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Frontespizio

Frontespizio. Some specific comments on DMT/SDMT. Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it. 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.).

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Frontespizio

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  1. Frontespizio Some specific comments on DMT/SDMT Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it

  2. 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…)

  3. Drill rod   pushrod quickest (S)DMT can be pushed by DRILL-RIGTwo distinct methods – not confuse Torpedo method or “Downhole mode” Cable exits laterally in the hole Test starts from bottomhole Sciacca method or “Penetrometer mode” Cable exits laterally in air Test starts from ground surface

  4. Central component clean.  Electrical contact

  5. Disc & small components : Clean ! In general not necessary to clean Necessary if membrane or tube broken : mud inside • Absence of B reading

  6. IS THE BLADE IN SHORT CIRCUIT ? (THE SOUND NEVER STOPS) Use the continuity tester as in the picture. Insert plug behind. There has to be sound when you touch the metal washer, no sound in any other part of the blade Possible reasons could be : A piece of metal is floating somewhere below the sensing disk (remedy: clean and blow compressed air) The inner longitudinal cable inside the blade is broken and is in contact with the metal of the blade

  7. Yellow flag - on back of low press gage : OPEN OPEN ! If you have observed in the past a variable zero offset, such inconvenience should disappear. Avoids the “barometer effect” i.e. avoids that the zero offset depends on the ambient atmospheric pressure only in low pressure gages 6-8 bar

  8. 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 Hencecentralmovement S=1.1 couldbeanyvalue (twopoints). But : If S toosmall : (P1-P0) couldbetoosmalltomeasureitaccurately Iftoo high : Membrane “inertia” wouldrapidlyincrease (would work in tensionrather in bending)

  9. INFLATION SPEED. Timeto A and to B • ADVANCING SPEED NO NEED 2 cm/s(twice or half ok) Start inflationimmediatelyafterbladestops (say 2 sec) Keep the “time 0 to A” 15 sec (10-20 sec) , same A to B. If A in <<10 sec: excessive press. dropalongpneumaticcableIf A in >>20 sec: appreciabledrainagemayoccur, esp. in silts Seasonedoperators “fast-slow” metod: inflate fast up 75% of expectedreading. Theninflateslowlyto the reading. Takeshalf the time. Recommended in silts, topossibly test in undrained conditions.

  10. 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.

  11. “Complaint” : Cu field vane > Cu dmt(in very plastic clay) From Book “SoilMechanics in Eng. Practice” (Terzaghi, Peck, Mesri) : Cu field vaneneeds a correctionfactorbeforeit can beused in stabilityanalysys. The Bjerrumcorrectionis eg 0.70 when PI = 70. Cu field vanereducedbyBjerrum’s correctionisoftenconsidered the best available Cu forstabilityanalysis. The DMT 1980 correlationsfor Cu weredevelopedusingforcalibrationsuch “operative” Bjerrum’s-corrected Cu values. Itistherefore Cu field vaneuncorrectedwhichistoo high - in plastic clays.

  12. Here just few tips for semi liquid soils paper. Offset of pressure gage Take A, B before &after each sounding, several times Start inflation immediately after reaching the test depth (in practice within a couple of sec), particularly in silts. Inflate Zero to A in 15 sec and A to B in 15 sec If semiliquid soil is silt, try to speed, to possibly remain in undrained conditions. Seasoned operators inflate "rapidly" until 70% of expected reading (A or B), then slow to accurately read the pressure (“brief inflation”  8 sec). See also Sect 15.4 : Semiliquid and submerged (e.g. bottom slurry of mining wastes hydraulically transported and discharged in a pond).

  13. Drainage conditions. “Niche silts” Sand : drained Clay : undrained Silts : partial Ideally A & B should be taken simultaneously If we stop at a given z and take repeated A-readings… A B   In niche silts : B-A, Id,Ed,M. But a reasonable A may still be obtained (brief inflation 8 sec), and the parameters dependent only on A, notably Cu. Can still do undrained analysis E.g. in a tailings dam of niche silt : can do undrained analysis More details in the paper Undrained no h decay Contact Stress h A substantial h decay Clay Niche silt log time In niche silts B is too low (hence too low B-A and B-A derived Id,Ed,M). Niche silts recognizable : Id0 (low Ed,M)

  14. Displaying the DMT results Recommended graphical output TC16. Diagrams should be presented not separated, but side by side, + expressive Displaying just po and p1 is unexpressive The struggle is between factuality (po,p1) and expressivity (figure) The "conventional" formulae are "average" correlations in textbook soils. In non textbook soils an alternative could be to plot, superimposed, results by site specific and conventional correlations (also evidencing deviations vs "average" sites). Recommending the format in Fig. is not to suggest one set over another set of correlations, but preserve simultaneous vision of various profiles.

