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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