1. Use of SDMT results for engineering applications
Workshop on Penetration Testing – University of Pisa, DESTEC
Pisa – Italy, 9th October 2014
Flat dilatometer (DMT) & Seismic DMT (SDMT)
Use of SDMT results for engineering applications
Sara Amoroso
(Istituto Nazionale di Geofisica e Vulcanologia, L’Aquila, Italy)

2. Outline of the presentation
Flat dilatometer (DMT)
Seismic dilatometer (SDMT)
Interpretation of the parameters
Engineering applications

3. Flat dilatometer (DMT) & Seismic DMT (SDMT)

4. DMT Flat dilatometer equipment
BLADE
FLEXIBLE MEMBRANE (D = 60mm)

5. DMT Test layout & components
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
Measurements performed after penetration  independent from insertion method

6. DMT insertion with penetrometer
Most efficient method:
direct push with penetrometer

7. (electrically insulated)
DMT Working principle A B
Sensing disk
(electrically insulated)
Sensing disk
Retaining Ring
Membrane
Blade is like an electrical switch, can be off or on
NO ELECTRONICS  no zero drift, no temperature effects
Nothing that the operator can regulate, adjust, manipulate

8. DMT Intermediate parameters
DMT Readings
Intermediate Parameters
Id: Material Index P0
Kd: Horizontal Stress Index P1
Ed: Dilatometer Modulus

9. KD contains information on stress history
σ’v
(p0 - u0)
D M T
formula similar to K0: (p0 – u0)  σ’h
KD is an “amplified” K0, because p0 is an “amplified” σh due to penetration p0
Very roughly KD ≈ 4K0 E.g. in NC K0 ≈ 0.5 and KD ≈ 2
KD well correlated to OCR and K0 (clay)

10. DMT Formulae – Interpreted parameters
Intermediate
Parameters Id Kd Ed
Interpreted Parameters
M: Constrained Modulus
Cu: Undrained Shear Strength
Ko: Earth Pressure Coeff (clay)
OCR: Overconsolidation ratio (clay)
: Safe floor friction angle (sand)
 : Unit weight and description

11. KD correlated to OCR (clay)= Kd
1.56
Marchetti 1980 (experimental)
0.5
Experimental
Kamei & Iwasaki 1995
Theoretical
Finno 1993
Theoretical
Yu 2004

12. Cu correlation from OCR Ladd SHANSEP 77 (SOA TOKYO)
Ladd: best Cu measurement not from TRX UU !!
best Cu from oed  OCR  Shansep Cu
σ’v OC = NC
OCR m
OCR =
0.5 Kd
1.56
Using m  0.8 (Ladd 1977) and (Cu/’v)NC  0.22 (Mesri 1975) Cu =
σ’v
0.5 Kd
1.25
0.22

13. DMT Formulae (1980 – today) Po and P1 Intermediate parameters
Interpreted parameters

14. DMT results KD = 2  NC clay ID  M Cu   KD  soil type
  KD 
soil type
(clay, silt, sand)
common use
shape similar to OCR helps understand history of deposit
Generally dependable

15. Seismic dilatometer (SDMT)

16. Seismic Dilatometer (SDMT)
Combination S + DMT
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
DMT Marchetti SDMT Hepton 1988
ASTM D6635 – EC7 Martin & Mayne 1997, TC

17. Hammer for shear wave

18. Example seismograms SDMT at Fucino
Delay well conditioned from Cross Correlation  coeff of variation of Vs 1-2 %

19. SDMT results
High repeatability
GO= ρ Vs2
DMT
Seismic DMT

20. Vs at National Site FUCINO – ITALY
SDMT (2004)
SCPT
Cross Hole
SASW
AGI (1991)
Fucino-Telespazio
National Research Site (Italy) 2004 20 20

21. 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 Flat Dilatometer Test (DMT).
ASTM (2002 and 2007). Standard Test Method D , 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 , Prova SDMT pp
Consiglio Superiore dei Lavori Pubblici (2008) – Istruzioni per l'applicazione Norme Tecniche per le Costruzioni NTC08. Circolare 02/02/09 , paragrafo C6.2.2

22. Use of SDMT results for engineering applications

23. 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)
Ratio G0 /MDMT vs. KD
for various soil types
(Marchetti et al. 2008, Monaco et al. 2009)
MDMT, ID, KD (DMT)  G0  VS

24. Experimental interrelationship
between G0 and MDMT
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 …

25. Estimates of VS from DMT data
Comparison of profiles of VS measured by SDMT
and estimated from mechanical DMT data (Monaco et al. 2013)

26. 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

27. 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 …

28. Tentative method for deriving in situ
G- 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 ? ?

29. Shear strain "DMT"
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)
same-depth "reference" stiffness decay curve

30. Typical ranges of DMT in different soil types
"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)

31. Tentative equation for deriving
G/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)

32. from SDMT (under study)
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

33. from SDMT (under study)
Validation of in situ G- decay curves
from SDMT (under study)
HSS model – PLAXIS
Assumptions:
G/G0 = 0.722
γ0.7

34. from SDMT (under study)
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)
Phase 9
“Pumping down
to a depth of 10 m”

35. Concluding remarks
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)

36. Thank you for your attention