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Frontespizio

University of PISA – DESTEK Oct . 9 th 2014 Workshop on Penetration Testing. Frontespizio. Flat dilatometer (DMT) & Seismic DMT (SDMT). Recent developments. Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it. DMT results. or Stress History Index.

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Frontespizio

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  1. University of PISA – DESTEK Oct. 9th 2014 Workshop on PenetrationTesting Frontespizio Flat dilatometer (DMT) & Seismic DMT (SDMT) Recent developments Silvano Marchetti University of L'Aquila, Italy silvano@marchetti-dmt.it

  2. 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

  3. SeismicDilatometer

  4. SDMT results repeatability ≈ 1-2% SHEAR WAVE VELOCITY GO= ρ Vs2 Vs (m/s) Seismic DMT mechanical DMT (Recommended graphical format – no just po p1)

  5. 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)

  6. 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.

  7. (3/7) Two sites : same Qc , but different KD.Site 2 much “stronger” (higher SH) settlement and liquefaction.

  8. 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. CPT No mathematics, plaxis, statistics, FEM… can replace low degree of correlation

  9. 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 simulate AGING (grain slippage) KD+20% qD+3%

  10. M BEFORE AFTER DMT M Q DMT c Q c that DMT MORE REACTIVE TO STRESS HISTORY confirmed in the field … Jendeby 92 Measured in a loose sandfill Qc & Mdmtbefore-after compaction NC : M/Qc  5-12 OC : M/Qc  12-24 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 wrong target and Dr correlations v. uncertain)

  11. Estimate OCR in sand.Qc or Mdmt alone : not sufficient (multiparameter). Need both, one sensitive to SH, other less sensitive Can estimate OCR based onratio =M/Qc If  = M/Qc  5-12  NC If  = M/Qc  12-24  OC (Monaco et al. Asce Jan 2014) Principle behind : To convert Qc to M (by M=Qc) we need  = 4 to 20 f(OCR) (?) If we know =M/Qc, can get an idea of OCR Difficult enough with 2 parameters (CPT,DMT) … …once havingOCR : Ko=Ko,nc (OCR)m

  12. COMPACTION ( applying 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 effective in reflecting benefits of compaction Resonant vibro-compaction technique Van Impe, De Cock, Massarsch, Mengé, New Delhi (1994)

  13. ….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) (Multi parameter – both DMT)

  14. 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

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

  16. 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

  17. 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”.

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

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

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

  21. 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 !

  22. Predicting settlements is application # 1 of DMT. • Settlements obviously 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”

  23. 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

  24. 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”

  25. 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 … difficult situation considering…

  26. Soil Liquefaction due to EarthquakeLatest Research TREND in 2014 onwards (Extract from Geo-Congress, ASCE 2014 Panel Discussion)Panelists: Prof. Idriss, Prof. Boulanger, Prof. Robertson, Prof. Cetin, Prof. Finn, Prof. Green, Prof. Stokoe, Prof. Mayne No laboratory tests are suitable for liquefaction estimation. Only suitable field tests MUST be used. (Terzaghi Lecture-2011)

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

  28. Estimating CRR using KD Many curves developed in the last 30 years.Curves are converging to a narrow stripe Latest CRR(Kd) : Robertson (2012) : CRR = 93 (0.025 KD)3 + 0.08

  29. ESTIMATING CRR As today : 2 CRR estimates, fromtwo separate one-to-onecorrelations One estimate from Qc(Idriss & Boulanger 2006) One estimate from Kd(Robertson 2012) Recentresearch (2015) hasproduced a combinedCRR-Qcn-Kdcorrelation. Providesestimates of CRR based at the sametime on Qc & Kd. Note. When SH (Kd) is high, CRR ishigherthanpredictedbybaseline.

  30. SEAFLOOR DILATOMETER WATERDEPTH 0 to 100 m (nearshore jobs) PUSH CAPACITY 7 ton Max test depth is the depth penetrable with 7 ton push. Shipped by air(50 Kg) 4 bolts 7 ton ballast (built locally)

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

  32. Seafloor DMT lifted

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

  34. First Seafloor DMT test: 13 June 2014

  35. Krabbenhoff (Delhi 2014) : FEM programs like mob phones. We just want to talk, not bothered by complexity of the wires. In sand (lab no possible) : Designer assigns just the raw data (inequivocallymeasured) e.g. CPT & DMT Then FEM gives the solution. Dream for practitioner.Separates responsibility. Practicioners amateurs vs model specialists, profes-sionals payed for running FEM avoiding pitfalls. Assign to each region : Strength Stress History Stiffness Soil type Qc Kd Ed Id

  36. This idea of FEM possibly oversimplified.But main message is not FEM, is input (sands) Moving lab  in situ OK. But in lab : Strength, Stiffness, Stress History … Can we just input strength (Qc) withoutStress History and Stiffness ? Need multiple (significant) in situ soil responses). 3 unknowns  3 Eqns. Assign to each region : Rupture Stress History Stiffness Soil type Qc Kd Ed Id CPT (1) & DMT(2) : 3 indep. responses Same for evaluating liquefaction Can we do with just Qc, without SH and Stiffness ? Same for evaluating porosity n= f(Qc) does not work Try n= f(Qc, Kd, Ed, Id) ---------------------------------------- As material index is indicated : Id (DMT) or FR(CPT) ? Id is believed having more solid soil paternity

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

  38. Sensitivity to h of fs and KD CIRCULAR PROBE FLAT PROBE fs highly unstable, being what is left after an enormous stress reduction 38

  39. Mc Connell 2014 : fs& KD much in common fs & KD both reflect hagainst probe KD measures h directly (i.e. po) fsindirectly, transforming h to Fvertical Thus fs an attenuated KD , weaker and much less stable and direct. And repeatibility... 39

  40. (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.

  41. Detecting slip surfaces in clay slopes (look for Kd  2) 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

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

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

  44. OTHERAPPLICATIONS

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

  46. 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

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

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

  49. Website: www.marchetti-dmt.it

  50. CONCLUDING REMARKS (1/7) 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.

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