Procedure, Operative and Technical Aspects on DMT Dr. Eng. Francesca Buselli

1. Procedure, Operative and Technical Aspects on DMT Dr. Eng. Francesca Buselli francesca@marchetti-dmt.it Studio Prof. Marchetti s.r.l. Via Bracciano 38 00189 Rome - Italy

2. Background and References; • DMT Equipment • Test Layout and the WorkingPrinciple • How to Insert the DMT Bladeintosoil • The Membrane Calibration • C-Reading and Dissipation Test • Interpretation of the Results • 7.1 Intermediate Parameters (ID, KD, EDMT) • 7.2 GeotechnicalSoilParameters (MDMT, Cu, f, etc.) • 8. QualityChecks and Maintenance

3. Soil Investigation Identification of potential limit states Critical parameters essential to the successful completion of the project Laboratory testing In situ testing Previous site investigation or published data Back analysisof performance ofnearbyconstruction In Situ Testing: when? • Good quality sampling is not possible; • The parameter required cannot be obtained from laboratory test (in situ horizontal stress); • In situ tests are cost effective and quick • Appropriate methods may be able to test large volumes of ground ensuring that the effects of large particle size and discontinuities are fully represented.

4. In situ Testing Method (Mayne et al., 17th Int. Conf. on Soil Mech. and Geotech. Eng., 2009)

5. SDMT and SCPTU “... In this fast-paced world, a more efficientapproach … In particular, the SeismicPiezocone (SCPT) and the SeismicDilatometer (SDMT) ... offerclearopportunities in the economical and optimalcollection of data” “... SCPT and SDMT direct-pushtestsshould serve as the basis … in routine daily site investigationpractices …” Mayne P.W., Georgia Institute of Technology, Atlanta, USA (17th Int. Conf. on Soil Mech. and Geotech. Eng., Alessandria d’Egitto 2009)

6. SDMT and SCPT 4° International Conference on Geotechnical and Geophysical Site Characterization, Brazil, September 2012 • Total 226 papers: 57 references to SDMT, 40 on SDMT • Papersrecommending SCPT and SDMT for routine investigation • Robertson (Mitchell lecture): “more efficient and cost effective approach is the utilization of direct-push methods using multi-measurement in-situ devices, such as the seismic cone (SCPT) and the seismic flat dilatometer (SDMT)” • Howi (session report): ‘”The uncertainty [of SPT] is a strong argument in support of the recommendation by Mayne et al. (2009) that the SCPT or SDMT should be used instead of SPT for routine investigations’” • Mlynarek (session report): ‘”Several papers created an excellent foundation for further, global analyses of results from different countries in areas, where CPTU and SDMT/DMT are becoming basic methods for the evaluation of subsoil properties under in situ conditions”’ • De Vincenzi, Cruz, ..

7. The Flat Dilatometer Test DMT

8. DMT and SDMT Users Community (>200 in USA) (°) Algeria, Angola, Argentina, Australia, Austria, Bahrain, Bangladesh, Belgium, Bolivia, Bosnia, Brazil, Bulgaria, Canada, Czech Republic, China, Chile, Cyprus, Colombia, Costa Rica, Croatia, Denmark, Ecuador, Egypt, United Arab Emirates, Estonia, Finland, France, Germany, Greece, Guadalupe, Guatemala, Honduras, Hong Kong, Hungary, India, Indonesia, Iran, Israel, Italy, Japan, Korea, Kosovo, Kuwait, Lithuania, Malaysia, Mexico, Netherland, New Zeland, Norway, Oman, Pakistan, Peru, Poland, Portugal, Romania, Russia, Saudi Arabia, Serbia, Singapore, Slovenia, South Africa, Spain, Sri Lanka, Sweden, Switzerland, Taiwan, Thailand, Tunisia, Turkey, United Kingdom, United States of America, Venezuela, Vietnam.

