1. Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it Flat dilatometer (DMT). Seismic DMT. 1 Frontespizio Australian Geomechanics Society July 2014 DMT / SDMT Workshop Main applications and recent developments

2. In the last decades : massive migration from lab testing to insitu testing. Often today in situ testing is the major part of an investigation. In situ : Fast, economical, reproducible, informative, many data, reduced scatter, cost much less than sampling & testing…. True in SAND : Recovering samples difficult (tailings). Field tests are the state-of-practice. Caution : lab remains fundamental for research FROM LAB TO INSITU TESTING 2

3. Collection of the many existing in situ tools… Mayne et al. SOA ICSMGE Egypt 2009 Mayne : …direct push CPT DMT increasingly recognized as fast & convenient tools for everyday practice. This presentation : DMT SDMT 3

4. DMT components DMT pushed by a truck mounted penetrometer 4

5. In general DMT executed with same rigs for pushing CPT. But many more insertion methods : no need 2 cm/sec speed. Unlike CPT, push just for advancing, is not the test.. comes later. DMT can also be executed with small inexpensive pushing machines 5

6. ( S)DMT can be pushed by DRILL-RIG e.g. with the “Torpedo method” 6 Penetrometer quickest Blade can also be driven by SPT hammer (quasi static preferable) Assemble a Torpedo :  3 ms rods + blade Do 3m of DMT starting from bottomhole Extract blade, clean hole, restart DMT from bottom Advantage : Method permits to overcome obstacles

7. 7 Example of torpedo 3 m long Test starts from bottom of the hole

8. Nearly liquid soils : highly accurate due to the “balance of zero” method Hard soils (e.g. Cu 800 kPa), or weak rock: OK but need strong push - heavy truck Robust. Safe push 25 ton Suitable for penetrable soils (sand, silt, clay) 8 LIMITS Clays Cu=2-4 kPa up to 1 MPa (marl) Moduli M=0.5 to 400 Mpa

9. DMT BLADE Retaining Ring Membrane Sensing disk Sensing disk. Electrically insulated Blade is like an electrical switch, can be off or on. NO ELECTRONICS  no zero drift, no temperature effects. Nothing that the operator can regulate, adjust, manipulate 9

10.    p o, p 1  Id, Kd, Ed  Common soil parameters (M, Cu …) HOW DMT WORKS (mechanical) REDUCTION FORMULAE  DMT Rep. TC16 (2001) of ISSMGE 10 Material index Stress History Index Stiffness

11. DMT FORMULAE DMT Report TC16 of ISSMGE 2001 11

12. DMT results K D = 2  NC clay  amplified Ko IDID M Cu  KDKD soil type (clay, silt, sand) common use shape similar to OCR helps understand history of deposit or Stress History Index 12 1-D modulus @  ’ vo. Treat as if obtained by oed

13. K D = σ’vσ’v (p 0 - u 0 ) p0p0 DMTDMT K D an “amplified K 0 ” due to penetration. Will see : K D reflects“stress history” Very roughly Kd  4 Ko E.g. in NC : Ko  0.5 and Kd  2 K D important Definition of K D : is similar to Ko 13

14. SEISMIC DILATOMER : DMT with the addition of a seismic module (tube)  Vs 14 Vs from delay of pulse 2 receivers vs 1 receiver: Same blow Trigger not critical No mitical 1st arrival Delay well conditioned Amplified + digitiz at depth SDMT Operator independent Interpreter independent Much faster & economical than Down hole – X hole No hole/ no samples, no grouting pipes ( supervision for voids? Stop for cement..) Same day X correlation

15. Seismic Dilatometer 15

16. 16

17. Example seismograms SDMT at Fucino Delay : from Cross Correlation Repeatability Vs : 1-2 % 17

18. Vs (m/s) SHEAR WAVE VELOCITY mechanical DMT Seismic DMT SDMT results repeatability ≈ 1-2% 18 G O = ρ Vs 2 Provides considerable information on the site

