Silvano Marchetti University of L'Aquila, Italy Flat dilatometer (DMT). Deformation parameters, compaction, liquefaction Frontespizio ISSMGE TC 207 Soil-Structure Interaction ISSMGE TC 212 Deep Foundations Workshop in Pune, India 16 Dec

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

Selected DMT applications 3 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

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

DMT components Truck mounted penetro- meter pushing the blade 5

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

DRILL-RIG DMT can also be executed using a DRILL-RIG 7 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.

DMT executed using an SPT rig 8 Driving the blade is not the preferred way. But in some countries (e.g. Switzerland) : the majority of DMTs

Can push 25 ton DMT suitable for sand, silt, clay 9 semi-liquid soils hard soils water Blade can break obstacles

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

     REDUCTION FORMULAE : DMT Rep. TC16 (2001) of ISSMGE po, p 1 Id, Kd, Ed (intermediate) M, Cu … (common soil parameters) HOW DMT WORKS (mechanical) 11 Every 20 cm DMT 30 m : ½ day

DMT FORMULAE DMT Report TC16 of ISSMGE

DMT results shape similar to OCR helps understand history of deposit 13 IDID M Cu  KDKD soil type (clay, silt, sand) common use K D = 2  NC clay 1-D  ’ vo. Treat as if obtained by oed or Stress History Index

p0p0 DMTDMT K D important parameter of DMT K D same definition of K o, but is > K o because K o has been “amplified” by the penetration K D is a measure of soil reluctance to decrease in volume Will see : K D reflects“stress history” 14

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 & economical than Down hole – X hole 15

Seismic Dilatometer 16

17 SHEAR WAVE SOURCE

Example seismograms SDMT at Fucino 18 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?

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

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

General considerations on today’s trends in Site Investigation 21

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) IN LAST DECADES MASSIVE MIGRATION FROM LAB TESTING TO INSITU TESTING 22

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.

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

Diagrams compare sensitivity of CPT-DMT to Stress History Lee 2011, Korean Researchers. Calibration Chamber in sand 26 Kd much more reactive than Q cn to Stress History Kd distinguish sands with SH / no SH. Q cn  less CPT DMT Diagr.1. Effect of SH on Q cn Diagr. 2. Effect of SH on Kd OCR = 1,2,4,8 With OCR With OCR

27 Settlement prediction Compaction control Liquefiability assessment 

Jamiolkowski (Isopt-1,‘88) : “without Stress History, impossible to select reliable E (or M) from q c ” 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). Sensitivity of Kd to Stress History important for Settlements 28

29 M DMT = E D x R m (Kd, Id) Operative modulus is obtained by factorizing the dilatometer modulus E D according to R m depending primarily on Kd (SH) Operative modulus is obtained as :

Accuracy of settlements prediction : confirmed by over three decades of good comparisons measured vs DMT-predicted settlements. by Boussinesq Terzaghi 1-D Settlement predictions by DMT 30

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

M at Sunshine Skyway Bridge. Tampa Bay – Florida USA Modulus M from DMT: M  200 MPa (  1000 DMT test points) M from laboratory : M  50 MPa From obs. Settlements: M  240 Mpa Conclusion : M DMT  Ok. M LAB : too soft (factor 4) World record span for cable stayed post-tensioned concrete box girder concrete construction ( Schmertmann – Asce Civil Engng – March 1988) 32

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) Possible reasons DMT predicts well settlement 33

Citations by world experts on predicting settlements by DMT 34 Schmertmann 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 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 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 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 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. ………………………………………..

Citations by world experts on predicting settlements by DMT 35 Schmertmann 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 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 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. ………………………………………

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

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

38 Settlement prediction Compaction control Liquefiability assessment 

Compaction control (vibroflotation, heavy tamping…) Schmertmann (1986) & many others, e.g. Balachowski (2015) : COMPACTION produces a gain of M DMT > twice gain of q c. Hence M DMT 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. 39

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

41 M DMT /q c in sand is a proxy of OCR On average it is found : In uncompacted NC sand M DMT /q c  5-12 In compacted OC sand M DMT /q c  M DMT / q c permits estimates of OCR in sands OCR=f(M DMT /q c )

42 Designers like to know not only the gain in M, but also the gain in OCR (growing new trend !). Hence they plot M DMT /q c - a proxy of OCR Jendeby 1992 Balachowsky DMT’15 When M DMT /q c > 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 M DMT 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 M DMT  80 MPa (avoiding Dr).

44 Settlement prediction Compaction control Liquefiability assessment 

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, V S ) underestimated CRR by a large 60 %” Salgado et al. (Jnl Asce 1997). “OCR increases liquefaction resistance CRR, but changes negligibly q c ” Liquefiability evaluations also in need of info on Stress History / Aging 45

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". CRR is most commonly estimated by CPT correlations. However some ??? 46

Panel Discussion at Geo-Congress, ASCE Panelists: Prof. Idriss, Prof. Boulanger, Prof. Robertson, Prof. Cetin, Prof. Finn, Prof. Green, Prof. Stokoe, Prof. Mayne Latest Research 2014 NO LABORATORY TESTS ARE SUITABLE FOR LIQUEFACTION ESTIMATION NO LABORATORY TESTS ARE SUITABLE FOR LIQUEFACTION ESTIMATION. Only suitable FIELD TESTS MUST be used... difficult situation … lab too is problematic..

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

49 An even better method is to estimate CRR based at the same time on Q cn and K D : CRR = f(Qc, K D ) in Figure CRR based at the same time on two parameters expected to be better than based on one parameter Example : Q cn =100, Kd=3 See paper : Marchetti 2015 Jnl. GED Asce

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. 50

PREDICTING SETTLEMENTS A large number of comparisons appear to confirm that DMT predicts well settlement. Good estimates of settlements permit a more rational and economical design. E.g. entity of settlement is needed to decide : piles or shallow foundations ? Info = savings (2/5) 51

K D reflects benefits of Stress History on settlement and liquefaction. Stress History scarcely sensed by other tools, which ignore SH  benefits are wasted. (3/5) K D can lead to a more economical design 52

Best estimates of CRR possibly obtained using at same time Q cn (CPT) & K D (DMT) CRR = f(Q cn, K D ) (4/5) ESTIMATING CRR (liquefaction) 53

No electronics, no temperature effects, no deairing, no area correction. Not many things can go wrong As soon as on the site, start immediately to test (no saturation or preliminary) Easy to run, short training time (  half day) Highly repeatable. Operators get same results No need highly skilled workers (5/5) 54 DMT is simple to operate

END Thank you 55