuremeter method. Furthermore, with the reserva-tion mentioned above, they are permitted by the new standards (Eurocode 7, for example, AFNOR,1996).

In practice, the “elastic” moduli that are used are drawn directly from the results of laboratory tests (forexample, undrained shear tests using the triaxial apparatus), or, as is frequently the case on economicgrounds or because of an inability to extract undisturbed samples, derived from in-situ

tests (seismic andpressuremeter tests in France, Standard Penetration Tests (SPT) or Cone Penetration Test (CPT) in other

countries) on the basis of theoretical and empirical formulae when the test measures a modulus of strain(seismic, pressuremeter tests) or, if not, on the basis of exclusively empirical formulae (SPT, CPT, etc.).In no case is a clear account given of the domain of application of these moduli or, even less, of the val-idation of the calculations.

Usefullness of a cyclic pressuremeter test

The points we have raised above have led to thereintroduction of cyclic Ménard pressuremetertests. There is nothing new about the principalinvolved, in fact Louis Ménard introduced this pro-cedure as early as 1962 (unloading and reloading

are performed during expansion of the probe). Hegave the name “alternating” modulus E

a ” to thepressuremeter strain modulus measured over thecycle and mentioned that this modulus is practicallyidentical to the elastic modulus or microstrain mod-ulus denoted by E

ε

. He suggested use of this modu-lus to characterize the behaviour of soils undervibratory equipment (Ménard and Lambert, 1966).In Figure 1 we have reproduced the original dia-gram from the article by Ménard and Rousseau(1962) which could profitably be read or reread.This diagram shows an idealized test conductedunder conditions which differ from those that applyto the current practice. It is possible, however, toapproximate these conditions, as the developmentof self-boring pressuremeters has made it possibleto insert probes with practically no disturbance tothe soil. As a result, it is possible to obtain volumetric strain-stress curves which are identical to thoseshown in Figure 1.

Theoretical studies of the expansion of spherical and cylindrical cavities in an elastic-perfectly plasticsoil (Wroth, 1982; Mestat, 1993a; Mestat, 1993b; Monnet and Khlif, 1994), have provided additionalsupport for Ménard’s ideas, notably the two analyses conducted by Mestat which in the context of thevalidation of the CÉSAR-LCPC computation codes (Mestat, 1994), provided full analytical equations

for an unloading-reloading cycle for cylindrical expansion in an elastic-perfectly plastic material whichcomplies respectively with the Mohr Coulomb and Tresca plasticity criteria (respectively for a frictionalsoil as in Fig. 2 and for a purely cohesive soil as in Fig. 3). These analyses are of considerable interest

20

15

10

5 3

1 2 4

Deformations (%)

StressE

Ea

Eε

pε pf

0

1 : elastic phase2 : quasi elastic phase3 : unloading elastic phase4 : plastic phase

Fig. 1 - Cyclic pressuremeter test (after Ménard and Rousseau, 1962).





39

as they show clearly the elastic nature of the unloading-reloading curves over large ranges of stress,which makes it possible to estimate the elastic modulus of the soil by theoretical means.

As the rheological models used were fairly simple in comparison with the complex behaviour of real soil(nonlinear elasticity, dilatancy, confinement, creep), it is obvious that it is slightly more complex toderive a modulus for an unloading-reloading cycle in a real pressuremeter test.

These factors nevertheless allow us to assume that

it is possible to measure a strain modulus over anunloading-reloading cycle during pressuremeterexpansion which is characteristic of the behaviourof soils undergoing small deformations, and that itwould be possible for a whole range of problems,to use a modulus of this type directly for the calcu-lations that assume a “linear elastic” behaviour of the soil.

We should also mentioned the hope that someresearchers have expressed that a cyclic test willbe able to partially eradicate the effects of soil dis-

turbance. It is true that some other geotechnicaltest procedures (plate bearing test, deep founda-tion loading test, oedometer test, etc.) include anunloading-reloading phase and the deformationbehaviour measured during this loop is exploited.In the rest of this paper, we will unfortunately seethat this academic hope has proved sterile and thatsoil appears to “remember” the disturbance towhich it has been subjected.

The network of Laboratoires des Ponts et Chaussées (LPC) has conducted various experimental studiesof the feasibility of cyclic Ménard pressuremeter testing. These were conducted on in situ

soils and havedealt with the following topics:

➢ the unload-reload pressuremeter test procedure,

➢ the effect of the boring mode on the parameters obtained,

0 0,25 0,50 0,75 1,00 1,25 1,50 1,750

1

2

3

4P (kPa)

u(r1) (mm)

A

B

C

D

E

F

Fig. 2 - Expansion of a cylindrical cavity in an elastic-perfectlyplastic formation, Mohr Coulomb criterion (after Mestat, 1993b).

Key: Radial displacement on the abscissa; Radial stress on the ordinate

N.B.: – the path OA is linear elastic; – the path AB is elastic-perfectly plastic; – the path BC is linear -elastic; – the path CD is elastic-perfectly plastic; – the path DE is linear elastic; – the path EF is elastic-perfectly plastic;

0 1 2 3 4 5 60

0,5

1

1,5

2

2,5

3

P (kPa)

u(r1) (mm)

Fig. 3 – Expansion of a cylindrical cavity in an elastic-perfectlyplastic formation, Tresca criterion (after Mestat, 1993a).





40

➢ the accuracy of the cyclic modulus measurements,➢ the E

cyclic

/E

M

ratios obtained for the main categories of soil,➢ application of the cyclic pressuremeter modulus to the design of structures.

This paper reports the results obtained by the Rouen and East Paris Laboratoires Régionaux des Ponts etChaussées (LRPC) with regard to the first four of these points.

Selection of the test procedure

Selection of the test procedure was influenced by the desire to conduct the cyclic pressuremeter testswith the same equipment that is used for standard pressuremeter tests, while at the same time loggingpressure and volume.

The measurement devices were those in existence when the tests were conducted (APAGEO and GEO-MATECH prototype). The measurement uncertainty stated by the manufacturers was ± 0.5 cm

3 for vol-umes and ± 1% for pressure.

The study essentially concerned the unload-reload procedure (starting pressure “p

c

”, range of the cycle“p

c – p

d

” and the number of steps of pressure during the “cycle”).

In view of the uncertainty with regard to the volume measurements, it was desirable that the range of thedeformations be as large as possible. It was also necessary for the operator in the field to be able to decideeasily on the pressure at which to start the cycle. These considerations, in combination with theoreticaldata (Mestat, 1993a and b) concerning the amplitude of the elastic phases during unloading*, caused usto start the “cycle” at a pressure “p

c

” close to the creep pressure “p

f

” and to unload until a pressure of “p

d

” was reached such that p

o < p

d < p

c

/2. Reloading was then conducted step by step until the limit pres-sure or the maximum possible pressure was obtained.

There was unanimous agreement among the geotechnical engineers who performed this type of test asregards the test procedure. However there was some debate about the type of unloading procedure:

➢ should the soil be decompressed rapidly, in a single step, which is what we recommend (on thegrounds that uncertainty with regard to measurements means it is impossible to obtain reliable interme-

diate moduli)?,➢ or should stepped unloading be performed following a path which is the inverse of initial loading(and with the same duration)?.

The above two unloading modes were applied at a site near Paris in an overconsolidated saturated clay(green plastic Romainville Lower Sannosian clay with w

L = 60 to 80; I

P

between 30 and 50; γ

d = 15 to16 kN/m

3

).

Twenty-four tests, incorporating an unloading-reloading cycle and using a probe with a flexible “mem-brane” and a diameter of 63 mm, were conducted in eight pressuremeter boreholes (P

1

to P

8

) that hadbeen bored with a continuous flight auger in dry conditions. All the boreholes were located near a coresample sounding, within an area measuring 3 m × 3 m, and the tests carried out at three different depths.Four tests for each unloading mode were performed at each depth.

Figure 4 shows two standard curves that were obtained, one (see Fig. 4a) with several steps during theunloading phase from p

c

to p

d

(test L), the other (see Fig. 4b) with a continuous unloading phase (test R).Table 1 sets out the test procedure used for each test.

The pressuremeter characteristics (p

, p

f

, E

M

) were determined for each test in accordance with the pro-cedures laid down in the AFNOR standard NF P 94-110. Two cyclic moduli were also calculated:

➢ an unloading secant modulus “p

c – p

d

” denoted by E

d;

➢ a reloading secant modulus “p

d – p

c

” denoted by E

r

.

