Performance-Based Design in Earthquake GeotechnicalEngineering – Kokusho, Tsukamoto & Yoshimine (eds)

© 2009 Taylor & Francis Group, London, ISBN 978-0-415-55614-9

Interrelationship between small strain modulus G0 and operative modulus

P. Monaco, S. Marchetti & G. TotaniUniversity of L’Aquila, Italy

D. MarchettiMarchetti, Rome, Italy

ABSTRACT: This paper presents experimental diagrams constructed using same-depth values of the smallstrain modulus G0 and of the working strain modulus (constrained modulus) M determined by seismic dilatometer(SDMT) at 34 different sites in a variety of soil types, in order to investigate the interrelationship between thetwo moduli. The ratio G0/M is plotted as a function of the DMT horizontal stress index KD (stress history)and of the DMT material index ID (indicative of clay, silt or sand). Such experimental diagrams offer someelements of reply to the questions: (1) Is it feasible, as sometimes suggested, to estimate the operative modulusas G0 divided by a constant? (2) Is it feasible, for a seismic classification, to use su or NSPT as a substitute forVS—when VS has not been measured? Lines of research on the possible use of SDMT for deriving the in situG-γ decay curves are also outlined.

1 INTRODUCTION

The seismic dilatometer (SDMT) is the combination ofthe traditional ‘‘mechanical’’ Flat Dilatometer (DMT)introduced by Marchetti (1980) with a seismic mod-ule placed above the DMT blade. The SDMT mod-ule is a probe outfitted with two receivers, spaced0.5 m, for measuring the shear wave velocity VS . FromVS the small strain shear modulus G0 may be deter-mined using the theory of elasticity. Motivations ofthe combined probe:

– VS and G0 are at the base of any seismic analysis.– The G-γ decay curves of stiffness with strain level

are an increasingly requested input in seismic anal-yses and, in general, in non linear analyses.

– Increasing demand for liquefiability evaluations.– Seismic site classification using directly VS rather

than the SPT blow count NSPT or the undrained shearstrength su.

– Availability of the usual DMT results (e.g. con-strained modulus MDMT ) for common design appli-cations (e.g. settlement predictions).

The SDMT equipment and test procedure are brieflydescribed in the paper. Comments on SDMT resultsand applications can be found in previous papers, inparticular in Marchetti et al. (2008).

This paper is focused, essentially, on the experimen-tal interrelationships between the small strain shearmodulus G0 and the operative (working strain) con-strained modulus MDMT , investigated by use of SDMTresults obtained in the period 2004–2007 from a largenumber of tests at 34 sites, in a variety of soil types.

It must be emphasized the well known notion that,while the small strain shear modulus is unique, theoperative modulus varies with strain. Hence, in the-ory, such comparison is impossible. However the termoperative modulus sounds very familiar to practicingengineers, because they use it very often in designand would find useful methods providing even roughestimates of it. The price to pay is to accept (non negli-gible) approximation in the definition of the operativemodulus, which however maybe still useful in practice,in view of the often very large errors in estimating suchmodulus.

2 THE SEISMIC DILATOMETER (SDMT)

The seismic dilatometer (SDMT) is the combinationof the standard DMT equipment with a seismic modulefor measuring the shear wave velocity VS .

Initially conceived for research, the SDMT is grad-ually entering into use in current site investigationpractice. The test is conceptually similar to the seismiccone (SCPT). First introduced by Hepton (1988), theSDMT was subsequently improved at Georgia Tech,Atlanta, USA (Martin & Mayne 1997, 1998, Mayneet al. 1999). A new SDMT system (Fig. 1) has beenrecently developed in Italy.

The seismic module (Fig. 1a) is a cylindrical ele-ment placed above the DMT blade, outfitted with tworeceivers spaced 0.5 m. The signal is amplified anddigitized at depth. The true-interval test configura-tion with two receivers avoids possible inaccuracy inthe determination of the ‘‘zero time’’ at the hammer

1315

a) b) c) d)

Figure 1. (a) DMT blade and seismic module. (b) Schematic layout of the seismic dilatometer test. (c) Seismic dilatometerequipment. (d) Shear wave source at the surface.

impact, sometimes observed in the pseudo-intervalone-receiver configuration. Moreover, the couple ofseismograms recorded by the two receivers at a giventest depth corresponds to the same hammer blow andnot to different blows in sequence, which are notnecessarily identical. Hence the repeatability of VSmeasurements is considerably improved (observed VSrepeatability ≈1–2%).

