frontespizio flat dilatometer (dmt). seismic dmt
TRANSCRIPT
Silvano Marchetti University of L'Aquila, Italy [email protected]
Flat dilatometer (DMT). Seismic DMT. Frontespizio
CONGRESO INTERNATIONAL FUNDACIONES PROFUNDAS. 2° C.F.P.B. - SANTA CRUZ BOLIVIA 12-15 Mayo 2015
Description, Execution, Applications
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Penetration tests CPT and DMT often used today in many investigations
Fast, economical, reproducible, informative, many data, reduced scatter, cost much less than sampling & testing….
Instrumental accuracy of CPT-DMT is “laboratory-grade” (unlike SPT)
IN LAST DECADES MASSIVE MIGRATION FROM LAB TESTING TO INSITU TESTING
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DMT components Truck mounted penetro-meter pushing the blade
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DMT can also be executed with small inexpensive pushing machines
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DMT can also be executed using a DRILL-RIG
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Test starts from bottom of a borehole
Can push 25 ton
Suitable for sand, silt, clay
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semi-liquid soils
hard soils
water
DMT BLADE
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All mechanical NO ELECTRONICS , no zero drift, no temperature effects Blade is like an electrical switch. Can be off or on.
REDUCTION FORMULAE DMT Report TC16 (2001) of ISSMGE
po, p1 Id, Kd, Ed Soil parameters
(M, Cu …)
HOW DMT WORKS (mechanical)
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Every 20 cm DMT 30 m : ½ day
DMT FORMULAE DMT Report TC16 of ISSMGE 2001
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Theoretical 1993 Finno
Experimental 1980 & 1995
Theoretical 2004 Yu
How the OCR and Cu correlations were derived (clay)
DERIVATION OF Cu CORRELATION Once having OCR Ladd’s SHANSEP 77 SOA Tokyo
(Ladd : best Cu not from TRX UU but from oed OCR Shansep)
Using m ≈ 0.8 (Ladd 1977) and (Cu/σ’v)NC ≈ 0.22 (Mesri 1975)
OCR, Ko, Cu well founded derivation. They use OCR confirmed by theory + SHANSEP
⇒
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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 12
Oed modulus Undr strength
KD =is po normalized to sigma’vo
SEISMIC DILATOMER : DMT with the addition of a seismic module (tube) Vs
SDMT
SDMT is TRUE interval (two sensors) 2 Seismograms - same blow
Operator independent
Much faster & economical than Down hole – X hole
Instant results
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Seismic Dilatometer
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SHEAR WAVE SOURCE
Example seismograms SDMT at Fucino
Delay : automatically calculated using Cross Correlation Repeatability Vs : 1-2 % 16
Automatic Vs interpretation real time
Vs (m/s)
SHEAR WAVE VELOCITY
mechanical DMT Seismic DMT
DMT results REPEATABILITY ≈ 1-2%
GO= ρ Vs2
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US EU
EA
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EUROCODE 7 (2005) ASTM (2007) TC16 (1997) Standards:
Diffusion : DMT used in 70 countries (°) (200 DMT in US)
(°) Algeria, Angola, Argentina, Australia, Austria, Bahrain, Bangladesh, Belgium, Bolivia, Bosnia, Brazil, Bulgaria, Canada, Ctzch Republic, People Republic of China, Chile, Cyprus, Colombia, Costa Rica, Croatia,Denmark, Ecuador, Egypt, United Arabian Emirates,
Estonia, Finland, France, Germany, Greece, Guadalupe, Guatemala, Honduras, Hong Kong, Hungary, India, Indonesia, Iran, Ireland, Israel, Italy, Japan, Korea, Kosova, Kuwait, Lithuania, Malaysia, Netherland, New Zeland, Norway, Oman, Pakistan, Peru, Philippines, Poland,
Portugal, Romania, Russia, Saudi Arabia, Serbia, Singapore, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Taiwan, Thailand, Tunisia, Turkey, United Kingdom, United States of America, Venezuela, Vietnam.
Brazil Australia NZ
Main SDMT applications Settlements prediction Liquefability evaluation Compaction control Detecting slip surfaces in OC clay Laterally loaded piles Diaphragm walls “springs” for design FEM input parameters In situ G-γ decay curves
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But before : focus on Kd sensitive to Stress History. Kd important : not many alternatives to sense SH in situ (sand). Kd is a real protagonist
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•Kd by DMT is important, a real protagonist
•Not many alternatives to sense SH in situ (especially in sand).