19. CPT & DMT : a mutation vs SPT. Instrumental accuracy & resolution equal to lab 19 LAB Advantage : able to measure "pure" soil properties, e.g. “E “(in principle..) Disadvantage : test disturbed samples (at least in sand). CPT and DMT Advantage : test the in-situ-soil (..besides fast..many data.. economical) Disadvantage : cannot measure "pure" soil properties, only "mixed responses" (mix of say strength, stiffness, stress history…). Hence in situ necessity multiparameter investigation. (E.g. : For Ko and Ø : need both Kd and Qc. For M, need both Ed and Kd). SOIL : Strength, stiffness, Stress History : 3 unknowns... Impossible get 3 unknowns from just 1 Eq.

20. Method works because the two travelpaths in sand include a short length in the sand backfill, similar for both receivers – cancel out 20 The Vs profile can be obtained by SDMT even in non penetrable soils : executed in a sandfilled borehole The sand travelpath is similar Shows validation by two tests

21. US EU EA 2006 21 EUROCODE 7 (2005) ASTM (2007) TC16 (1997) Standards : Diffusion : DMT used in 70 countries.  500 DMTs. Majority in US  200

22. 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) 22

23. Diagrams compare sensitivity of CPT & DMT to Stress History Lee 2011, Eng. Geology  30 CC in sand 23 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. DMT CPT Box 1. Effect of SH on Qc Box 2. Effect of SH on Kd OCR = 1 2 4 8

24. Given the scarce sensitivity of Qc to OCR, is it possible to estimate OCR from CPT ? Effect of OCR on Qc 24 Many formulae OCR-Qc proposed, even relatively complex. OCR =  p ’ /  vo ’ Mathematics (plaxis, statistics…) cannot replace lack of correlation Mayne at CPT’14

25. PRESTRAINING CYCLES simulate AGING (grain slippage) CC TEST N. 216 IN TICINO SAND They applied prestraining cycles in calibration chamber. Found : K D (DMT) 3 to 7 times more sensitive to AGING than penetration resistance K D + 20 % q D + 3 % Similarly higher sensitivity of Kd to SH & aging observed by Jamiolkowski (ISC'98 Atlanta) 25

26. that DMT MORE REACTIVE TO STRESS HISTORY confirmed in the field … M DMT M Q c Q c BEFOREAFTER Jendeby 92 Had a loose sandfill and measured Qc & Mdmt before-after compaction NC : M/Qc  5-12 OC : M/Qc  12-24  OCR in sand  K o =K o,nc (OCR) m 26 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 indirect target and Dr correlations v. uncertain)

27. Estimate OCR = f(Qc/Mdmt) = f(  ) Qc or Mdmt alone : insufficient (multiparameter). SAND NC :  = M/Qc  5-12 OC :  = M/Qc  12-24 27 ( from OCR  K o =K o,nc (OCR) m ) Treporti embankment (Monaco et al. 2014) Need both, one sensitive to SH, other insensitive. Just one not enough. Mdmt high could be due to high Dr, rather than to SH.

28. M DMT before-after compaction Resonant vibro-compaction technique Van Impe, De Cock, Massarsch, Mengé, New Delhi (1994) COMPACTION (  impose SH) produces a M DMT % 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". bar …hence Mdmt v. effective in reflecting benefits of compaction 28

29. 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) M DMT = E D x R m (Kd, Id) (combines E D with Stress History) ….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 29

30. 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 by Boussinesq Settlement predictions by DMT In general classic Terzaghi 1-D (even in 3-D (Poulos : modulus, not formula !! ) 30

31. SETTLEMENT CALCULATION 31 M DMT + 1-D method Calculation every 20 cm, not because thicker layers are inadequate. It is just more convenient, since Mdmt available in the computer every 20 cm