VS is obtained (Fig. 1b) as the ratio between thedifference in distance between the source and the tworeceivers (S2 – S1) and the delay of the arrival of theimpulse from the first to the second receiver (�t). VSmeasurements are obtained every 0.5 m of depth.

The shear wave source at the surface (Fig. 1d) is apendulum hammer (≈10 kg) which hits horizontallya steel rectangular base pressed vertically against thesoil (by the weight of the truck) and oriented with itslong axis parallel to the axis of the receivers, so thatthey can offer the highest sensitivity to the generatedshear wave.

The determination of the delay from SDMT seismo-grams, normally carried out using the cross-correlationalgorithm, is generally well conditioned, being basedon the two seismograms—in particular the initialwaves—rather than being based on the first arrivaltime or specific marker points in the seismogram.Figure 2 shows an example of seismograms obtainedby SDMT at various test depths at the site of Fucino (itis a good practice to plot side-by-side the seismogramsas recorded and re-phased according to the calculateddelay).

Figure 3 (Fiumicino) is an example of the typicalgraphical format of the SDMT output. Such outputdisplays the profile of VS as well as the profiles of fourbasic DMT parameters—the material index ID (soiltype), the constrained modulus M , the undrained shearstrength su and the horizontal stress index KD (relatedto OCR)—obtained using current DMT correlations.(Information on the mechanical DMT, not described inthis paper, can be found in the comprehensive reportby the ISSMGE Technical Committee TC16 2001).It may be noted in Figure 3 that the repeatability of the

Figure 2. Example of seismograms obtained by SDMT atthe site of Fucino (Italy).

VS profile is very high, similar to the repeatability ofthe other DMT parameters.

VS measurements by SDMT have been validatedby comparison with VS measurements obtained byother in situ seismic tests at various research sites.As an example Figure 4 shows VS comparisons atthe research site of Fucino, Italy (NC cemented clay),extensively investigated at the end of the ’80s. Theprofile of VS obtained by SDMT in 2004 (Fig. 4) isin quite good agreement with VS profiles obtained bySCPT, Cross-Hole and SASW in previous investiga-tions (AGI 1991). Similar favourable comparisons arereported e.g. by Hepton (1988), McGillivray & Mayne(2004) and Młynarek et al. (2006).

3 INTERRELATIONSHIPS BETWEENEXPERIMENTAL G0 AND MDMT

The experimental diagrams presented in this sectionhave been constructed using same-depth values of G0(small strain shear modulus from VS ) and MDMT (con-strained modulus from the usual DMT interpretation)

1316

Figure 3. SDMT profiles from two parallel soundings at the site of Fiumicino (Italy).

SCPTCross HoleSASW

AGI (1991)

SDMT(2004)

Figure 4. Comparison of VS profiles obtained by SDMTand by SCPT, Cross-Hole and SASW (AGI 1991) at theresearch site of Fucino (Italy).

determined by SDMT at 34 different sites, in a vari-ety of soil types. The majority of the sites are in Italy,others are in Spain, Poland, Belgium, USA.

SDMT generates plentiful data points because eachsounding routinely provides profiles of G0 and MDMT ,in addition to other parameters. Of the over 2000 datapoints available, only 800 high quality data pointshave been considered, relative to ‘‘uniform’’ one-msoil intervals where log ID, KD, ED, MDMT , VS all dif-fer less than 30% from their average—used then to plotthe data points—to insure a proper match of the data.

ID, KD and ED are ‘‘index parameters’’ (Marchetti1980, see also TC16 2001, Table 1) obtained from thetwo DMT pressure readings: p0 = pressure necessary

to balance the soil pressure and start the movementof the membrane, and p1 = pressure necessary to movethe center of the membrane 1.1 mm against the soil.

