Presentazione di PowerPoint

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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, LAquila, Italy) sara.amoroso_at_ingv.i
t
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Outline of the presentation

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

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Flat dilatometer (DMT) Seismic DMT (SDMT)
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DMT Flat dilatometer equipment
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DMT Test layout components
p0 Lift-off pressure p1 Pressure for 1.1 mm
expansion
Measurements performed after penetration ?
independent from insertion method
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DMT insertion with penetrometer
Most efficient method direct push with
penetrometer
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DMT Working principle
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
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DMT Intermediate parameters
Intermediate Parameters
DMT Readings
Id Material Index
P0
Kd Horizontal Stress Index
P1
Ed Dilatometer Modulus
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KD contains information on stress history
DMT
formula similar to K0 (p0 u0) ? sh
KD is an amplified K0, because p0 is an
amplified sh 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)
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DMT Formulae 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
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KD correlated to OCR (clay)
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Cu correlation from OCRLadd SHANSEP 77 (SOA
TOKYO)
Ladd best Cu measurement not from TRX UU !!
best Cu from oed ? OCR ? Shansep
Using m ? 0.8 (Ladd 1977) and (Cu/?v)NC ? 0.22
(Mesri 1975)
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DMT Formulae (1980 today)
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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
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Seismic dilatometer (SDMT)
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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 1980 SDMT Hepton 1988 ASTM
D6635 EC7 Martin Mayne 1997,1998
... TC16 2001
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Hammer for shear wave
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Example seismograms SDMT at Fucino
Delay well conditioned from Cross Correlation ?
coeff of variation of Vs 1-2
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SDMT results
High repeatability
GO ? Vs2
DMT
Seismic DMT
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Vs at National Site FUCINO ITALY
Fucino-Telespazio National Research Site (Italy)
2004
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Standards
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Use of SDMT results for engineering applications
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Experimental interrelationship between G0 and
MDMT

• 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
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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

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

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Main SDMT applications

• Settlements of shallow foundations
• Compaction control
• Slip surface detection in OC clay
• Quantify s'h relaxation behind a landslide
• Laterally loaded piles
• Diaphragm walls
• FEM input parameters
• Liquefiability evaluation
• In situ G-? decay curves

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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)
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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)

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Typical ranges of ?DMT in different soil types
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Tentative equation for deriving G/G0-? curves
from SDMT
(Amoroso, Monaco, Lehane, Marchetti Paper under
review)
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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)

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

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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)

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Thank you for your attention