INDIAN GEOT. SOCIETY National SeminarGEOTECHNIQUE TODAY Kolkata 28 Feb 2014GEOTECHNIQUE TODAY Kolkata 28 Feb 2014

Flat dilatometer (DMT). Seismic DMT.Frontespizio

Description ApplicationsDescription, Applications.Settlements, Liquefaction.

Silvano MarchettiUniversity of L'Aquila, Italysilvano@marchetti-dmt.it

1

FROM LAB TO INSITU TESTINGIn the last decades : massive migration from lab testing to insitu testing. Often today in situ testing is g g y gthe major part of an investigation.

In situ : Fast economical reproducible informativeIn situ : Fast, economical, reproducible, informative, many data, reduced scatter, cost much less than sampling & testingsampling & testing….

True in Sand : Recovering samples difficult. Field t t th t t f titests are the state-of-practice.

Caution : lab remains fundamental for research

2

Of the many existing in situ tools…

…direct push CPT DMT increasingly recognized as fast & convenient tools for everyday practice (Mayne et al. SOA ICSMGE Egypt 2009).gyp )

This presentation : DMT SDMT 3

DMT components DMT pushed by a truckmounted penetrometerp

4

DMT can also be executed with small inexpensive pushing machinesinexpensive pushing machines

Use same rigs used for pushing CPT. But many more insertion methods : no need of 2 cm/sec.Unlike CPT, push is just for advancing, is not the test… comes later. 5

(S)DMT can be pushed by DRILL-RIGTwo distinct methods – not confuse

quickest

Two distinct methods – not confuse

Sciacca methodor “Penetrometer mode”

Torpedo methodor “Downhole mode” or Penetrometer mode

Cable exits laterally in airTest starts from ground surface

Penetrable soil

or Downhole modeCable exits laterally in the hole

Test starts from bottomholeSoil with obstacles

Drillrod

pushrod

6Blade can also be driven by SPT hammer (quasi static preferable)

Robust. Safe push 25 tonSuitable for penetrable

N l li id il hi hl

psoils (sand, silt, clay)Nearly liquid soils : highly accurate due to the “balance of zero” methodbalance of zero methodHard soils (e.g. Cu 800 kPa), weak rock: OK but needweak rock: OK but need strong push - heavy truck

LIMITSClays Cu=2-4 kPa up to 1 MPa (marl)Moduli M=0.5 to 400 Mpa

7

DMTRetaining Ring DMT

BLADEMembrane

Sensing diskdisk

Sensing disk.Sensing disk.Electricallyinsulated

Bl d i lik l t i l it h b ffBlade is like an electrical switch, can be off or on.NO ELECTRONICS no zero drift, no temperature effects8

HOW DMT WORKS (mechanical)

po p Id Kd Ed po, p1 Id, Kd, Ed Soil parameters

(M, Cu …)( , )

REDUCTION FORMULAE DMT Rep. TC16 (2001) of ISSMGE9

DMT FORMULAE DMT Report TC16 of ISSMGE 2001

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DMT resultsor Stress

History IndexHistory Index

KD = 2 NC clay

ID

M Cu

KD

soil type common use shape similar to OCRyp(clay, silt, sand)

common use phelps understand history of deposit 11

DM

Definition of KD : is similar to Ko

KD = (p0 - u0)

MT

KD σ’vp0

KD an “amplified K0” due to penetration.

Will see : K reflects“stress history”Will see : KD reflects stress history

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SEISMIC DILATOMER : DMT with the addition of a seismic module (tube) Vsaddition of a seismic module (tube) Vs

Vs from delay of pulse2 receivers vs 1 receiver:SDMT 2 receivers vs 1 receiver:

Same blowTrigger not criticalNo mitical 1st arrival

SDMT

No mitical 1st arrivalDelay well conditioned

Amplified + digitiz at depth

Operator independentInterpreter independent M h f t & i lMuch faster & economicalthan Down hole – X holeNo hole/ no samples, no

ti i ( i igrouting pipes (supervisionfor voids? Stop for cement..) Same day 13

SeismicSeismicDilatometer

14

15

Example seismograms SDMT at Fucino

Delay : from Cross Correlation Repeatability Vs : 1-2 %16

SHEAR WAVE

SDMT results repeatability ≈ 1-2%

SHEAR WAVEVELOCITY

GO= ρ Vs2

Vs (m/s)

h i l DMT S i i DMTmechanical DMT Seismic DMTWhen designing : helpful such clear vision of the site17

