Frontespizio

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Frontespizio
University of PISA DESTEK Oct. 9 th
2014 Workshop on Penetration Testing
Flat dilatometer (DMT) Seismic DMT (SDMT)
Recent developments
Silvano Marchetti University of L'Aquila,
Italy silvano_at_marchetti-dmt.it
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DMT results
or Stress History Index
KD 2 ? NC clay ? amplified Ko
ID ?
M Cu ? ?
KD ?
soil type (clay, silt, sand)
common use
shape similar to OCR helps understand history of
deposit
1-D modulus _at_ ?vo . Treat as if obtained by oed
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SeismicDilatometer
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SDMT results repeatability 1-2
SHEAR WAVE VELOCITY
GO ? Vs2
Vs (m/s)
Seismic DMT
mechanical DMT
(Recommended graphical format no just po p1)
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Main SDMT applications (details ? papers)

• Settlements of shallow foundations
• Liquefability evaluation
• Compaction control
• Detecting slip surfaces in OC clay
• Laterally loaded piles
• Diaphragm walls springs for design
• FEM input parameters
• In situ G-? decay curves
• Seismic design (NTC08, Eurocode 8)

Have in common need of Stress History (by Kd)
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Diagrams compare sensitivity of CPT-DMT to Stress
History
Lee 2011, Eng. Geology ? 30 CC in sand
DMT
CPT

• Kd reactive than Qc to Stress History
• For a given Qcn can be many Kd, depending on SH
• Kd distinguish sands with SH / no SH. Qcn ? much
  less.

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Two sites same Qc , but different KD.Site 2
much stronger (higher SH) ? settlement and
liquefaction.
(3/7)
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Given the scarce sensitivity of Qc to OCR, is it
possible to estimate OCR from CPT ?
Many formulae OCR-Qc proposed, even relatively
complex.
CPT
No mathematics, plaxis, statistics, FEM can
replace low degree of correlation
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Similarly higher sensitivity of Kd to SH aging
observed by Jamiolkowski (ISC'98 Atlanta)
They applied prestraining cycles in calibration
chamber. Found KD (DMT) 3 to 7 times more
sensitive to AGING than penetration resistance
PRESTRAINING CYCLES simulate AGING (grain
slippage)
KD 20 qD 3
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that DMT MORE REACTIVE TO STRESS HISTORY
confirmed in the field
Jendeby 92 Measured in a loose sandfill Qc
Mdmtbefore-after compaction NC M/Qc ? 5-12 OC
M/Qc ? 12-24

Mdmt v. effective in reflecting benefits of
compaction Schmertmann 1988 Since aim of
compaction is reduce settlements ? More logic
specs in terms of M instead of Dr (Dr wrong
target and Dr correlations v. uncertain)
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Estimate OCR in sand. Qc or Mdmt alone not
sufficient (multiparameter). Need both, one
sensitive to SH, other less sensitive
Can estimate OCR based onratio ?M/Qc
If ? M/Qc ? 5-12 ? NC If ? M/Qc ? 12-24 ?
OC

Principle behind To convert Qc to M (by M?Qc)
we need ? 4 to 20 f(OCR) (?) If we know ?
M/Qc, can get an idea of OCR Difficult enough
with 2 parameters (CPT,DMT)
once having OCR KoKo,nc (OCR)m
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COMPACTION (? applying SH) produces a MDMT
increase ? twice the Qc increase
MDMT before-after compaction
Schmertmann (1986) DYNAMIC COMPACTION of sand
site. MDMT increase ? twice increase in
Qc. Jendeby (1992) monitored DEEP COMPACTION in a
sand fill by VIBROWING. MDMT increase ? twice
increase in qc. Pasqualini Rosi (1993)
VIBROFLOTATION job "DMT clearly detected
improvement even in layers where benefits were
undetected by CPT". Ghent group (1993)
before-after CPTs DMTs to evaluate effects (???h
, Dr) by PILE (Atlas) INSTALLATION "DMTs
before-after installation demonstrate more
clearly than CPT beneficial effects of Atlas
installation".
bar
hence Mdmt effective in reflecting benefits of
compaction
Resonant vibro-compaction technique Van Impe, De
Cock, Massarsch, Mengé, New Delhi (1994)
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.conclusion good sensitivity of KD to Stress
History (SH OCR overburden, aging, any factor
better grain interlocking) Sensitivity to SH
important (1) not many SH tools (2) SH
important for settlements and liquefaction
Importance of SH to predict Settlements Jamiolkows
ki (Isopt-1,88,1) without Stress History,
impossible to select reliable E (or M) from
Qc(also Terzaghi, Leonards, Schmertmann) Yoshim
i (1975) the NC sand specimens were six times
more compressible than the prestressed sand
hence imperative SH to characterize
compressibility of sand Application 1 DMT
predict settlements (operative modulus) MDMT ED
x Rm(Kd, Id) (combines ED with Stress History)
(Multi parameter both DMT)
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Settlement predictions by DMTIn general classic
Terzaghi 1-D (even in 3-D(Poulos modulus, not
formula !! )
Accuracy of DMT-predicted settlements
confirmed by a large number case histories in the
last decades
Cruz (2010), Vargas (2009), Bullock (2008),
Monaco (2006), Lehane Fahey (2004), Mayne
(2001, 2004), Failmezger (1999, 2000, 2001),
Crapps Law Engineering (2001), Tice Knott
(2000), Woodward (1993), Iwasaki et al. (1991),
Hayes (1990), Mayne Frost (1988), Schmertmann
(1986,1988), Steiner (1994), Leonards (1988),
Lacasse (1986) gt 40 papers at ISC4-Brazil
2012
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Silos on Danube's Bank (Belgrado)
SETTLEMENTS Measured 63 cm DMTpredicted 77
cm (22) (D. Berisavijevic 2013)
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M at Sunshine Skyway Bridge, Tampa Bay Florida
(Schmertmann Asce Civil Engng March 1988)
World record span for cablestayed post-tensioned
concretebox girder concrete construction

