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The Flat Dilatometer Test (DMT): Design Applications and Recent Developments

The Flat Dilatometer Test (DMT): Design Applications and Recent Developments. P. Monaco, S. Marchetti & G. Totani University of L'Aquila, Italy . KEY DMT REFERENCES. ORIGINAL PAPER MARCHETTI S. (1980). In Situ Tests by Flat Dilatometer. J. Geotech. Engrg. Div. ASCE, 106(GT3), 299-321

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The Flat Dilatometer Test (DMT): Design Applications and Recent Developments

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

  2. KEY DMT REFERENCES 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 www.marchetti-dmt.itbiblio site (download papers)

  3. FLAT DILATOMETER (DMT) BLADE FLEXIBLE MEMBRANE

  4. GENERAL LAYOUT of DMT 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 p0 & p1 readings at 20 cm depth intervals

  5. SOILS that can be TESTED by DMT • CLAY, SILT, SAND – But can cross through GRAVEL layers 0.5m • 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

  6. Basic DMT reduction formulae (TC16 2001)

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

  8. Design using soil parameters • 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)

  9. Comparisons CuDMT vs. Cureference Nash et al. (1992) AGI (1991) Research Site Bothkennar (UK) Research Site Fucino (Italy)

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

  11. by Boussinesq 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)

  12. 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)

  13. Compaction control • 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) ...

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

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

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

  17. DMT for LIQUEFACTION • 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 … • Correlation KD– Relative Density • Correlation KD–In situ State Parameter • 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. 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 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

  21. 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)

  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. SDMT (2004) SCPT Cross Hole SASW AGI (1991) Validation of Vs by SDMT Comparison of Vs profiles by SDMTand by other testsFucino research site(Italy)

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

  25. In situ G- decay curves by SDMT Mayne (2001) Ishihara (2001) SDMT small strain modulusG0 from Vs working strain modulusMDMT(settlements) • Tentative methods to derive in situ G- curves by SDMT • Two points help in selecting the G- curve

  26. SDMT for LIQUEFACTION 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

  27. 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 – ...

  28. 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 Special thanks to Allan McConnell (IGS)

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