The Vs profile can be obtained by SDMT even in non penetrable soils : executed in a sandfilled borehole

It works because the two

penetrable soils : executed in a sandfilled borehole

travelpaths in sand include a short length in the sand backfill, similar for both receivers

The sand 

travelpath 

is similaris similar

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Diffusion : DMT used in 70 countries (200 DMT in US)2006

EUUS

EA

EUROCODE 7 (2005) ASTM (2007) TC16 (1997)Standards:

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EUROCODE 7 (2005) ASTM (2007) TC16 (1997)Standards:

Main SDMT applications ( papers)

Preliminary : Recognize Kd indicator of Stress History

S ttl t f h ll f d ti Settlements of shallow foundations Compaction control

Dete ting lip f e in OC l Detecting slip surfaces in OC clay

Laterally loaded piles

Diaphragm walls “springs” for design

Have in commonneed Stress History

Diaphragm walls springs for design

FEM input parameters

Liquefability evaluation Liquefability evaluation In situ G- decay curves

Seismic design (NTC08 Eurocode 8) Seismic design (NTC08, Eurocode 8)

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Diagrams compare sensitivity of CPT-DMT to Stress History

Effect of SH on. Qc Effect of SH on Kd

to Stress HistoryLee 2011, Eng. Geology

30 CC in sand

•Kd ++ reactive than Qc to Stress History•Kd ++ reactive than Qc to Stress History•In a sand having Qc : many Kd, depending on SH21

Similar results by Jamiolkowski (ISC'98 Atlanta)

DMT far more sensitive to SH & agingThey applied prestraining cycles in calibration chamber. Found : KD (DMT) 3 to 7 times more sensitive to AGING

g g

CC TEST N. 216 IN TICINO SAND

than penetration resistance

PRESTRAINING CYCLES simulate AGING (grain slippage)simulate AGING (grain slippage)

KD + 20 %q + 3 %qD + 3 %

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DMT MORE REACTIVE TO STRESS HISTORY

MDMTBEFORE AFTERConfirmed in the field …

MDMTQc QcJendeby 92Measured in aMeasured in a loose sandfillQc & Mdmtb f ftbefore-after compaction

OCR in sandNC : M/Qc 5-12 OC M/Q 12 24OC : M/Qc 12-24

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COMPACTION ( impose SH) produces a M % increase twice the Qc% increase

MDMT before-after compaction

MDMT% increase twice the Qc% increase

Schmertmann (1986) DYNAMIC COMPACTION of sand it MDMT % i t i % i i Q compactionsite. MDMT % increase twice % increase in Qc.

Jendeby (1992) monitored DEEP COMPACTION in a sand fill by VIBROWING. MDMT increase twiceincrease in qc.

bar

increase in qc.Pasqualini & Rosi (1993) VIBROFLOTATION job :"DMT clearly detected improvement even in layerswhere benefits were undetected by CPT".

Ghent group (1993) before-after CPTs DMTs to evaluate effects (h , Dr) by PILE (Atlas) INSTALLATION"DMTs before-after installation demonstrate more clearly [than CPT] beneficial effects of Atlasclearly [than CPT] beneficial effects of Atlas installation".

hence Mdmt particularly suitable forResonant vibro-compaction techniqueVan Impe, De Cock, Massarsch, Mengé, New Delhi (1994)

…hence Mdmt particularly suitable for evidencing the benefits of compaction

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….conclusion : good sensitivity of Kd to Stress History …… sensitivity to SH key feature of Kd (not many SH tools) because SH is important for settlements …

Importance of SH to predict SettlementsJamiolkowski (Isopt-1,‘88,1) : “without Stress History, impossibleJamiolkowski (Isopt 1, 88,1) : without Stress History, impossible to select reliable E (or M) from Qc”(also Terzaghi, Leonards, Schmertmann…)

Yoshimi (1975) “… upon initial loading, the NC sand specimens were six times more compressible than the prestressed sand” hence imperative SH to characterize compressibility of sand

Application #1 DMT : predict settlements (operative modulus)

Mdmt= Ed x Rm(Kd Id) (combines Ed with Stress History)Mdmt= Ed x Rm(Kd, Id) (combines Ed with Stress History)

