Frontespizio

1. ISSMGE TC 207 Soil-Structure InteractionISSMGE TC 212 Deep Foundations Workshop in Pune, India 16 Dec 2015 Frontespizio Flat dilatometer (DMT). Deformation parameters, compaction, liquefaction Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it

2. Topics of interest in this workshop • Soil-Structure Interaction and • Deep Foundations • Present topic is :In situ tests by Flat Dilatometer • Selected few applications of DMT more directly connected to workshop

3. Selected DMT applications • Settlement prediction • Compaction control • Liquefability assessment • Laterally loaded piles • Detecting slip surfaces in clay slopes • Diaphragm walls : “springs” for design • FEM input parameters • In situ G- decay curves

4. For those unfamiliar : Start with brief description :DMT and SDMT in situ test

5. DMT components Truckmounted penetro-meter pushing the blade

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

7. 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.

8. DMT executed using an SPT rig Driving the bladeisnot the preferred way. But in some countries (e.g. Switzerland) : the majority of DMTs

9. DMT suitable for sand, silt, clay Can push 25 ton water semi-liquidsoils hardsoils Blade can break obstacles

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

11. HOW DMT WORKS (mechanical) Every 20 cm DMT 30 m : ½ day po, p1 Id, Kd, Ed (intermediate) M, Cu … (common soil parameters)    REDUCTION FORMULAE : DMT Rep. TC16 (2001) of ISSMGE

12. DMT Report TC16 of ISSMGE 2001 DMT FORMULAE

13. DMT results or Stress History Index 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

14. KD important parameter of DMT KD same definition of Ko, but is > Ko because Ko has been “amplified” by the penetration KD is a measure of soil reluctance to decrease in volume Will see : KD reflects“stress history” DMT p0

15. 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 : operator (and interpreter !) independent Vs profile in Real Time Much faster & economicalthan Down hole – X hole

16. SeismicDilatometer

17. SHEAR WAVE SOURCE

18. 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?

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

20. Diffusion : DMT used in 70 countries (200 DMT in US) EU US EA Brazil Australia NZ Indian Institute of Technology IIT Bombay (Prof. D. Choudhury) Jadavpur University Kolkata (Prof. K. Bandyopadhyay) Standards: EUROCODE 7 (2005) ASTM (2007) ISO(2016)

21. General considerations ontoday’s trends in Site Investigation

22. IN LAST DECADES MASSIVE MIGRATION FROM LAB TESTING TO INSITU TESTING In many parts of the world CPT and DMT are 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)

23. CPT reflects mainly strength - rupture DMT reflects mainly deformation properties (vital for Soil-Structure Interaction) Many top experts worldwide consider DMT the best presently available tool for predicting settlements, notoriously not well predicted by conical probes

24. Before going to applications • Emphasize importance of the Stress History (SH) parameter Kd provided by DMT. • Kd is uniquely sensitive to SH. Kd is not obtained by other in situ probes • Not easy to detect SH by other in situ probes (sand). • Sensitivity of Kd to SH important : Stress History fundamental for realistic prediction of settlements and liquefaction resistance.

25. Explain : “KD sensitive to prestressing” NC PRESTRESSED Stiffer stronger SAME STATE OF STRESS, but… KD,DMT sensitive to prestressing Other probes : scarcely sensitive to prestressing (hence scarcely able to recognize prestressed elements as stiffer, stronger). KD able to recognize…

26. Diagr. 2. Effect of SH on Kd Diagr.1. Effect of SH on Qcn 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 Qcnto Stress History • Kd distinguishsandswith SH / no SH. Qcn less

27. Settlement prediction • Compaction control • Liquefiability assessment 

28. Sensitivity of Kd to Stress History important for Settlements Jamiolkowski (Isopt-1,‘88) : “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 is imperative information on stress history to characterize compressibility of a sand Application #1 DMT : predict settlements (operative modulus).

29. Operative modulus is obtained as : MDMT = ED x Rm(Kd, Id) Operative modulus is obtained by factorizing the dilatometer modulus ED according to Rm depending primarily on Kd (SH)

30. 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.