The material index ID = (p1 − p0)/(p0 − u0) pro-vides information on soil type—sand, silt, clay (u0 =pre-insertion in situ pore pressure).

The horizontal stress index KD = (p0 − u0)/σ ′v0

is related to stress history (σ ′vo = pre-insertion in

situ overburden stress). The profile of KD is similarin shape to the profile of the overconsolidation ratioOCR. In clays KD ≈ 2 indicates OCR = 1, KD > 2indicates overconsolidation.

The dilatometer modulus ED = 34.7(p1 − p0),derived by simple theory of elasticity, is generally tobe used only in combination with ID, KD (by use ofMDMT ), primarily because ED lacks information onstress history (reflected by KD).

The constrained modulus MDMT (vertical drainedconfined 1-D tangent modulus at σ ′

v0) is obtained asMDMT = RM ED by applying to ED the correctionfactor RM = f (ID, KD), mostly in the range 1 to 3and increasing with KD (major influence). MDMT rou-tinely takes into account overconsolidation and pos-sible high lateral stresses (incorporated via KD), thatreduce considerably soil compressibility.

3.1 Diagrams of the ratio G0/MDMT

The values of the ratio G0/MDMT (800 high qualitydata points from 34 sites) are plotted in Figure 5 asa function of the horizontal stress index KD for clay(having material index ID < 0.6), silt (0.6 < ID < 1.8)and sand (ID > 1.8). Best fit equations are indicatedfor each soil type.

Recognizable trends in Figure 5 are: (a) The datapoints tend to group according to their ID (soil type).

1317

(b) G0/MDMT is mostly in the range 0.5 to 3 in sand, 1 to10 in silt, 1 to 20 in clay. (c) The widest range and themaximum variability of G0/MDMT are found in clay.(d) For all soils G0/MDMT decreases as KD (related toOCR) increases.

Considerations emerging from the diagram:

1. The ratio G0/M varies in a wide range (≈0.5 to20 for all soils), hence it is far from being a con-stant. Its value is strongly dependent on multipleinformation, e.g. (at least) soil type and stress his-tory. Therefore it appears next to impossible toestimate the operative modulus M by dividing G0by a constant, as suggested by various Authors.

2. If only mechanical DMT data are available, Figure 5permits to obtain rough estimates of G0 (and VS )by use of the three parameters ID, KD, M . Howeverthere is no reason for not measuring directly VS(e.g. by SCPT or SDMT).

3. Figure 5 highlights the dominant influence of KD onthe ratio G0/M . In case of non availability of KD,all the experimental data points would cluster onthe vertical axis. In absence of KD—which reflectsthe stress history—the selection of the ratio G0/Mwould be hopelessly uncertain. Hence as many asthree informations, i.e. ID, KD, M (though onlytwo independent), are needed to formulate roughestimates of G0 and VS .

4. In view of the consideration (3), the use of NSPTor su alone as a substitute of VS (when not mea-sured) for the seismic classification of a site, asproposed e.g. by the Eurocode 8 and by variousnational codes, does not appear founded on a firmbasis. In fact, if VS is assumed to be the primaryparameter for the classification of the site, then thepossible substitute of VS must be reasonably cor-related to VS . If three parameters (ID, KD, M ) arebarely sufficient to obtain rough estimates of VS ,

0

5

10

15

20

25

30

0 5 10 15 20 25 30

CLAY ID

< 0.6 G0/M

DMT = 26.177 K

D

–1.0066

R2 = 0.61

SILT 0.6 < ID

< 1.8 G0/M

DMT = 15.686 K

D

–0.921

R2 = 0.81

SAND ID

> 1.8 G0/M

DMT = 4.5613 K

D

–0.7967

R2 = 0.65

KD

G0

MDMT

Figure 5. Ratio G0/MDMT vs. KD (OCR) for various soiltypes.

then the possibility to estimate VS from only oneparameter appears remote.

NOTE: Reason of plotting G0/M (ID, KD) rather thanG0/ED (ID, KD), i.e. reason of selecting a format notsimilar to the 1980 correlation M/ED (ID, KD).

