Workshop on Penetration Testing – University of Pisa, DESTEC
Pisa – Italy, 9 th 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) sara.amoroso@ingv.it

Outline of the presentation
1.
Flat dilatometer (DMT)
2.
Seismic dilatometer (SDMT)
3.
Interpretation of the parameters
4.
Engineering applications

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

DMT Test layout & components
Pneumatic – electric cable
Control box
Push force
Pneumatic cable
Gas tank
Push rods
DMT blade p
0
Lift-off pressure p
1
Pressure for 1.1 mm expansion
Measurements performed after penetration  independent from insertion method

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

DMT Working principle
Sensing disk
(electrically insulated)
Sensing disk
A
B
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
Retaining Ring
Membrane

DMT Intermediate parameters
DMT Readings Intermediate Parameters
P
0
P
1
Id : Material Index
Kd : Horizontal Stress Index
Ed : Dilatometer Modulus

K
D contains information on stress history
D
M
T
K
D
=
(p
0
- u
0
)
σ’ v formula similar to K
0
: (p
0
– u
0
)  σ’ h p
0
K
D is an “amplified” K
0
, because p
0 is an “amplified” σ h due to penetration
Very roughly K
D
≈ 4K
0
E.g. in NC K
0
≈ 0.5 and K
D
≈ 2
K
D well correlated to OCR and K
0
(clay)

DMT Formulae – Interpreted parameters
Intermediate
Parameters
Id
Ed
Kd
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

K
D correlated to OCR (clay)
OCR = 0.5
K d
1.56
Experimental
Kamei & Iwasaki 1995
Marchetti 1980 (experimental)
Theoretical
Finno 1993
Theoretical
Yu 2004

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
=
Cu
σ’ v
NC
OCR m OCR = 0.5
K d
1.56
Using m  0.8 (Ladd 1977) and (Cu/  ’ v
)
NC
 0.22 (Mesri 1975)
Cu = 0.22
σ’ v
0.5 K d
1.25

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

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

Seismic dilatometer (SDMT)

Seismic Dilatometer (SDMT)
Combination S + DMT
2 receivers
V
S determined from delay arrival of impulse from 1st to 2nd receiver (same hammer blow)
Signal amplified + digitized at depth
V
S measured every 0.5 m
DMT Marchetti 1980
ASTM D6635 – EC7
TC16 2001
SDMT Hepton 1988
Martin & Mayne 1997,1998 ...

Hammer for shear wave

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

SDMT results High repeatability
G
O
= ρ Vs 2
DMT Seismic DMT

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

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

Experimental interrelationship between G
0 and M
DMT
SDMT data from 34 sites
● Data points tend to group according to soil type (I
D
)
● G
0
/M
DMT
 constant, varies in wide range (≈ 0.5 to
20), especially in clay
● G
0
/M
DMT largely influenced by stress history (K
D
)
● By-product  rough estimates of V
S
(when not measured)
Ratio G
0
/ M
DMT vs. K for various soil types
D
(Marchetti et al. 2008, Monaco et al. 2009)
M
DMT
, I
D
, K
D
(DMT)  G
0
 V
S

Experimental interrelationship between G
0 and M
DMT
COMMENTS
 Use of c u
(or N
SPT
) alone as a substitute of V
S
(when not measured) for seismic classification of a site (Eurocode 8) does not appear founded on a firm basis
 If V
S classification, then a possible surrogate must be reasonably correlated to V
(M
DMT assumed as primary parameter for site
, I
D
, K
D estimates of V
S
S
… But if 3 parameters
) barely sufficient to obtain rough
, then estimating V parameter appears problematic …
S from only 1

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

Vs prediction from CPT and DMT
 DMT predictions of V
S appear more reliable and consistent than the CPT predictions (Amoroso 2014)
 V
S from DMT includes K
D
, sensitive to stress history, prestraining/aging and structure, scarcely detected by q c

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 Gγ decay curves
 …

Tentative method for deriving in situ
G decay curves from SDMT
SDMT  small strain modulus working strain
G modulus
0 from V
G
DMT
S from M
DMT
(track record DMT-predicted vs. measured settlements)
But which  associated to G
DMT
?
?

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

Typical ranges of 
DMT in different soil types
"Typical shape"
G/G
0
 curves in different soil types
(Amoroso, Monaco, Lehane,
Marchetti – Paper under review)
Range of values of G strain 
DMT
DMT
/G
0 and corresponding shear determined by the "intersection" procedure in different soil types

Tentative equation for deriving
G/G
0
 curves from SDMT
SDMT data points used to assist construction of hyperbolic equation
G
G
0

1



G
0
G
DMT
1

1




DMT
Roio Piano – L'Aquila
Comparison between
G/G
0
 decay curves obtained in Lab and estimated from SDMT by hyperbolic equation
DSDSS (Double Sample Direct
Simple Shear tests): University of Roma La Sapienza
(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

35
40
25
30
45
15
20
5
10
Validation of in situ G decay curves from SDMT (under study)
0
0
Oedometric modulus Eoed (MPa)
20 40 60 80 100
HSS model – PLAXIS
Eoed from SDMT (Eoed=Mdmt)
Eoed from HSS model (PLAXIS)
G
0

G
0 ref


1
' p ref
 m
Assumptions:
M
DMT

E oed

E
50

E ur
/ 4
1.2
VERGE MONTSERRAT
UG4 Sand
GDMT/G0
Hyperbolic curve
1
0.8
0.6
0.4
G/G
0
= 0.722
0.2
0
1.00E-04 1.00E-03
γ
0.7
1.00E-02 1.00E-01 shear strain, γ (%)
1.00E+00 1.00E+01

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”
-10
Diaphragm wall horizontal movement (mm)
-5 0 5
0
5
10
15
20
25
30
35
40
O BSERVED
N
UMERICAL
A
NALYSIS
10

Concluding remarks
 At sites where V
S has not been measured and only mechanical DMT results from past investigations are available, rough estimates of from mechanical DMT data
V
S
(via G
0
) can be obtained
 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 ( G and a working strain modulus G
DMT derived by usual DMT interpretation)
0 from
(obtained from M
V
DMT
S
)
 Use of proposed hyperbolic relationship, which requires to input ratio G estimate of needed)
DMT
G / G
/ G
0
0
+ presumed "typical" shear strain for a given soil type, can provide a useful first order

DMT
 curves from SDMT (further validation