Frontespizio

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Frontespizio
SDMT Workshop and Field Demonstration Cesano 18
novembre 2011
Applicazioni alla progettazione geotecnica
Università degli Studi dellAquila Ing. Sara
Amoroso
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REFERENCE State-of-the-art Lecture No. 1
(Alessandria Egitto Oct 2009) 17th Int.
Conf. on Soil Mechanics and Geotechnical Engng,
2009 Mayne P.W. Georgia Institute of
Technology, Atlanta, USA Coop M.R.
Imperial College, London, UK Springman S.M.
Swiss Federal Institute of Technology, Zurich,
CH Uang A.B. National Chiao Tung
University, Taiwan, China Zornberg J.G.
University of Texas, Austin, USA
Soil borings laboratory testing SPT
pressuremeter (PMT) vane (VST) crosshole
(CHT) Taken together, all of these are suitable
yet at considerable cost in time and money
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... In this fast-paced world, a more efficient
approach In particular, the Seismic Piezocone
(SCPT) and the Seismic Dilatometer (SDMT) ...
offer clear opportunities in the economical and
optimal collection of data. ... SCPT and SDMT
direct-push tests should serve as the basis in
routine daily site investigation practices
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FLAT DILATOMETER (DMT)
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Design via DMT parameters

• ID material index
• KD horizontal stress index
• ED dilatometer modulus
• K0 coeff. earth pressure in situ
• OCR overconsolidation ratio
• cu undrained shear strengh
• F friction angle
• ch consolidation coefficient
• kh permeability coefficient
• g unit weight and description
• M vertical drained constrained modulus
• u0 equilibrium pore pressure

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Main DMT applications

• Settlements of shallow foundations
• Laterally loaded piles
• Diaphragm walls
• Detecting slip surfaces in OC clay
• Monitoring densification/stress increase
• Liquefability evaluation
• Subgrade compaction control
• FEM input parameters

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1 - 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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Possible reasons DMT good settlement predictions
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Observed and DMT predicted modulus
M by DMT vs. M back-calculated from local
vertical strains measured under Treporti
full-scale test embankment (Italy)
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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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2 - 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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3 - 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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4 - Detecting slip surfaces in OC clay
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
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5 - Monitoring densification / stress increase

• 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) ? DMT clearly detected
  improvement even in layers where benefits were
  undetected by CPT
• Ghent group (1993) ? DMTs before-after
  installation demonstrate more clearly than CPT
  beneficial effects of Atlas installation

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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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6 - Liquefability evaluation

• 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
  (Marchetti, 2010)
• Correlation KD Relative Density (Reyna
  Chameau, 1991)
• Correlation KD In situ State Parameter (Yu,
  2004)

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

• All past CRR-KD curves were based on correlations
  Qc-Dr-KD or NSPT-Dr-KD. Tsai et al (2009)
  translated CPT-SPT using correlations Qc-KD or
  NSPT-KD and cutting out Dr.

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7 - 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), (Marchetti, 1994)

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8 - FEM input parameters

• Linear elastic model E ? 0.8 MDMT
• (Hamza Richards, 1995)
• DMT aims to calibrate FEM parameters
• PLAXIS hardening soil model
• E50,ref is correlated to MDMT (Schanz, 1997)

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Seismic Dilatometer (SDMT)
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Correlation to estimate Vs (G0) frommechanical
DMT data (ID, KD, ED)
From large amount SDMTs at 34 sites various soils
geography ?

• No point today. Vs direct(but might provide
  rough Vs in previous sites DMT).
• Important w/o stress history (KD) hopeless
  estimate Vs.
• Difficulty Qc-Vs NSPT-Vs ???
• Use 1 parameter (NSpt, Su) as surrogate of Vs
  questionable (as suggested by some codes).

Decay decreases with KD (stress history)
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Earthquake in LAquila, 6 April 2009
Monaco et al. (2009)
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Main SDMT applications

• DMT applications
• Seismic design (NTC08, Eurocode 8)
• In situ G-g decay curves
• Liquefability evaluation

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9 - Vs for seismic design
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10 - In situ G-? decay curves by SDMT

• SDMT ? small strain modulus G0 from Vs
• working strain modulus GDMT from MDMT
• (Marchetti et al. 2008)
• Tentative methods to derive in situ G-? curves by
  SDMT
• Two points help in selecting the G-? curve

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Earthquake in LAquila, 6 April 2009
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11 - Liquefability evaluation
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Earthquake in LAquila, 6 April 2009
Vittorito LAquila (April 2009) Moment
magnitude MW 6.3 Distance from the epicentre 45
km Peak ground acceleration PGA 0.065 g
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Earthquake in LAquila, 6 April 2009
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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