•Yet Stress History fundamental for realistic prediction of settlements and liquefaction resistance.
Diagrams compare sensitivity of CPT-DMT to Stress History Lee 2011, Korean Researchers.
Calibration Chamber in sand
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•Kd much more reactive than Qc to Stress History
•Kd distinguish sands with SH / no SH. Qcn ≈ less
CPT DMT
Diagr.1. Effect of SH on Qc Diagr. 2. Effect of SH on Kd
OCR = 1,2,4,8
With OCR
With OCR
That DMT is MORE REACTIVE TO SH CONFIRMED IN THE FIELD, during COMPACTION (apply SH)
Schmertmann (1986) & many others : •COMPACTION produces a % increase of MDMT ≈ twice the % increase of Qc. •MDMT particularly suitable for evidencing the benefits of compaction
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Jendeby 92 : during compaction of a loose sandfill found
M DMT
M DMT Q c Q c No se puede mostrar la imagen en este momento.
No se puede mostrar la imagen en este momento.
BEFORE AFTER
Often in compaction jobs the ratio MDMT/ qc is plotted before-after.
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The MDMT / Qc profiles also permit an evaluation of the achieved OCR increase, using e.g. Monaco et al. Eqn. (2014)
Typically the ratio increases from 5-8 (NC) to 20-25 (OC). The fact that MDMT /Qc increases with compaction, indicates that MDMT increases at a faster rate than Qc, confirming higher sensitivity of DMT to SH.
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Schmertmann 1984 explained the different sensitivity of DMT and CPT to stress history :
"the cone appears to destroy a large part of the modification of the soil structure caused by the overconsolidation and it therefore measures very little of the related increase in modulus.
In contrast the lower strain penetration of the DMT preserves more of the effect of overconsolidation.“
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Qcn reflects essentially Dr (only to minor extent stress history) KD reflects the TOTAL effect Dr plus various stress history effects such as aging, Ko, structure (cementation)
Jamiolkowski (Isopt-1,‘88,1) : “without Stress History, impossible to select reliable E (or M) from Qc”
Yoshimi et al. (1975) “The NC sand specimens were six times more compressible than the prestressed sand, hence it is imperative to have information on stress history to characterize compressibility of a sand
Similar statements : Terzaghi, Leonards, Schmertmann, Robertson etc.
Application #1 DMT : predict settlements (operative modulus)
Sensitivity of Kd to SH important for Settlements
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Accuracy of settlements prediction : confirmed by a large number of good comparisons measured vs DMT-predicted settlements 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)………and > 40 papers at ISC4-2012 ….
by Boussinesq Terzaghi 1-D
zM
SDMT
vDMT ∆
∆=∑−
σ1
Settlement predictions by DMT
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Silos on Danube's Bank (Belgrado)
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SETTLEMENTS Measured 63 cm DMTpredicted 77 cm (+22%)
(D. Berisavijevic 2013)
M at Sunshine Skyway Bridge. Tampa Bay – Florida USA
Modulus M from DMT : M ≈ 200 MPa (≈1000 DMT test points) M from laboratory : M ≈ 50 MPa From obs. Settlements : M ≈ 240 Mpa Conclusion : DMT = good evaluation of constrained modulus M
World record span for cable stayed post-tensioned concrete box girder concrete construction
(Schmertmann – Asce Civil Engng – March 1988)
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Schmertmann 1986 16 CASE HISTORIES. Predicted/Observed ave : 1.18
31 1986 - Proc. In Situ '86 ASCE Spec. Conf. VIP, Blacksburg, p.303
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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Research embankment D=40 m(Venezia) Comparison MDMT vs Mback-calculated from LOCAL vertical strains
measured under center
Sliding Micrometers installed every meter
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SETTLEMENTS Measured 36 cm DMT predicted 29 cm (∆ = 24%)
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 2-parameter test. Fundamental to have both: Ed and Kd) 4.The soil is loaded at a lower, more appropriate, strain level
Possible reasons DMT predicts well settlement
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⇒ Need moduli, not strength ! Stiffnes
≠ Strength
Mayne (2001)
Strain levels imposed by DMT and other in-situ tests
Mayne 2001
As soon as DMT is completed… settlement are calculated
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Various types of foundation
building
viaduct
pile group
SETTLEMENT CALCULATION
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MDMT + 1-D method
zM
SDMT
vDMT ∆
∆=∑−
σ1
Calculation every 20 cm, not because thicker layers are inadequate. It is just more convenient, since Mdmt available in the computer every 20 cm
e.g. for a building possible to select at end of DMT : adopt
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If s = 3cm (or 4 or 5) no piles (ok shallow)
COMPUTER PROGRAM Input load Input Mdmt
Ave load ≈ 10 kPa / floor
Shallow foundation Piles
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”
Liquefiability evaluations also in need of information on Stress History / Aging
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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 (2006) "The allure of relying on a single approach (e.g. CPT - only) should be avoided".
