Diapositiva 1

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The Flat Dilatometer Test (DMT) Design
Applications and Recent Developments
P. Monaco, S. Marchetti G. Totani University of
L'Aquila, Italy
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KEY DMT REFERENCES
ORIGINAL PAPER MARCHETTI S. (1980). In Situ Tests
by Flat Dilatometer. J. Geotech. Engrg. Div.
ASCE, 106(GT3), 299-321 STANDARDS ASTM D6635-01
(2001). Standard Test Method for Performing the
Flat Plate Dilatometer. EUROCODE 7 Geotechnical
Design Part 2 Ground Investigation and
Testing. EN 1997-22007 SOA REPORT TC16 (2001).
The Flat Dilatometer Test (DMT) in Soil
Investigations. May 2001, 41 pp. Reprint in Proc.
2nd Int. Conf. on Flat Dilatometer, Washington
D.C., 7-48 INTERNET www.marchetti-dmt.it biblio
site (download papers)
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FLAT DILATOMETER (DMT)
BLADE
FLEXIBLE MEMBRANE
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GENERAL LAYOUT of DMT
Push force provided by penetrometer or drill rig
? DMT blade ? Push rods (e.g. CPT) ?
Pneumatic-electrical cable ? Control unit ?
Pneumatic cable ? Gas tank ? MEMBRANE EXPANSION
p0 p1 readings at 20 cm depth intervals
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SOILS that can be TESTED by DMT

• CLAY, SILT, SAND But can cross through GRAVEL
  layers ? 0.5 m
• Soils from VERY SOFT to VERY STIFF (upper limit
  is push capacity of rig)
• Clays Cu 2-4 to 1000 kPa (marls)
• Moduli up to 400 MPa

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Basic DMT reduction formulae (TC16 2001)
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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
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Design using soil parameters

• In most cases DMT used to determine common
  geotechnical design parameters
• Experience has shown undrained shear strength Cu
  and constrained modulus M by DMT generally
  accurate and dependable for design
• Comparisons at several research sites indicate
  quite good agreement between profiles of Cu and M
  by DMT and reference values by other tests ( see
  TC16 2001)

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Comparisons Cu DMT vs. Cu reference
Nash et al. (1992)
AGI (1991)
Research Site Bothkennar (UK)
Research Site Fucino (Italy)
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Comparisons MDMT vs. Mreference
MDMT
M back-calculated
Marchetti et al. (2006)
Lacasse (1986)
M by DMT vs. M back-calculated from local
vertical strains measured under Treporti
full-scale test embankment (Italy)
M by DMT vs. M by high quality oedometers Onsøy
(Norway)
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Settlement prediction No. 1 DMT application

• Classic linear elastic 1-D approach or 3-D with
  E ? 0.8 MDMT (similar predictions)
• Settlement under working loads (Fs ? 2.5-3.5)

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Summary of comparisons DMT-predicted vs. observed
settlements

• Large No. of case histories ? good agreement for
  wide range of soil types, settlements, footing
  sizes
• Average ratio DMT-calculated/observed settlement
  ? 1.3
• Band amplitude (ratio max/min) lt 2
  i.e. observed settlement within 50 from
  DMT-predicted

Monaco et al. (2006)
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Compaction control

• Experience suggests DMT well suited to detect
  BENEFITS of SOIL IMPROVEMENT due to its high
  sensitivity to changes of stresses/density in
  soil
• Several comparisons of CPT and DMT before/after
  compaction
• Schmertmann et al. (1986), Jendeby (1992) ?
  increase in MDMT after compaction of sand ? 2
  increase in qc (CPT)
• Pasqualini Rosi (1993) ...