9. Basic DMT and SDMT references: www.marchetti-dmt.it Website: www.marchetti-dmt.it

10. Basic DMT and SDMT References: www.marchetti-dmt.it

11. Basic SDMT References Manuals, Reports … TC16 (2001). “The DMT in soil Investigations”, a report by the ISSMGE Technical Committee TC16 on Ground Property Characterization from in-situ testing. European Standards EUROCODE 8 (2007). “Standard Test Method, European Committee for Standardization”, Design Assisted by Field Testing, Flat Dilatometer Test (Part 3 - Section 9), EUROPE. SGF Report (1994). “Recommended Standard for Dilatometer Tests, SGF Report” 1:95E, Swedish Geotechnical Society, SWEDEN. Nuove Norme Tecniche per le Costruzioni NTC08 – CIRCOLARE 02/02/2009 (2009). “Istruzioni per l’applicazione delle Norme Tecniche per le Costruzioni”, sez. C6.2.2, Consiglio Superiore dei Lavori pubblici, ITALY. ISO/TS 22476-11:2005(F) (2005). “Geotechnical Investigation and Testing – Field Testing – Flat Dilatometer Test”, (parte 11), FRANCE. Worlwide Standards ASTM (2002 – reapproved 2007). “The standard test method for performing the Flat Dilatometer Test (DMT)” (D6635-01), American Society for Testing and Materials, AMERICA. TB10018 (2003). “In situ Measurementofrailwayengineeringgeology”, MinistryofRailway; GB50021 (2003). “Code forinvestigationofgeotechnicalengineering”, MinistryofHousing and Urban-RuralDevelopment; DGJ08-37 (2012). “Code forinvestigationofgeotechnicalengineering”, CHINA.

12. DMT Flat Dilatometer Equipment

13. The DMT Blade Stainless steel blade width: 0.095 m blade thickness: 0.015 m Blade : pushing thrust up to 250 kN membrane diameter: =0.06 m (Marchetti, 1980)

14. 3 4 7 2 1 DMT Test Layout 5 6 • Dilatometer Blade • Push Rods (i.e. CPT) • Push Force or dynamic penetration • Pneumatic – electric cable • Control Box • Pneumatic cable • Gas Tank • A Lift-off pressure • B Pressure for 1.1 mm expansion A B

15. Control Box details 1/3 pressure gages connected in parallel-different scale ranges (1 MPa / 6 MPa)

16. Control Box details 2/3 galvanometer and audio buzzer signal main valve Provides a shutoff between the gas source and the blade-control unit system slow vent valve to vent the system slowly for C-readings toggle vent valve to vent quickly the system pressure to the atm micrometer flow valve to control the rate of flow during the test

17. Control Box details 3/3 tank rods p/e cable to DMT

18. DMT Working Principle A • The blade works like an electric switch (On/Off) • Fix the displacement and measure the required pressure B

19. Schematic DMT Test sequences Audio signal: Readings: ON OFF ON (OFF) ON A(p0)B(p1)C (p2)

20. Pushing equipment DMT using a penetrometer DMT using a drill rig Depth incrementistypically 20 cm The DMT penetration rate from 1 to 3 cm/s are acceptable (Eurocode 7, 1997)

21. Truck Penetrometer (most efficient) cable exits from rods

22. Light penetrometer Juan Santamaria Intnl. Airport – Costarica • Drill rigs or light rigs may be used only in soft soils or for very short depth • Capability of penetrating through cemented layers /obstacles

23. Field equipment for inserting the DMT blade Driven or pushed by light penetrometer Pushed by drill rig Driven by Spt tripod Pushed from a jackup From floating barge Driven by drill rig

24. Seafloor Dilatometer

25. Push rods and rods adaptator A B

26. Lower adaptor to DMT

27. Upper slotted adaptor to DMT cable exits from rods

28. Drill rig - Downhole Torpedo Method • TORPEDO pre-assembledbefore test (blade + 3 m of rods + intermediate slottedadaptor) • Rods + torpedo are insertedat bottom of borehole • Cable exits from slot, runsthroughchannel in collar and istaped to rods

29. Drill rig used as a penetrometer: Sciacca Method The DMT blade can also be inserted by a drill rig, used as a penetrometer for pushing (Sciacca Method). Drill rod Adaptor drill rod to push rod Slotted Adaptor Push rod

30. The Membrane Calibration

31. The calibration … misconcept ! • The DMT doesnotrequireanycalibration or equipmenttuning ! • The term “Calibration” isonlyreferred to the non-zero rigidity of the membrane and itsmeasurementissubtracted to fieldreadings

32. Membrane calibration: definitions DA: the external pressure which must be applied to the membrane in free air to collapse it against its seating (i.e. A position). (This negative pressure as a positive DA value!) DB: the internal pressure which in free air lifts the membrane center 1.1 mm from its seating (i.e. B position).