The results of all the tests conducted are given in Annex 2. Table II sets out for each unloading modeand each different depth the following results: the mean values (m), standard deviations (

σ

) and coeffi-cients of variation (cv = σ

/m) obtained for the “standardized” pressuremeter characteristics (E

M

, p

), the

cyclic characteristics (E

d

, E

r

) and the ratios E

r

/E

M

, E

d

/E

M

and E

M

/p

.

* p

c

-p

d

≈

2 c

u

in the case of a purely cohesive soil and p

c

-p

d

≈

p

c

.(2.sin

ϕ′

)/(1 + sin

ϕ′

) in the case of a purely frictional soil.





41

TABLE I

Unload-reload pressuremeter tests – Boring modes used

BOREHOLES P1 P2 P3 P4 P5 P6 P7 P8

Depth (m)

1.6 – 2.0 L R L R L R L R

2.6 – 3.0 R L R L R L R L

3.6 – 4.0 L R L R L R L R

Note: Rapid unloading is denoted by R and stepped unloading by L.

TABLE II

Unload-reload pressuremeter tests – Results obtained at each depth

p

(MPa) E

M

(MPa) E

d

(MPa) E

r

(MPa) E

r

/E

M

E

d

/E

M

E

M

/p

z = 1.6 m – 2 mMean 0.65 8.37 34.25 35.50 4.36 4.86 12.54

Standard deviation 0.16 3.27 5.58 22.48 1.94 2.82 2.23

cv 0.25 0.39 0.16 0.63 0.45 0.58 0.18

z = 2.6m – 3mMean 0.85 9.08 35.15 35.04 3.91 3.92 10.74

Standard deviation 0.09 1.62 7.95 8.21 0.87 0.85 1.47

cv 0.11 0.18 0.23 0.23 0.22 0.22 0.14

z = 3.6m – 4m

Mean 0.73 7.36 24.48 24.12 3.29 3.32 10.03Standard deviation 0.04 0.93 6.04 3.34 0.35 0.64 0.98cv 0.05 0.13 0.25 0.14 0.11 0.19 0.10

Boissy - Sounding P1 - Z = 1,6 m

100

2

400

500

1

2

300

400

0 0,2 0,4 0,6 0,8 0,2 0,4 0,6 0,8p (MPa)

Boissy - Sounding P4 - Z =1,6 m

p (MPa)

v (cm )v (cm3)

Fig. 4 - Unload-reload pressuremeter tests – Raw results.

a. Type L test – stepped unloading. b. Type R test – rapid unloading.





42

In addition, Tables IIIa and IIIb give, for both unloading modes, the measured mean values, the standarddeviations and the coefficients of variation for each depth and throughout the thickness of the clay for-mation.

Lastly, Figures 5a and 5b set out the values of the cyclic moduli measured using test procedure R (rapidunloading) and L (slow unloading by steps) versus the modulus E

M.

.

In spite of the fact that little data is available (four tests for each depth and each procedure), these Tablesand Figures elicit several remarks. First of all, we can observe that the secant moduli E

r and E

d

are threeto five times higher than the Ménard pressuremeter moduli E

M

and have values of the order of 25 to40 MPa. In other terms, the volumetric changes during the unloading-reloading phases are very low (3to 5 cm

3 per cycle)*.

When the E

r

and E

d

results obtained with the two unloading modes are compared, no significant differ-ences as a result of rapid unloading are apparent (see Fig. 5a and 5b). Lastly, it is noteworthy that thetwo test procedures lead to similar dispersions (cv = 0.2 to 0.3) which are of the same order of magnitudeas those observed for the modulus E

M

during standard tests (see Table III).

Conclusions about the test procedure

The unload-reload test procedure

The results obtained in an overconsolidated clay, together with uncertainties about volume measure-ments (± 0.5 cm3), show that it is unrealistic to expect to calculate reliable intermediate moduli oversmall ranges of pressure (p /10). It therefore seems pointless to incorporate loading steps within thecycle in order to measure this type of modulus.

However, the mean modulus over an unloading-reloading loop with a minimum pressure range of thecycle of p /2 to p/4, can be measured with an accuracy that is satisfactory, that is to say similar to thatof the Ménard pressuremeter modulus EM.

Questions are nevertheless raised about how the mode of unloading (slow or rapid) affects the results,particularly in the case of clayey materials.

* ∆V ≈ 2.66.Vs.(pc-pd)/E 10 cm3 over the range “pc-pd”, that is to say approximately 3 to 5cm3 on average per cycle whichever modulus is measured (with available equipment, the current test procedure consists of (ten loading stepsages to reach p )and (pc-pd)/Ecyclic ratios ≈ 1/300 to 1/500).

TABLE IIIaRapid unloading (Type R) - Results obtained at each depth and for the entire layer of clay

(MPa)EM

(MPa)Ed

(MPa)Er

(MPa) Er /EM Ed /EM EM /

z = 1.6 m – 2 mMean 0.65 8.64 31.10 29.47 4.00 3.94 13.02Standard deviation 0.16 3.26 4.74 6.74 2.41 1.36 2.05cv 0.25 0.38 0.15 0.23 0.60 0.34 0.16


z = 3.6m – 4m


Entire layer (z = 1.6 m – 4 m)


p p



BULLETIN DES LABORATOIRES DES PONTS ET CHAUSSÉES - 233 - JULY-AUGUST 2001 - RÉF. 4381 - PP. 37-67

43

The tests conducted show that there is no discernable difference between the two procedures we haveinvestigated when measurement uncertainty is taken into account. In view of the conventional way in

which moduli are calculated there is no advantage for the testing procedure to select a stepped unloading

phase (the also same applies to reloading but to a lesser degree).

We still need, of course, to consider the relevance and usefulness of mean cyclic modulus measurements.

However, this is a different matter. To measure the unloading modulus under very low volumetric

TABLE IIIb

Stepped unloading (Type L) - Results obtained at each depth and for the entire layer of clay

(MPa)E

M

(MPa)E

d

(MPa)E

r

(MPa)E

r

/E

M

E

d

/E

M

E

M

/



z = 3.6m – 4mMean 0.72 7.57 27.92 23.89 3.18 3.69 10.46Standard deviation 0.03 1.09 6.98 3.16 0.42 0.69 1.21cv 0.04 0.14 0.25 0.13 0.13 0.19 0.12

Entire layer (z = 1.6 m – 4 m)


p p

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0 5 10 15

Cycle R

Cycle L

Er = 2,5 EM

Er = 5 EM

0 5 10 15

Cycle RCycle L

Ed = 2,5 EM

Ed = 5 EM

Er (MPa)

EM (MPa) EM (MPa)

Ed (MPa)

Fig. 5 - Unload-reload pressuremeter tests. Cyclic modulus versus pressuremeter modulus.

a. Reloading modulus E r . b. Unloading modulus E d .




changes, the test procedure and equipment would need to be modified (it would probably be necessaryconduct tests at a constant rate of strain and/or use probes with a greater expansion capability, of theorder of between 1,500 and 2,000 cm3 in order to reduce measurement uncertainty).

To conclude, in order to determine the cyclic modulus with a sufficient degree of accuracy using theequipment that is in normal use, the modulus in question should be determined over the complete rangeof the cycle. In this case, rapid decompression of the soil is sufficient. It is this procedure which wasadopted for a possible standardized test (XP P 94-110-2) using existing equipment.

Data logging devices

As has been seen above, the contraction and expansion of the pressuremeter cell during a loading-unloading loop is very limited (a few cubic centimetres between two consecutive loading steps at themost). Consequently, volume measurements must be as accurate as possible.

For the same reasons, the loading relationship p = f(t) must also be monitored during the test as must thefollowing aspects:

➢ variation in the pressure applied to the soil during a loading step,➢ loading step duration,➢

pressure difference between the guard cells and the measuring cell.Automatic logging of pressure and volume measurements are therefore an important factor for the qual-ity of cyclic pressuremeter tests. In addition to the devices used in the tests described in this paper, newequipment is also available on the market.

All the manufacturers state measurement uncertainties of at least (0.5 cm3 for volume and (1% for pressure.

This equipment has been designed to collect the data of a Ménard pressuremeter test (NF P 94-110-1).The pressure and volume sensors seem to be satisfactory for cyclic tests. The following points must, nev-ertheless, be considered (and if necessary the data acquisition software should be modified accordingly):

➢ ability to access raw pressure and volume measurements, not just the rounded-off values that are dis-played,➢ logging of gas and water pressure read-offs, at least at the start and end of each loading step, and

above all during the soil decompression phase,➢ recording of pressure and volume at least at 1 s – 15 s – 30 s – 60 s after the start of a step of pressure.