The first attempt by the writers was to plot G0/ED(ID, KD)—where ED is the dilatometer modulus, asmany researchers had done before (Tanaka & Tanaka1998, Sully & Campanella 1989, Baldi et al. 1989,Lunne et al. 1989, Hryciw 1990, Baldi et al. 1991,Cavallaro et al. 1999, Ricceri et al. 2001). The plotG0/ED was expected to contain less dispersion thanthe plot G0/M , since the relationship M from ED hasits own variability. However it was found, contraryto expectations, that the degree of correlation in theG0/ED plot was lower (see Figure 6).

3.2 Diagrams of the ratio GDMT /G0

The diagrams in Figure 7 show the same experimentalinformation as in Figure 5, but involve the additionalmodulus GDMT derived from MDMT using the formulaof linear elasticity:

G = M/[2(1 − ν)/(1 − 2ν)] (1)

For an often assumed value ν = 0.20:

GDMT = MDMT /2.67 (2)

All the GDMT have been derived from MDMT usingEq. 2, then the ratios GDMT /G0 have been calculatedtoo and plotted vs. KD for clay, silt and sand (Fig. 7).

The reason of constructing Figure 7 is the following.The ratio G/G0 is the usual ordinate of the normal-ized G-γ decay curve and has the meaning of a straindecay factor. Since MDMT is a working strain modulusone might hypothesize that GDMT is a working strain

0

5

10

15

20

25

30

0 5 10 15 20 25 30

CLAY ID

< 0.6

SILT 0.6 < ID

< 1.8

SAND ID

> 1.8G0

ED

KD

Figure 6. Ratio G0/ED vs. KD for various soil types.

1318

0

0.5

1

0 5 10 15 20 25 30

CLAY ID

< 0.6 GDMT

/G0 = –0.0002 K

D

2 + 0.022 K

D

– 0.0173

R2 = 0.85

SILT 0.6 < ID

< 1.8 GDMT

/G0 = 0.0241 K

D

0.919

R2 = 0.81

SAND ID

> 1.8 GDMT

/G0 = 0.0826 K

D

0.7961

R2 = 0.66

KD

GDMT

G0

Figure 7. Decay ratio GDMT /G0 vs. KD for various soiltypes.

shear modulus too, in which case GDMT /G0 could beregarded as the shear modulus decay factor at workingstrains.

It is emphasized that, at this stage, the legitimacy ofusing linear elasticity for deriving GDMT from MDMT(Eq. 2) and the assumption that GDMT is a workingstrain shear modulus are only working hypotheses,likely more difficult to investigate than verifying thatMDMT is a working strain constrained modulus (thematter is discussed later in the paper). The very des-ignation working strain shear modulus (or operativeshear modulus) requires clarification. Anyway, if theabove hypotheses were acceptable, Figure 7 could pro-vide, if ID and KD are known, rough estimates of thedecay factor at working strains. If complete SDMT areavailable, then said rough estimates of the decay fac-tor could be skipped and the factor could be obtaineddirectly as the ratio between GDMT derived from MDMT(Eq. 2) and G0.

Experimental information on the decay factor couldpossibly be of interest to researchers in the area of theG-γ decay curves, who might find of interest experi-mental data indicating how fast G0 decays dependingon soil type and stress history.

Trends emerging from Figure 7 are: (a) The G decayin sands is much less than in silts and clays. (b) Thesilt and clay decay curves are very similar. (c) For allsoils the decay is maximum in the NC or lightly OCregion (low KD).

4 IN SITU G-γ DECAY CURVES BY SDMT

Research in progress investigates the possible use ofthe SDMT for deriving ‘‘in situ’’ decay curves of soilstiffness with strain level (G-γ curves or similar).

Such curves could be tentatively constructed by fit-ting ‘‘reference typical-shape’’ laboratory curves (see

Figure 8, where G is normalized to G0) through twopoints, both obtained by SDMT: (1) the initial mod-ulus G0 from VS , and (2) a working strain modulusGDMT corresponding to MDMT (Eq. 2).