  15. 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

  16. 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 Specs in terms of Dr problematic Schmertmann, 1986 in a paper on monitoring compaction : Since objective of compaction: limit settlements…..more rational specs on Modulus (e.g. Mdmt) than Dr

  17. Question by Mike LongDMT repeatible as it is made in just one place or other…? DMT : load-displacement test. Two ingredients. 1 DISPLACEMENT The fixed 1.10 mm is H between two solids1% (of quantity, NOT of full scale !). 0.01 mm Operator cannot regulate, spoil, tamper. No skill. … 1 % Despite being AT DEPTH ! 2 PRESSURE Pressure gage (transducer) AT SURFACE : Zero offset continously checkable. Or reset – eliminated. [in tools with sensor at depthZero offset real problem – uncontrollable -!] Can use even a v high sensitivity gage (low scale) – semiliquid soil. Repeatibility : inherent in the construction of the device

  18. May 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 2-3)

  19. Using the 1-D formula in 3-D problemse.g.small isolated footings Boussinesq solutions M=MDMT (simple, engineer independent) E  0.8-0.9 MDMT(elasticity) denominator is less sign minus Difference 1-D vs 3-D : 10-15% Moreover : Engineer has to choose  (?) Dx e Dy not well predicted by elasticity (?) Poulos Istanbul : What is important is the modulus, not the formula !

  20. Reliability of material index Id Obviously Id is not a sieve analysis. Eg. a mixture sand-clay would probably be "wrongly" interpreted as silt. On the other hand such mixture could perhaps behave mechanically as a silt. The engineer is often interested to the grain size distribution not "per se", but just to infer mechanical properties, PERHAPS, in SOME cases, it could be better to have the Id interpretation than the sieve analysis results and to infer from them the mechanical behaviour. A “mechanical” information (a sort of Soil Type Behaviour Index) that, in design, might be even more important than the granulometric composition.

  21. How derive M (drained) from Ed (undrained) ??? 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.

  22. SETTLEMENT CALCULATION MDMT + 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

  23. Pouso Alegre / MGPiso de galpão de logística para 5,0 tf/m2Ensaio DMT em aterro compactado com solo local

  24. Ladd 1971 (44 yrs ago)Short course MIT Soft Ground ConstructionEvengood OC samplesmaygiveoedometers moduli 2 to 5 timestoo low (Terzaghi & Peck book 1967)

  25. Ed mustbecorrectedtoobtain M M=Rm Ed withRm=f(Kd,Id) Don’t use Ed as Young’s Modulus Rm hasvariouscorrectiontasks DistortionHoriztoverticalDrained Undrained Once Ed isconvertedto MYoung’s E’  0.8-0.9 M (elasticity)

  26. OCR and Ko in sand OCR in sands can be  evaluated from ratio MDMT/qc. MDMT/qc = 5-10 in NC sandsMDMT/qc = 12-24 in OC sands. or from the continuous Monaco’s curve Ko in sand. See TC16 DMT Report A way can be (once estimated  OCR) : Ko=KoncOCRm

  27. KPa KPa 0 5 10 15 20 Z (m) Z (m) Cu at National SiteBOTHKENNAR Cu at NationalSiteFUCINO A.G.I., 10th ECSMFE Firenze 1991,1 : 37 Nash et al., Géotechnique, June 1995: 73 Nc= 14 to 22 ?

  28. INPUT PARAMETERS FOR PLAXIS (Hard Soil model “HS”) Recommended basic input E50ref (Trx modulus confined at 1 bar). Schanz found for quartz sand E50ref =15 to 75 MPa (loose to very dense sand). He also found E50ref correlated to Eoedref. In sand the range of MDMT by DMT is remarkably similar to above range (15-75 MPa). Hence as a 1st approximation may assume E50ref MDMT ------------------------------- Predicting settlement by DMT may  replace a costly load test. Often load tests executed to adjust assumed FEM parameters.