32. 32

33. Silos on Danube's Bank (Belgrado) 33 SETTLEMENTS Measured 63 cm DMTpredicted 77 cm (+22%) (D. Berisavijevic 2013)

34. M at Sunshine Skyway Bridge, Tampa Bay – Florida 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 World record span for cable stayed post-tensioned concrete box girder concrete construction ( Schmertmann – Asce Civil Engng – March 1988) 34

35. Schmertmann 1986 16 CASE HISTORIES. Predicted/Observed ave : 1.18 35 1986 - Proc. In Situ '86 ASCE Spec. Conf. VIP, Blacksburg, p.303

36. 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 36 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”.

37. Lacasse & Lunne (1986) of NGI compare observed vs DMT-predicted settlements of a silos on sand in Norway. 37

38. Paul Mayne Prof. at Georgia Tech (2005) compares observed vs DMT-predicted settlements of a building in residual soil in Atlanta 38

39. Agreement of settlements not sufficient (might be compensating errors). Must check moduli. M by DMT vs. M back-calculated from LOCAL vertical strains measured under Treporti full-scale test embankment (Italy) Sliding Micrometers installed every meter 39

40. 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 40  Need moduli, not strength ! Stiffnes  Strength

41. Predicting settlements is application # 1 of DMT. 41 Settlements are 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”

42. OCR??? 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”. 42 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  ? Qc cannot be used twice : (1) as denominator In E/Qc (2) As parameter to select which curve

43. 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” Liquefiability evaluations also in need of info on Stress History / Aging 43

44. 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 … not easy considering that “No lab tests suitable for liquefaction estimation. Only field tests MUST be used (Terzaghi Lecture 2011) “ Is reason of v. cautious recommendations on CRR(CPT) : Ignoring Stress History  omit a primary parameter. Consequence : CRR predicted by CPT (insensitive to SH) uncertain 44

45. Why expect a stricter correlation and a more accurate CRR if CRR is predicted by Kd 45

46. Youd & Idriss 2001 OK DMT is more sensitive to SH. But there is much more experience for CPT. Therefore Tsai translated the large CPT experimental base to DMT. q c1 = f(Kd) Tsai (2009) ran side-by-side CPT-DMT. From profiles-CPT next to profiles-DMT he had pairs (Qc1, Kd)  Qc1=f(Kd) Replace q c1 with Kd Thus : obtain CRR-Kd 46

47. A notable feature of the Qc-Kd correlation (used for the translation) is the high scatter. At first sight one might consider doubtful the resulting Kd-CRR correlation, being the translation based on the highly dispersed Qc1-Kd correlation. Not so. The scatter is just natural, is the consequence of Kd reacting to factors unfelt by Qc1. If there was no scatter would mean Qc1 and Kd contain the same information, which is not the case, as Kd is reactive to SH, Qc1 is not. Scatter of the Qc1-Kd relation 47

48. Consider two sites identical except one has had SH. Qcn is the same, but Kd is higher in site with SH. Eg we might find the same Qcn= 90 in sands having : Kd=2.4 (  liq  CRR=0.12) or Kd=5 (no liq  CRR=0.22) In conclusion while Qcn=90 predicts CRR = 0.15, CRR could in reality be 0.12-0.22 (factor 2). Note : 0.12-0.22 are both right ! explains historical controversies by researchers. 48

49. 49 2013: CRR=0.0038K D 3 -0.0176K D 2 +0.0532K D +0.0264 Assumed as most likely (intermediate : Monaco 2005 & Robertson 2012) Estimating CRR using Kd Many curves developed in the last 30 years. Curves are converging to a narrow central band

50. 50 Recent research : CPT-clean-sand curve not unique but comprised in a wide band f(Stress History) For a given Qcn, can have v.different CRR depending on SH. SH can even double the resistance to liquefaction The CPT “consensus” curve can be v. uneconomical in prestressed/ aged sands. Coincides with Lewis 1999 : “using CPT current correlations in old/ aged sands will, at best, result in v. conservative and uneconomical design, at worst in v. costly remedial measures or cancellation of a project” Preferred format. Rather than one-to-one (CRR to Qcn) or (CRR to Kd), better multiparameter. Uses both Qcn & Kd.