These requirements have, moreover, been included in the most recent version of the standard for thepressuremeter test (NF P 94-110-1 and NF P 94-110-2).

Test procedure and calculation of the unload-reload pressuremeter modulus

To conclude, the recommended procedure is as follows:

➢ start cycle at pc ≈ pf ≈ p /2,➢ range of cycle: p /4 ≤ ∆p ≤ p /2 or in practice ∆p ≈ pc /2,➢ rapid decompression of soil (with monitoring of the pressure in the guard cells and measuring cell),➢ step by step reloading phase,➢ volume and pressure read-offs at 1 s, 15 s, 30 s et 60 s at least.

It is also recommended to characterize the loading-unloading cycle by means of a single conventional“cyclic” modulus Ec which corresponds to the mean modulus of reloading Er that is determined betweenpd and pc using the formula given below

Ec = 2.66.∆p.V/ ∆V

where

➢ ∆p = pc – pd,➢ ∆V = Vc – Vd,➢ V = Vs + (Vc – Vd)/2,➢ V

s: volume of the measuring cell,

➢ Vc, Vd: corrected volume corresponding to corrected pressures pc and pd.

This is the procedure which was applied for the cyclic tests described below.




Influence of the boring mode on the cyclic modulus ErGood quality boring, as has already been stated, is essential for the quality of the standard pressuremetertest. A wide variety of factors determine the quality and reliability of the parameters measured by thepressuremeter. Boring tools, the length of the boring passes and boring parameters all affect soil distur-bance and influence the test results – i.e. the limit pressure p and the modulus EM (the latter being gen-

erally more affected than the former). It is therefore essential to comply with the recommendationswhich are reproduced in Annex 1 in order to obtain results which are indicative of real soil behaviourand be able to use pressuremeter-based design methods.

One of the reasons a loading cycle was conducted during the tests was to investigate to what extent thecycle was able to overcome the dispersion exhibited by EM values and provide much lower dispersionfor the modulus Er, irrespective of whether the mode of boring was acceptable or not.

For the tests described below, we therefore varied the boring techniques, from the one we have termedthe reference method (hand auger) to methods which are highly disruptive and obviously prohibited.

The Rouen LRPC conducted measurements in three soils (silt, very plastic clay, river sand).

SiltThe soil in question was aeolian low plasticity silt. This is a very common geological formation in Nor-mandy, as it covers all the plateaux. The site which overlooks Le Havre (Le Mont Gaillard) has a layerof between 4 and 5 metres thick of this silt, whose density increases with depth, as we know from pre-vious studies in the area. Below the silt the soil becomes very much more dense and structured and con-tains flint.

Three boring modes were tested, with one borehole for each mode; each was located at the summit of anequilateral triangle with sides of 2 metres.

❶ Mode 1 (HA). Hand auger in dry conditions, with a diameter of 63 mm.The borehole, with a total length of 6 m, was bored by lengths of 1 m at a time, each metre requiring fiveor six auger passes. Silt was therefore extracted, with practically no “disturbance” of the wall of the cav-ity: This was the reference boring mode. A pressuremeter test was performed after each meter was bored.

❷ Mode 2 (CFA). Continuous flight auger in dry conditions with a diameter of 63 mm, according tothe following procedure which minimized “reaming” of the cavity:➢ boring from 0 to 2.5 m with two pressuremeter tests performed at depths of 2 m and 1 m,➢ boring from 2.5 to 4.5 m with a pressuremeter test performed at a depth of 3 metres,➢ boring from 4.5 to 5.5 m, with a pressuremeter test performed at a depth of 5 metres.

This is the most frequently used boring mode in soil of this type.

❸ Mode 3 (DTS). “Three-blade” desagregating tool with a diameter of 64 mm in a single pass, from 0to 5 m, followed by subsequent conduct of pressuremeter tests, from bottom to top.The results obtained are gathered together in Annex 3.1 (Tables IIIa to IIIc). Figures 6a and 6b show the

effect of the mode of boring on the values of the Ménard pressuremeter modulus EM and the cyclicreloading modulus Er.

The Tables given in Annex 3.1 and Figure 6 elicit the following remarks:

■ In general, the hand auger provides the highest modulus values. On average, the EM and Er valuesfrom the continuous flight auger (CFA) are 1.5 times lower than those from the hand auger(EM = 10.8 MPa, Er = 33 MPa as opposed to EM = 7 MPa and Er = 20.4 MPa for the flight auger). Thedesagregating tool (DTS), with a single 5 m metre boring pass leads to greater dispersion among results,which vary from being slightly higher to very much lower than those obtained with the hand auger.■ Irrespective of the boring mode, the Er /EM ratios remain at about 3. This shows that the unloading-reloading cycle does not re-create an Er modulus which is independent of the mode of boring, and there-fore does not eradicate the effect of disturbance.

It should also be noted that the number of tests conducted was very small and that the density of the siltincreases considerably with depth, as illustrated by the limit pressure p profiles (fig. 6d).




Very plastic clay

The formation consisted of black Albian clay, known as Gault clay, located below the water table (thesite is at Callengeville, in the exhumed and eroded anticlimal fold of the Pays de Bray in the départementof Seine Maritime). The homogeneous zone of this geological horizon was tested by using seven veryclosely spaced boreholes, placed about 2 metres apart.

Seven boring modes were employed (Table IV), ranging from the hand auger without soil “disturbance”and with 1m passes (mode 1) to direct driving of the probe (mode 7), protected by a slotted tube, whichis an absolutely prohibited method.

5 10 15 20

D e p t h z ( m )

D e p t h z ( m )

D e p t h z ( m )

D e p t h z ( m )

MODE 1 (HA)MODE 2 (CFA)

MODE 3 (DTS) 1

4

20 40 0

0

1

4

5

2

4

0, 1,

r (MPa)EM (MPa)

l (MPa)E / E

MODE 1 (HA)MODE 2 (CFA)

MODE 3 DTS

MODE 1 (HA)

MODE 2 (CFA)MODE 3 (DTS)

MODE 1 (HA)

MODE 2 (CFA)

MODE 3 (DTS)

Fig. 6 - Effect of the boring mode on the strain modulus – Silt.

a. Ménard pressuremeter modulus E M . b. Cyclic modulus E r .

c. E r /E M ratio d. Limit pressure p .




Tables IVa to IVg in Annex 3.2 set out all the results from each boring mode. Figures 7a and 7b showhow the boring mode affected the values of the Ménard pressuremeter modulus EM and the cyclic reload-ing modulus Er. Figures 7c and 7d show change in the Er /EM ratios, with depth z and EM respectively.

9

10

12

0 10 20 0 40

MODE 1 : HA 1m pass

MODE 2 : CFA 1m passMODE 3 : CFA 1 passMODE 4 : ROTOP 1m passMODE 5 : DTS 1 passMODE 6 : DTS 1m passMODE 7 : DST

9

1

11

12

1 2 4

9

10

0 1 3 4

10

20

0

40

2 4 6 10

D e p t h z ( m )

D e p t h z ( m )

D e p t h z ( m )

E (MPa)E (MPa)

E m

( M P a )

Er / E Er / EM

MODE 1 : HA 1m passMODE 2 : CFA 1m passMODE 3 : CFA 1 passMODE 4 : ROTOP 1m passMODE 5 : DTS 1 passMODE 6 : DTS 1m passMODE 7 : DST

MODE 1 : HA 1m pass

MODE 2 : CFA 1m pass

MODE 3 : CFA 1 pass

MODE 4 : ROTOP 1m pass

MODE 5 : DTS 1 pass

MODE 6 : DTS 1m pass

MODE 7 : DST

MODE 1 : HA 1m pass

MODE 2 : CFA 1m passMODE 3 : CFA 1 passMODE 4 : ROTOP 1m passMODE 5 : DTS 1 passMODE 6 : DTS 1m passMODE 7 : DST

Fig. 7-– Effect of boring mode on strain modulus – Clay.

a. Ménard pressuremeter modulus E M . b. Cyclic modulus E r .

c. E r /E M ratio. d. E r /E M versus E M.




The highly destructive nature of modes 5 and 6 (desagregating tool without percussion) is apparent. Thisprovides very low EM modulus values, with limit pressures also being considerably affected (Table IV– Annex 3). In spite of Er /EM ratios which are higher than those obtained with the hand auger (approx-imately 4 in one case and 2 in the other), the cycle does not completely eradicate soil disturbance andthe Er values remain below those obtained with recommended boring modes.

