1. Recent developments Flat dilatometer (DMT) & Seismic DMT (SDMT)
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 1

2. DMT results KD = 2  NC clay ID  M Cu   KD  soil type
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 ’vo . Treat as if obtained by oed

3. Seismic Dilatometer

4. 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)

5. 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) 5

6. Lee 2011, Eng. Geology  30 CC in sand
Diagrams compare sensitivity of CPT-DMT to Stress History
Lee 2011, Eng. Geology  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.

7. (3/7)
Two sites : same Qc , but different KD. Site 2 much “stronger” (higher SH)  settlement and liquefaction.

8. Many formulae OCR-Qc proposed, even relatively complex.
Given the scarce sensitivity of Qc to OCR, is it possible to estimate OCR from CPT ?
Effect of OCR on Qc
Many formulae OCR-Qc proposed, even relatively complex.
CPT
No mathematics, plaxis, statistics, FEM… can replace low degree of correlation

9. 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 %
qD %

10. that DMT MORE REACTIVE TO STRESS HISTORY confirmed in the field …Q c
BEFORE
AFTER
Jendeby 92
Measured in a loose sandfill Qc & Mdmt before-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)

11. Can estimate OCR based on ratio =M/Qc
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
(Monaco et al. Asce Jan 2014)
If  = M/Qc  5-12  NC
If  = M/Qc   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

12. MDMT before-after compaction
COMPACTION ( applying SH) produces a MDMT% increase  twice the Qc% increase
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".
MDMT before-after compaction
bar
…hence Mdmt effective in reflecting benefits of compaction
Resonant vibro-compaction technique
Van Impe, De Cock, Massarsch, Mengé, New Delhi (1994)

13. (Multi parameter – both DMT)
….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)

14. Settlement predictions by DMT In general classic Terzaghi 1-D (even in 3-D (Poulos : modulus, not formula !! )
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

15. Silos on Danube's Bank (Belgrado)
SETTLEMENTS
Measured 63 cm DMTpredicted 77 cm (+22%)
(D. Berisavijevic 2013)

16. 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

17. 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”.

18. Lacasse & Lunne (1986) of NGI compare observed vs DMT-predicted settlements of a silos on sand in Norway.

19. Paul Mayne Prof. at Georgia Tech (2005) compares observed vs DMT-predicted settlements of a building in residual soil in Atlanta

20. Sliding Micrometers installed every meter
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

21. Possible reasons DMT predicts well settlement
Wedges deform soil << cones
Modulus by mini load test relates better to modulus than to penetr. resistance
Availability of Stress History parameter Kd. (DMT is a 2- parameter test. Fundamental to have both: Ed and Kd)
The soil is loaded at a lower, more appropriate, strain level
Stiffnes 
Strength
 Need moduli, not strength !

22. 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”

23. 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”.
OCR???
Qc cannot be used twice : (1) as denominator
In E/Qc (2) As parameter to select which curve

24. 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”

25. Ignoring Stress History  omit a primary parameter
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…

26. 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)

27. Why expect a stricter correlation and a more accurate CRR if CRR is predicted by Kd

28. 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)

29. 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.

30. 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)

31. Ballast (iron blocs) are put into container

32. Seafloor DMT lifted

33. Seafloor DMT lowered in water : rods pre-charged

34. First Seafloor DMT test: 13 June 2014

35. Krabbenhoff (Delhi 2014) : FEM programs like mob phones
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.
Dream for practitioner. Separates responsibility.
Practicioners 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

36. CPT (1) & DMT(2) : 3 indep. responses
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
Assign to each region :
Rupture Stress History Stiffness Soil type
Qc Kd Ed Id
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

37. Repeatibility v. good v. bad
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

38. Sensitivity to h of fs and KD
fs highly unstable, being what is left after an enormous stress reduction
CIRCULAR
PROBE
FLAT 38

39. fs & KD both reflect h against probe
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... 39

40. (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.

41. 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

42. Validation of DMT-KD method
LANDSLIDE "FILIPPONE" (Chieti)
DOCUMENTED SLIP SURFACE
(inclinometers)
LANDSLIDE "CAVE VECCHIE" (S. Barbara)
DOCUMENTED SLIP SURFACE
(inclinometers)
active: Kd=2
quiescent: Kd=2

43. Kd  2 detects both active (moving) and quiescent slip surfaces
active: Kd=2
quiescent: Kd=2
active: Kd=2
quiescent: Kd=2

44. OTHER APPLICATIONS

45. Totani, Calabrese, Monaco (1998)
Dissipation test in cohesive soils. Estimate coefficient consolidation & permeability
From u(t) in a singular highly disturbed point
Time (min)
σ h (kPa)
Totani, Calabrese, Monaco (1998)
From a mini embankment. Larger volume less disturbed

46. LATERALLY LOADED PILES
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

47. 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

48. Subgrade compaction control
Bangladesh Subgrade Compaction Case History
90 km Road Rehabilitation Project
10 cm interval
MDMT acceptance profile
(max M always found at 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)

49. Website: www.marchetti-dmt.it

50. 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.

51. PREDICTING SETTLEMENTS
(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).

52. KD may lead to a more economical design
(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

53. “CPT costs less than DMT. Is CPT therefore preferable ?”
(4/7)
“CPT costs less than DMT. Is CPT therefore preferable ?”
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.

54. SETTLEMENTS ARE IMPORTANT
(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=$.

55. When considering costs : into account
(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.

56. 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

57. 3rd International Conference on the Flat Dilatometer (DMT)
Rome 14th-16th June 2015

58. Highlights of the conference include
Highlights of the conference include
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

59. Venue is in the town center
Venue is in the town center

60. Rome touristic attractions
Rome touristic attractions

61. St. Peters and Pope Francesco
St. Peters and Pope Francesco

62. Difficult booking ( Hotel, Flights ) expected in June 2015:
Difficult booking ( Hotel, Flights ) expected in June 2015:
June is high season
High popularity of the Pope
EXPO 2015 (Milan-Rome)