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Frontespizio

Frontespizio. Some 2015 Updates to the TC16 DMT Report 2001. Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it. IN LAST DECADES MASSIVE MIGRATION FROM LAB TESTING TO INSITU TESTING. CPT and DMT often used today as the major part of everyday investigations

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Frontespizio

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  1. Frontespizio Some 2015 Updates to the TC16 DMT Report 2001 Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it

  2. IN LAST DECADES MASSIVE MIGRATION FROM LAB TESTING TO INSITU TESTING CPT and DMT often used today as the major part of everyday 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)

  3. DMT components Truckmounted penetro-meter pushing the blade

  4. DMT can also be executed with small inexpensive pushing machines

  5. DMT can alsobeexecutedusing a DRILL-RIG Test starts from bottom of a borehole (like SPT, but say 3m) No need 2 cm/sec. Speed can be half or twice. Penetration is just for inserting the blade. Test starts later.

  6. Suitable for sand, silt, clay Can push 25 ton water semi-liquidsoils hardsoils Blade can break obstacles

  7. DMT BLADE All mechanical NO ELECTRONICS , no zerodrift, no temperature effects Blade is like an electrical switch. Can be off or on.

  8. HOW DMT WORKS (mechanical) Every 20 cm DMT 30 m : ½ day po, p1 Id, Kd, Ed  Soil parameters (M, Cu …)    REDUCTION FORMULAE  DMT Report TC16 (2001) of ISSMGE

  9. DMT FORMULAE DMT Report TC16 of ISSMGE 2001

  10. Two primary “DMT Manuals”. TC16 DMT Report 2001 Contains 95% of what is needed to know on DMT 1 Some 2015 Updates (SM paper to this Conf.) A supplement / Upgrade. Clarifications and new developments 2 Both are in the proceedings book (and USB key) Then for SDMT : operator manual & software manual (down loadable) Standards : Eurocode 7 (2005), ASTM (2007) ISO (Tech. Spec. 22476 being converted to Standard (info Powell, Arroyo…)

  11. As to formulae : Mayne at DMT'15 shows systematic validation of the 1997 Ø - Kdeqn. Hemeasured Ø on undisturbed sand samples acquired by freezing technologies or special piston samplers. TRX Ø 1997 Eqn Marchetti (1997) Eq. Ø-Kd Mayne shows that the 1997 Kd-Ø Eq. conservatively matches all the TRX Ø data.

  12. DMT results or Stress History Index KD=is po normalized to ’vo Definition : as Ko, but an amplified Ko V. roughly 4 times Ko KD=2NC clay ID  M Cu   KD  common use soil type (clay, silt, sand) shape similar to OCR helpsunderstand history of deposit 1-D modulus @ ’vo . Treat as if obtained by oed

  13. SEISMIC DILATOMER is a DMT with the addition of a seismic module (tube) Vs SDMT SDMT is TRUE interval(two sensors) Both Seismograms from same blow Vs instantly and operator (and interpreter !) independent Much faster & economicalthan Down hole – X hole

  14. SeismicDilatometer

  15. SHEAR WAVE SOURCE

  16. Example seismograms SDMT at Fucino Delay T : automatically calculated using Cross Correlation Repeatability Vs : 1-2 %. Mayne : Why obtain T from 1st arrival (?) - just 1 point, when can obtain T optimized from 1000 points?

  17. DMT results REPEATABILITY ≈ 1-2% SHEAR WAVE VELOCITY GO= ρ Vs2 Vs (m/s) Seismic DMT mechanical DMT

  18. Routinely energize at each depth several blows to get several Vs Zelazny Most – Repeatability of Vs (10 blows) e.g. SDMT repeatibility : a few m/sec

  19. Comparison of Vs,sdmt vs Vs by other methods Cross-hole, Down-Hole, SCPTU, SASW... Some 20 slides. Will show Wednesday. No time here. Generally very good agreement

  20. Main SDMT applications. Details  TC16 or specific 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 Have in common : need of Stress History (by Kd)

  21. But before : focus on sensitivity of Kd to Stress History. • Sensitivity of Kd to SH important : not many alternatives to sense SH in situ (sand). • Kd is a protagonist in many correlations. • Stress History fundamental for realistic prediction of settlements and liquefaction resistance.

