Transcript DMT

University of PISA – DESTEK
Oct. 9 th 2014
Workshop on Penetration Testing
Frontespizio
Flat dilatometer (DMT) & Seismic DMT (SDMT)
Recent developments
Silvano Marchetti
University of L'Aquila, Italy
[email protected]
1
DMT results
or Stress
History Index
KD = 2  NC clay
 amplified Ko
ID

soil type
(clay, silt, sand)
M
Cu


common use
1-D modulus @ ’vo .
Treat as if obtained by oed
KD

shape similar to OCR
helps understand
history of deposit
2
Seismic
Dilatometer
3
SDMT results
repeatability ≈ 1-2%
SHEAR WAVE
VELOCITY
GO= ρ Vs2
Vs (m/s)
mechanical DMT
Seismic DMT
(Recommended graphical format – no just po p1)
4
Main SDMT applications (details  papers)
Settlements of shallow foundations
Liquefability evaluation
Have in common :
need of Stress
History (by Kd)
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)
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Diagrams compare sensitivity of CPT-DMT
Lee 2011, Eng. Geology
to Stress History
 30 CC in sand
Box 1. Effect of SH on Qc
Box 2. Effect of SH on Kd
OCR = 1,2,4,8
CPT
DMT
•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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(3/7)
Two sites : same Qc , but different KD.
Site 2 much “stronger” (higher SH)
 settlement and liquefaction.
7
Given the scarce sensitivity of Qc to OCR,
is it possible to estimate OCR from CPT ?
Effect of OCR on Qc
CPT
Many formulae
OCR-Qc proposed,
even relatively
complex.
No mathematics, plaxis, statistics, FEM…
can replace low degree of correlation
8
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
CC TEST N. 216 IN TICINO SAND
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 & Mdmt
before-after compaction
BEFORE
Qc
AFTER
MDMT
MDMT
Qc
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)
10
Estimate OCR in sand.
Qc or Mdmt alone : not sufficient (multiparameter).
Need both, one sensitive to SH, other less sensitive
Can estimate OCR based on
ratio =M/Qc
If  = M/Qc  5-12  NC
(Monaco et al.
Asce Jan 2014)
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 :
Ko=Ko,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.
bar
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".
…hence Mdmt effective in reflecting
benefits of compaction
Resonant vibro-compaction technique
Van Impe, De Cock, Massarsch,
Mengé, New Delhi (1994)
12
….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
Jamiolkowski (Isopt-1,‘88,1) : “without Stress History, impossible
to select reliable E (or M) from Qc”
(also Terzaghi, Leonards, Schmertmann…)
Yoshimi (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 DMT
In general classic Terzaghi 1-D (even in 3-D
(Poulos : modulus, not formula !! )
S 1  DMT 
 v
M
z
DMT
by Boussinesq
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)……………
> 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)
15
M at Sunshine Skyway Bridge,
Tampa Bay – Florida
(Schmertmann – Asce Civil Engng – March 1988)
World record span for cable
stayed post-tensioned concrete
box 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”.
17
Lacasse & Lunne (1986) of NGI compare observed vs
DMT-predicted settlements of a silos on sand in Norway.
18
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)
Sliding Micrometers
installed every meter
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Possible reasons DMT predicts well settlement
1.Wedges deform soil << 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 2parameter 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 !
21
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”
22
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 : 
OCR???
= 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
23
Liquefiability evaluations also in need of
info on Stress History / Aging
•Jamiolkowski et al. (S. Francisco 1985) "Reliable predictions
of sand liquefiability...require…some 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…
25
Soil Liquefaction due to Earthquake
Latest 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
27
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 combined
CRR-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)
Shipped
by air
(50 Kg)
PUSH CAPACITY 7 ton
Max test depth is the depth
penetrable with 7 ton push.
4
bolts
7 ton
ballast
(built
locally)
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Ballast (iron blocs) are put into container
BALLAST
(IRON BLOCS)
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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 (inequivocally
measured) e.g. CPT & DMT 
Then FEM gives the solution.
Assign to each region :
Strength Stress History Stiffness Soil type
Qc
Kd
Ed
Id
Dream for practitioner.
Separates responsibility.
Practicioners amateurs vs
model specialists, professionals payed for running FEM
avoiding pitfalls.
35
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.
CPT (1) & DMT(2) : 3 indep. responses
Same for evaluating liquefaction
Can we do with just Qc, without SH and
Stiffness ?
Assign to each region :
Rupture
Qc
Stress History Stiffness Soil type
Kd
Ed
Id
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
36
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…
Repeatibility
v. 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
measure…for 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
37
Sensitivity to h of fs and KD
fs highly unstable,
being what is left after
an enormous stress
reduction
CIRCULAR
PROBE
FLAT
PROBE
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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)
1 . S L ID IN G
3 . R E C O N S O L ID A T IO N
(N C S T A T E )
2 . R E M O U L D IN G
4 . IN S P E C T K D P R O F IL E
0 2
10
20
K D (D M T ) 2
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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
LANDSLIDE "FILIPPONE" (Chieti)
DOCUMENTED
SLIP SURFACE
(inclinometers)
LANDSLIDE "CAVE VECCHIE" (S. Barbara)
DOCUMENTED
SLIP SURFACE
(inclinometers)
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Kd2 detects both active (moving)
and quiescent slip surfaces
active: Kd=2
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OTHER
APPLICATIONS
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Dissipation test in cohesive soils. Estimate
coefficient consolidation & permeability
σ h (kPa)
From u(t) in a
singular highly
disturbed point
From a mini
embankment.
Larger volume
less disturbed
Totani, Calabrese, Monaco (1998)
Time (min)
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DMT for P-y CURVES for
LATERALLY LOADED PILES
Robertson et al. (1987)
Marchetti et al. (1991)
M o rta io lo (Ita ly)
N C s o ft c la y
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)
g .l.
s
H
L
 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)
48
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.
DMT’s 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.
50
(2/7)
PREDICTING SETTLEMENTS
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).
51
(3/7)
KD may lead to a more economical design
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
52
“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.
53
(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…).
Important jobs cannot do w/o Accurate Settlements 
more economical design. Info=$.
54
(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.
55
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 oneto-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
www.dmt15.com
 Prof. Roger Frank (ISSMGE president) Welcome
speech
 Prof. J. Schmertmann’s 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
www.dmt15.com
59
Rome touristic attractions
www.dmt15.com
60
St. Peters and Pope Francesco
www.dmt15.com
61
www.dmt15.com
Difficult booking ( Hotel, Flights )
expected in June 2015:
• June is high season
• High popularity of the Pope
• EXPO 2015 (Milan-Rome)
62
END
Thank you
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