To locate the second point it is necessary to know,at least approximately, the shear strain correspond-ing to GDMT . Indications by Mayne (2001) locate theDMT moduli at an intermediate level of strain (γ ≈0.05–0.1%) along the G-γ curve. Similarly Ishihara(2001) classified the DMT within the group of meth-ods of measurement of soil deformation characteristicsinvolving an intermediate level of strain (0.01–1%).The above indications, to be supplemented by furtherinvestigations, could possibly help develop methodsfor deriving in situ G-γ curves from SDMT.

Lines of research on this topic were first outlined byLehane & Fahey (2004). Lines of research currentlyunder investigation (Marchetti et al. 2008) are:

a. Enter the GDMT /G0 ratios of Figure 7 in the verticalaxis of ‘‘reference typical-shape’’ G-γ curves rec-ommended in the literature for the correspondingsoil type. The range of abscissas of the intersec-tion points with the G-γ curves could possibly helpto better define the shear strain corresponding toGDMT .

b. Develop a procedure for selecting the G-γ curve,among the typical curves recommended in the lit-erature, making use of ID for choosing the bandof curves recommended for the soil type (sand orsilt or clay), and KD (possibly G0/MDMT too) forselecting one curve in the band.

c. Evaluate for each of the 800 data points in Figure 5the settlement under a simple loading scheme usingthe simple linear analysis with input MDMT (opera-tion equivalent to converting a DMT investigationinto a ‘‘virtual’’ load test). Then calculate the set-tlement by non linear analyses with G-γ curveshaving variable rates of decay as input. By trial anderror identify the G-γ curve (originating in G0)producing agreement between the two predictedsettlements. Consider such G-γ curve reasonably

HARA (1973)

YOKOTA et al. (1981)

TATSUOKA (1977)

SEED & IDRISS (1970)

ATHANASOPOULOS (1995)

CARRUBBA & MAUGERI (1988)

0.05 to 0.1%

HARA (1973)

YOKOTA et al. (1981)

TATSUOKA (1977)

SEED & IDRISS (1970)

ATHANASOPOULOS (1995)

CARRUBBA & MAUGERI (1988)

0.05 – 0.1%

Maugeri (1995)

Figure 8. Tentative method for deriving G-γ curves fromSDMT.

1319

correct and use it in the development of proceduresfor selecting the G-γ curves from SDMT data.

5 MDMT AS AN OPERATIVE OR WORKINGSTRAIN MODULUS

The possible use of the SDMT for deriving ‘‘in situ’’G-γ decay curves is heavily founded on the basicpremise that MDMT is as a reasonable estimate of theoperative or working strain modulus, i.e. the modu-lus that, introduced into the linear elasticity formu-lae, predicts with acceptable accuracy the settlementsunder working loads. (The terms operative modulusand working strain modulus are considered synonymsand used interchangeably in this paper).

It is therefore considered appropriate to recall herethe presently available evidence.

5.1 Comparisons of surface settlements

Schmertmann (1986) reported 16 case histories atvarious locations and for various soil types, with mea-sured settlements ranging from 3 to 2850 mm. Inmost cases settlements from DMT were calculatedusing the Ordinary 1-D Method. The average ratio

DMT-calculated/observed settlement was 1.18, withthe value of the ratio mostly in the range 0.7 to 1.3 anda standard deviation of 0.38.

Monaco et al. (2006) reviewed numerous real-life well documented comparisons of DMT-predictedversus measured settlements. The average ratio DMT-calculated/observed settlement for all the casesreviewed by Monaco et al. (2006) is ≈1.3, with anobserved settlement within ±50% from the DMT-predicted settlement.

The above settlements comparisons appear to sup-port the assumption that MDMT is a reasonable estimateof the constrained working strain modulus.

