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Frontespizio

SDMT Workshop and Field Demonstration Cesano 18 novembre 2011. Frontespizio. Applicazioni alla progettazione geotecnica. Università degli Studi dell’Aquila Ing. Sara Amoroso. REFERENCE: State-of-the-art Lecture No. 1 ( Alessandria Egitto Oct 2009 )

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Frontespizio

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  1. SDMT Workshop and FieldDemonstration Cesano 18 novembre 2011 Frontespizio Applicazioni alla progettazione geotecnica Università degli Studi dell’Aquila Ing. Sara Amoroso

  2. REFERENCE: State-of-the-art Lecture No. 1 (Alessandria Egitto Oct 2009) 17th Int. Conf. on Soil Mechanics and Geotechnical Engng, 2009 Mayne P.W. Georgia Institute of Technology, Atlanta, USA Coop M.R. Imperial College, London, UK Springman S.M. Swiss Federal Institute of Technology, Zurich, CH Uang A.B. National Chiao Tung University, Taiwan, China Zornberg J.G. University of Texas, Austin, USA “Soil borings … laboratory testing … SPT … pressuremeter (PMT) … vane (VST) … crosshole (CHT) … Taken together, all of these are suitable … yet at considerable cost in time and money …”

  3. “... In this fast-paced world, a more efficient approach … In particular, the Seismic Piezocone (SCPT) and the Seismic Dilatometer (SDMT) ... offer clear opportunities in the economical and optimal collection of data. ... SCPT and SDMT direct-push tests should serve as the basis … in routine daily site investigation practices …”

  4. DMT TEST 1. BLADE INSERTION (20 cm) BLADE 2. HORIZONTAL LOAD TEST EXECUTION FLEXIBLE MEMBRANE FLAT DILATOMETER (DMT)

  5. Design via DMT parameters • ID = material index • KD = horizontal stress index • ED = dilatometer modulus • K0 = coeff. earth pressure in situ • OCR = overconsolidation ratio • cu = undrained shear strengh • Φ = friction angle • ch = consolidation coefficient • kh = permeability coefficient • g = unit weight and description • M = vertical drained constrained modulus • u0 = equilibrium pore pressure

  6. Main DMT applications • Settlements of shallow foundations • Laterally loaded piles • Diaphragm walls • Detecting slip surfaces in OC clay • Monitoring densification/stress increase • Liquefability evaluation • Subgrade compaction control • FEM input parameters

  7. by Boussinesq 1 - Settlement prediction No. 1 DMT application • Classic linear elastic 1-D approach – or 3-D with E0.8MDMT (similar predictions) • Settlement under working loads (Fs2.5-3.5)

  8. Stiffnes  Strenght Possiblereasons DMT goodsettlementpredictions • Wedges deform soil << than cones • Modulus by mini load test relates better to modulus than penetr. resistance • Availability of Stress History parameter Kd.(DMT is a 2-parameter test. Fundamental to have both: Ed and Kd) Baligh & Scott (1975) Jamiolkowski (1988) “Without Stress History, impossible to select reliable E (or M) from Qc” Strength

  9. MDMT Mback-calculated Marchetti et al. (2006) Observed and DMT predicted modulus M by DMT vs. M back-calculated from local vertical strains measured under Treporti full-scale test embankment (Italy)

  10. Summary of comparisons DMT-predicted vs. observed settlements • Large No. of case histories good agreement for wide range of soil types, settlements,footing sizes • Average ratio DMT-calculated/observed settlement 1.3 • Band amplitude (ratio max/min)<2 i.e. observed settlement within ±50% from DMT-predicted Monaco et al. (2006)

  11. 2 - Design of 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) • Independent validations  2 methods provide similar predictions, in very good agreement with observed full-scale pile behaviour

  12. 3 - Design of 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

  13. 4 - Detecting slip surfaces in OC clay DMT-KDmethod Verify if an OC clay slope contains ACTIVE (or old QUIESCENT) SLIP SURFACES (Totani et al. 1997)

  14. LANDSLIDE "FILIPPONE" (Chieti) LANDSLIDE "CAVE VECCHIE" (S. Barbara) Validation of DMT-KDmethod DOCUMENTED SLIP SURFACE DOCUMENTED SLIP SURFACE (inclinometers) Totani et al. 1997

  15. 5 - Monitoring densification / stress increase • Experience suggests DMT well suited to detect BENEFITS of SOIL IMPROVEMENT due to its high sensitivity to changes of stresses/density in soil • Several comparisons of CPT and DMT before/after compaction Schmertmann et al. (1986), Jendeby (1992) Increase in MDMT after compaction of sand  2 increase in qc (CPT) • Pasqualini & Rosi (1993) DMT clearly detected improvement even in layers where benefits were undetected by CPT • Ghent group (1993)  DMTs before-after installation demonstrate more clearly [than CPT] beneficial effects of Atlas installation

  16. MDMT MDMT qc qc DMT vs. CPT before/after compaction Ratio MDMT/qc before/after compaction of a loose sand fill (Jendeby 1992)