51. Liquefaction (spontaneous, earthq. induced etc.). Complex, involves many soil properties 51 [Also : Qc  Dr Kd  (Dr+SH) : need both Qc & Kd to separate] Too many unknowns. One condition (Qc alone) : not enough. Need multiparameter CRR = f (Qcn, Kd, Ed, Id, Go/Mdmt). East Germany 1000s hect unstable, sudden collapse “butterfly triggered”. Qc (?). Compact (?) rigs may sink, vibrations >> than earthquake. Condition C stable any Earthquake. But - if there is cementation (or SH) - can A be stable ? Can we rely on cementation (SH)? If Cement. Fragile : destroyed by strong Earthquake (partly also by direct-push tests). Unreflected by  Kd. Reflected by high Vs (high Go/M). If Cement. Ductile : not destroyed, reflected by a  Kd

52. Liquefaction : SDMT 2 independent estimates of CRR 52 Light earthquakes CRR from Vs SDMT Andrus and Stokoe 2000 Monaco (2007) "Evaluating Liquefaction Potential by Seismic Dilatometer (SDMT) accounting for Aging/Stress History" 4th Int. Conf. Earthquake Geotechn. Eng. - Thessaloniki Strong earthquakes CRR from Kd DMT Monaco 2005 VSVS KDKD CRR Cyclic Resistance Ratio for Seed & Idriss (1971) simplified procedure

53. Jamiolkowski 1992 Soils & Foundations Sometimes the two independent CRR estimates (from Kd from Vs) are different. We consider more reliable CRR from Kd Vs insensitive to Stress History : Diagram shows Vs measured on sand specimens in the calibration chamber in loading / unloading (  same) Waves produce strains too small to initiate trend to dilate/ contract (essence of liquefaction) 53

54. K D evidences Stress History crusts nearly unfelt by V S. V S  insensitive to SH suggests lesser ability of V S 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)KDKD K D crust Catania Sand crust? “lazy” 54

55. BARCELONA AIRPORT 55

56. Mayne (2001) Ishihara (2001) STIFFNESS DEGRADATION WITH STRAIN 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) More info in : - Marchetti et al (2008) in Schmertmann Volume - Lehane & Fahey (2004) Porto ISC-2 – non linear settlement analysis from in situ tests 56

57. SEAFLOOR DILATOMETER WATERDEPTH 0 to 100 m (nearshore jobs) 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 57

58. Ballast (iron blocs) are put into container BALLAST (IRON BLOCS) 58

59. Seafloor DMT lifted 59

60. Seafloor DMT lowered in water : rods pre-charged 60

61. First Seafloor DMT test: 13 June 2014 61

62. INPUT PARAMETERS FOR PLAXIS (Hard Soil model “HS” - basic input E 50 ref ) 1. Schanz : quartz sand E 50 ref =15 to 75 MPa (loose to very dense sand). In those sands M DMT also in above range (15-75 MPa). Hence as 1st approx may adopt E 50 ref  M DMT Sometimes FEM parameters are checked by executing load tests. Predicting settlement by DMT may  replace (costly) load test. Assume e.g. a uniformely loaded circular area. Do DMT and, using Mdmt, predict settlements. Then predict settlements using the assumed FEM parameters. Verify agreement. Some regulations impose load tests if designer wants to assume  >3 in M=  Qc. This $ could be saved. A DMT settlement calculation may serve as a “virtual load test”. 62

