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Silvano Marchetti University of L'Aquila, Italy Flat dilatometer (DMT) & Seismic DMT (SDMT) 1 Frontespizio University of PISA.

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Presentation on theme: "Silvano Marchetti University of L'Aquila, Italy Flat dilatometer (DMT) & Seismic DMT (SDMT) 1 Frontespizio University of PISA."— Presentation transcript:

1 Silvano Marchetti University of L'Aquila, Italy Flat dilatometer (DMT) & Seismic DMT (SDMT) 1 Frontespizio University of PISA – DESTEK Oct. 9 th 2014 Workshop on Penetration Testing Recent developments

2 DMT results K D = 2  NC clay  amplified Ko IDID M Cu  KDKD soil type (clay, silt, sand) common use shape similar to OCR helps understand history of deposit or Stress History Index 2 1-D  ’ vo. Treat as if obtained by oed

3 Seismic Dilatometer 3

4 Vs (m/s) SHEAR WAVE VELOCITY mechanical DMT Seismic DMT SDMT results repeatability ≈ 1-2% 4 G O = ρ Vs 2 (Recommended graphical format – no just p o p 1 )

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) 5 Have in common : need of Stress History (by Kd)

6 Diagrams compare sensitivity of CPT-DMT to Stress History Lee 2011, Eng. Geology  30 CC in sand 6 Kd ++ reactive than Qc to Stress History For a given Qcn : can be many Kd, depending on SH Kd distinguish sands with SH / no SH. Qcn  much less. CPT DMT Box 1. Effect of SH on Qc Box 2. Effect of SH on Kd OCR = 1,2,4,8

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

8 Given the scarce sensitivity of Qc to OCR, is it possible to estimate OCR from CPT ? Effect of OCR on Qc 8 Many formulae OCR-Qc proposed, even relatively complex. No mathematics, plaxis, statistics, FEM… can replace low degree of correlation CPT

9 PRESTRAINING CYCLES simulate AGING (grain slippage) CC TEST N. 216 IN TICINO SAND They applied prestraining cycles in calibration chamber. Found : K D (DMT) 3 to 7 times more sensitive to AGING than penetration resistance K D + 20 % q D + 3 % Similarly higher sensitivity of Kd to SH & aging observed by Jamiolkowski (ISC'98 Atlanta) 9

10 that DMT MORE REACTIVE TO STRESS HISTORY confirmed in the field … M DMT M Q c Q c BEFOREAFTER Jendeby 92 Measured in a loose sandfill Qc & Mdmt before-after compaction NC : M/Qc  5-12 OC : M/Qc  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 11 …once having OCR : K o =K o,nc (OCR) m (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) … If  = M/Qc  5-12  NC If  = M/Qc   OC Can estimate OCR based on ratio  =M/Qc

12 M DMT before-after compaction Resonant vibro-compaction technique Van Impe, De Cock, Massarsch, Mengé, New Delhi (1994) COMPACTION (  applying SH) produces a M DMT % increase  twice the Qc% increase Schmertmann (1986) DYNAMIC COMPACTION of sand site. M DMT % 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 12

13 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) M DMT = E D x R m (Kd, Id) (combines E D with Stress History) (Multi parameter – both DMT) ….conclusion : good sensitivity of K D 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 13

14 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 by Boussinesq Settlement predictions by DMT In general classic Terzaghi 1-D (even in 3-D (Poulos : modulus, not formula !! ) 14

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

16 M at Sunshine Skyway Bridge, Tampa Bay – Florida 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 World record span for cable stayed post-tensioned concrete box girder concrete construction ( Schmertmann – Asce Civil Engng – March 1988) 16

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 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. 18

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

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 20

21 1.Wedges deform soil << cones 2.Modulus by mini load test relates better to modulus than to penetr. resistance 3.Availability of Stress History parameter Kd. (DMT is a 2- parameter test. Fundamental to have both: Ed and Kd) 4.The soil is loaded at a lower, more appropriate, strain level Possible reasons DMT predicts well settlement 21  Need moduli, not strength ! Stiffnes  Strength

22 Predicting settlements is application # 1 of DMT. 22 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??? 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”. 23 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  ? Qc cannot be used twice : (1) as denominator In E/Qc (2) As parameter to select which curve

24 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” Liquefiability evaluations also in need of info on Stress History / Aging 24

25 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… Is reason of v. cautious recommendations on CRR(CPT) : Ignoring Stress History  omit a primary parameter. Consequence : CRR predicted by CPT (insensitive to SH) uncertain 25

26 Soil Liquefaction due to Earthquake Latest Research 26 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 27

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

29 29 Recent research (2015) has produced a combined CRR-Qcn-Kd correlation. Provides estimates of CRR based at the same time on Qc & Kd. Note. When SH (Kd) is high, CRR is higher than predicted by baseline. ESTIMATING CRR As today : 2 CRR estimates, from two separate one-to-one correlations One estimate from Qc (Idriss & Boulanger 2006) One estimate from Kd (Robertson 2012)