  17. 6 - Liquefability evaluation • Correlations for evaluating Cyclic Resistance Ratio CRR from KD developed in past 2 decades, stimulated by: • Sensitivity of KD to factors known to increase liquefaction resistance: Stress History, prestraining/aging, cementation, structure … (Marchetti, 2010) • Correlation KD– Relative Density (Reyna & Chameau, 1991) • Correlation KD–In situ State Parameter (Yu, 2004) • Key element supporting well-based CRR-KD correlation: ability of KD to reflect aging in sands (1st order of magnitude influence on liquefaction) + sensitivity of KD to non-textbook OCR crusts in sands

  18. Curves for evaluating CRR from KD (Seed & Idriss 1971 simplified procedure) • Summary + latest version CRR-KD correlation see Monaco et al. (2005 ICSMGE Osaka) • Magnitude M=7.5 – Clean sand

  19. Curves for evaluating CRR from KD (Seed & Idriss 1971 simplified procedure) Tsai et al. (2009) • All past CRR-KD curves were based on correlations Qc-Dr-KD or NSPT-Dr-KD. Tsai et al (2009) translated CPT-SPT using correlations Qc-KD or NSPT-KD and cutting out Dr.

  20. 7 - Subgrade compaction control Bangladesh Subgrade Compaction Case History 90 km Road Rehabilitation Project MDMT acceptance profile (max always found at 25-26cm) • Acceptance MDMT profile fixed and used as alternative/fast acceptance tool for quality control of subgrade compaction, with only occasional verifications by originally specified methods (Proctor, CBR, plate), (Marchetti, 1994)

  21. 8 - FEM input parameters • Linear elastic model: E0.8MDMT • (Hamza & Richards, 1995) • DMT aims to calibrate FEM parameters • PLAXIS hardening soil model: • E50,ref is correlated to MDMT (Schanz, 1997) Monaco & Marchetti (2004)

  22. Seismic Dilatometer (SDMT) Combination S+DMT • 2 receivers spaced 0.5m • Vs determined from delay arrival of impulse from 1st to 2nd receiver (same hammer blow) • Signal amplified + digitized at depth • Vs measured every 0.5m Hepton 1988 Martin & Mayne 1997, 1998 ... (Georgia Tech, USA)

  23. Correlation to estimate Vs (G0) frommechanical DMT data (ID, KD, ED) From large amount SDMTs at 34 sites various soils & geography  • No point today. Vs direct(but might provide rough Vs in previous sites DMT). • Important : w/o stress history (KD) hopeless estimate Vs. • Difficulty: Qc-Vs NSPT-Vs ??? • Use 1 parameter (NSpt, Su) as surrogate of Vs : questionable (as suggested by some codes). Marchetti et al. (2008) Decay decreases with KD (stress history)

  24. Vs profiles Earthquake in L’Aquila, 6 April 2009 measured by SDMT estimated from "mechanical" DMT data Monaco et al. (2009)

  25. Main SDMT applications • DMT applications • Seismic design (NTC08, Eurocode 8) • In situ G-g decay curves • Liquefability evaluation

  26. 9 - Vsforseismic design Vs profile Vs 30 Soil category (NTC08, Eurocode 8)

  27. 10 - In situ G- decay curves by SDMT 0.05 – 0.1 % Mayne (2001) 0.01 – 1 % Ishihara (2001) • SDMT small strain modulusG0 from Vs • working strain modulus GDMTfrom MDMT • (Marchetti et al. 2008) • Tentative methods to derive in situ G- curves by SDMT • Two points help in selecting the G- curve

  28. Earthquake in L’Aquila, 6 April 2009 GDMT/G0from SDMT γDMT= 0.1 – 0.5 % Amoroso (2011)

  29. 11 - Liquefability evaluation SDMT2 parallel independent evaluations of CRR fromVS e KD (Seed & Idriss 1971 simplified procedure) CRR from Vs CRR from KD Andrus & Stokoe (2000) Andrus et al. (2004) Monaco et al. (2005) ICSMGE Osaka

  30. Vs Kd Earthquake in L’Aquila, 6 April 2009 Vittorito – L’Aquila (April 2009) Moment magnitude MW: 6.3 Distance from the epicentre: 45 km Peak ground acceleration PGA: 0.065 g

  31. Earthquake in L’Aquila, 6 April 2009 Liquefaction depth from KD: 2-6 m Liquefaction depth from Vs: 1-2.5 m Monaco et al. (2009, 2010)

  32. FINAL REMARKS • DMTquick, simple, economical, highly reproducible in situ test • Executable with a variety of field equipment • Dependable estimates of various design parameters/information – soil type – stress state/history – constrained modulus M – undrained shear strength Cu in clay – consolidation/flow parameters – ...

  33. FINAL REMARKS • Variety of design applications • Most effective vs. common penetration tests when settlements/deformations important for design (e.g. strict specs or need to decide: piles or shallow ?) • SDMT accurate measurements of Vs (and G0) + usual DMT results – greatly enhances DMT capability

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