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Settlement predictions by DMT

zM

SDMT

vDMT

1

Accuracy of DMT predicted by Boussinesq

y psettlements is confirmed by a large number case histories :

Cruz (2010), Vargas (2009), Bullock (2008), Monaco (2006), Lehane & Fahey (2004) Mayne (2001 2004) Failmezger (1999 2000 2001) CrappsFahey (2004), Mayne (2001, 2004), Failmezger (1999, 2000, 2001), Crapps & Law Engineering (2001), Tice & Knott (2000), Woodward (1993), Iwasaki et al. (1991), Hayes (1990), Mayne & Frost (1988), Schmertmann (1986,1988), Steiner (1994), Leonards (1988), Lacasse (1986)……………

(see > 40 papers at ISC4-2012).26

Silos on Danube's Bank (Belgrado)

SETTLEMENTS

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Measured 63 cm DMTpredicted 77 cm (+22%)(D. Berisavijevic 2013)

M at Sunshine Skyway Bridge, Tampa Bay – Florida

World record span for cablestayed post-tensioned concretebox girder concrete construction

(Schmertmann – Asce Civil Engng – March 1988)

DMT results: M 200 MPa (1000 DMT test points)Laboratory results: M 50 MPaLaboratory results: M 50 MPa

From observed Settlements: M 240 MPa DMT = good evaluation of constrain modulus

Schmertmann 1986 16 CASE HISTORIES. P di t d/Ob d 1 18Predicted/Observed ave : 1.18

1986 - Proc. In Situ '86 ASCE Spec. Conf. VIP, Blacksburg, p.303 29

M observed vs. predicted by DMT

Marchetti et al. (2006)Sliding Micrometers

M by DMT vs. M back-calculated from LOCAL

installed every meter

vertical strains measured under Treporti full-scale test embankment (Italy)

Venezia :Truck lifted to repeat SDMT ft t ti t tafter construction at center

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Treporti Test Embankment (Venezia)Before embankment construction After embankment removal

0

1

0 100 200 300

Vs (m/s)

SDMT 140

1

0 40 80 120 160M (MPa)

SDMT 190

1

0 2 4 6 8 10Qc (MPa)

CPT 19

2

3

4

Z (m

)

2

3

4

5

Z (m

)

2

3

4

5Z (m

)

5

6

7

8

5

6

7

8

5

6

7

8

Conclusion:OC increases stiffnessespecially at operative

modulus (workingt i )strain)

Schmertmann (2008) : SDMT at Cape p

Kennedy Space Center

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SDMT carried out for ROMA METRO-C

34{ DMT '15 (3rd Int. Conf.) Rome, Italy 15-17 June

2015 }

SETTLEMENTSETTLEMENT CALCULATION

MDMT + 1-D method

zM

SDMT

vDMT

1

Calculation every 20 cm, not because thicker layers are yinadequate. It is just more convenient, since Mdmt available in the computer every 20 cm

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M can also be predicted as M= Qc. Problem is : depends on SH (OCR) – missing info. Who will tell usdepends on SH (OCR) missing info. Who will tell us OCR to select the curve?

= 2.5 to 25 !

Jamiolkowski concludes :"without Stress History it isOCR??? without Stress History it is impossible to select reliable E (or M) from Qc“(Isopt-1, '88, Vol. 1, p.263)

Might use Kd to select curve. Then more direct to use MThen more direct to use Mdmt.

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Possible reasons DMT predicts well settlement

1.Wedges deform soil << cones2 Modulus by mini load test2.Modulus by mini load testrelates better to modulus than to penetr. resistance 3 Availability of Stress History3.Availability of Stress History parameter Kd. (DMT is a 2-parameter test. Fundamental to have both: Ed and Kd)4.The soil is loaded at a lower, more appropriate, strain level

For the same strength : various moduli must

Stiffnes

Strength various moduli must measure moduli, not strength !

