Workshop on Penetration Testing – University of Pisa, DESTECWorkshop on Penetration Testing – University of Pisa, DESTEC

Pisa – Italy, 9Pisa – Italy, 9thth October 2014 October 2014

Sara Amoroso (Istituto Nazionale di Geofisica e Vulcanologia, L’Aquila, Italy)sara.amoroso@ingv.it

Flat dilatometer (DMT) & Seismic DMT (SDMT)Use of SDMT results for engineering

applications

1. Flat dilatometer (DMT)

2. Seismic dilatometer (SDMT)

3. Interpretation of the parameters

4. Engineering applications

Outline of the presentation

Flat dilatometer (DMT) & Seismic DMT (SDMT)

DMT Flat dilatometer equipment

BLADE

FLEXIBLE MEMBRANE

(D = 60mm)

DMT Test layout & components

Measurements performed after penetration independent from insertion method

DMT blade

Push rods

Push force

Pneumatic – electric cable Control

box

Gas tank

Pneumatic cable

p0 Lift-off pressure

p1 Pressure for 1.1 mm expansion

DMT insertion with penetrometer

Most efficient method:

direct push with

penetrometer

DMT Working principle

A

B

Sensing disk

Retaining Ring

Membrane

Sensing disk (electrically insulated)

Blade is like an electrical switch, can be off or onNO ELECTRONICS no zero drift, no temperature effectsNothing that the operator can regulate, adjust, manipulate

DMT Intermediate parameters

Intermediate Parameters

Id: Material Index

DMT Readings

P0

P1

Kd: Horizontal Stress Index

Ed: Dilatometer Modulus

KD contains information on stress history

KD is an “amplified” K0, because p0

is an “amplified” σh due to

penetration

KD = σ’v

(p0 - u0)

KD well correlated to OCR and K0

(clay)

p0

DMT

formula similar to K0: (p0 – u0)

σ’h

Very roughly KD ≈ 4K0 E.g. in NC K0 ≈ 0.5 and KD

≈ 2

DMT Formulae – Interpreted parameters

IntermediateParameters

Id

Kd

Ed

Interpreted Parameters

Cu: Undrained Shear Strength

Ko: Earth Pressure Coeff (clay)

OCR: Overconsolidation ratio (clay)

: Safe floor friction angle (sand)

: Unit weight and description

M: Constrained Modulus

ExperimentalKamei & Iwasaki

1995 TheoreticalFinno 1993

TheoreticalYu 2004

OCR = Kd

1.56Marchetti 1980 (experimental)0.5

KD correlated to OCR (clay)

Cu correlation from OCRLadd SHANSEP 77 (SOA TOKYO)

Ladd: best Cu measurement not from TRX UU !!

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

Cu

σ’v OC

=Cu

σ’v NC

OCR m OCR = 0.5 Kd

1.56

Cu = σ’v 0.5 Kd1.250.22

best Cu from oed OCR Shansep

DMT Formulae (1980 – today)

Po and P1

Intermediate parameters

Interpreted parameters

DMT results

KD = 2 NC clay

ID

M Cu

KD

soil type(clay, silt,

sand)

common use shape similar to OCR helps understand history of deposit

Generally dependable

Seismic dilatometer (SDMT)

2 receivers

VS determined from delay arrival of impulse from 1st to 2nd receiver (same hammer blow)

Signal amplified + digitized at depth

VS measured every 0.5 m

Combination S + DMT

DMT Marchetti 1980 SDMT Hepton 1988ASTM D6635 – EC7 Martin & Mayne

1997,1998 ...TC16 2001

Seismic Dilatometer (SDMT)

Hammer for shear wave

Example seismograms SDMT at Fucino

Delay well conditioned from Cross Correlation coeff of variation of Vs 1-2 %

SDMT results

DMT Seismic DMT

GO= ρ Vs2

High repeatability

20

Fucino-Telespazio National Research Site

(Italy) 2004

SDMT (2004)

SCPTCross HoleSASW

AGI (1991)

Vs at National Site FUCINO – ITALY

Standards

EUROCODE 7 (1997 and 2007). Standard Test Method, European Committee for Standardization, Part 2: Ground investigation and testing, Section 4. Field tests in soil and rock. 4.10. Flat Dilatometer Test (DMT).

ASTM (2002 and 2007). Standard Test Method D6635-01, American Society for Testing and Materials. The standard test method for performing the Flat Dilatometer Test (DMT), 14 pp.

TC16 (1997). “The DMT in soil Investigations”, a report by the ISSMGE Technical Committee tc16 on Ground Property, Characterization from in-situ testing, 41 pp.

ASTM (2011) – Standard Test Method D7400 – 08, “Standard Test Methods for Downhole Seismic Testing“, 11 pp.