  22. Diagr. 2. Effect of SH on Kd Diagr.1. Effect of SH on Qc Diagrams compare sensitivity of CPT-DMT to Stress History Lee 2011, KoreanResearchers. CalibrationChamber in sand OCR = 1,2,4,8 DMT CPT With OCR With OCR • Kd much more reactivethan Qc to Stress History • Kd distinguishsandswith SH / no SH. Qcn  less

  23. The indication is : reflects essentially Dr (only to minor extent stress history) reflects Dr + various stress history effects such as OCR, aging, Ko, structure (cementation) Qcn KD

  24. Schmertmann 1984 explained the different sensitivity of DMT &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.“

  25. Diagrams also demonstrate: OCR in sand cannot be predicted by CPT alone nor from DMT alone. OCR in sand : both Qcn and Kd needed OCR = 1,2,4,8 DMT CPT With OCR With OCR • 1° diagramconfirms low sensitivity of Qcn to SH DifficultrelateQcn-OCR. Long algebraicformulae / statistics / numericalmodels : can notmake up fortenuouscorrelation.

  26. BUT even Kd alone not sufficient, as Kd increases with either Dr and OCR E.g. Kd = 3 could be due : low Dr -high OCR high Dr - low OCR. To evaluate OCR in sand, Qc must also be available : provides an indication of Dr in the horizontal axis DMT Example of necessity multi parameter approach CPT+DMT Monaco ..J. Asce 2014 Beware of software OCR=f(Qcn) or OCR = f(Kd) ! ? Move to a correlation based on both M and Qc

  27. M BEFORE AFTER DMT M Q DMT c Q c That DMT is more REACTIVE to Stress History CONFIRMED in the FIELD, during COMPACTION (apply SH) Jendeby 92 Measured in a loose sandfill Qc & MDMTbefore-after compaction NC : M/Qc  5-12 OC : M/Qc  12-24 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.

  28. Schmertmann (1986) & many others, including Balachowski DMT’15 : COMPACTION produces a % increase of MDMT twice the % increase of Qc. This higher sensitivity to compaction (by factor 2) of MDMTvs Qc documented systematically in a large No. of papers  MDMT particularly fit for evidencing 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, Dr correlations sand dependent, Dr elusive ).E.g. Balachowski DMT’15 : acceptance criterion of compacted ground MDMT80 MPa (avoiding slippery Dr).

  29. Elusivity of Dr in situ Thereis no uniquemappingDr=f(Qc). Jefferies – Been ISOPT 1995 : “Hilton Minessand at Dr=60% produces the same Qc as Monterey sands at Dr=40%” Verydifficult estimate Dr in situ  unmeasurable

  30. Jendeby’s results were the cradle of the MDMT/Qc vs OCR correlation Based on Jendeby and similar : Semi quantitative Guidelines in TC16 DMT 2001 Report : NC : M/Qc  5-10 OC : M/Qc  12-24 In 2014 Monaco et al. constructed a continuous MDMT /Qc vs OCR curve using the Treporti results, where a trial embankment was built then removed, thereby obtaining an OCR profile permitting a calibration….

  31. This is the Monaco (2014) curve MDMT/ qc to estimate OCR in sands Monaco’s curve in v good agreement with the Semi quantitative Guidelines in TC16 DMT 2001 Report : NC : M/Qc  5-10 OC : M/Qc  12-24 Thus Jendeby & Monaco corroborate each other (despite the v. different origin – textbook OCR by embankment and violent SH by compaction). Monaco approx but solid correlation. OCR sand is difficult with DMT, CPT. Imagine with just one !Once havingOCR : Ko Ko,nc (OCR)m

  32. Besides the 2-parameter OCR vs MDMT/Qc Monaco also constructed a 1-parameter OCR-Kd correlation (only DMT) Found similarly good regression coefficient (0.927-0.917). OCR = f (MDMT/Qc) OCR = f (Kd)) OCR-Kd) has a good regression just because in Treporti Dr is more or less uniform. If Dr is variable , OCR-Kd would not work (it is local). Lesson : When a key parameter is missing, only local (not general) correlations can possibly be obtained.

  33. A third independent support to Monaco’s OCR-MDMT/qc Eq. comes from  . (Note : The ratio M/Qc is nothing less  used in M= Qc !!) • Calibration chamber in sand : •   3 to 4 in NC, up to 20 on OC sand (which are also the  values chosen by designers who use M= Qc). • Principle why  permits to estimate OCR : • If OCR is unknown, difficult to estimate . • But if  is known, we may estimate OCR. 