CRR by CPT correlations : some ??
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• 2014 Panel Discussion at Geo-Congress, ASCE Panelists: Prof. Idriss, Prof. Boulanger, Prof. Robertson, Prof. Cetin, Prof. Finn, Prof. Green, Prof. Stokoe, Prof. Mayne
• But already Peck (1979) : it is "manifestly impossible" to obtain a completely undisturbed sample
Latest Research 2014 NO LABORATORY TESTS ARE SUITABLE
FOR LIQUEFACTION ESTIMATION. Only suitable FIELD TESTS MUST be used.
.. difficult situation … lab too is problematic ..
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However these are one-to-one correlations.
Liquefaction Resistance CRR : is today estimated by two separate methods
(°) Robertson 2012 ..progresssively abandon SPT... crude unreliable...
CRR from CPT CRR from DMT
Idriss & Boulanger (2006) marchetti 2015
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Better to estimate CRR based at the same time on Qc and KD
CRR in two Steps (1) Estimate CRR from Qcn using everyday CPT correlations. (2) Then, if Kd is high, increase CRR, if Kd is low, reduce CRR
Get CRR = f(Qc, KD ) (unpublished J. Asce 2015)
2015
input
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If sand has Fine content, Cementation… : adding KD to Qcn , for CRR, may not be sufficient
E.g. cementation can be ductile (toothpaste-like) or fragile (glasslike). Fine Content : possibly effects ≈ as ductile cementation. Clearly too many unknowns. It may be not sufficient to add the KD information to Qcn. Go could possibly help : high Go/ Qc and/or high Go/ MDMT also indicators of cementation. Even modulus ED from DMT could possibly help. A lot additional study necessary ⇒ multi-parameter
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Cemented soils : higher Go/ MDMT and Go/Qc than sedimentary soils (black) (Schnaid 2004, Rocha et al. 2015).
Possible reason of High Vs : cemented contacts of the grains allow a faster transmission
A possibly useful info on cementation
Mayne (2001) Ishihara (2001)
SDMT provides Go (small strain modulus) & Mdmt (working strain modulus). Two points of the G-γ curve. May help select the design G-γ curve. (Mayne & Martin 1999)
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SEAFLOOR DILATOMETER to run DMT from sea bottom
WATERDEPTH up to 100 m PUSH CAPACITY 7 ton Max test depth is the depth penetrable with 7 ton push.
7 ton ballast (built
locally)
Shipped by air
(50 Kg) 4
bolts
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Seafloor DMT lifted
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Seafloor DMT lowered in water : rods pre-charged
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SEAFLOOR DILATOMETER
An alternative “model” of ballast
(Roger Failmezger Apr 2015, Virginia)
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
0 2
10
20
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D
1. SLIDING
K (DMT) 2=
3. RECONSOLIDATION(NC STATE)
4. INSPECT D PROFILEK
2. REMOULDING
Detecting slip surfaces in clay slopes (look for Kd ≈ 2)
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LANDSLIDE "FILIPPONE" (Chieti)
LANDSLIDE "CAVE VECCHIE" (S. Barbara)
DOCUMENTED SLIP SURFACE
DOCUMENTED SLIP SURFACE (inclinometers)
Validation of DMT-KD method
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Kd ≈ 2
Kd ≈ 2
The practitioner’s Dream
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Geotechnician just assign the elementary in situ data raw data (inequivocally measured)
The 3 independent parameters (if CPT & DMT) are Qc Kd Ed
Model specialist (able to avoid pitfalls) prepare FEM
Assign to each mesh element: Qc Kd Ed
Website: www.marchetti-dmt.it
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CONCLUDING REMARKS (1/5)
More and more CPT & DMT replace laboratory for everyday jobs.