Strength

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Liquefiability evaluations also in need of

Jamiolkowski et al (S Francisco 1985) :

info on Stress History / Aging

Jamiolkowski et al. (S. Francisco 1985) :

"Reliable predictions of sand liquefiability i i it d i [ th th...require…some new in situ device [other than

CPT or SPT], more sensitive to effects of past STRESS-STRAIN HISTORIES”STRESS-STRAIN HISTORIES

S l d t l (J l A 1997)Salgado et al. (Jnl Asce 1997)

“OCR cause an increase of liquefaction resistance

39CRR, but negligible change of Qc”

Why expect a stricter correlation and a more accurate CRR if CRR is predicted by Kdaccurate CRR if CRR is predicted by Kd

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Figure shows the currently recommended CRR from Kd

(based on Monaco 2005, Tsai 2009, Robertson 2012 – are i th b d)in a rather narrow band)

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The CPT correlation for predicting CRR isThe CPT correlation for predicting CRR is not unique but is quite wide.

CRR from CPT

For the same Qcn Kd can vary considerably, depending on SHdepending on SH.

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Liquefaction : SDMT 2 independent estimates of CRRCRR Cyclic Resistance Ratio for Seed & Idriss (1971) simplified procedure

CRR from VsSDMT

Andrus and Stokoe 2000VS

Light earthquakes

CRR from KdDMT

Strong earthquakes

Monaco 2005 KD

Monaco (2007) "Evaluating Liquefaction Potential by Seismic Dilatometer (SDMT) accounting for Aging/Stress History" 4th Int. Conf. Earthquake Geotechn. Eng. - Thessaloniki 43

Sometimes the two independent CRR estimates(from Kd from Vs) are different.(from Kd from Vs) are different.

We consider more reliable CRR from Kd

V i iti t St Hi tVs insensitive to Stress History :Diagram shows Vs measured on sand specimens in the calibration

Jamiolkowski 1992Soils & Foundations

Waves produce strains too small to

pchamber in loading / unloading

pinitiate trend to dilate/ contract (essence of liquefaction)

In cemented sands CRR(Vs) usually higher (optimistic) …(cementation increases Vs) . But strong earthquakes may destroy weak bonding.

CRR from Vs possibly ok in cemented sands if light earthquakes expected –(bonding preserved). 44

KD evidences Stress History crustsStress History crusts –clearly evidenced by KD but "unfelt" by VS suggests lesser ability of VS to profile SH, hence liquefiability & CRR

MATERIAL CONSTRAINED UNDRAINED HORIZONTAL SHEAR WAVEMATERIALINDEX

CONSTRAINEDMODULUS

UNDRAINEDSHEAR STRENGTH

HORIZONTALSTRESS INDEX

SHEAR WAVEVELOCITY

CLAY SILT SAND

K t crust?KD crust

CataniaSand

crust?“lazy”

Vs (m/s)KD 45

BARCELONA AIRPORT

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SDMT provides Go (small strain modulus) & Mdmt (working strain modulus) Two points of the G-γ curve(working strain modulus). Two points of the G-γ curve.May help select the design G-γ curve. (Mayne & Martin 1999)

Maugeri (1995)

HARA (1973)

YOKOTA et al. (1981)

TATSUOKA (1977)

SEED & IDRISS (1970)

HARA (1973)

YOKOTA et al. (1981)

TATSUOKA (1977)

SEED & IDRISS (1970)

ATHANASOPOULOS (1995)

CARRUBBA & MAUGERI (1988)

0 05 to 0 1%

ATHANASOPOULOS (1995)

CARRUBBA & MAUGERI (1988)

0 05 – 0 1% Mayne (2001)0.05 to 0.1% 0.05 0.1 % Mayne (2001)Ishihara (2001) More info in :

- Marchetti et al (2008) in Schmertmann VolumeL h & F h (2004) P t ISC 2 li ttl t l i- Lehane & Fahey (2004) Porto ISC-2 – non linear settlement analysis from in situ tests

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SEAFLOOR DILATOMETER

WATERDEPTH 0 to 100 mPUSH CAPACITY 7 tonPUSH CAPACITY 7 tonMax test depth is the depth penetrable with 7 ton push.

Shippedb iby air

(50 Kg)4

bolts

7 ton

bolts

ballast(built

locally)

48

Vp - Seismic Dilatometer (SPDMT)Vp (m/s)

Pianola (AQ) 2013

wav

e

wav

e

lower sensor

upper sensor

s wp w

epth

(m) sensor

De

DM T

Two vertical axis sensors provide two independent Vp profiles (pseudo interval) 49

INPUT PARAMETERS FOR PLAXIS(Hard Soil model “HS”)(Hard Soil model HS )

Recommended basic input E50ref (Trx modulus confined at 1 bar).