  34. Often today in compaction jobs (°) the ratio MDMT/ qc is plotted before-after. Jendeby 1992 Balachowsky DMT’15 The profiles MDMT / Qc permit to evaluate OCR increase, by converting MDMT / Qc into OCR using Monaco’s Eq. MDMT / Qc  proxy of OCR. Examples of using MDMT / Qc for OCR in Sharif Recommended distance of adjacent CPT & DMT : 1 m, no more no less

  35. Sensitivity of Kd to SH important for Settlements 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 Leonards & Frost (1988). “Correlations between penetration resistance and soil modulus will seriously overestimates settlements if the deposit has been prestressed”. Robertson et al. (1986). “Predictions of soil modulus from qc can be rather poor, especially for OC soils, with a large potential error”. Application #1 DMT : predict settlements (operative modulus).

  36. Application #1 DMT : predict settlements (operative modulus) Insensitive to SH Idea at base of MDMT : factorize Ed based on SH (Kd) MDMT= ED x Rm(Kd, Id) The analogous for CPT : MCPT= Qc x Rm(Qc) ??? … appears more difficult - cannot use Qc twice : Qc to be factorized and Qc to estimate the correction

  37. byBoussinesq Terzaghi 1-D Settlement predictions by DMT Accuracy of settlements prediction : confirmed by over three decades of good comparisons measured vs DMT-predicted settlements.

  38. M at Sunshine Skyway Bridge. Tampa Bay – Florida USA World record span for cablestayed post-tensioned concretebox girder concrete construction (Schmertmann – Asce Civil Engng – March 1988) Modulus M from DMT : M 200 MPa (1000 DMT test points) M from laboratory : M 50 MPa From obs. Settlements : M 240 Mpa Conclusion : MDMT  Ok. MLAB : too soft (factor 4)

  39. 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) Stiffnes  Strength  Need moduli, not strength !

  40. Mayne compared strain levels by DMT and other in situ tests Mayne 2001 Mayne (2001)

  41. COMPUTER PROGRAM Input load Input MDMT   As soon as DMT is completedpossible to estimate settlements Ave load  10 kPa / floor If s = 3cm (or 4 or 5) : OK shallow. Otherwise piles . V. rough but instant indication.

  42. 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”

  43. CRR most commonly estimated by CPT correlations. However some ?? 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".

  44. .. difficult situation … lab too is problematic .. LatestResearch 2014 NO LABORATORY TESTS ARE SUITABLE FOR LIQUEFACTION ESTIMATION. Only suitable FIELD TESTS MUST be used. • 2014 Panel Discussion at Geo-Congress, ASCEPanelists: 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

  45. Liquefaction Resistance CRR : is today estimated by CPT - or by DMT - but separately CRR from CPTCRR from DMT Idriss & Boulanger (2006) marchetti 2015 However these are both one-to-one correlations.

  46. Betterto estimate CRR based at the sametime on Qc and KD : CRR = f(Qc, KD) in Fig. • Get CRR in twoSteps • Estimate CRR exactlyaswenormally do today, namelyusing the everyday CPT-CRR correlations. • Then, if Kd is high, increase CRR, if Kd is low, reduce CRR 2015 Method appears also as just fruit of common sense (Fig. here is qualitative. Quantitative will soon be published Jnl. Asce 2015)

  47. Possible similarity with OCR (need CPT & DMT) Lesson with OCR: When a key parameter is missing, only local (not general) correlations can possibly be obtained. Below two sites same Qc , different KD : In site 2 CRR can be much higher. If design is based on Qc (the same) the two sites would be treated equally, and benefits due to SH are wasted.

  48. Ifsandhas Fine content, Cementation… : adding KDtoQcn, for CRR, maynotbesufficient E.g. cementation can beductile (toothpaste-like) or fragile (glasslike). Clearly too many unknowns. Go could possibly help : high Go/Qc or high Go/ MDMTindicate cementation. Even modulus ED from DMT could possibly help. Additional study necessary  combining multi-parameter

  49. Cemented soils : Go / MDMT and Go/Qc (black) higher than sedimentary soils(Schnaid 2004, Rocha et al. 2015) (Possible reason of high Vs : cemented contacts of the grains allow a faster transmission) Schnaid 2004 Rocha 2015 Go/ MDMT and Go/Qc : are possibly additional useful info

  50. Multiparameter  inevitable. A fashionable MIT model requires 19 lab parameters. If we use insitu, we need not 19 (!), but at least a few. Ten years ago already Mayne ridiculed deriving 30 parameters from just one (NSPT). Computer programs based on just one parameter could mislead young unexperienced engineers, whoo could believe uncritically in the output.

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