Frontespizio

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

2. FROM LAB TO INSITU TESTING 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

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

4. DMT pushed by a truck mounted penetrometer DMT components

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

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

7. Robust. Safe push 25 ton Suitableforpenetrablesoils (sand, silt, clay) 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 strongpush - heavy truck LIMITS Clays Cu=2-4 kPa up to 1 MPa (marl) Moduli M=0.5 to 400 Mpa

8. DMTBLADE 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. HOW DMT WORKS (mechanical) Material index Stress History Index Stiffness po, p1 Id, Kd, Ed  Common soil parameters (M, Cu …)   REDUCTION FORMULAE  DMT Rep. TC16 (2001) of ISSMGE

10. DMT FORMULAE DMT Report TC16 of ISSMGE 2001

11. DMT results or Stress History Index KD=2NC clay  amplified Ko ID  M Cu   KD  soiltype (clay, silt, sand) common use shapesimilartoOCRhelpsunderstandhistory of deposit 1-D modulus @ ’vo . Treat as if obtained by oed

12. (p0 - u0) KD = σ’v KD important Definition of KD: is similar to Ko DMT KD an “amplified K0” due to penetration.Will see : KD reflects“stress history” Very roughly Kd  4 Ko E.g. in NC : Ko  0.5 and Kd  2 p0

13. SEISMIC DILATOMER : DMT with the addition of a seismic module (tube) Vs 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

14. SeismicDilatometer

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

17. SDMT results repeatability ≈ 1-2% SHEAR WAVE VELOCITY GO= ρ Vs2 Vs (m/s) Seismic DMT mechanical DMT Provides considerable information on the site

18. CPT & DMT : a mutation vs SPT.Instrumental accuracy & resolution equal to lab 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 multiparameterinvestigation. (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.

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

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

21. 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. Box 2. Effect of SH on Kd Box 1. Effect of SH on Qc Diagrams compare sensitivity of CPT & DMT to Stress History Lee 2011, Eng. Geology 30 CC in sand OCR = 1 2 4 8 DMT CPT • Kd ++ reactivethan Qc to Stress History • For a given Qcn : can bemany Kd, depending on SH • Kd distinguishsandswith SH / no SH. Qcn  muchless.

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

24. 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%

25. M BEFORE AFTER DMT M Q DMT c Q c that DMT MORE REACTIVE TO STRESS HISTORY confirmed in the field … Jendeby 92 Had a loose sandfill and measured Qc & Mdmtbefore-after compaction NC : M/Qc  5-12 OC : M/Qc  12-24  OCR in sand  Ko=Ko,nc (OCR)m 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)

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

27. COMPACTION ( impose SH) produces a MDMT% increase twice the Qc% increase MDMT before-after compaction 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 Resonant vibro-compaction technique Van Impe, De Cock, Massarsch, Mengé, New Delhi (1994)

28. ….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)

29. byBoussinesq Settlementpredictionsby DMTIn generalclassic Terzaghi 1-D (even in 3-D(Poulos : modulus, not formula !! ) 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

30. 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

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

33. M at Sunshine Skyway Bridge, Tampa Bay – Florida (Schmertmann – Asce Civil Engng – March 1988) World record span for cablestayed post-tensioned concretebox 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

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

35. 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”.

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

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

38. 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. 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 !

40. Predicting settlements is application # 1 of DMT. • 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”

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

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. 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 … not easy considering that “No lab tests suitable for liquefaction estimation. Only field tests MUST be used (Terzaghi Lecture 2011) “

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

45. 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. Tsai (2009) ran side-by-side CPT-DMT. From profiles-CPT next to profiles-DMT he had pairs (Qc1, Kd)  Qc1=f(Kd) qc1 = f(Kd) Replace qc1 with Kd Thus : obtain CRR-Kd

46. Scatter of the Qc1-Kd relation 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.

47. 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. Estimating CRR using Kd Many curves developed in the last 30 years.Curves are converging to a narrow central band 2013: CRR=0.0038KD3-0.0176KD2+0.0532KD+0.0264 Assumed as most likely (intermediate : Monaco 2005 & Robertson 2012)

49. 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.

50. Liquefaction (spontaneous, earthq. induced etc.). Complex, involves many soil properties 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 [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).