Schanz found for quartz sand E50ref =15 to 75 MPa (loose to very dense

sand). He also found E50ref correlated to Eoed

ref .

In sand the range of MDMT is remarkably similar to above range (15-75 MPa). Hence as 1st approx may assume E50

ref MDMT

Predicting settlement by DMT may replace the costly load testoften executed to verify/ adjust assumed FEM parameters.y j p

Info from Sherif 2013: In Dubai often load tests must be executed if one wants to assume >3 in M= Qc This $ could be saved Aif one wants to assume >3 in M= Qc. This $ could be saved. A DMT settlement calculation may serve as a “virtual load test”.

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Detecting slip surfaces in clay slopes(look for Kd 2)

1. SLIDING 2. REMOULDING

(look for Kd 2)

0 2

3. RECONSOLIDATION(NC STATE)

4. INSPECT D PROFILEK

10

20

30

DK (DMT) 2

Method permits to verify if an OC clay slope contains active or quiescent slip surfaces(Totani et al 1997)quiescent slip surfaces(Totani et al. 1997)

Useful to know : Old slip surface may reactivate ! – Øresidual 51

Validation of DMT-KD methodLANDSLIDE "FILIPPONE" (Chieti)

DOCUMENTED SLIP SURFACE

LANDSLIDE "CAVE VECCHIE" (S Barbara)

(inclinometers)

LANDSLIDE CAVE VECCHIE (S. Barbara)

DOCUMENTEDDOCUMENTED SLIP SURFACE(inclinometers)

52

Kd2 detects both active (moving)Kd2 detects both active (moving) and quiescent slip surfaces

active: Kd=2

53

Miniera di lignite S. Barbara(San Giovanni Valdarno)

SS. N. 83 “Marsicana”Gioia dei Marsi (2006)

Bloccata da dissestoBloccata da dissesto

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When doing SDMT : get “same depth” Id Kd Ed (M) + GoId Kd Ed (M) + Go

Diagram is result of 34 SDMT sites various soils & geography.Can be used to estimate Vs (Go) from just-mechanical-DMT data i.e. Vs = f(Id Kd Mdmt)

•No point today. Vs directHowever :May provide rough Vs in previous sites DMT.pEstimates of expected Vs.

If Kd was not available, impossible to predict Go from just one parameter. Need at least two parameters. 55

VS predicted by mechanical DMTvs Vs measured by SDMT (L'Aquila)

Amoroso (2013) compares correlations for approximate estimates of Vs from DMT/CPT Concludes : Vs estimatesestimates of Vs from DMT/CPT. Concludes : Vs estimates based on DMT are closer (a two parameter test)

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CPT-DMT correlations – (Robertson Jnl Asce Nov 2009)

Estimate DMT parameters from CPT & viceversa)Estimate DMT parameters from CPT & viceversa)

(Usefulness not so clear - similar to Qc-Nspt)( p )

Robertson formulae DMT from CPT. But estimates not v accurate. dispersed : Kd from Qcn – (dispersion

) fcommented earlier). Inaccurate prediction of Kd expectable : no way of reconstructing sensitive Kd from insensitive Qcn.

Some researchers study opposite direction : Qc from DMT (not v clear the purpose) Should have +successDMT (not v clear the purpose). Should have +success. Should be easier to predict one parameter from two than viceversa. DMT a genuine two parameter test. In that DMT i f ti t tDMT appears a +informative test.

57

CPT in sand : essentially a one-parameter test (1.5?), since sleeve friction fs not very reliable

Eg. Frost (2001) : The "underuse" of fs is related to common sentiment that fs i li bl

Repeatibilityv. good v. bad

is unreliable…

Lunne (CPT10) had CPT done by 4 different well

g

done by 4 different well-qualified firms. Qc was found repeatable, fs highly variable.

Also : fs is a measurement not so “fundamental”. fs highly unstable, being what is left after an enormous stress reduction – in a situation of arching, with a stiff soil ring surrounding the sleeve.

