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The Flat Dilatometer Test (DMT): and Recent Developments

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1 The Flat Dilatometer Test (DMT): and Recent Developments
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), STANDARDS ASTM D (2001). Standard Test Method for Performing the Flat Plate Dilatometer. EUROCODE 7 – Geotechnical Design – Part 2: Ground Investigation and Testing. EN :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)


4 GENERAL LAYOUT of DMT  DMT blade  Push rods (e.g. CPT)
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  0.5 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

6 Basic DMT reduction formulae (TC16 2001)

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

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

10 Comparisons MDMT vs. Mreference
M back-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 Settlement prediction
No. 1 DMT application by Boussinesq Classic linear elastic 1-D approach – or 3-D with E  0.8 MDMT (similar predictions) Settlement under working loads (Fs  )

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

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

16 Validation of DMT-KD method

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

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

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 cm) 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 0.5 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 Hepton 1988 Martin & Mayne 1997, (Georgia Tech, USA)

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

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

25 In situ G- decay curves by SDMT
Mayne (2001) Ishihara (2001) SDMT  small strain modulus G0 from Vs working strain modulus MDMT (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 from VS 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 Special thanks to Allan McConnell (IGS)
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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