frontespizio flat dilatometer (dmt). seismic dmt

Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it

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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