Direct driving (mode 7) leads to very high EM modulus values in comparison with the hand auger modeand to an Er /EM ratio equal to 1, which is lower than the values of between 2 and 4 obtained with boringmodes 2, 3, 4 or even 1. At first sight, the cycle would seem to attenuate the effect of disturbance. Inreality, however, the considerable increase in pore pressures that occurs when the probe is driven isdoubtless partly responsible for this result.

In the case of modes 2, 3, 4 and 1, the values of EM (and to a lesser degree, those of Er) are relatively closetogether. It should be noted that the Er modulus values obtained with mode 1, which is the most carefullyperformed (reference boring method), are slightly lower than those obtained with modes 2, 3 and 4.

River sand

These tests were conducted at Honfleur on the southern bank of the Seine, and involved a thick layer(about 15 m) of fine sand which lies underneath silty alluvium. This sand is below the water table andthe tests were conducted at depths of 6, 7 and 8 metres (Fig. 8).

Four boring modes were tested, with two boreholes per mode:

❶ Mode 1 (HA): hand auger with injection of bentonite slurry, by means of successive passes of 1m

with conduct of a pressuremeter test after each pass,❷ Mode 2 (CFA): continuous flight auger with slurry circulation, by means of successive passes of 1m with conduct of a pressuremeter test after each pass,❸ Mode 3 (CFA): continuous flight auger with slurry circulation, by means of a single boring pass andwith conduct of the pressuremeter tests from the bottom of the borehole to the top,❹ Mode 4 (ROTOP): rotary percussion drilling; by means of successive 1 m passes and conduct of apressuremeter test after each pass.

The results of these tests are summarized in Tables VIa to VIe in Annex 3.3. Of the twenty-four teststhat were conducted, three were at a depth of eight metres and were not taken into account, in view of the very high limit pressures that were measured. These tests involved much more dense layers of sandin the lower part of the tested formation (1.35, 1.70 and 1.70 MPa).

Although statistical analysis is made impossible by the small number of tests, we can nevertheless

observe that in general the boring modes have a considerable influence on the Er measurements, even if the dispersion with regard to the cyclic modulus seems lower than that for the pressuremeter modulusEM and the limit pressure p.

Conclusion with regard to the effect of the boring mode

The tests conducted in the cavities that used the various techniques, whether accepted or prohibited,show that an unloading-reloading cycle does not eradicate the effect that the soil disturbance of the wallof boreholes has on the modulus values derived from a pressuremeter test. In fact, the dispersion of Ervalues, when all boring modes are considered, is similar to that obtained for the modulus EM.

Although this conclusion is open to question in view of the small number of tests conducted at each depthand for each boring mode, given the current state of knowledge it nevertheless seems necessary when

conducting cyclic pressuremeter tests to ensure the boring equipment is correctly selected and that bor-ing is correctly performed. We therefore recommend that the rules laid down for borings in the case of standardized pressuremeter tests be followed (Annex 1).

TABLE IVBoring modes used in the clay

Mode 1: Hand Auger, metre by metre (HA) Mode 5: Desagregating tool, in a single pass (DTS)

Mode 2: Continuous flight auger, metre by metre (CFA) Mode 6: Desagregating tool metre by metre (DTS)

Mode 3: Continuous flight auger, in a s ingle pass (CFA) Mode 7: Driven slotted tube (DST)

Mode 4: Rotary percussion, metre by metre (ROTOP)




49

“Accuracy” of cyclic modulus measurements

Once the test procedure had been fixed and the influence of boring techniques studied, the East Paris

LRPC investigated the repeatability of cyclic modulus measurements at three sites in the Greater ParisRegion. The tests were conducted at former LPC experimental sites and three soils of different types

with different characteristics were tested:

➢ Fontainebleau sand (at Bourron-Marlotte),

➢ Brie plateau silt (at Jossigny),

➢ Senonian chalk (at Chatenay-sur-Seine).

Fifteen tests were conducted at each site. These were located 1.5 m apart within a rectangle measuring

6 m × 3 m. The borings were conducted either with a hand auger (silt) or a flight auger (sand and chalk)

5

6

7

8

9

10

0 10 20 30 40 50Er (MPa)

MODE 1 : HA 1m pass


MODE 3 : CFA 1 pass

MODE 4 : ROTOP 1m

D e p t h z ( m )

5

6

7

8

9

10

0 0,5 1 1,5 2p

l (MPa)

MODE 1 : HA 1m pass


MODE 3 : CFA 1 pass

MODE 4 : ROTOP 1m

D e p t h z ( m )

5

6

7

8

9

10

0 2 4 6 8 10EM (MPa)

MODE 1 : HA 1m passMODE 2 : CFA 1m pass

MODE 3 : CFA 1 passMODE 4 : ROTOP 1m

D e p t h z ( m )

a. Pressuremeter modulus Ménard E M .

b. Cyclic modulus E r . c. Limit pressure p .

Fig. 8 - Effect of boring mode on strain modulus – Sand.




and the tests performed at a same depth on each site (– 1 m at Bourron-Marlotte and Jossigny, – 1.5 mat Chatenay-sur-Seine).

Tables which set out the main results are to be found in Annex 4. The characteristics of the tested soilsand the dispersion in the measurements of the pressuremeter modulus EM and the cyclic modulus Er aregiven below.

Fontainebleau sand

This is a marine formation (Stampian stage) consisting of fine quartzous sand with grains of practicallythe same size. Outcrops occur essentially in the South of the Paris Region. The main characteristics of this material (particle size distribution, density) are given in Table V.

The modulus dispersions of the pressuremeter tests performed are set out on Figures 9a and 9b.

Brie plateaux silts

This is a recent formation (plio-pleistocene) which is to be found the Brie plateau and elsewhere. Thissilt (Stampian stage) consists of very fine particles ((80 µm) but nevertheless contains few clay particles

(passing a 2 µm sieve). Its main characteristics are set out in Table VI.The detailed results from the tests are given in Annex 4. Figures 10a and 10b show the observed modulusdispersions.

TABLE VCharacteristics of the tested Fontainebleau sand – Bourron-Marlotte

Particle size Unit weight Shear strength

d50 = 0,27

γs = 26.44 kN/m3

γdmin

= 13.64 kN/m3

emax = 0.94γdmax = 16.83 kN/m3

emin = 0.615

TABLE VIMean characteristics of the silt – Jossigny

VI a – Identification parameters (0.9 – 1.5 m)

% weight not passing Atterberg limits γs(kN/m3)(0.2 mm) (80 µm) (2 µm) wL wP

1 % 4 % 75 % 35 24 26.5

VI b –Laboratory shear strength measured on saturated samples using the triaxial apparatus

cu(kPa)

ϕ'(degré)

c'(kPa)

38 32 12

VI c – Mean in-situ characteristics

Soil layer

Pressuremeter test (NF P94-110) Field Vane test (NF P94-112)

(MPa)Pf

(MPa)EM

(MPa)su ( τpic)

(MPa)sr ( τrésiduel)

(MPa)

0 – 1.5 m 0.43 0.16 5.7 0.092 0.064

0 – 3.5 m 0.52 0.22 6.6 0.094 0.067

CU

d60

d10-------- 1.47= =

CC

d30( )2

d60 d10⋅( )---------------------------- 1= =

γ 16.1– 0.2+ 0.2

kN/m3=

ϕ' 40.5– 1.5+ 1.5

degré=

c' 0– 0+ 5

kPa=

p




5

10

20

25

35

4

Fontainebleau sandFontainebleau sand

0

1

150

2

2

00

50

2 3 4 8 9 10 1 12 13 14 151 1 1

Mean : 205 MPa

Standard deviation : 56 MPacv = 0,2

Test num erTest number

r MPaM MPa

Mean : 27,1 MPa

Standard deviation : 6,4 MPacv = 0,23

0

1

2

6

7

8Brie plateau silt Brie plateau silt

0

5

1

15

20

25

1 2 3 5 6 7 9 10 1 12 13 14 15Test number Test number

1 3 4 5 6 7 9 10 11 12 13 14 15

E (MPa)E (MPa)

Mean : 4,4 MPa MPaStandard deviation : 1

cv = 0,2

Mean : 19 MPaStandard deviation : 4 MPacv = 0,2

a. Pressuremeter modulus E M . b. Cyclic modulus E r .