5.2 Comparisons of moduli

Even more direct, but rarely available, are data com-paring MDMT with moduli back-figured from localvertical strain measurements—by far more realisticand preferable for calibration or comparison purposes.In 2002 a major research project, funded by the ItalianMinistry of University and Scientific Research and byConsorzio Venezia Nuova, was undertaken by a con-sortium of three Italian Universities (Padova, Bolognaand L’Aquila). A full-scale cylindrical heavily instru-mented test embankment (40 m diameter, 6.7 m height,

0

4

8

12

16

20

24

28

32

36

40

44

0 100 200 300 400

VS

(m/s)z

(m)

(a) Test embankment. Pene trometer truck for test-ing after construction. (b) Superimposed profiles of all SDMT data

6.7

0

290360

480

Em

ba

nk

me

nt

he

igh

t (m

)

Se

ttle

me

nt

(mm

) Time (days)

End of construction

(q = 104 kPa)

180 720

Measured

DMT predicted

u (from piezometers) 0 throughout embankmentconstruction and subsequently

M (MPa)

0

10

20

30

40

0 20 40 60 80

z (

m)

M back-calculatedfrom vertical strain

M from DMT

0

10

20

30

40

0 100 200 300 400

S (mm)

z(m

)

Measured at end ofconstruction (H=6.7 m)

Calculated by DMT

(c) Set tlement vs. time at the center of the em-bankment and comparison of measured vs. DMT-predicted set tlements at the end of construction

(d) M vs. M back-calculated from lo-DMT

cal measured at 1 m depth intervalsv

under the center at the end of construction

(e) Observed vs. DMT-predicted settlement under thecenter at the end of construction

Figure 9. Venezia-Treporti Research Embankment. SDMT profiles. Predicted vs. observed moduli and settlements(Marchetti et al. 2006).

1320

applied load 104 kPa—Fig. 9a) was constructed at thesite of Venezia-Treporti, typical of the highly strat-ified, predominantly silty deposits of the Venezialagoon (Fig. 9b). The loading history, the progressionof the settlements and the drainage conditions—prac-tically fully drained—are shown in Figure 9c.

A specific aim of the research was to obtain a pro-file of the observed 1-D operative modulus M underthe center of the embankment. For this purpose ahigh precision sliding micrometer was used to accu-rately measure the local vertical strain εv at 1 m depthintervals.

M values were back-calculated from local verti-cal strains εv in each 1 m soil layer as M = �σv/εv ,with vertical stress increments �σv calculated at themid-height of each layer by linear elasticity formu-lae (approximation considered acceptable in view ofthe very low εh). Figure 9d, which is believed to beone of the most important results of the Venezia-Treporti research, shows an overall satisfactory agree-ment between MDMT and moduli back-figured fromthe test embankment performance, also consideringthe marked soil heterogeneity. Figure 9e compares theobserved versus DMT-predicted settlements at eachdepth. Again the agreement is rather satisfactory, con-sidering that the DMT predicted settlements werecalculated using the simple linear 1-D conventionalapproach s = �(�σv/MDMT )�H , where �σv iscalculated by Boussinesq linear elasticity formulae.

As to the surface settlements, the total settlementmeasured under the center of the embankment at theend of construction (180 days) was ≈36 cm (Fig. 9c).The settlement predicted by MDMT using the 1-Dapproach (before knowing the results) was 29 cm.Hence the 29 cm predicted by DMT (which does

not include secondary) are in good agreement withthe 36 cm observed settlement (which includes somesecondary during construction).

More details on the Venezia-Treporti research canbe found in Marchetti et al. (2006), also containingnumerous additional bibliographic references.

In conclusion also the Venezia-Treporti case-history supports the assumption that MDMT is a rea-sonable estimate of the constrained working strainmodulus.

6 DERIVABILITY OF THE OPERATIVEMODULUS M FROM G0

Figure 10 (Barcelona airport site) shows that at ≈12 mdepth (transition from an upper stiff sand layer to alower very soft clay layer) the modulus MDMT exhibitsa drastic drop, while VS shows only a minor decrease.Hence G0 = ρV 2

S (even considering the power 2)is far from being proportional to the working strainmodulus M .

Similar lack of proportionality, with variations ofthe ratio G0/MDMT often of one order of magnitude,has been observed at many sites (including Venezia,Figure 9d), suggesting that it is next to impossible(at least without local layer-specific correlations) toderive the working strain modulus by simply reducingthe small strain modulus by a fixed percent factor (e.g.50%, Simpson 1999).