Moreover : horiz stress transformed vert force, via Øsoil-steel 58

Sensitivity to horiz. stress h

59

OTHEROTHERAPPLICATIONS

60

Dissipation test in cohesive soils. Estimate coefficient consolidation & permeability

From u(t) in a singular highly di t b d i t

)

disturbed point

σh

(kP

a

From a mini embankment. σ

Totani, Calabrese, Monaco (1998)

Larger volume less disturbed

Time (min)

, , ( )

61

DMT for P-y CURVES forLATERALLY LOADED PILESLATERALLY LOADED PILES

Robertson et al (1987)Robertson et al. (1987)Marchetti et al. (1991)2 methods recommended

Mortaiolo (Italy)NC f lMortaiolo (Italy)NC f l 2 methods recommended

for deriving P-y curves for laterally loaded piles from DMT ( i l il 1 t ti

NC soft clayNC soft clay

DMT (single pile, 1st time monotonic loading)

Figure shows that the 2 methods provide similar predictions both in very good agreement withpredictions, both in very good agreement with observed full-scale pile behaviour 62

DMT for coeff. subgrade reaction Kh for DIAPHRAGM WALLSDIAPHRAGM WALLS

Monaco & Marchetti (2004 – ISC'2 Porto)g.l.g.l.g.l.

Monaco & Marchetti (2004 ISC 2 Porto)

Tentative correlation for deriving the coefficient of

s Hss HH

deriving the coefficient of subgrade reaction Kh for design of multi-propped HHH diaphragm walls from MDMT

Indications on how to select f

LLLinput moduli for FEM analyses(PLAXIS Hardening Soil model) based on MDMT) DMT

63

Subgrade compaction controlBangladesh Subgrade Compaction Case History

90 km Road Rehabilitation Project

10 cm interval

MDMT acceptance profile(max M always found at

interval

(max M always found at 25-26 cm)

An acceptance MDMT profile was established and An acceptance MDMT profile was established and used as alternative/fast acceptance tool for quality control of subgrade compaction, with only occasional verifications by originally specifiedoccasional verifications by originally specified methods (Proctor, CBR, plate) 64

Website: www.marchetti-dmt.it

CONCLUDING REMARKS (1/6)( )

Direct push CPT and DMT are increasinglyDirect push CPT and DMT are increasingly recognized as fast and convenient tools for everyday investigations.everyday investigations.

Important : sensitivity of DMT’s Kd to Stress fHistory, scarcely felt by other tools.

Sensitivity to SH is fundamental for goodSensitivity to SH is fundamental for good predictions of settlements and of CRR.

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PREDICTING SETTLEMENTS(2/6)

Countless researchers : without Stress History it is impossible to predict modulus from CPT or SPT.p p

M can be predicted by CPT as M= Qc. Problem : v uncertain to select varies 2-20 1 order magnitudev. uncertain to select, varies 2 20, 1 order magnitude.

A large number of comparisons confirm DMT predicts ll ttl twell settlement.

With DMT no value to guess. DMT correlations gguide without subjective choices to M, taking into account soil type (Id) and Stress History (Kd).

67

(3/6)

ESTIMATING CRR (li f ti )ESTIMATING CRR (liquefaction)

The availability of Kd

(1)Reduces scatter in estimating settlements(1)Reduces scatter in estimating settlements and CRR

(2)Permits a more economical design, as Kd reflects the benefits of SH on settlement and li f ti b h i SH i l dliquefaction behaviour. SH is scarcely sensed by other tools, which ignore SH, so that benefits are wastedbenefits are wasted.

68

(4/6)Question…cost “CPT costs less than DMT.

Is CPT therefore preferable ?”

As to pure cost CPT preferable. But info /cost

A CPT investigation costs less, but remains orphan of capability of providing SOA predictions of settlements.

Been : State of Art at CPT 2010 Los Angeles :“If purpose is parameters CPT cannot be used in p p pisolation - must be supplemented by lab /other methods. CPT can easily mislead in terms of soil t t th d ti l l d l ”type, strength and particularly modulus”.

69

(5/6)

Estimating settlements is important?

Most people think settlements are important

Every Geotechnical Report has a section "Settlements”Every Geotechnical Report has a section Settlements

Often settlement is a delicate chapter. Has important $ consequences (piles/ shallow foundations )consequences (piles/ shallow foundations…).

+accurate settlements +economical design. Info=$.

All this to be taken into account when comparing costs.