  29. Research embankment D=40 m(Venezia) ComparisonMDMT vs Mback-calculated from LOCAL vertical strains measured under center Sliding Micrometers installed every meter SETTLEMENTS Measured36 cm DMT predicted29cm ( = 24%)

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

  31. Exponent n used for obtaining the normalized parameters Kd and Qcn(used for predicting CRR) Qcn = [(qc - v )/ pa] (pa/'v )n Uniform NC sand Due to arching : qc(z) increases less than linearly Kd = (p0-u0)/'v n = 1 a welcome simplification – avoids the iterative procedure to determine Qcn and n, an additional soil unknown (n=0.5-1) Blade no arching : side ratio 6

  32. Determining “n” (0.5 to 1) not straightforward Flow chart - Iterations by computer Robertson & Wride – Canad.G.J. 1998

  33. DMT CORRELATIONS IN NON-TEXTBOOK SOILS(Residual, Unsaturated…) (Giacheti, Mayne, Chang, Failmezger, Fonseca…) In general The correlationsinvolvingpwp (e.g. Cu=…) are generallynotapplicable. The correlationsforestimating moduli/ settlementsgenerallyapplicable, since DMT is a load test determining a pressure-settlement relation.

  34. Liquefaction (spontaneous, earthq. induced etc.) : complex, involves many soil properties East Germany 1000s hectares higly unstable (fence : keep out). Often high sudden settlements - spontaneous collapse - “butterfly triggered” Dangerous to compact them, rigs may sink. Vibrations >> than earthquake. C is stable for any Earthquake. But - if there is cementation (or SH) - can A be stable ? Can we rely on cementation (SH)? If Fragile : Cement destroyed by strong Earthquake – and more or less alsoby direct push tests? Not reflected by a Kd. But reflected by a high Vs (high Go/M). If Ductile : Cement not destroyed, reflected by a Kd Also : Qc  Dr Kd  (Dr+SH) : need both to separate Many unknown. Qc alone is not enough. Need multi-parameter triangulation CRR = f (Qcn, Kd, Ed, (Id), Go/MDMT).

  35. CALCAREOUS SAND (Plouasne – France – 1991) Id  sand - Kd very low

  36. SEAFLOORDILATOMETER WATERDEPTH 0 -100 mPUSH CAPACITY 7 ton Ballast 7 ton buid locally Ballast connected by bolts to the pushing system (60 Kg) 6-7 pushrods already charged vertically on top – can add more Limitation : Cannot push CPT (no 1 m stroke)

  37. ENDThankyou

  38. MODULI CAN ONLY BE POSITIVE - INHERENTLY What to do if you have several Ed<0? (Tell operator to be more careful when taking DA,DB) Shoud not happen ! However : Verify if you have just one Ed<0 or many Ed<0 If “Just one” you may accept (but cancel that depth) If “many” Ed<0 : it means DA, DB too high. Reduce them gradually (eg in proportion) until all Ed positive (maybe one negative) (“Regular” DA,DB 0.15 0.45 bar)