63. Krabbenhoff (Delhi 2014) : FEM programs as mob phones. We just want to talk, not bothered by complexity of the wires. 63 Sand. Since no lab, Designer just assigns the raw data (inequivocally measured), e.g. from CPT & DMT. Then FEM gives the solution. Dream for practitioner Separates responsibility. Practicioners are amateurs vs model specialists, professionals payed just for running FEM avoiding pitfalls. Assign to each region : Strength Stress History Stiffness Soil type Qc Kd Ed Id

64. This idea of FEM possibly oversimplified. But main message is not FEM, is input (sands) 64 Same for evaluating liquefaction Can we do with just Qc, without SH and Stiffness ? Assign to each region : Rupture Stress History Stiffness Soil type Qc Kd Ed Id As material index use : Id (DMT) or FR(CPT) ? Id is believed having more solid soil paternity In absence of lab  in situ parameters. Can we just input strength (Qc) without Stress History and Stiffness ? Need multiple “bricks” (significant soil responses) to triangulate. Same for evaluating porosity n= f(Qc) does not work Try n= f(Qc, Kd, Ed, Id) ----------------------------------------

65. CPT in sand is essentially a one-parameter test (or 1.5?). Sleeve friction f s not very reliable 65 Eg. Frost (2001) "Underuse" of fs is related to common sentiment that fs is unreliable… Reason not just instrumental ! f s not so “fundamental”. f s highly unstable, being what is left after an enormous stress reduction – in a situation of arching, with a stiff soil ring surrounding the sleeve. 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” Repeatibility v. good v. bad Moreover :  h sleeve is transformed into vert force, via Ø soil-steel

66. Sensitivity to  h of f s and K D 66 Note. f s, CPT and K D, DMT are both responses reflecting  h against the probe. K D directly via p o. f s indirectly, transforming horiz. stress to vertical. Thus f s appears an attenuated K D, weaker and much less stable and direct. Circular probe Flat probe 66

67. (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. 67

68. 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 Detecting slip surfaces in clay slopes (look for Kd  2) 68 Kd=2 is a number ! not just a weak zone

69. LANDSLIDE "FILIPPONE" (Chieti) LANDSLIDE "CAVE VECCHIE" (S. Barbara) DOCUMENTED SLIP SURFACE (inclinometers) DOCUMENTED SLIP SURFACE (inclinometers) Validation of DMT-K D method 69 active: Kd=2 quiescent: Kd=2

70. 70 active: Kd=2 quiescent: Kd=2 active: Kd=2 quiescent: Kd=2 Kd  2 detects both active (moving) and quiescent slip surfaces

71. No point today. Better to measure Vs directly However :May provide rough Vs in previous sites If Kd was not available, impossible to predict Go from just one parameter. Need at least two parameters. 71 Diagram permits to estimate Vs (Go) from just mechanical-DMT data i.e. Vs = f(Id Kd Mdmt) Di agram is result of 34 SDMT sites various soils & geography.

72. Comparisons V s measured by SDMT with V s estimated by mechanical DMT using the previous diagram (L’Aquila) 72 Amoroso (2013) compares correlations for approximate estimates of Vs from DMT/CPT. Concludes : Vs estimates based on DMT are closer (a two parameter test)

73. OTHER APPLICATIONS 73

74. Dissipation test in cohesive soils. Estimate coefficient consolidation & permeability 74 Time (min) σ h (kPa) Totani, Calabrese, Monaco (1998) From u(t) in a singular highly disturbed point From a  mini embankment. Larger volume less disturbed

75. 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 75

76. DMT for coeff. subgrade reaction K h for DIAPHRAGM WALLS Monaco & Marchetti (2004 – ISC'2 Porto)  Tentative correlation for deriving the coefficient of subgrade reaction K h for design of multi-propped diaphragm walls from M DMT  Indications on how to select input moduli for FEM analyses (PLAXIS Hardening Soil model) based on M DMT 76