Fig. 9 - Repeatability of results – Fontainebleau sand (Bourron-Marlotte).


Fig. 10 - Repeatability of results – Silt (Jossigny).




Senonian chalk

This is a carbonated Upper Cretaceous “rock” with a calcium carbonate content of 98%. At the Chate-nay-sur-Seine site, its consistency is that of a paste in which are embedded, locally, harder blocks of theorder of a few decimetres in size.

The laboratory shear characteristics of this chalk are unknown, as it is very difficult or even impossible

to extract undisturbed samples. The pressuremeter characteristics of the experimental site are given inTable VII.

Figures 11a and 11b give the modulus dispersions that were observed during the cyclic pressuremeter testinvestigation. It should be noted that on several occasions, the cyclic modulus could not be calculated dueto the fact that a significant volumetric change was not measured during the unloading-reloading loop.

Conclusions about the repeatability of cyclic modulus measurements

From the Tables in Annex 4 and Figures 9 to 11 it can be seen that, generally, the repeatability of the“cyclic” modulus results is the same as that of the Ménard pressuremeter modulus EM. For example, irre-spective of which soil is tested, the coefficient of variation (cv = σ /m) is similar to or lower than that

obtained for EM. We can therefore consider that performing an unloading-reloading loop leads to thesame cyclic modulus dispersion factor as is obtained for EM during the conduct of a standardized pres-suremeter test. Moreover, the order of magnitude of the coefficient of variation cv is of interest. Its value

TABLE VIIMean pressuremeter characteristics of the chalk – Chatenay-sur-Seine

Soil layer (MPa)pf

(MPa)EM

(MPa)

0 – 1.5 m 1.61 0.67 19.8

0 – 3 m 1.48 0.60 19.4

p

10

15

2

2

1 1

Mean : 12,6 MPaStandard deviation : 6,4 MPacv = 0,5

enonian chal enonian chal

20

40

80

100

12

140

160

180

1 1 1

Mean : 67,1 MPa,4 MPaStandard deviation : 37

cv = 0,5

Er (MPa)M (MPa)

Test number Test number

Fig. 11 - Repeatability of results – Chalk (Chatenay-sur-Seine).





is 0.2 for Fontainebleau sand and Brie plateau silt, for both p, and Er. It is slightly higher (cv » 0,5) inthe chalk formation for EM and Er. This is due to the heterogeneous nature of this layer which consistsof blocks set in a softer matrix. It should nevertheless be noted that the dispersion of p is low in all cases(cv (0,2) because of the applied deformations (∆R/R0 (40% for p; ∆R/R0 (5% for EM) and the volumeof soil that are loaded during a pressuremeter test.

Representative values of Er /EM and Er /p

Two LRPCs, those of Rouen and Melun, conducted tests at sites in Normandy and the Greater ParisRegion (Combarieu et al., 1995; Canépa, 1996). In view of the uncertainties with regard to the measuredvalues that have been discussed above, in order to determine representative values of the Er /EM and Er /p

ratios, only those derived from tests for which a minimum volumetric increase of 2 cm3 was measured(over the range of pressure “pcr – pd” where Er was calculated) were considered.

Table VIII summarizes the mean values obtained for the tested soils (after elimination of the boreholesthat were conducted to investigate the effect of soil disturbance, and performed with a boring modewhich is not recommended by current standards).

Table IX gives the order of magnitude of the ratios Er /E

M and E

r /p which were obtained for the different

soil types investigated (sand, clay, intermediate soils). The Er /p ratio seems to be of particular interest.

Justification of the results and application of the cyclic pressuremeter modulusThis section of the paper examines the representativeness of the measured cyclic pressuremeter modulus.It is interesting to compare the results obtained on site with theoretical results, particularly for the “E/p”ratio. This comparison has been made for both cohesive and frictional soils.

Cohesive soil

In the case of purely cohesive soils, with linearly elastic and plastic behaviour, the relationship between

the ultimate limit pressure (denoted by pu what follows in order to avoid confusion with the pressurem-eter limit p) and the shear modulus G of the soil is written as follows (Combarieu, 1995):

or

where ρ

➢ cu is the undrained cohesion,

➢ p0 is the horizontal earth pressure at the test depth.The following expression relates the conventional limit pressure p (doubling of the initial cavity diam-eter) and the shear modulus G of the soil:

or

or alternatively with ν = 0.33

pu p0– cu 1 n

Gcu-----+

,⋅=

Gpu p0–

-------------------cu

pu p0–

------------------- e

pu p0–

cu------------------- 1–

⋅=

p

p0– cu 1 nG

2 c⋅ u------------+

,⋅=

Gp

p0–----------------- 2

cu

p

p0–----------------- e

p

p0–

cu----------------- 1–

⋅ ⋅=

Ep

p0–----------------- 5,32 cu

p

p0–----------------- e

p

p0–

cu----------------- 1– ⋅=




Figure 12a compares the theoretical results, given by the above relationship, with the experimental dataobtained at the clay sites (Romainville clay and Gault clay) and the Brie silt site. Figure 12b comparesthe measured Er modulus values with the theoretical modulus values E derived from the measured limit

pressure and the cohesion values obtained from laboratory tests or measured in situ. As can be seen, ingeneral the use of the cyclic modulus Er as an elastic modulus provides a good approximation of the the-oretical pressuremeter expansion results.

TABLE VIIICyclic pressuremeter tests

Summary of the results obtained by the Rouen and Melun LRPCs

(MPa) EM (MPa) Er (MPa) Er /EM EM / Er /

Wind blown silt at

Le Havre (1)

Mean 0.74 8.70 25 2.91 11.7 33.8

Standard deviation 0.24 3.57 11.5 0.53 2.0 8.60

cv 0.32 0.41 0.46 0.18 0.17 0.25

Gault Clay (2)) Mean 0.75 7.1 19.4 2.74 9.4 25.6


cv 0.09 0.3 0.39 0.23 0.24 0.34

River sand (3) Mean 0.81 5.1 28.4 5.96 6.4 35.1


cv 0.17 0.26 0.27 0.35 0.28 0.20

Romainville clay(4) Mean 0.74 8.70 25 2.91 11.7 33.8

Standard deviation 0.24 3.57 11.5 0,53 2.0 8.60cv 0.32 0.41 0.46 0.18 0.17 0.25

Fontainebleau sand (5) Mean 2.62 27.1 205 7.5 10.3 77.9

Standard deviation 0.53 6.4 56 1.6 1.1 19.3

cv 0.20 0.23 0.25 0.21 0.11 0.25

Plateau Brie silt – Île-de-France (6)

Mean 0.46 4.4 19 4.5 9.5 41.2

Standard deviation 0.06 1.0 4 0.9 1.7 6.2

cv 0.13 0.23 0.21 0.21 0.18 0.15

Senonian chalk atChatenay-sur-Seine (7)

Mean 0.74 12.6 67.1 5.4 16.5 88

Standard deviation 0.15 6.4 37.4 2.4 6.0 34cv 0.20 0.51 0.56 0.44 0.37 0.40

(1) This recapitulative table takes into account the three boring modes carried out.(2) This table considers only modes 1, 2, 3, 4 which give similar results(3) Mode 3 (a single boring pass) gave low results and was not taken into account.(4) All types of tests (rapid and stepped unloading) were taken into account.(5) (6) (7) All the tests have been taken into account.

TABLE IXUnload-reload pressuremeter tests

Typical characteristic ratios Er /EM and Er /

Soil Er /EM Er /

Stiff overconsolidated clay 2.5 – 3.5 25 – 45

Silt 3 – 4.5 35 – 45

Sand 6 – 7.5 35 – 80

Chalk 5.5 80

p

p

p

p

p




However, this conclusion cannot be extended to displacement calculations for geotechnical structures,as the soil deformation generated by structures can be very different from those associated with thecyclic modulus (∆R/R0 ≈ 10-2) measured during a conventional pressuremeter test*.

Purely frictional soil (c′ = 0)In the case of a purely frictional soil, in an isotropic elastic-perfectly plastic soil model with dilatancy,the limit pressure p is expressed as follows (Combarieu, 1995):

where

➢ a(ϕ ) = max [1; K0.(1 + sinϕ)],

➢

in which➢ ϕ is the angle of internal friction,➢ Ψ is the angle of dilatancy,

➢ G is the shear modulus,

➢ γ is the unit weight of the soil,➢ K0 is the coefficient of earth pressure at rest.

