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The Flat Dilatometer Test (DMT): Design Applications and Recent Developments P. Monaco, S. Marchetti & G. Totani University of L'Aquila, Italy.

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Presentation on theme: "The Flat Dilatometer Test (DMT): Design Applications and Recent Developments P. Monaco, S. Marchetti & G. Totani University of L'Aquila, Italy."— Presentation transcript:

1 The Flat Dilatometer Test (DMT): Design Applications and Recent Developments P. Monaco, S. Marchetti & G. Totani University of L'Aquila, Italy

2 ORIGINAL PAPER MARCHETTI S. (1980). In Situ Tests by Flat Dilatometer. J. Geotech. Engrg. Div. ASCE, 106(GT3), 299-321 STANDARDS ASTM D6635-01 (2001). Standard Test Method for Performing the Flat Plate Dilatometer. EUROCODE 7 – Geotechnical Design – Part 2: Ground Investigation and Testing. EN 1997-2:2007 SOA REPORT TC16 (2001). The Flat Dilatometer Test (DMT) in Soil Investigations. May 2001, 41 pp. Reprint in Proc. 2nd Int. Conf. on Flat Dilatometer, Washington D.C., 7-48 INTERNET biblio site (download papers) KEY DMT REFERENCES


4 Push force provided by penetrometer or drill rig  DMT blade  Push rods (e.g. CPT)  Pneumatic-electrical cable  Control unit  Pneumatic cable  Gas tank  MEMBRANE EXPANSION GENERAL LAYOUT of DMT p 0 & p 1 readings at 20 cm depth intervals

5 CLAY, SILT, SAND – But can cross through GRAVEL layers  0.5 m Soils from VERY SOFT to VERY STIFF (upper limit is push capacity of rig) Clays: Cu = 2-4 to 1000 kPa (marls) Moduli: up to 400 MPa SOILS that can be TESTED by DMT

6 Basic DMT reduction formulae (TC16 2001)

7 DMT results K D = 2  NC clay IDID M Cu  KDKD soil type (clay, silt, sand) common use shape similar to OCR helps understand history of deposit

8 In most cases DMT used to determine common geotechnical design parameters Experience has shown undrained shear strength Cu and constrained modulus M by DMT generally accurate and dependable for design Comparisons at several research sites indicate quite good agreement between profiles of Cu and M by DMT and reference values by other tests ( see TC16 2001) Design using soil parameters

9 Comparisons Cu DMT vs. Cu reference Research Site Bothkennar (UK) Research Site Fucino (Italy) AGI (1991) Nash et al. (1992)

10 M by DMT vs. M by high quality oedometers Onsøy (Norway) Comparisons M DMT vs. M reference Lacasse (1986) M DMT M back-calculated M by DMT vs. M back- calculated from local vertical strains measured under Treporti full-scale test embankment (Italy) Marchetti et al. (2006)

11 by Boussinesq 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  2.5-3.5)

12 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

13 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)... Compaction control

14 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

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

16 LANDSLIDE "FILIPPONE" (Chieti) LANDSLIDE "CAVE VECCHIE" (S. Barbara) DOCUMENTED SLIP SURFACE (inclinometers) Validation of DMT-K D method

17 DMT for LIQUEFACTION 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 … –Correlation K D – Relative Density –Correlation K D – In situ State Parameter

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 DMT for 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

20 DMT for 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)

21 Subgrade compaction control M DMT acceptance profile (max always found at 25-26 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)

22 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 Seismic Dilatometer (SDMT) Hepton 1988 Martin & Mayne 1997, 1998... (Georgia Tech, USA)

23 Validation of Vs by SDMT Comparison of Vs profiles by SDMT and by other tests Fucino research site (Italy) SDMT (2004) AGI (1991) SCPT Cross Hole SASW

24 Vs (m/s) SHEAR WAVE VELOCITY SDMT results SDMT profiles at the site of Fiumicino (Italy) SDMT  accurate and highly repeatable Vs (in addition to usual DMT results)

25 SDMT  small strain modulus G 0 from Vs working strain modulus M DMT (settlements) Tentative methods to derive in situ G-  curves by SDMT Two points help in selecting the G-  curve In situ G-  decay curves by SDMT Mayne (2001) Ishihara (2001)

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

27 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

28 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 Special thanks to Allan McConnell (IGS)

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