• DMT results M ? 200 MPa (?1000 DMT test
  points)
• Laboratory results M ? 50 MPa
• From observed Settlements M ? 240 MPa
• ? DMT good evaluation of constrained modulus

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CAPE HATTERAS LIGHT HOUSE was moved from its
original location to protect it from a receding
coastline. Selected as one of ASCE outstanding
civil engineering achievement 2000
DMTs executed by Law Engineering Allan Tice,
Assistant Vice President "DMT data provided
reliable settlement estimates in the
predominately sandy soils along the path and at
the final destination of the light house.
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Lacasse Lunne (1986) of NGI compare observed vs
DMT-predicted settlements of a silos on sand in
Norway.
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Paul Mayne Prof. at Georgia Tech (2005) compares
observed vs DMT-predicted settlements of a
building in residual soil in Atlanta
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Agreement of settlements not sufficient (might be
compensating errors). Must check moduli at each
depth. M by DMT vs. M back-calculated from LOCAL
vertical strains measured under Treporti
full-scale test embankment (Italy)
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Possible reasons DMT predicts well settlement

1. Wedges deform soil ltlt cones
2. Modulus by mini load test relates better to
   modulus than to penetr. resistance
3. Availability of Stress History parameter Kd.
   (DMT is a 2-parameter test. Fundamental to have
   both Ed and Kd)
4. The soil is loaded at a lower, more appropriate,
   strain level

Stiffnes ? Strength
? Need moduli, not strength !
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Predicting settlements is application 1 of DMT.

• Settlements obviously important, a key section in
  all Geotechnical Reports
• De Vincenzi (2001) More and more, today, the
  factor controlling the design is not the bearing
  capacity, but the necessity of limiting
  settlements

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M can also be predicted as M ? Qc Problem is
? depends on SH (OCR) missing info. Who will
tell us OCR to select the curve and select ? ?
Calibration chamber ? 2.5 to 25
! Jamiolkowski concludes "without Stress
History impossible to select reliable E (or M)
from Qc (Isopt-1, '88, Vol. 1, p.263) Powell
(BRE) The scarce ability to predict modulus is
a well known weakness of CPT.
Qc cannot be used twice (1) as denominator In
E/Qc (2) As parameter to select which curve
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Liquefiability evaluations also in need of info
on Stress History / Aging

• Jamiolkowski et al. (S. Francisco 1985) "Reliable
  predictions of sand liquefiability...requiresome
  new in situ device other than CPT or SPT, more
  sensitive to effects of past STRESS-STRAIN
  HISTORIES
• Leon et al. (ASCE GGE 2006) South Carolina
  sands. Ignoring AGING and evaluating CRR from in
  situ tests insensitive to aging (SPT, CPT, VS)
  underestimated CRR by a large 60
• Salgado et al. (Jnl Asce 1997). OCR increases
  liquefaction resistance CRR, but changes
  negligibly Qcn