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

32. 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)

33. 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)

34. Citations by world expertson predicting settlements by DMT Schmertmann 1986. A DMT sounding can usually provide the data needed for the calculation of expected settlements with an accuracy adequate for most practical purposes. Penna, Brazil 2013. In my practical experience the DMT is the best approach for settlements prediction Leonards 1988 It has been argued (Leonards 1985) that, at the present time, the Marchetti dilatometer is the most generally applicable practical tool for sensing soil compressibility Mayne 2004. Over two decades of calibration between the DMT and measured foundation performance records have shown its value & reliability in settlements computation. Crapps (2001). Users prefer DMT data over any other soils data to estimate settlements. A user with Law Engineering in Atlanta told me yesterday that the settlements are "always right on (meaning close to) the predictions from DMT data when they have the opportunity to make settlement measurements. KCI Technologies Usa (2000). By DMT a more cost effective design can result compared to using the SPT alone, producing savings in construction cost. Tice & Knott (2000). Good agreement was observed between DMT-predicted and measured settlements at the sandy site under Cape Hatteras Light Station Steiner W. 1994. An earthfill on a loose sandy-silt produced settlements substantially higher than anticipated based on conventional soil borings. DMT were then performed. “The DMT-predicted settlements agreed well with observed settlements. Woodward & McIntosh (1993). Use of modulus from DMT permitted considerable savings vs using data from SPT. SPT, for this project, underpredicted the modulus. Geopac Quebec 1992 Settlements predicted by PMT and DMT were very similar, but cost and time for DMT were a fraction of PMT Failmezger & Bullock GeoRisk 2011. DMT is a static deformation test that strains the soil to intermediate strains. It is also a good predictor of settlement. Tests are generally performed at depth intervals of 0.20 m. Tests typically take about 1 minute to perform. The dilatometer test is therefore the best choice of in-situ tests for settlement prediction of shallow foundations. ………………………………………..

35. Citations by world expertson predicting settlements by DMT Schmertmann 1986. A DMT sounding can usually provide the data needed for the calculation of expected settlements with an accuracy adequate for most practical purposes. Penna, Brazil 2013. In my practical experience the DMT is the best approach for settlements prediction Leonards 1988 It has been argued (Leonards 1985) that, at the present time, the DMT is the most generally applicable practical tool for sensing soil compressibility Mayne 2004. Over two decades of calibration between the DMT and measured foundation performance records have shown its value & reliability in settlements computation. Woodward & McIntosh (1993). Use of modulus from DMT permitted considerable savings vs using data from SPT. ………………………………………

36. Various types of foundation As soon as DMT is completed, it is possible to estimate settlement building viaduct pile group

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

38. Settlement prediction • Compaction control • Liquefiability assessment 

39. Compaction control(vibroflotation, heavy tamping…) Schmertmann (1986) & many others, e.g. Balachowski (2015) : COMPACTION produces a gain of MDMT >twice gain of qc. Hence MDMT particularly suitable for evidencing the benefits of compaction( increase of Stress History) For this reason before-after DMTs are increasingly used to monitor the gain in modulus and the gain in OCR.

40. M BEFORE AFTER DMT M Q DMT c Q c Jendeby 1992. Measured in a loose sandfill qc& MDMT before - after compaction He found that : MDMT increases at a faster rate than qc (gain  twice) Confirm+sensitive to SH As a consequence the ratio MDMT /qc increased from  8-10 to  15-22

41. OCR=f(MDMT /qc) On averageit is found : In uncompactedNC sand MDMT/qc 5-12 In compactedOC sand MDMT/qc 12-24 MDMT/ qc permits estimates of OCR in sands MDMT /qc in sand is a proxy of OCR

42. Designers like to know not only the gain in M, but also the gain in OCR (growing new trend !). Hence they plot MDMT/qc - a proxy of OCR Balachowsky DMT’15 Jendeby 1992 When MDMT/qc > 12-15, sand is appreciably OC

43. Schmertmann (1986) : a more rational acceptance criterion is a min modulus rather than a min difficult-to-determine in situ Dr. Since aim of compaction is reduce settlements it is more logic to write the specifications in terms of MDMT instead of Dr. Dr wrong target, Dr correlations sand dependent, Dr elusive. Same change in specs was adopted e.g. by Balachowski DMT’15. The acceptance criterion of compacted ground was MDMT 80 MPa (avoiding Dr).

44. Settlement prediction • Compaction control • Liquefiability assessment 

45. 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 qc”

46. CRR is 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".

47. .. 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

48. An independent estimate of CRR can be obtained by DMT : CRR=f(Kd) CRR=f(Kd) has attracted considerable interest : Kd is sensitive to SH, while CPT less. But SH increases the liquef resistance. Important to predict CRR based on Kd sensitive to SH

49. An evenbettermethodisto estimate CRR based at the sametime on Qcn and KD : CRR = f(Qc, KD) in Figure See paper : Marchetti 2015 Jnl. GED Asce CRR based at the sametime on twoparametersexpectedtobebetterthanbased on oneparameter Example : Qcn=100, Kd=3

50. CONCLUDING REMARKS (1/5) More and more CPT & DMT replace laboratory for everyday jobs. Sensitivity of DMT’s Kd to Stress History is important. There are not many Stress History tools. Stress History is indispensable for good predictions of settlements and liquefaction.