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

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Presentation on theme: "Università degli Studi dell’Aquila Ing. Sara Amoroso SDMT Workshop and Field Demonstration Cesano 18 novembre 2011 Applicazioni alla progettazione geotecnica."— Presentation transcript:

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

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

5 Design via DMT parameters I D = material index K D = horizontal stress index E D = dilatometer modulus K 0 = coeff. earth pressure in situ OCR = overconsolidation ratio c u = undrained shear strengh Φ = friction angle c h = consolidation coefficient k h = permeability coefficient g = unit weight and description M = vertical drained constrained modulus u 0 = 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  0.8 M DMT (similar predictions) Settlement under working loads (Fs  )

8 Possible reasons DMT good settlement predictions Jamiolkowski (1988) “Without Stress History, impossible to select reliable E (or M) from Qc” Stiffnes  Strenght 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) Strength

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

10 Summary of comparisons DMT- predicted vs. observed settlements Monaco et al. (2006) 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

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 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 Monaco & Marchetti (2004 – ISC'2 Porto)

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

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

15 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 M DMT after compaction of sand  2 increase in q c (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 5 - Monitoring densification / stress increase

16 Ratio M DMT /q c before/after compaction of a loose sand fill (Jendeby 1992) DMT vs. CPT before/after compaction M DMT qcqc qcqc

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

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

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

20 7 - Subgrade compaction control M DMT acceptance profile (max always found at cm) Bangladesh Subgrade Compaction Case History 90 km Road Rehabilitation Project Acceptance M DMT 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 Linear elastic model: E  0.8 M DMT (Hamza & Richards, 1995) DMT aims to calibrate FEM parameters PLAXIS hardening soil model: E 50,ref is correlated to M DMT (Schanz, 1997) 8 - FEM input parameters Monaco & Marchetti (2004)

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

23 No point today. Vs direct (but might provide rough Vs in previous sites DMT). Important : w/o stress history (K D ) hopeless estimate Vs. Difficulty: Qc-Vs N SPT -Vs ??? Use 1 parameter (N Spt, Su) as surrogate of Vs : questionable (as suggested by some codes). Correlation to estimate Vs (G 0 ) from mechanical DMT data (I D, K D, E D ) From large amount SDMTs at 34 sites various soils & geography  Decay decreases with K D (stress history) Marchetti et al. (2008)

24 measured by SDMT estimated from "mechanical" DMT data Vs profiles Earthquake in L’Aquila, 6 April 2009 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 - Vs for seismic design Vs profile Vs 30 Soil category (NTC08, Eurocode 8)

27 SDMT  small strain modulus G 0 from Vs working strain modulus G DMT from M DMT (Marchetti et al. 2008) Tentative methods to derive in situ G-  curves by SDMT Two points help in selecting the G-  curve 10 - In situ G-  decay curves by SDMT 0.05 – 0.1 % Mayne (2001) 0.01 – 1 % Ishihara (2001)

28 Amoroso (2011) G DMT /G 0 from SDMT γ DMT = 0.1 – 0.5 % Earthquake in L’Aquila, 6 April 2009

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

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

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

32 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 –... FINAL REMARKS

33 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 G 0 ) + usual DMT results – greatly enhances DMT capability FINAL REMARKS


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