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DMT vs. CPT before/after compaction
Ratio MDMT /qc before/after compaction of a loose
sand fill (Jendeby 1992)
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Detecting slip surfaces in clay slopes
DMT-KD method ? Verify if an OC clay slope
contains ACTIVE (or old QUIESCENT) SLIP
SURFACES (Totani et al. 1997)
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Validation of DMT-KD method
DOCUMENTED SLIP SURFACE
DOCUMENTED SLIP SURFACE (inclinometers)
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DMT for LIQUEFACTION

• Correlations for evaluating Cyclic Resistance
  Ratio CRR from KD developed in past 2 decades,
  stimulated by

• Sensitivity of KD to factors known to increase
  liquefaction resistance Stress History,
  prestraining/aging, cementation, structure
• Correlation KD Relative Density
• Correlation KD In situ State Parameter

• Key element supporting well-based CRR-KD
  correlation ability of KD to reflect aging in
  sands (1st order of magnitude influence on
  liquefaction) sensitivity of KD to non-textbook
  OCR crusts in sands

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Curves for evaluating CRR from KD (Seed Idriss
1971 simplified procedure)

• Summary latest version CRR-KD correlation see
  Monaco et al. (2005 ICSMGE Osaka)
• Magnitude M 7.5 Clean sand

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DMT for DESIGN of LATERALLY LOADED PILES
Robertson et al. (1987) Marchetti et al. (1991) 2
methods recommended for deriving P-y curves for
laterally loaded piles from DMT (single pile, 1st
time monotonic loading)

• Independent validations ? 2 methods provide
  similar predictions, in very good agreement with
  observed full-scale pile behaviour

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DMT for DESIGN of DIAPHRAGM WALLS
Monaco Marchetti (2004 ISC'2 Porto)

• Tentative correlation for deriving the
  coefficient of subgrade reaction Kh for design of
  multi-propped diaphragm walls from MDMT
• Indications on how to select input moduli for FEM
  analyses (PLAXIS Hardening Soil model) based on
  MDMT

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Subgrade compaction control
Bangladesh Subgrade Compaction Case History 90 km
Road Rehabilitation Project
MDMT acceptance profile (max always found at
25-26 cm)

• Acceptance MDMT profile fixed and used as
  alternative/fast acceptance tool for quality
  control of subgrade compaction, with only
  occasional verifications by originally specified
  methods (Proctor, CBR, plate)

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Seismic Dilatometer (SDMT)
Combination S DMT

• 2 receivers spaced 0.5 m
• 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

Hepton 1988 Martin Mayne 1997, 1998 ...
(Georgia Tech, USA)
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Validation of Vs by SDMT
Comparison of Vs profiles by SDMTand by other
testsFucino research site(Italy)
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SDMT results
SDMT profiles at the site of Fiumicino (Italy)
SDMT ? accurate and highly repeatable Vs (in
addition to usual DMT results)
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In situ G-? decay curves by SDMT
Mayne (2001) Ishihara (2001)

• SDMT ? small strain modulus G0 from Vs
• working strain modulus MDMT (settlements)
• Tentative methods to derive in situ G-? curves by
  SDMT
• Two points help in selecting the G-? curve

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SDMT for LIQUEFACTION
SDMT ? 2 parallel independent evaluations of CRR
from VS e KD (Seed Idriss 1971 simplified
procedure)
CRR from Vs
CRR from KD
Andrus Stokoe (2000) Andrus et al. (2004)
Monaco et al. (2005) ICSMGE Osaka
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FINAL REMARKS

• DMT ? quick, simple, economical, highly
  reproducible in situ test
• Executable with a variety of field equipment
• Dependable estimates of various design
  parameters/information
• soil type
• stress state/history
• constrained modulus M
• undrained shear strength Cu in clay
• consolidation/flow parameters
• ...

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FINAL REMARKS

• Variety of design applications
• Most effective vs. common penetration tests when
  settlements/deformations important for design
  (e.g. strict specs or need to decide piles or
  shallow ?)
• SDMT ? accurate measurements of Vs (and G0)
  usual DMT results greatly enhances DMT
  capability

Special thanks to Allan McConnell (IGS)