On the other hand the poor correlability M to G0was expected, since at small strains the soil tendencyto dilate or contract is not active yet. Such tendencysubstantially affects the operative modulus M , butdoes not affect G0. Said in a different way, M includes

Figure 10. SDMT profiles at the site of Barcelona—El Prat Airport (Spain).

1321

some stress history information, G0 does not (Powell &Butcher 2004). It may be noted that the high variabilityof the ratio G0/M is already clearly expressed byFigure 5.

7 CONCLUSIONS

The seismic dilatometer SDMT provides routinelyat each depth both a small strain modulus (G0 fromVS ) and working strain modulus (constrained mod-ulus MDMT —as indicated by numerous favourablereal-life comparisons of DMT-predicted vs. measuredsettlements or moduli).

Based on a large number of results by SDMT, dia-grams showing experimental interrelationshipsG0 −MDMT have been constructed. Figure 5 illustratesthe most significant observed trends.

Figure 5 permits to obtain rough estimates of G0(and VS ) when VS is not measured and only mechani-cal DMT results are available (ID, KD, M ). MoreoverFigure 5 indicates:

1. Deriving the operative modulus M for settlementpredictions from G0, by dividing G0 by a fixednumber (as suggested by various Authors), appearsarduous. Often to drastic variations in the M profilecorrespond barely visible variations in the G0 pro-file. The ratio G0/M varies in the wide range 0.5 to20, hence it is far from being a constant, especiallyin clays and silts. Its value is strongly dependenton multiple information, e.g. soil type and stresshistory.

2. To use only one information (e.g. NSPT or su) as asubstitute of VS (when not measured) for the seis-mic classification of a site, as suggested by variouscodes, appears of dubious validity.

Current research investigates the possible use ofthe SDMT for deriving ‘‘in situ’’ decay curves of soilstiffness with strain level, by fitting ‘‘reference G-γcurves’’ through two points provided by SDMT at dif-ferent strain levels: the small strain shear modulus G0(from VS ) and a working strain modulus correspondingto MDMT .

REFERENCES

AGI. 1991. Geotechnical Characterization of Fucino Clay.Proc. X ECSMFE, Firenze, 1: 27–40.

Baldi, G., Bellotti, R., Ghionna, V.N. & Jamiolkowski, M.1991. Settlement of Shallow Foundations on GranularSoils. (a) Discussion. J. Geotech. Engrg., 117(1): 72–175.ASCE.

Baldi, G., Bellotti, R., Ghionna, V., Jamiolkowski, M. & LoPresti, D.C.F. 1989. Modulus of Sands from CPT’s andDMT’s. Proc. XII ICSMFE, Rio de Janeiro, 1: 165–170.

Cavallaro, A., Lo Presti, D.C.F., Maugeri, M. & Pallara, O.1999. Caratteristiche di deformabilità dei terreni da provedilatometriche: analisi critica delle correlazioni esistenti.Proc. XX Italian Geotech. Conf. CNG, Parma: 47–53 (inItalian). Bologna: Pàtron.

Hepton, P. 1988. Shear wave velocity measurements duringpenetration testing. Proc. Penetration Testing in the UK :275–278. ICE.

Hryciw, R.D. 1990. Small-Strain-Shear Modulus of Soil byDilatometer. J. Geotech. Engrg., 116(11): 1700–1716.ASCE.

Ishihara, K. 2001. Estimate of relative density from in-situpenetration tests. In P.P. Rahardjo & T. Lunne (eds), Proc.Int. Conf. on Insitu Measurement of Soil Properties andCase Histories, Bali: 17–26.

Lunne, T., Lacasse, S. & Rad, N.S. 1989. State of the ArtReport on In Situ Testing of Soils. Proc. XII ICSMFE,Rio de Janeiro, 4: 2339–2403.

Marchetti, S. 1980. In Situ Tests by Flat Dilatometer.J. Geotech. Engrg. Div., 106(GT3): 299–321. ASCE.

Marchetti, S., Monaco, P., Calabrese, M. & Totani, G. 2006.Comparison of moduli determined by DMT and back-figured from local strain measurements under a 40 mdiameter circular test load in the Venice area. In R.A.Failmezger & J.B. Anderson (eds), Proc. 2nd Int. Conf.on Flat Dilatometer, Washington D.C.: 220–230.