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Ignoring Stress History ? omit a primary
parameter. Consequence CRR predicted by CPT
(insensitive to SH) uncertain
Is reason of v. cautious recommendations on
CRR(CPT)
Robertson Wride (1998) ? CRR by CPT adequate
for low-risk projects. For high-risk estimate
CRR by more than one method Youd Idriss 2001
(NCEER Workshops ) ? use 2 or more tests for a
more reliable evaluation of CRR Idriss
Boulanger (2004) ? the allure of relying on a
single approach (e.g. CPT-only) should be
avoided difficult situation considering
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Soil Liquefaction due to EarthquakeLatest
Research
TREND in 2014 onwards (Extract from Geo-Congress,
ASCE 2014 Panel Discussion)Panelists Prof.
Idriss, Prof. Boulanger, Prof. Robertson, Prof.
Cetin, Prof. Finn, Prof. Green, Prof. Stokoe,
Prof. Mayne
No laboratory tests are suitable for liquefaction
estimation. Only suitable field tests MUST be
used. (Terzaghi Lecture-2011)
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Why expect a stricter correlation and a more
accurate CRR if CRR is predicted by Kd
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Estimating CRR using KD Many curves developed in
the last 30 years.Curves are converging to a
narrow stripe
Latest CRR(Kd) Robertson (2012) CRR 93
(0.025 KD)3 0.08
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ESTIMATING CRR
As today 2 CRR estimates, from two separate
one-to-one correlations One estimate from Qc
(Idriss Boulanger 2006) One estimate from Kd
(Robertson 2012)
Recent research (2015) has produced a
combinedCRR-Qcn-Kd correlation. Provides
estimates of CRR based at the same time on Qc
Kd. Note. When SH (Kd) is high, CRR is higher
than predicted by baseline.
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SEAFLOOR DILATOMETER
WATERDEPTH 0 to 100 m (nearshore jobs) PUSH
CAPACITY 7 ton Max test depth is the depth
penetrable with 7 ton push.
Shipped by air(50 Kg)
4 bolts
7 ton ballast (built locally)
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Ballast (iron blocs) are put into container
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Seafloor DMT lifted
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Seafloor DMT lowered in water rods pre-charged
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First Seafloor DMT test 13 June 2014
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Krabbenhoff (Delhi 2014) FEM programs like mob
phones. We just want to talk, not bothered by
complexity of the wires.
In sand (lab no possible) Designer assigns just
the raw data (inequivocallymeasured) e.g. CPT
DMT ?Then FEM gives the solution. Dream for
practitioner.Separates responsibility. Practicion
ers amateurs vs model specialists, profes-sionals
payed for running FEM avoiding pitfalls.
Assign to each region Strength Stress
History Stiffness Soil type Qc
Kd Ed Id
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This idea of FEM possibly oversimplified.But
main message is not FEM, is input (sands)
Moving lab ? in situ OK. But in lab Strength,
Stiffness, Stress History Can we just input
strength (Qc) without Stress History and
Stiffness ? Need multiple (significant) in situ
soil responses). 3 unknowns ? 3 Eqns.
Assign to each region Rupture Stress History
Stiffness Soil type Qc Kd
Ed Id
CPT (1) DMT(2) 3 indep. responses
Same for evaluating liquefaction Can we do with
just Qc, without SH and Stiffness ?
Same for evaluating porosity n f(Qc) does not
work Try n f(Qc, Kd, Ed, Id) -------------------
---------------------
As material index is indicated Id (DMT) or
FR(CPT) ? Id is believed having more solid soil
paternity
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CPT in sand is essentially a one-parameter test
(or 1.5?). Sleeve friction fs not very reliable
Eg. Frost (2001) "Underuse" of fs is related to
common sentiment that fs is unreliable
Repeatibilityv. good v. bad
Lunne (CPT10) had CPT done by 4 different
well-qualified firms. Qc was found repeatable, fs
highly variable. with the present large
variations in fs, impossible to utilize this
measurefor soil parameters
Reason not just instrumental ! fs not so
fundamental. fs highly unstable, being what is
left after an enormous stress reduction in a
situation of arching, with a stiff soil ring
surrounding the sleeve.
Moreover ?h sleeve is transformed into vert
force, via Øsoil-steel
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Sensitivity to ?h of fs and KD
fs highly unstable, being what is left after an
enormous stress reduction
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Mc Connell 2014 fs KD much in common fs KD
both reflect ?h against probe
KD measures ?h directly (i.e. po) fs indirectly,
transforming ?h to Fvertical Thus fs ? an
attenuated KD , weaker and much less stable and
direct. And repeatibility...
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(Robertson Jnl Asce Nov 2009)CPT-DMT inter
correlations
Robertson has formulae for estimating DMT from
CPT. V. dispersed in particular Kd from
Qcn. Expectable no way reconstructing Kd
sensitive to Stress History from insensitive
Qcn. Some researchers study opposite direction
Qc from DMT. Should have success. Should be
easier to predict one parameter from two than
viceversa. DMT a genuine two parameter test. In
that DMT appears a informative test.
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Detecting slip surfaces in clay slopes (look for
Kd ? 2)
Method permits to verify if an OC clay slope
contains active or quiescent slip
surfaces(Totani et al. 1997) Useful to know Old
slip surface may reactivate ! Øresidual
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Validation of DMT-KD method
DOCUMENTED SLIP SURFACE (inclinometers)
DOCUMENTED SLIP SURFACE (inclinometers)
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Kd ? 2 detects both active (moving) and quiescent
slip surfaces
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OTHERAPPLICATIONS
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Dissipation test in cohesive soils. Estimate
coefficient consolidation permeability
From u(t) in a singular highly disturbed point
From a ?mini embankment. Larger volume less
disturbed
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DMT for P-y CURVES for 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)
Figure shows that the 2 methods provide similar
predictions, both in good agreement with observed
full-scale pile behaviour
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DMT for coeff. subgrade reaction Kh for
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
10 cm interval
MDMT acceptance profile (max M always found at
25-26 cm)