  39. REPRODUCIBILITY of DMT Cestari (SGI), Lacasse (NGI), Lunne (NGI), Marchetti (Aq) NC clay Onsoy, Norway

  40. SDMT in NON-TEXTBOOK SOILS : SOME EXPERIENCE Nuno’s thesis Giacheti H.L. et al. (2006) “Flat Dilatometer Testing in BrazilianTropical Soils”, Proc. 2nd Int. Conf. on Flat Dilatometer, Washington D.C.: 110 D.A. Brown, J. Vinson, 1998. Comparison of strength and stiffness parameters for a Piedmont residual soil. Proceedings of the First International Conference on Site Characterization - ISC’98, Atlanta, Georgia, USA, Vol. 2, pp 1229-1234. G.K. Martin, P.W. Mayne, 1998. Seismic flat dilatometer tests in Piedmont residual Soils. Proceedings of the First International Conference on Site Characterization - ISC’98, Atlanta, Georgia, USA, Vol. 2, pp 837-843. Chang, M.F. 1988. In Situ Testing of Residual Soils in Singapore. Proc. 2nd Int. Conf. on Geomechanics in Tropical Soils, Singapore, Vol. 2: 97-108. Dec. Wang Chainchye E. and Borden Roy H."Deformation Characteristics of Piedmont Residual Soils" Jnl ASCE GE, Vol. 122, No. 10, October 1996, pp. 822-830 Failmezger, R.A., Rom, D. & Ziegler, S.B. 1999. SPT? A better approach to site characterization of residual soils using other in-situ tests. Behavioral characteristics of residual soils, ASCE Geotech. Spec. Publ. No. 92, 158-175. Mayne, P.W. 2005. Unexpected but foreseeable mat settlements of Piedmont residuum. Int. Jnl of Geoengineering Case Histories, http://casehistories.geoengineer.org, Vol. 1, Issue 1, 5-17. A. Viana da Fonseca, M.M. Fernandes, A.S. Cardoso, 1988. Characterization of a saprolitic soil from Porto granite by in situ testing. Proceedings of the First International Conference on Site Characterization - ISC’98, Atlanta, Georgia, USA, Vol. 2, pp 1381-1387. General comment : estimating by DMT modulus / settlement should be appli-cable whatever the material (glass, lead, residual, artificial fills…), because DMT is a load test determining directly a pressure-settlement relation.

  41. Significant – systematic research in CC by Koreans (sand) “Effects of stress history on CPT and DMT(Lee 2011, Eng. Geology) Qc: 1.10 - 1.15 larger Kd: 1.30 - 2.50 larger  Kd ++ reactive to SH than Qcn

  42. CC TEST N.216 IN TICINO SAND 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 AGINGthan penetration resistance PRESTRAINING CYCLES simulateAGING (grain slippage) KD+20% qD+3%

  43. Reconstituted sand specimens at same Dr “Testing on sandspecimensreconstitutedeven at exactly the same density ishighlyquestionable” (Ladd 1977). Alreadyknown at the time (SOA 1977 Tokyo) Hoeg (2000) showedthat… “naturalsandshaddilativebehaviourwhilereconstitutedspecimenswith the samevoidratioswerecontractive” Hence the needoftestingsand in situ

  44. Vp - Seismic Dilatometer (SPDMT) Pianola (AQ) 2013 Vp (m/s) lower sensor p wave s wave upper sensor Depth (m) DMT Two vertical axis sensors provide two independent Vp profiles (pseudo interval)

  45. Recent results indicate : the CPT-clean-sand curve not unique but comprised in a wide band band - f(Kd) E.g. CRR = 0.12 (SH low), but 0.24 (SH high). Factor 2 ! The CPT “consensus” curve is generally conservative. BUT can be v. uneconomical in prestressed/ aged sands where Qcn predicts liquef just because Qcn does’not feel SH. 0.12-0.24 are both right ! explains historical controversies by researchers Kd may help to choose the line in the band But then may be even + direct to obtain CRR from f(Kd)

  46. CONCLUDING REMARK 1 The most important of the evidenced aspects is probably the capability of DMT to sense Stress History, not easily felt by other tools. SH is necessary for reasonable predictions of CRR and of settlements. Migrating from the SPT-blowcount N to Qcn for predicting CRR and settlements has had the merit of eliminating that part of scatter due to the poor repeatability of the SPT. The use of KD should reduce even that part of scatter due to the scarce ability of conical tips to distinguish between freshly deposited sands and prestressed or aged sands.

  47. CONCLUDING REMARK 2 DMT is approx 1½ costlier than CPT. Hence, if one considers only the cost, CPT is preferable. However CPT may be sufficient only if your geotechnical report does not include a section “settlements prediction”. If settlements are important to the designer, CPT cannot help, and DMT should be executed, because of the well known weakness of CPT – unable to provide realistic settlement predictions (eg Powell & countless others). Frequently adopted is a combination of both, since they complement and since the penetrometer can push both.

  48. It is often said that DMT interpretation is empirical... STORY of the correlation OCR-KD in clay Theoretical 1993 Finno Theoretical 2004 Yu Experimental 1980 & 1995

  49. DERIVATION OF Cu CORRELATION Once having OCR Ladd’s SHANSEP 77 SOA Tokyo  Using m  0.8 (Ladd 1977) and (Cu/’v)NC 0.22 (Mesri 1975) (Ladd : best Cu not from TRX UU but from oed  OCR  Shansep) OCR, Ko, Cu well founded derivation. They use OCR confirmed by theory + SHANSEP

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