77. Subgrade compaction control M DMT acceptance profile (max M always found at 25-26 cm) Bangladesh Subgrade Compaction Case History 90 km Road Rehabilitation Project An acceptance M DMT 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) 10 cm interval 77

78. Website: www.marchetti-dmt.it 78

79. CONCLUDING REMARKS (1/7) 79 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.

80. PREDICTING SETTLEMENTS 80 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). Similarly for Cu : no N kt (8 to 25) to guess. (2/7)

81. K D reflects benefits of Stress History on settlement and liquefaction. SH scarcely sensed by other tools, which ignore SH  benefits are wasted. (3/7) K D leads to a more economical design 81 Two sites : same Qc, but different. Site 2 much “stronger” In Site 2 Stiffness & CRR can be 2-3 times higher

82. As to pure cost CPT preferable. But info / cost (though Class 1 CPTU when pp neg.ve can take longer and cost more than DMT) A CPT investigation costs less, but remains orphan of capability of providing SOA 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. (4/7) “CPT costs less than DMT. Is CPT therefore preferable ?” 82

83. SETTLEMENTS ARE IMPORTANT If we do CPT only : may save in investigation. But if we spend a bit more by 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=$. (5/7) 83

84. With DMT "not many things can go wrong" (no electronics, no deairing, no saturation, no area correction, no glicerine, no wait when negative pp, no classes…). When the reliability of data is doubtful : a big cost. Designer looses time in choosing parameters, gets nervous, increases Fs, often overdesigns). DMT v. 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. When considering costs : into account (6/7) 84

85. 85 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. Can reduce settlements 2-4 times and can double CRR. Hence SH is a substantial $ resource. Ignoring SH when present  wasting $. BUT must be able to distinguish when SH is present / not. Not easily done by CPT or SPT. -------------------------- Multiparameter better than one-to-one correlations. Soil has many unknowns : need multiple responses CONCLUDING REMARK (7/7)

86. 3 rd International Conference on the Flat Dilatometer (DMT) Rome 14 th -16 th June 2015 Official web site: www.dmt15.com Abstracts max 1 page by July 15 th 2014 to: papers@dmt15.com Contact Info: info@dmt15.com 86

87. END Thank you 87

88. Slides for possible discussion 88

89. Clay. Initial idea (1980) : investigate E d -E u. Problem: E u, lab too dispersed, impossible set up correlations. Hence  E d -M. Link E d -M presumably weaker, but at least can be tested. NOTE. E d -M must be a complex function of many variables, among them the Skempton p. p. parameters A & B and anisotropy (E d horizontal, M vertical), which in turn depend on soil type (~represented by I d ) and on OCR (~ represented by K d )  some basis to expect at least some degree of correlation E d -M using I d and K d as parameters. Final word : real world observation. Large number case histories favourable comparisons measured vs DMT-predicted settlements - or M dmt -M reference. 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 E d (undrained) ??? 89

90. 90 Reconstituted sand specimens at same Dr “Testing on sand specimens reconstituted even at exactly the same density is highly questionable” (Ladd 1977). Already known at the time (SOA 1977 Tokyo) Hoeg (2000) showed that… “natural sands had dilative behaviour while reconstituted specimens with the same void ratios were contractive” Hence the need of testing sand in situ

91. 91 Elusivity of Dr in situ There is no unique mapping Dr=f(Qc). Jefferies – Been ISOPT 1995. Hilton Mines sand at Dr=60% produces the same Qc as Monterey sands at Dr=40% Very difficult estimate Dr in situ  unmeasurable Specs in terms of Dr problematic Schmertmann, 1986 in a paper about monitoring compaction : Since objective of compaction: limit settlements…..more rational specs on Modulus (e.g. M dmt ) than Dr

92. (  Giacheti, Mayne, Chang, Failmezger, Fonseca…) In general The correlations involving pwp (e.g. Cu=…) are generally not applicable. The correlations for estimating moduli/ settlements generally applicable, since DMT is a load test determining a pressure-settlement relation. 92 DMT CORRELATIONS IN NON-TEXTBOOK SOILS (Residual, Unsaturated…)