• An acceptance MDMT profile was established 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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Website www.marchetti-dmt.it
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CONCLUDING REMARKS (1/7)
Direct push CPT and DMT are increasingly
recognized as fast and convenient tools for
everyday investigations. DMTs KD has the
peculiarity of being sensitive to Stress History,
scarcely felt by other tools. Sensitivity to SH
is fundamental for good predictions of
settlements and of CRR.
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PREDICTING SETTLEMENTS
(2/7)
Countless researchers without Stress History it
is impossible to predict modulus from CPT or
SPT. A large number of comparisons confirm DMT
predicts well settlement. With DMT no ? (2 to 20)
to guess in M? Qc.DMT correlations guide
without subjective choices to M, taking into
account soil type (Id) and Stress History (Kd).
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KD may lead to a more economical design
(3/7)
KD reflects benefits of Stress History on
settlement and liquefaction. SH scarcely sensed
by other tools, which ignore SH ? benefits are
wasted.
Site 2 stronger despite the same Qc
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CPT costs less than DMT.Is CPT therefore
preferable ?
(4/7)
As to pure cost CPT preferable. But info / cost
A CPT investigation costs less, but does not
provide accurate predictions of settlements. Been
State of Art at CPT 2010 Los Angeles CPT can
easily mislead in terms of soil type, strength
and particularly modulus. Robertson (1986)
Prediction of modulus from Qc can be rather poor,
especially for OC soils, with a large potential
error.
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(5/7)
SETTLEMENTS ARE IMPORTANT If we do CPT only
may save in investigation. But if we spend a bit
more doing DMT, predict more accurate
settlements, save in design of foundation, where
the is. Settlements can have important
consequences (piles/ shallow foundations). Import
ant jobs cannot do w/o Accurate Settlements
?more economical design. Info.
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(6/7)
When considering costs into account
With DMT "not many things can go wrong No
electronics, no temperature effects, no vacuum
pump, no saturation-deairing, no glycerin, no
area correction start testing immediately
uncertain data, when present big cost. Designer
looses time choosing parameters, becomes nervous,
increases Fs ? overdesign. DMT easy to run,
short training time ( ? 3 hours) Any operator
gets same results. In remote regions easy to
instruct a local technician. No need to leave a
highly skilled (costly) operator.
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CONCLUDING REMARK (7/7)
Stress History is sometimes considered a gourmet
property, as not directly used in calculations as
c Ø Cu Or of academic interest, to
separate elastic/ plastic behaviour Not so. SH
makes the soil much stronger. It is a substantial
resource. Ignoring SH when present ? wasting
. BUT must be able to distinguish when SH is
present / not. Not easily done by penetration
tests.
-------------------------- TREND today ?
Multiparameter approach better than one-to-one
correlations. Soil has many unknowns need
multiple responses
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3rd International Conference on the Flat
Dilatometer (DMT)
Rome 14th-16th June 2015
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Highlights of the conference include

• Prof. Roger Frank (ISSMGE president) Welcome
  speech
• Prof. J. Schmertmanns dinner talk
• Prof. M. Jamiolkowski use of SDMT in the Zelazny
  Most dam in Poland
• Prof. F. Schnaid use of DMT and SDMT in tailings
  dam

Sofar 120 abstracts from 32 Countries
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Venue is in the town center
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Rome touristic attractions
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St. Peters and Pope Francesco
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• Difficult booking ( Hotel, Flights ) expected in
  June 2015
• June is high season
• High popularity of the Pope
• EXPO 2015 (Milan-Rome)

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ENDThank you