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Even when comparing pure cost of testing :(6/6)

With DMT "not many things can go wrong" (no

Even when comparing pure cost of testing :

With DMT not many things can go wrong (no electronics, no saturation-deairing, no area correction…). (uncertainty, when present, is a big cost).

Very easy to run, short training time ( 3 hours)

Any operator gets same resultsAny operator gets same results.

No need highly skilled workers.

In remote countries : easy to instruct a local technician.

Can overturn the balance of relative cost CPT DMT.

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LAST REMARK (7/7)LAST REMARK (7/7)

Migrating from Nspt to Q for predicting CRR andMigrating from Nspt to Qc for predicting CRR and settlements has had the merit of eliminating that part of scatter due to the poor repeatability of SPT.

Expectable that the use of KD might reduce not only that part of scatter due to the poor repeatability of the SPTpart of scatter due to the poor repeatability of the SPT, but even that part of scatter due to the scarce ability of conical tips to distinguish between freshly deposited sands and prestressed or aged sands, having a different settlement/ liquefaction behavior.

72

ENDENDThank youy

73

How derive M (drained) from Ed (undrained) ???Clay. Initial idea (1980) : investigate Ed-Eu. Problem: Eu, lab too dispersed, impossible set up correlations. Hence Ed-M.Link Ed-M presumably weaker, but at least can be tested.d p y ,

NOTE. Ed-M must be a complex function of many variables, among them the Skempton p. p. parameters A & B and anisotropy (Edhorizontal M vertical) which in turn depend on soil typehorizontal, M vertical), which in turn depend on soil type (~represented by Id) and on OCR (~ represented by Kd) some basis to expect at least some degree of correlation Ed -M using Id

d K tand Kd as parameters.

Final word : real world observation. Large number case histories favourable comparisons measured vs DMT-predicted settlements -favourable comparisons measured vs DMT predicted settlements or Mdmt-Mreference.

Lambe et al (Jnl ASCE March 1977 “Foundation Performance of Tower of Pisa” p 246) : “Drained moduli of saturated clays are typically about one third to onep.246) : “Drained moduli of saturated clays are typically about one-third to one-fourth the undrained values”. Hence a broad connection drained-undrained stiffness already invoked in the past. 74

Reconstituted sand specimens at same Dr

“Testing on sand specimens reconstituted even at exactlythe same density is highly questionable” (Ladd 1977).Already known at the time (SOA 1977 Tokyo)

Hoeg (2000) showed that… “natural sands haddilative behaviour while reconstituted specimens withthe same void ratios were contractive”

Hence the need of testing sand in situHence the need of testing sand in situ

75

Elusivity of Dr in situyThere is no unique mapping Dr=f(Qc).

Jefferies – Been ISOPT 1995.Hilton Mines sand at Dr=60% produces the same Qc asMonterey sands at Dr=40%y

Very difficult estimate Dr in situ unmeasurable

Specs in terms of Dr problematicSpecs in terms of Dr problematic

S h t 1986 i b t it iSchmertmann, 1986 in a paper about monitoringcompaction :Since objective of compaction: limit settlements…Since objective of compaction: limit settlements…..more rational specs on Modulus (e.g. Mdmt) than Dr

76

DMT CORRELATIONS IN NON TEXTBOOK SOILSDMT CORRELATIONS IN NON-TEXTBOOK SOILS(Residual, Unsaturated…)

(Giacheti, Mayne, Chang, Failmezger, Fonseca…)

In generalThe correlations involving pwp (e.g. Cu=…) are

ll t li blgenerally not applicable.

The correlations for estimating moduli/ settlementsgenerally applicable since DMT is a load testgenerally applicable, since DMT is a load test determining a pressure-settlement relation.

77

OCR and Ko in sandOCR and Ko in sand

OCR in sands can be evaluated from ratio MDMTOCR in sands can be evaluated from ratio MDMT/qc.

MDMT /qc = 5-10 in NC sandsDMT qc

MDMT /qc = 12-24 in OC sands.

Ko in sand. See TC16 DMT Report.

A way can be (once estimated OCR) :

Ko=Konc OCRm

78

Legitimate to use M = constant if 'vl ?large ?

M = Eoed=1/mv='v/v (at 'vo)

Except highly structured clays (sharp break), M variationacross pc is moderate

Error in assuming M ~ constant : often acceptable (othermethods for M : not infrequent error factors 2-5)

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It is often said that DMT interpretation is empirical...