* Use of the cyclic modulus Er as an elastic modulus for displacement calculations for various geotechnical structures isanother differnet problem. In this case, it is necessary to compare the displacement calculation of structures and their realbehaviour while giving an account of the calculation method used in each case. This is not covered by this paper.

5

7

100

0 25 50 75 100E measured (MPa)

E calculed MPa

Calculed = measured

2

75

1

* /cu

E/pl ou Er/pl*

Theoretical

Green clayGault clay

Brie silt

Green clay

Gault clay

Brie sil

Fig. 12 - Pressuremeter theory – Cohesive soils.

a. “E/p ” versus“ p /c u ”. b. Comparison between the calculated modulus Eand the measured modulus E r .

p

z( ) a ϕ( ) γ zG z( )

2 γ z a ϕ( ) m ϕ( )⋅⋅ ⋅ ⋅---------------------------------------------------

m ϕ( )⋅⋅ ⋅=

m ϕ( )sin ϕ 1 sin Ψ+( )⋅

1 sin ϕ+-------------------------------------------- ;=

GE

2 1 ν+( )⋅------------------------,=




We therefore have:

or alternatively:

with ν = 0.33

Figure 13a is a plot of the theoretical relationship E/p versus (p / γ.z) for a friction angle range(37 degrees ≤ ϕ ≤ 43 degrees) which corresponds to laboratory measurements of the Honfleur sand*.This diagram also shows the experimental results for Er /p which were measured taking hydrogeologicalconditions into account (water table at a depth of 1.5 m) and using the unit weights (γ = 18 kN/m3 abovethe water table and 19,5 kN/m3 below the water table) reported by Combarieu (1995).

As can be seen, the Er /p ratios are between 25 and 50 and lie within the range of the theoretical E/p

curves obtained using the relationship given above. In Figure 13b, the measured modulus Er is comparedwith the theoretical modulus E derived from the mean internal angle of friction of river sand. Here too,there is good agreement between the cyclic modulus Er and the theoretical elastic modulus.

Lastly, it should be noted that when p(z) = λ.z.p (which is practically the case for purely frictionalsoils), the ratio E/p is constant, which is replicated experimentally for the EM /p ratios.

ConclusionsThe execution of a large number of cyclic pressuremeter tests with the Ménard apparatus, with the addi-tion of an unloading-reloading loop to the standardized procedure, has led us to the following conclusions:

➢ performing the unloading phase by steps does not allow us to obtain reliable intermediate deforma-

tion modulus results with the equipment used for standard pressuremeter tests;* Whose in-situ cohesion can be assumed to be nil, unlike other sands such as the Fontainebleau sand, for example.

Gp

----- 2 mp

a γ z⋅ ⋅-----------------

1m---- 1–

⋅ ⋅=

Ep

----- 5.32 mp

a γ z⋅ ⋅-----------------

1m---- 1–

⋅ ⋅=

25

50

7

100

5 10 15 20

/ γ

0

2

50

7

100

2 7 1

E measured (MPa)

E calculed (MPa)

River san

calculed = measured

ϕ = 4 ˚

Theoretical 37˚

Theoretical 43˚

River san

a(ϕ) = 1 et ψ = ϕ - 30˚

E/p or Er/p

Fig. 13 - Pressuremeter theory – Purely frictional soils.

a. E/p versus (p / γ z). b. Comparison between the calculated modulus Eand the measured modulus E r .




➢ the mean (secant) modulus over one cycle that is determined with the procedure described in thispaper is little affected by rapid unloading;➢ as long as the recommended test procedure is followed, the dispersion factors for the mean cyclicmodulus are similar to those for the conventional pressuremeter modulus EM;➢ including an unloading-reloading cycle in the pressuremeter test procedure does not provide a meansof “salvaging” an incorrectly performed test. In particular, disturbance of the borehole walls which

affects the value of the modulus EM also affects the value of the modulus Er calculated from the reload-ing curve;➢ the comparisons we have conducted (in particular those concerning the Er /p ratio) with the theoret-ical cavity expansion expressions derived from an elastic-perfectly plastic soil model, appear to validatesome knowledge that has been derived from the pressuremeter tests, that is to say that the EM /p andEr /p ratios remain constant with depth in the case of a homogeneous formation;➢ the values of these ratios nevertheless depend on the nature and density of the soil. It is therefore pref-erable to measure the modulus Er directly by means of a cyclic pressuremeter test rather than to deriveits value on the basis of correlation with the pressuremeter modulus EM,;➢ lastly, it should be remembered that this study is part of a larger research project that concerns thedetermination of the shear modulus of soil with reference to its deformation and the calculation of thedisplacement of geotechnical structures. For this reason, application of the cyclic pressuremeter modulus

to the design of structures has not been covered in this paper. At this stage, we can nevertheless statethat, as long as certain conditions are satisfied, the use of the cyclic modulus instead of Young’s modulusgives good results and is quite adequate for calculating the displacement of certain types of geotechnicalstructure. Encouraging calculations have already been performed and validated. A future paper will dealwith this topic.

REFERENCES

Norme française NF P94-110-1, Essai pressiométrique Ménard, Partie 1: Essai sans cycle, AFNOR, janvier 2000,43 pages.

Norme française XP ENV 1997-1, Calcul géotechnique Partie 1: Règles générales, AFNOR, décembre 1996,

112 pages.BRU J.-P., BAGUELIN F., GOULET G., JÉZÉQUEL J.-F., Prévision de tassement au pressiomètre et constata-tion, Proc. VIIIe Congrès international de Mécanique des sols et des travaux de fondation; tome 1.3, Moscou, 1973,pp. 25-31.

CANÉPA Y., Fondations superficielles, Facteurs empiriques de portance et de tassement, Pressiomètre normal,Sujet de recherche 1.17.02.0, mai 1990.

CANÉPA Y., DEPRESLES D., Catalogue des essais de chargement de fondations superficielles sur sites par les LPC (1978 -1990), Sujet de recherche 1.17.02.0, décembre 1990.

CANÉPA Y., Essais pressiométriques avec cycle de déchargement-rechargement. Influence du mode opératoire,Sujet de recherche 2.24.05.4 de la commission technique 24, Mécanique des sols, roches et fondations, 1996.

COMBARIEU O., L’essai pressiométrique et la résistance au cisaillement des sols, Bulletin de liaison des labora-

toires des Ponts et Chaussées, 196, mars-avril 1995 pp. 43-51.

COMBARIEU O., CANÉPA Y., Essais pressiométriques Ménard avec boucle de déchargement-rechargement. Analyse des procédures et des résultats d’essais, Sujet de recherche 2.24.19.3 et 2.24.02.4 de la commission tech-nique 24, Mécanique des Sols, roches et fondations, 1995.

Fascicule 62 Titre V, Règles techniques de conception et de calcul des fondations des ouvrages de génie civil, Min-istère de l’Équipement, du logement et des transports, 1993.

FRANK R., Quelques développements récents sur le comportement des fondations superficielles, Xe Congrèseuropéen de Mécanique des sols et des travaux de fondation, Florence, 1991, 28 pages.

MÉNARD L., ROUSSEAU J., L’évaluation des tassements. Tendances nouvelles, Sols Soils, 1, 1962, pp. 13-30.

MÉNARD L., LAMBERT Ph., Étude expérimentale d’un massif de fondation soumis à des vibrations, Sols Soils,

17, 1966, pp. 9-30.MESTAT Ph., Analyse théorique d’un cycle déchargement-rechargement dans le problème de l’expansion d’unecavité cylindrique dans un matériau élastoplastique de Tresca, rapport interne, LCPC, janvier 1993.




MESTAT Ph., Analyse théorique d’un cycle déchargement-rechargement dans le problème de l’expansion d’unecavité cylindrique dans un matériau élastoplastique de Mohr-Coulomb, rapport intene, LCPC, janvier 1993.

MESTAT Ph., Validation du progiciel CÉSAR-LCPC en comportement mécanique non linéaire, vol. 1: Fonda-tions superficielles et tunnels, Études et recherches des laboratoires des Ponts et Chaussées, Série Géotechnique,GT 58, juin 1994.

MONNET J., KHLIF J., Étude théorique de l’équilibre élasto-plastique d’un sol pulvérulent autour du pressiomè-

tre, Revue française de géotechnique, 73, 1994, pp. 3-12.

WROTH C.P., British experience with the self-boring pressuremeter , Proc. 1st Symp. Pressuremeter and its MarineApplications, Paris; Colloques et séminaires 37, Ed. Technip, 1982, pp. 143-164.