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. 7 ton ballast (built locally) Shipped by air (50 Kg) 4 bolts 30

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

32 Seafloor DMT lifted 32

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

34 First Seafloor DMT test: 13 June

35 Krabbenhoff (Delhi 2014) : FEM programs like mob phones. We just want to talk, not bothered by complexity of the wires. 35 In sand (lab no possible) : Designer assigns just the raw data (inequivocally measured) 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) 36 Same for evaluating liquefaction Can we do with just Qc, without SH and Stiffness ? Assign to each region : Rupture Stress History Stiffness Soil type Qc Kd Ed Id As material index is indicated : Id (DMT) or FR(CPT) ? Id is believed having more solid soil paternity Moving lab  in situ OK. But in lab : Strength, Stiffness, Stress History … Can we just input strength (Qc) without Stress History and Stiffness ? Need multiple (significant) in situ soil responses). 3 unknowns  3 Eqns. Same for evaluating porosity n= f(Qc) does not work Try n= f(Qc, Kd, Ed, Id) CPT (1) & DMT(2) : 3 indep. responses

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

38 Sensitivity to  h of f s and K D 38 f s highly unstable, being what is left after an enormous stress reduction CIRCULAR PROBE FLAT PROBE

39 Mc Connell 2014 : f s & K D much in common f s & K D both reflect  h against probe 39 K D measures  h directly (i.e. p o ) f s indirectly, transforming  h to F vertical Thus f s  an attenuated K D, 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. 40

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

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

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


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

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 46

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

48 Subgrade compaction control M DMT acceptance profile (max M always found at cm) Bangladesh Subgrade Compaction Case History 90 km Road Rehabilitation Project An acceptance M DMT 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) 10 cm interval 48

49 Website: 49

50 CONCLUDING REMARKS (1/7) 50 Direct push CPT and DMT are increasingly recognized as fast and convenient tools for everyday investigations. DMT’s K D 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.

51 PREDICTING SETTLEMENTS 51 Countless researchers : without Stress History it is impossible to predict modulus from CPT or SPT. A large number of comparisons confirm DMT predicts well settlement. With DMT no  (2 to 20) to guess in M=  Qc. DMT correlations guide without subjective choices to M, taking into account soil type (Id) and Stress History (Kd). (2/7)

52 K D reflects benefits of Stress History on settlement and liquefaction. SH scarcely sensed by other tools, which ignore SH  benefits are wasted. (3/7) K D may lead to a more economical design 52 Site 2 “stronger” despite the same Qc

53 As to pure cost CPT preferable. But info / cost A CPT investigation costs less, but does not provide accurate predictions of settlements. Been : State of Art at CPT 2010 Los Angeles : CPT can easily mislead in terms of soil type, strength and particularly modulus”. Robertson (1986) : Prediction of modulus from Qc can be rather poor, especially for OC soils, with a large potential error. (4/7) “CPT costs less than DMT. Is CPT therefore preferable ?” 53

54 SETTLEMENTS ARE IMPORTANT If we do CPT only : may save in investigation. But if we spend a bit more doing DMT, predict more accurate settlements, save in design of foundation, where the $ is. Settlements can have important $ consequences (piles/ shallow foundations…). Important jobs cannot do w/o Accurate Settlements  more economical design. Info=$. (5/7) 54

55 With DMT "not many things can go wrong“ No electronics, no temperature effects, no vacuum pump, no saturation-deairing, no glycerin, no area correction… start testing immediately … … uncertain data, when present : big cost. Designer looses time choosing parameters, becomes nervous, increases Fs  overdesign. DMT easy to run, short training time (  3 hours) Any operator gets same results. In remote regions : easy to instruct a local technician. No need to leave a highly skilled (costly) operator. When considering costs : into account (6/7) 55

56 56 Stress History is sometimes considered a gourmet property, as not directly used in calculations as c’ Ø’ Cu … Or of academic interest, to separate elastic/ plastic behaviour… Not so. SH makes the soil much stronger. It is a substantial $ resource. Ignoring SH when present  wasting $. BUT must be able to distinguish when SH is present / not. Not easily done by penetration tests TREND today  Multiparameter approach better than one- to-one correlations. Soil has many unknowns : need multiple responses CONCLUDING REMARK (7/7)

57 3 rd International Conference on the Flat Dilatometer (DMT) Rome 14 th -16 th June

58 Highlights of the conference include  Prof. Roger Frank (ISSMGE president) Welcome speech  Prof. J. Schmertmann’s dinner talk  Prof. M. Jamiolkowski: use of SDMT in the Zelazny Most dam in Poland  Prof. F. Schnaid: use of DMT and SDMT in tailings dam Sofar 120 abstracts from 32 Countries 58

59 Venue is in the town center 59

60 Rome touristic attractions 60

61 St. Peters and Pope Francesco 61

62 Difficult booking ( Hotel, Flights ) expected in June 2015: June is high season High popularity of the Pope EXPO 2015 (Milan-Rome) 62

63 END Thank you 63

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