STORY of the correlation OCR-KD in clay

Theoretical1993 Finno

Experimental1980 & 1995

Theoretical2004 Yu

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DERIVATION OF Cu CORRELATIONOnce having OCR Ladd’s SHANSEP 77 SOA Tokyo

Using m 0.8 (Ladd 1977) and (Cu/’v)NC 0.22 (Mesri 1975)

(Ladd : best Cu not from TRX UU but from oed OCR Shansep)( p)

OCR, Ko, Cu well founded derivation. They OCR fi d b th + SHANSEPuse OCR confirmed by theory + SHANSEP

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Two diagrams obtained by instrumented blades : expansion PoP1 approx linearblades : expansion Po P1 approx linear

Campanella et al. (1985)Proc 11 ICSMFE, S. Francisco, 2, p. 852. Fretti et al. 1992

Rig 26,4, 237-243

Hence central movement S=1.1 could be any value (two points). But :

If S too small : (P1-P0) could be too small to measure it accuratelyIf too high : Membrane “inertia” would rapidly increase (wouldIf too high : Membrane “inertia” would rapidly increase (would

work in tension rather in bending)82

SOIL NEAR SURFACE MAY APPLY PRESSURE NOT ENOUGH FOR CLOSING THE MEMBRANEENOUGH FOR CLOSING THE MEMBRANE

If soil applies h < A, the membrane will not close. No usual sound upon penetration. Apply depression with the syringe and simply write a negative A value (algebra will take care correctly). Then B.

NOTE. While doing Seismic DMT, the membrane must be closed (contact). Hence near surface, if there is no sound, depression must be kept with the syringe to insure contactdepression must be kept with the syringe, to insure contact.This lack of contact happens frequently near surface if operator has already done a DMT expansion.

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Ladd 1971 (42 yrs ago)Short course MIT

Soft Ground Construction

Even good OC samples maygive oedometers moduli 2 to 5

times too lowtimes too low(Terzaghi & Peck book 1967)

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Ed must be corrected to obtain M

M=Rm Ed with Rm=f(Kd Id)M=Rm Ed with Rm=f(Kd,Id)

Don’t use Ed as Young’s

Rm has various correction tasks

Distortion Horiz to vertical Drained Undrained

Once Ed is converted to M, Young’s E’ 0.8-0.9 M (elasticity)

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INFLATION SPEED. Time to A and to B

Keep the “time to A” 15 sec. Particularly in silts, where partialp y , pdrainage occurs during the test. Not so important in sands(fully drained) and in clay (fully undrained) .

If A in <<10 sec: excessive press. drop along pneumaticcable

fIf A in >>20 sec: appreciable drainage may occur, esp. in silts

Seasoned operators : inflate very fast to say 75% ofexpected reading. Then go very slowly to the reading.

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“Complaint” : Cu field vane > Cu dmtp field vane dmt(in very plastic clay)

S B k “S il M h i i E P ti ”See eg Book “Soil Mechanics in Eng. Practice” (Terzaghi, Peck, Mesri)

Cu needs a correction factor before it can be used inCu field vane needs a correction factor before it can be used in stability analysys. The Bjerrum correction is eg 0.70 whenPI = 70. Cu field vane reduced by Bjerrum’s correction isoften considered the best available Cu for stability analysis.

The DMT 1980 correlations for Cu were developed using forlib ti h “ ti ” Bj ’ t d C lcalibration such “operative” Bjerrum’s-corrected Cu values.

It is therefore Cu field vane uncorrected which is too high - in plastic clays.

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WHY EXPECT A “GOOD” Kd-CRR•Liquefiability needs SH-agingKd is sensitive to SH-aging expect “good” Kd-CRR

•Yu (2004), Robertson (2012) found correlations Kd-( State Parameter, close proxy of liquefiability) reinforce expectation good Kd CRR reinforce expectation good Kd-CRR.

Note : alone is incomplete indicator of resistance to li f ti (l k t t t hi t i )liquefaction (lacks structure, stress history, aging).

Two identical sites of same “e” (hence same ) - but the second prestressed : same but the second has higher CRR (andprestressed : same , but the second has higher CRR (and higher Kd)

Kd being related to but at the same time incorporating StressKd , being related to , but at the same time incorporating StressHistory and aging, possibly uniquely well correlated with CRR 88