ANNEX 1Drilling techniques for pressuremeter boreholes (NF P 94-110-1)

TABLE IRecommendations laid down in the standard NF P 94-110-1 (Table C1 p 34)

Soil type

Preboring mode SoildisplacementRotary drilling* Driving and other

HA HAS/CFAS CFA DTS CD ROTOP DS VDS STDT DST/TWS

Sludge and soft clay - R° - O° - - OTWCS

- - -

Medium stiff clay R R° R R° - O° - - O -

Stiff clay, stiff marl R R° R° O° - - - -

Silt:– above ground water table R O° R O° - O° O O O -

– below ground water table - R° - O° O° O° - - O▲ -

Loose sand:– above ground water table R R° O O° - O° - - O -

– below ground water table - R° - O° - O° - - - O

Medium dense sand anddense sand

R R° R R° - R° O O O▲ O*

Coarse soils: gravel, cob-bles, boulder clay, etc.

O O° R° O O O O+

Weathered rockSoft rock

R R O R° O O O+

Key:R: RecommendedO: Tolerated-: Not tolerated

: Unsuitable* Rotation speed < 60 rpm, tool diameter (1.15 ds+ Where necessary, a preliminary boring may be performed in small diameter (dt < ds)˚ Slurry circulation (pressure < 500 kPa, outflow < 15 l/min).When boring is conducted by rotary drilling, the pressure (measured at the top of the driving rods) transmitted to the drilling tool must be lessthan 200 kPa.▲ With specific care (for example keeping slurry level in casing higher than ground water table level, carry out the tests while going down,adding a guard tube at the toe of the slotted tube).HA Hand auger (spoon)HAS/CFAS Auger with slurry circulationCFA Continuous-f light auger ( in dry condi tions)

DTS Desagregating tool (drag bit) with slurry circulationCD Core drillingROTOP Rotary percussionDS Driven samplerVDS Vibro driven samplerSTDT Slotted tube with inside desagregating toolDST Driven slotted tubeTWS Thin wall samplerTWCS Thin wall core sampler




ANNEX 2Cyclic pressuremeter tests – Influence of the test procedure

TABLE IIUnloding-reloading test procedure

Summary of results (Green Romainville clay at Boissy-Saint-Léger)

BOREHOLE P1

z pf EM Ed Er EM / /pf Er /EM Ed /EM Mode

(m) (MPa) (MPa) (MPa) (MPa) (MPa)

1.6 0.74 0.42 9.5 39.1 41.5 12.8 1.8 4.4 4.1 L2.6 0.79 0.43 6.8 31.2 36.3 8.6 1.8 5.3 4.6 R3.6 0.73 0.44 6.8 24.3 25.9 93 17 38 36 L

BOREHOLE P2



1.7 0.51 0.32 5.2 30.2 39.0 10.2 1.6 7.5 5.8 R2.7 0.75 0.43 8.5 39.5 40.6 11.4 1.7 4.8 4.6 L

3.7 0.68 0.43 6.2 18.2 22.0 9.2 1.6 3.5 2.9 RBOREHOLE P3



2 0.4 0.30 3.4 39.4 14.6 8.6 1.3 4.2 11.5 L3 0.75 0.43 9.0 22.2 24.0 12.0 1.7 2.7 2.5 R4 0.68 0.44 6.5 23.4 19.6 9.5 1.5 3.0 3.6 L

BOREHOLE P4

z pf EM Ed Er EM / pl /pf Er /EM Ed /EM Mode


1.6 0.81 0.41 11.8 37.7 25.6 14.6 2.0 2.2 3.2 R2.6 0.99 0.56 12.0 50.0 50.9 12.2 1.8 4.2 4.2 L3.6 0.76 0.43 7.1 22.2 24.1 9.4 1.8 3.4 3.1 R

BOREHOLE P5



.1.7 0.83 0.42 12.3 40.9 86.8 14.9 2.0 7.0 3.3 L2.7 0.95 0.62 9.4 33.9 31.7 9.9 1.5 3.4 3.6 R3.7 0.74 0.44 8.3 38.3 23.5 11.2 1.7 2.8 4.6 L

BOREHOLE P6



1.9 0.51 0.31 6.6 26.5 23.9 12.8 1,6 3.6 4.0 R

2.9 0.79 0.42 9.7 36.0 36.8 12.3 1.9 3.8 3.7 L3.9 0.73 0.43 7.0 23.3 21.3 9.6 1.7 3.0 3.3 R

BOREHOLE P7



1.6 0.6 0.40 7.2 30.2 23.2 11.9 1.5 3.2 4.2 L2.6 0.91 0.64 9.8 31.2 30.5 10.8 1.4 3.1 3.2 R3.6 0.74 0.45 8.7 25.7 26.6 11.8 1.6 3.0 2.9 L

BOREHOLE P8



2 0.76 0.43 11.0 30.0 29.5 14.5 1.7 2.7 2.7 R3 0.83 0.48 7.3 36.9 29.5 8.8 1.7 4.0 5.0 L4 0.8 0.43 8.3 20.5 30.0 10.3 1.8 3.6 2.5 R

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ANNEX 3cyclic pressuremeter tests – Influence of boring mode

SILTTABLE IIIa

Silt – Hand auger – Mode 1

Depth(m) (MPa)

EM (MPa)

Er (MPa) Er /EM EM / Er /

1 0.39 5.20 17.00 3.27 13.30 43.60

2 0.71 9.00 30.00 3.33 12.70 42.40

3 0.91 11.70 28.00 2.40 12.90 30.10

4 1.20 17.50 57.00 3.26 14.60 47.50

(rejected) 5 1.74 37.00 93.30 2.52 21.30 53.60

Mean 0.80 10.80 33.00 3.06 13.37 40.90

TABLE IIIbSilt – 63 mm Continuous flight auger – Mode 2

Depth(m) (MPa)

EM (MPa)


1 0.42 4.30 14.00 3.25 10.20 33.30

2 0.75 7.00 21.00 3.00 9.30 28.00

3 0.80 7.00 17.50 2.50 8.75 21.90

4 0.75 9.70 29.00 3.00 12.93 38.70

(rejected) 5 1.85 22.50 80.00 3.55 12.20 43.20

Mean 0.68 7.00 20.40 2.94 10.30 30.47

TABLE IIIcSilt – “Three blades” desagregating tool Ø 64 mm – Mode 3

Depth(m) (MPa)

EM (MPa)


1 0.47 6.00 15.00 2.50 12.75 31.90

2 0.80 11.00 26.00 2.36 13.75 32.50

3 0.73 7.00 27.50 3.92 9.60 37.70

4 1.00 9.00 18.80 2.09 9.00 18.80

Mean 0.75 8.20 21.80 2.72 11.28 30.22

TABLE IIIdSilt – Results from all tests

(MPa)EM

(MPa)Er

(MPa) Er /EM EM / Er /

Mean 0.74 8.70 25.00 2.91 11.72 33.84

Standard deviation 0.24 3.57 11.5 0.53 2.00 8.60cv 0.32 0.41 0.46 0.18 0.17 0.25

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CLAYTABLE IVa

Clay – Hand Auger, metre by metre – Mode 1

Depth

(m) (MPa)

EM

(MPa)

Er

(MPa)

Er /EM EM / Er /

9.3 0.85 7.6 15.5 2.0 8.9 18.2

10.3 0.66 5 10.1 2.0 7.6 15.3

Mean 0.75 6.3 12.8 2.0 8.3 16.8

TABLE IVbClay – Continuous flight auger metre by metre – Mode 2

Depth(m) (MPa)

EM(MPa)

Er(MPa) Er /EM EM / Er /

9.3 0.81 9.3 24.2 2.6 11.5 29.9

10.3 0.7 5.4 16.3 3.0 7.7 23.3

Mean 0.75 7.4 20.2 2.8 9.6 26.6

TABLE IVcClay – Continuous flight auger in a single pass – Mode 3

Depth(m) (MPa)

EM(MPa)


8.3 0.8 10.5 36 3.4 13.1 45.0

9.3 0.79 7.5 26.7 3.6 9.5 33.8

10.3 0.66 4 13 3.2 6 19.7

Mean 0.75 7.3 25.2 3.4 9.6 32.8

TABLE IVdClay – Rotary percussion, metre by metre – Mode 4

Depth(m) (MPa)

EM(MPa)


8.3 0.68 6.5 17.5 2.7 9.6 25.7

9.3 0.71 5.6 18 3.2 7.9 25.3

10.3 0.81 9.5 16.5 1.7 11.7 20.4

Mean 0.73 7.2 17.3 2.5 9.7 23.8

TABLE IVeClay – Desagregating tool in a single pass – Mode 5

Depth(m) (MPa)