PROTEZIONE CIVILE Gruppo di lavoro (2008) – Indirizzi e criteri per la microzonazione sismica. Prova DMT pp. 391-397, Prova SDMT pp. 397-405

Consiglio Superiore dei Lavori Pubblici (2008) – Istruzioni per l'applicazione Norme Tecniche per le Costruzioni NTC08. Circolare 02/02/09 , paragrafo C6.2.2

Use of SDMT results for engineering applications

Ratio G0 /MDMT vs. KD

for various soil types(Marchetti et al. 2008, Monaco et al. 2009)

Experimental interrelationship between G0 and MDMT

SDMT data from 34 sites

● Data points tend to group according to soil type (ID)

● G0 /MDMT constant, varies in wide range (≈ 0.5 to 20), especially in clay

● G0 /MDMT largely influenced by stress history (KD)

● By-product rough estimates of VS (when not measured)

MDMT, ID, KD (DMT) G0 VS

MDMT, ID, KD (DMT) G0 VS

COMMENTS

Use of cu (or NSPT) alone as a substitute of VS (when not measured) for seismic classification of a site (Eurocode 8) does not appear founded on a firm basis

If VS assumed as primary parameter for site classification, then a possible surrogate must be reasonably correlated to VS … But if 3 parameters (MDMT, ID, KD) barely sufficient to obtain rough estimates of VS, then estimating VS from only 1 parameter appears problematic …

Experimental interrelationship between G0 and MDMT

Comparison of profiles of VS measured by SDMTand estimated from mechanical DMT data (Monaco et al.

2013)

Estimates of VS from DMT data

Vs prediction from CPT and DMT

DMT predictions of VS appear more reliable and consistent than the CPT predictions (Amoroso 2014)

VS from DMT includes KD , sensitive to stress history, prestraining/aging and structure, scarcely detected by qc

Main SDMT applications

Settlements of shallow foundations

Compaction control

Slip surface detection in OC clay

Quantify σ'h relaxation behind a landslide

Laterally loaded piles

Diaphragm walls

FEM input parameters

Liquefiability evaluation

In situ G-γ decay curves

…

Tentative method for deriving in situG- decay curves from SDMT

SDMT small strain modulus G0 from VS

working strain modulus GDMT from MDMT

(track record DMT-predicted vs. measured settlements)

But which associated to GDMT ?

?

Shear strain "DMT"

same-depth "reference" stiffness decay curve

Quantitative indications by comparing at various test sites and in different soil types SDMT data + “reference” stiffness decay curves:

back-figured from the observed behavior under a full-scale test embankment (Treporti) or footings (Texas)

obtained by laboratory tests (L'Aquila, Emilia Romagna, Fucino) reconstructed by combining different in situ/laboratory techniques

(Western Australia)

"Typical shape" G/G0- curves in different soil types

Range of values of GDMT/G0 and corresponding shear strain DMT determined by the "intersection" procedure in different soil types

(Amoroso, Monaco, Lehane, Marchetti – Paper under review)

Typical ranges of DMT in different soil types

DMTDMTG

GG

G

11

1

00

Tentative equation for derivingG/G0- curves from SDMT

SDMT data points used to assist construction of hyperbolic equation

DSDSS (Double Sample Direct Simple Shear tests): University of Roma La Sapienza

Roio Piano – L'Aquila

Comparison between G/G0 - decay curves obtained in Lab and estimated from SDMT by hyperbolic equation

(Amoroso, Monaco, Lehane, Marchetti – Paper under

review)

Validation of in situ G- decay curves from SDMT (under study)

Comparison between HSS model – PLAXIS from SDMT parameters and monitoring activities for the excavation of Verge de Montserrat Station (Barcelona, Spain)

Working group: Amoroso, Arroyo, Gens, Monaco, Di Mariano

Validation of in situ G- decay curves from SDMT (under study)

0

5

10

15

20

25

30

35

40

45

0 20 40 60 80 100

Dep

th (m

)

Oedometric modulus Eoed (MPa)

Eoed from SDMT (Eoed=Mdmt)

Eoed from HSS model (PLAXIS)

0

0.2

0.4

0.6

0.8

1

1.2

1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01

no

rmal

ized

sh

ear

mo

du

lus,

G/G

0

shear strain, γ (%)

GDMT/G0

Hyperbolic curveVERGE MONTSERRAT

UG4 Sand

G/G0 = 0.722

γ0.7

4/50 uroedDMT EEEM

mrefref pGG '100

HSS model – PLAXIS

Assumptions:

Validation of in situ G- decay curves from SDMT (under study)

Preliminary results show an acceptable agreement between experimental data (monitoring activities) and numerical analysis (based on SDMT data)

0

5

10

15

20

25

30

35

40

-10 -5 0 5 10

Dep

th (m

)

Diaphragm wall horizontal movement (mm)

OBSERVED

NUMERICAL ANALYSIS

Phase 9 “Pumping down

to a depth of 10 m”

Phase 9 “Pumping down

to a depth of 10 m”

At sites where VS has not been measured and only mechanical DMT results from past investigations are available, rough estimates of VS (via G0) can be obtained from mechanical DMT data

SDMT results could be used to assess the decay of in situ stiffness with strain level and to provide guidance in selecting G- curves in various soil types, thanks to its ability to provide both a small strain modulus (G0 from VS) and a working strain modulus GDMT (obtained from MDMT derived by usual DMT interpretation)

Use of proposed hyperbolic relationship, which requires to input ratio GDMT/G0 + presumed "typical" shear strain DMT for a given soil type, can provide a useful first order estimate of G/G0 - curves from SDMT (further validation needed)

Concluding remarks

Thank you for your attention