33. Membrane calibration Use syringe and short calibration cable for performing calibration

34. DMT Flat Dilatometer equipment: control box

35. DA and DB • A & B are used to correct the A & B readings into p0 & p1 (TARES to be detracted) • A & B must always be measured before and after each test • Calibration is a good indicator of equipment condition, hence of quality of data • A large difference between before/after A & B values should prompt a membrane change (usually apparent)

36. Acceptance values of DA and DB (Eurocode 7, 1997) • INITIAL values of A, B(before inserting the blade) must be in the ranges: • A= 5 - 30 kPa • B= 5 - 80 kPa • If not, replace the membrane before testing. FINAL values of A, B The change of A or B between beginning and end of sounding must be  25 kPa |(A)finale - (A)iniziale| 25 kPa |(B)finale - (B)iniziale| 25 kPa If not, test results must be discarded. • TYPICAL values of A, B • A= 15 kPa • B = 40 kPa

37. Importance of accurate DA and DB • Inaccurate A, B are virtually the only potential source of DMT instrumental error; • Any inaccuracy in A, B would propagate to all A, B of a sounding; • Accurate A, B are necessary in soft soils ( liquid clays or liquefiable sands) where A, B are just a bit higher than A, B (correction  difference between similar numbers); • Small inaccuracies in A, B are negligible in medium to stiff soils (A, B are a small part of A, B).

38. Determination of A and B To obtain A • Apply vacuum by pulling back the syringe piston and buzzer becomes active. • Slowly release the piston and read A on the low-range gage when buzzer stops. • Note this negative pressure as a positive value, e.g. A = 15 kPa for a vacuum of 15 kPa (the correction formula for p0 takes into account that a positive A is a vacuum). To obtain B • Push slowly the piston into the syringe and read B on the low-range gage when buzzer reactivates. REPEAT SEVERAL TIMES

39. STEP-by-STEP procedure: A, B (,C) As soon as rig operator reaches test depth, he signals go-ahead to DMT operator, who: • (Closes yellow vent valve). Slowly opens black micrometer valve (signal on). When sound stops, reads A. • Continues to inflate (signal off). When sound reactivates (1.1 mm) reads B. Immediately after B, follows 4 operations: • Open the toggle vent valve to depressurize membrane. • Close micrometer flow valve (pressure supply). • Gives go-ahead to rig operator to advance one depth increment. • Write A and B.

40. On the membrane expansion rate… (Eurocode 7, 1997) • Start of inflation 1-2 seconds • A reading in15 secondsfrom reaching the desired test depth • B reading in 15 secondsafter the A reading • Inflate the membrane relatively fast up toabout 70% of the expectedpressurereading, theninflateslowly in proximityof the expectedpressure • The rate of pressure increaseisvery • slow in weaksoils and • faster in stiffsoils

41. C readings • It is possible the determination of the pre-insertion equilibrium pore pressure • Sand, silt • Clay • Only in sandy, silty layers the closing pressure approximates u0

42. C-Readings in sands • Besides "normal" A & B readings, a third reading C - closing pressure - can also * be taken by slowly deflating the membrane just after B reading is reached. • To perform the C-reading, there is only one difference in the normal test sequence: • After B, open the slow vent valve instead of the fast toggle vent valve and wait  1 min until the pressure drops approaching the zero of the gage. At the instant the signal returns, take the C-reading. • Note that, in sands, the value to be expected for C is a low number (usually < 100 - 200 kPa, i.e. 10 or 20 m of water). Corrected C- reading p2 = C - ZM + A

43. C – readings in sand: pore water pressure SAND: C  Uodrainage ( piezometer) Du≈0 CLAY: C > Uono drainage (highlights u) Du0 UD=0free draining layer UD>0nofree draining layer p2-u0 p0-u0 UD= Du≈0 UD= Pore Pressure Index (Schmertmann 1988)

44. Example of C readings (Catania Harbour – 2012)

45. Example of C readings (Catania Harbour – 2012)

46. Example of C readings (Catania Harbour – 2012)

47. total contact horizontal stress σh (kPa) Time (min) Dissipation Test: estimation of in situ Consolidation and Permeability Coefficient (Totani, Calabrese & Monaco,1998) (not feasible in sandy silt, sand or gravel)

48. Acquisition DMT Dissipation (logt, A)

49. Acquisition DMT Dissipation (logt, A)

50. Validationof the consolidationcoefficient DMT vs. otherdissipationtests Totani et al. ISC '98 - Atlanta, Georgia (USA)