EM(MPa)


8.3 0.46 1.7 7.2 4.2 3.7 15.6

9.3 0.48 2.7 12 4.4 5.6 25.0

10.3 0.56 1.6 10.8 6.8 2.9 19.3

Mean 0.5 2 10 5.1 4.1 20

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TABLE IVfClay – Desagregating tool, metre by metre – Mode 6

Depth(m) (MPa)

EM(MPa)


8.3 0.55 2.3 9.3 4.0 4.2 16.9

9.3 0.68 4.2 10 2.4 6.2 14.7

10.3 0.62 4.6 15.3 3.3 7.4 24.7

Mean 0.62 3.7 11.5 3.2 5.9 18.8

TABLE IVgClay – Driven slotted tube – Mode 7

Depth(m) (MPa)

EM(MPa)


8.3 0.88 37.0 25 0.7 42.0 28.4

9.3 0.86 17.5 23.6 1.3 20.4 27.4

10.3 0.97 22.5 23.5 1.0 23.2 24.2

Mean 0.90 25.7 24 1 28.5 26.7

TABLE IVhClay – Results from all tests

Depth(m) (MPa)

EM(MPa)


Mean 0.7 8.7 17.4 11 2.9 23.8


cv 0.20 1.00 0.43 0.83 0.48 0.31

SAND

TABLE VaSand – Hand Auger, pass of one metre – Mode

Depth(m) (MPa)

EM(MPa)


6 0.93 5.3 25.7 4.88 5.7 27.8

7 0.69 5.1 24.7 4.88 7.4 36.1

6 0.73 4.9 26.4 5.35 6.8 36.4

7 0.89 6.5 40.3 6.23 7.3 45.5

Mean 0.81 5.4 29.3 5.3 6.8 36.4

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TABLE VbSand – Continuous flight auger, passes of one meter – Mode 2

Depth(m) (MPa)

EM(MPa)


6 0.68 5.1 16.9 3.29 7.6 257 0.92 5.4 29.1 5.39 5.9 31.8

6 0.68 7.4 21.6 2.91 11 32

7 0.94 2.6 27.8 10.61 2.8 29.7

8 0.90 6.3 26 4.16 7 29.1

Mean 0.82 5.4 24.3 5.3 6.9 29.5

TABLE VcSand – Continuous flight auger, single pass – Mode 3

Depth(m) (MPa)

EM(MPa)


6 0.43 1.7 9.2 5.40 4 21.6

7 0.74 3.8 33.9 8.87 5.2 46.1

8 0.72 6.1 21.8 3.59 8.5 30.5

6 0.58 4.4 21.2 4.79 7.7 36.9

7 0.79 4.9 31 6.37 6.2 39.5

8 0.65 4 23.8 5.95 6.2 36.9

Mean 0.65 4.2 23.5 5.8 6.3 35.3

TABLE Vd

Sand – Rotary percussion, passes of one meter – Mode 4Depth

(m) (MPa)EM

(MPa)Er


6 0.78 3.8 21.7 5.71 4.9 28

7 1.04 6.6 42.6 6.44 6.4 41.2

8 0.85 5.2 38.7 7.39 6.2 45.8

6 0.58 3.6 19.5 5.38 6.3 33.9

7 0.64 3 30 10.04 4.7 47.2

8 0.95 5.2 35.3 6.80 5.5 37.4

Mean 0.80 4.6 31.3 7 5.7 38.9

TABLE VeSand – Results from all tests

Depth(m) (MPa)

EM(MPa)


Mean 0.76 4.8 27 5.9 6.4 35.2

Standard deviation 0.15 1.4 8.1 2 1.7 7.3

cv 0.20 0.29 0.30 0.34 0.27 0.21

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ANNEX 4Cyclic pressuremeter tests – Repeatability of tests

SAND

TABLE VIFontainebleau sand – Complete results

Testnumber

(MPa)

EM (MPa)


Ed (MPa) Ed /EM

1 2.08 21.4 – – 10.3 – – –

2 2.38 31.1 273 8.8 13.0 114

3 3.0 35.7 193 5.4 11.9 64.3 625 17.5

4 3.05 33.9 270 8.0 11.1 88.5 376 11.1

5 2.8 26.6 179 6.7 9.5 63.9 413 15.5

6 2.42 22.8 124 5.4 9.4 51.2 276 12.17 3.22 29.1 178 6.1 9.0 55.3 420 14.4

8 2.38 22.8 204 8.9 9.6 85.7 275 12.1

9 2.3 21.5 218 10.2 9.3 94.8 248 11.5

10 2.1 21.2 159 7.5 10.1 75.7 184 8.7

11 2.35 26.0 211 8.1 11.1 89.4 501 19.3

12 3.2 36.0 332 9.2 11.3 103.8 474 13.1

13 3.8 37.7 210 5.6 10.2 55.3 374 9.9

14 2.05 19.3 172 8.9 9.4 83.9 293 15.2

15 2.18 21.3 142 6.6 9.8 65.1 203 9.5Mean 2.62 27.1 205 7.5 10.3 77.9 359 13.1

Standard deviation 0.53 6.4 56 1.6 1.1 19.3 128 3.2

cv 0.20 0.23 0.25 0.21 0.11 0.25 0.36 0.24

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SILTTABLE VII

Brie plateau silt – Complete results

Test

number

(MPa)

EM

(MPa)

Er

(MPa)E

r /E

ME

M / E

r / Ed

(MPa)E

d /E

M

1 0.46 4.2 20.6 4.9 9.1 44.7 35.8 8.6

2 0.46 4.5 18.4 4.1 9.8 40 31.5 7.0

3 0.45 4.1 19 4.6 9.1 42.2 26.6 6.5

4 0.45 4.1 21.6 5.2 9.2 48 37.1 9.0

5 0.43 5.0 14.6 2.9 11.6 34 20.5 4.1

6 0.45 4.0 14.4 3.6 8.8 32 18.4 4.6

7 0.51 5.0 25.1 5.0 9.8 49.2 52.4 10.4

8 0.48 6.8 19.9 2.9 14.2 41.5 27.3 4.0

9 0.47 3.4 17 5.0 7.3 36.1 36.3 10.510 0.48 3.6 19.9 5.5 7.5 41.5 29.4 8.2

11 0.51 4.6 24 5.2 9.1 47.1 28.9 6.3

12 0.52 5.1 24.5 4.8 9.8 47.1 36.4 7.2

13 No test performed

14 0.28 2.3 12.4 5.3 8.3 44.3 23.9 10.3

15 0.49 4.5 14.4 3.2 9.3 29.4 21.6 7.8

Mean 0.46 4.4 19 4.5 9.5 41.2 30.4 7.2

Standard deviation 0.06 1.0 4 0.9 1.7 6.2 8.8 2.3

cv 0.13 0.23 0.21 0.21 0.18 0.15 0.29 0.32

SENONIAN CHALK

TABLE VIIISenonian chalk – Complete results

Testnumber

(MPa)

EM (MPa)


Ed (MPa) Ed /EM

1 0.96 28.4 72.1 2.5 29.6 75 97.0 3.4

2 0.65 10.2 31.7 3.1 15.7 49 37.3 3.63 0.57 13.0 65.7 5.1 22.6 115

4 0.55 6.0 51.5 8.6 10.9 94

5 0.72 17.7 24.5

6 0.66 7.6 64.6 8.5 11.6 98 102.7 13.5

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SENONIAN CHALK

TABLE VIIISenonian chalk – Complete results

Test

number

(MPa)

EM

(MPa)

Er


Ed

(MPa) Ed /EM

7 0.85 8.4 9.8

8 0.81 9.1 53.0 5.8 11.2 65 99.7 11.0

9 0.68 11.1 16.4

10 0.86 10.4 12.0

11 0.88 12.2 13.9

12 1.00 24.1 153.9 6.4 24.1 154 226.2 9.4

13 0.79 14.5 44.6 3.1 18.3 56 97.1 6.7

14 0.54 8.0 14.9

15 0.63 7.6 12.1

Mean 0.74 12.6 67.1 5.4 16.5 88 110.0 8.0

Standard deviation 0.15 6.4 37.4 2.4 6.0 34 62.1 3.7

cv 0.20 0.51 0.56 0.44 0.37 0.40 0.56 0.47

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p p

unload-reload pressuremeter test

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