Marchetti, S., Monaco, P., Totani, G. & Marchetti, D.2008. In Situ Tests by Seismic Dilatometer (SDMT).In J.E. Laier, D.K. Crapps & M.H. Hussein (eds), FromResearch to Practice in Geotechnical Engineering, ASCEGeotech. Spec. Publ. No. 180 (honoring J.H. Schmert-mann): 292–311.

Martin, G.K. & Mayne, P.W. 1997. Seismic Flat DilatometerTests in Connecticut Valley Varved Clay. ASTM Geotech.Testing J., 20(3): 357–361.

Martin, G.K. & Mayne, P.W. 1998. Seismic flat dilatome-ter in Piedmont residual soils. In P.K. Robertson & P.W.Mayne (eds), Proc. 1st Int. Conf. on Site Characterization,Atlanta, 2: 837–843. Rotterdam: Balkema.

Mayne, P.W. 2001. Stress-strain-strength-flow parametersfrom enhanced in-situ tests. In P.P. Rahardjo & T. Lunne(eds), Proc. Int. Conf. on In Situ Measurement of SoilProperties and Case Histories, Bali: 27–47.

Mayne, P.W., Schneider, J.A. & Martin, G.K. 1999. Small-and large-strain soil properties from seismic flat dilatome-ter tests. Proc. 2nd Int. Symp. on Pre-Failure DeformationCharacteristics of Geomaterials, Torino, 1: 419–427.

McGillivray, A. & Mayne, P.W. 2004. Seismic piezocone andseismic flat dilatometer tests at Treporti. In A. Viana daFonseca & P.W. Mayne (eds), Proc. 2nd Int. Conf. onSite Characterization, Porto, 2: 1695–1700. Rotterdam:Millpress.

Mynarek, Z., Gogolik, S. & Marchetti, D. 2006. Suitabilityof the SDMT method to assess geotechnical parametersof post-flotation sediments. In R.A. Failmezger & J.B.Anderson (eds), Proc. 2nd Int. Conf. on Flat Dilatometer,Washington D.C.: 148–153.

Monaco, P., Totani, G. & Calabrese, M. 2006. DMT-predictedvs observed settlements: a review of the available expe-rience. In R.A. Failmezger & J.B. Anderson (eds), Proc.2nd Int. Conf. on Flat Dilatometer, Washington D.C.:244–252.

Powell, J.J.M. & Butcher, A.P. 2004. Small Strain StiffnessAssessments from in Situ Tests. In A. Viana da Fonseca

1322

& P.W. Mayne (eds), Proc. 2nd Int. Conf. on Site Charac-terization, Porto, 2: 1717–1722. Rotterdam: Millpress.

Ricceri, G., Simonini, P. & Cola, S. 2001. Calibration ofDMT for Venice soils. In P.P. Rahardjo & T. Lunne (eds),Proc. Int. Conf. on In Situ Measurement of Soil Propertiesand Case Histories, Bali: 193–199.

Schmertmann, J.H. 1986. Dilatometer to compute Founda-tion Settlement. Proc. ASCE Spec. Conf. on Use of InSitu Tests in Geotechnical Engineering In Situ ’86, Vir-ginia Tech, Blacksburg. ASCE Geotech. Spec. Publ. No.6: 303–321.

Simpson, B. 1999. Engineering needs. Proc. 2nd Int. Symp.Pre-Failure Deformation Characteristics of Geomateri-als, Torino.

Sully, J.P. & Campanella, R.G. 1989. Correlation of Max-imum Shear Modulus with DMT Test Results in Sand.Proc. XII ICSMFE, Rio de Janeiro, 1: 339–343.

Tanaka, H. & Tanaka, M. 1998. Characterization of SandySoils using CPT and DMT. Soils and Foundations, 38(3):55–65.

TC16. 2001. The Flat Dilatometer Test (DMT) in Soil Inves-tigations—A Report by the ISSMGE Committee TC16.Reprint in R.A. Failmezger & J.B. Anderson (eds), Proc.2nd Int. Conf. on Flat Dilatometer, Washington D.C.:7–48.

1323