93. 93 OCR and Ko in sand OCR in sands can be  evaluated from ratio M DMT /q c. M DMT /q c = 5-10 in NC sands M DMT /q c = 12-24 in OC sands. Ko in sand. See TC16 DMT Report. A way can be (once estimated  OCR) : K o =K onc OCR m

94. 94 Legitimate to use M = constant if  ' v large ? M = Eoed=1/mv=  ' v /  v (at  ' 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)  

95. 95 Theoretical 1993 Finno Experimental 1980 & 1995 Theoretical 2004 Yu How the OCR and Cu correlations were derived (clay)

96. 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/  ’ v ) NC  0.22 (Mesri 1975) OCR, Ko, Cu well founded derivation. They use OCR confirmed by theory + SHANSEP  96

97. 97 Two diagrams obtained by instrumented blades : expansion Po  P1 approx linear Campanella et al. (1985) Proc 11 ICSMFE, S. Francisco, 2, p. 852. Fretti et al. 1992 Rig 26,4, 237-243 Hence central movement S=1.1 could be any value (two points). But : If S too small : (P1-P0) could be too small to measure it accurately If too high : Membrane “inertia” would rapidly increase (would work in tension rather in bending)

98. SOIL NEAR SURFACE MAY APPLY PRESSURE NOT ENOUGH FOR CLOSING THE MEMBRANE If soil applies  h <  A, the membrane will not close. No usual sound upon penetration.  Apply depression with the syringe and simply write a negative A value (algebra will take care correctly). Then B. NOTE. While doing Seismic DMT, the membrane must be closed (contact). Hence near surface, if there is no sound, depression must be kept with the syringe, to insure contact. This lack of contact happens frequently near surface if operator has already done a DMT expansion. 98

99. Ladd 1971 (42 yrs ago) Short course MIT Soft Ground Construction Even good OC samples may give oedometers moduli 2 to 5 times too low (Terzaghi & Peck book 1967) 99

100. Ed must be corrected to obtain M M=Rm Ed with Rm=f(Kd,Id) Don’t use Ed as Young’s 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) 100

101. 101 INFLATION SPEED. Time to A and to B Keep the “time to A”  15 sec. Particularly in silts, where partial drainage occurs during the test. Not so important in sands (fully drained) and in clay (fully undrained). If A in <<10 sec: excessive press. drop along pneumatic cable If A in >>20 sec: appreciable drainage may occur, esp. in silts Seasoned operators : inflate very fast to say 75% of expected reading. Then go very slowly to the reading.

102. 102 Sometimes is found : Cu field vane > Cu DMT (in very plastic clay) See eg Book “Soil Mechanics in Eng. Practice” (Terzaghi, Peck, Mesri) Cu field vane needs a correction factor before it can be used in stability analysys. The Bjerrum correction is eg 0.70 when PI = 70. Cu field vane reduced by Bjerrum’s correction is often considered the best available Cu for stability analysis. The DMT 1980 correlations for Cu were developed using for calibration such “operative” Bjerrum’s-corrected Cu values. It is therefore Cu field vane uncorrected which is too high - in plastic clays.

103. Liquefiability needs SH-aging Kd is sensitive to SH-aging Yu (2004), Robertson (2012) found correlations Kd-  (  State Parameter, close proxy of liquefiability)  reinforce expectation good Kd-CRR.  expect “good” Kd-CRR WHY EXPECT A “GOOD” Kd-CRR 103 Note :  alone is incomplete indicator of resistance to liquefaction (lacks structure, stress history, aging). Two identical sites of same “e” (hence same  ) - but the second prestressed : same , but the second has higher CRR (and higher Kd) Kd, being related to , but at the same time incorporating Stress History and aging, possibly uniquely well correlated with CRR