Sensitivity of DMT’s Kd to Stress History is important. There are not many Stress History tools.
Stress History is indispensable for good predictions of settlements and liquefaction.
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PREDICTING SETTLEMENTS
A large number of comparisons confirm that DMT predicts well settlement.
Good estimates of settlements permit a better and more economical design. E.g. entity of settlement helps decide : piles or shallow foundations ? Info = $
(2/5)
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KD reflects benefits of Stress History on settlement and liquefaction. SH scarcely sensed by other tools, which ignore SH benefits are wasted.
(3/5) KD leads to a more economical design
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Two sites same Qc , different KD : Site 2 much “stronger”
In Site 2 Stiffness & CRR can be much higher
The best estimates of liquefaction resistance CRR are obtained using at same time Qcn -CPT and KD - DMT.
CRR = f(Qcn, KD )
In general : Multiparameter better than one-to-one correlations. Soil has many unknowns : need multiple responses
(4/5) ESTIMATING CRR (liquefaction)
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No electronics, no saturation, no deairing, no area correction… V. easy to run, short training time (≈ 3 hrs) Highly repeatable. Any operator gets same results No need highly skilled workers
(5/5)
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DMT is very simple
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 62
Conference venue in the town center www.dmt15.com
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Rome touristic attractions www.dmt15.com
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St. Peters and Pope Francesco www.dmt15.com
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END Thank you
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Slides for possible discussion
Sensitivity to σh of fs and KD
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fs highly unstable, being what is left after an enormous stress
reduction CIRCULAR
PROBE FLAT
PROBE
Note : fs & KD much in common both reflect σh against probe
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KD measures σh directly (i.e. po) fs indirectly, transforming σh to Fvertical
Thus fs ≈ an attenuated KD , weaker and much less stable and direct. And repeatibility...
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KD evidences Stress History crusts nearly unfelt by VS . VS ≈ insensitive to SH
suggests lesser ability of VS to profile SH, hence liquefiability & CRR
MATERIAL INDEX
CONSTRAINED MODULUS
UNDRAINED SHEAR STRENGTH
HORIZONTAL STRESS INDEX
SHEAR WAVE VELOCITY
CLAY SILT SAND
Vs (m/s) KD
KD crust
Catania Sand
crust? “lazy”
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Comparisons Vs measured by SDMT with Vs estimated by mechanical DMT using the previous diagram (L’Aquila)
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Amoroso (2013) compares correlations Vs from DMT and Vs from DMT. Concludes : Vs estimates from DMT are closer (a two parameter test)
Clay. Initial idea (1980) : investigate Ed-Eu. Problem: Eu, lab too dispersed, impossible set up correlations. Hence Ed-M. Link Ed-M presumably weaker, but at least can be tested. NOTE. Ed-M must be a complex function of many variables, among them the Skempton p. p. parameters A & B and anisotropy (Ed horizontal, M vertical), which in turn depend on soil type (~represented by Id) and on OCR (~ represented by Kd) ⇒ some basis to expect at least some degree of correlation Ed -M using Id and Kd as parameters. Final word : real world observation. Large number case histories favourable comparisons measured vs DMT-predicted settlements - or Mdmt-Mreference. Lambe et al (Jnl ASCE March 1977 “Foundation Performance of Tower of Pisa” p.246) : “Drained moduli of saturated clays are typically about one-third to one-fourth the undrained values”. Hence a broad connection drained-undrained stiffness already invoked in the past.
How derive M (drained) from Ed (undrained) ???
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Legitimate to use M = constant if ∆σ'v large ?
M = Eoed=1/mv= ∆σ'v/∆εv (at σ'vo)
Except highly structured clays (sharp break), M variation across pc is moderate
Error in assuming M ~ constant : often acceptable (other methods for M : not infrequent error factors 2-5)
• •
Ed must be corrected to obtain M
M=Rm Ed with Rm=f(Kd,Id)
Don’t use Ed as Young’s Modulus
Rm has various correction tasks
Distortion Horiz to vertical Drained Undrained
Once Ed is converted to M, Young’s E’ ≈ 0.8-0.9 M (elasticity)
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