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DMT MULTIPLE CHOICE QUESTIONNAIRE (ANSWERS)

!. DMT MULTIPLE CHOICE QUESTIONNAIRE (ANSWERS). . . . . . !. . Which types of soils are testable with the DMT: All fine soils All soils, including rock and gravel. . Soils testable by DMT. SANDS, SILTS, CLAYS (grains smaller vs membrane D=0.06 m).

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DMT MULTIPLE CHOICE QUESTIONNAIRE (ANSWERS)

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  1. ! DMT MULTIPLE CHOICE QUESTIONNAIRE (ANSWERS)      ! 

  2. Which types of soils are testable with the DMT: • All fine soils • All soils, including rock and gravel  Soils testable by DMT • SANDS, SILTS, CLAYS (grains smaller vs membrane D=0.06 m). • Clays: Cu = 10-3 MPa to 1 MPa (marls) • Moduli: M = 0.5 to 400 MPa • Very robust, fast and easy penetration in soft rocks and hard soils PROVIDED sufficient pushing capacity (safe push on blade 25 ton) • It can cross through GRAVEL layers  0.5 m

  3. 2) Before connecting the pneumatic cable from the gas tank pressure regulator to the female quick connector of the control unit, the operator should assure that: • The main valve is open, the vent valve is open and the flow valve is closed • The main valve is closed, the vent valve is open and the flow valve is closed • The main valve is closed, the vent valve is closed and the flow valve is open • The main valve is open, the vent valve is open and the flow valve is open STEP-by-STEP procedure: A, B (C)  • The pressure regulator must be able to supply a regulated output pressure of at least 7-8 Mpa (set the regulator so that the pressure supplied to the control unit is about 3 MPa). • NB Before open the gas tank we have to ensure that the main valve and the micrometer flow valve are closed and the toggle vent valve is open.

  4. 3) For each reading A, B and C, specify the transition of the audio-visual signal: • A pressure reading:  on-off  off-on • B pressure reading:  on-off  off-on • C pressure reading:  on-off  off-on    Schematic DMT Test sequences Audio signal: Readings: ON OFF ON (OFF) ON A (p0) B (p1) C (p2)

  5. 4) Order the 4 operations that the operator should perform immediately after the B pressure reading is taken: _C_ tell the penetrometer operator to advance to the next test depth _B_ close the flow vent valve _D_ write A and B readings (if no automatic acquisition available) _A_ open toggle vent valve STEP-by-STEP procedure: A, B (,C) 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.

  6. 5) If a DMT test has to be interrupted, when is the recommended moment to interrupt: • When the next test depth is reached, just before taking the readings • During penetration • After the readings have been taken, just before advancing to the next test depth Recommended SDMT Test Sequence  (DMT tests every 20 cm; Seismic test every 50 cm) • When both tests, DMT first; • If a DMT test has to be interrupted, the recommended moment is after the readings have been taken, just before advancing to the next test depth; • Seismic test useless before1 m, (first seismic test recommended after 1.50 m) the center of the 2 sensors is 0.5 m above DMT, so first sensor is at 0.25 m when DMT is at 1.0 m!

  7. 6) When performing both DMT and seismic measurements at the same depth, in what order should they be done: • Seismic measurements first • DMT measurements first • In any order Recommended SDMT Test Sequence  (DMT tests every 20 cm; Seismic test every 50 cm) • When both tests, DMT first; • If a DMT test has to be interrupted, the recommended moment is after the readings have been taken, just before advancing to the next test depth; • Seismic test useless before1 m, (first seismic test recommended after 1.50 m) the center of the 2 sensors is 0.5 m above DMT, so first sensor is at 0.25 m when DMT is at 1.0 m!

  8. 7) When the blade has advanced to the desired test depth, just after the penetration has stopped, when should the operator start to inflate the gas: • Immediately after stopping penetration • After a pause of approx 15 sec  On the membrane expansion rate… (Eurocode 7, 1997) • The timedelaybetween end ofpushing and start ofinflationis 1-2 seconds • A readingshouldbetypicallyobtained in 15 secondsfromreaching the desired test depth • B readingshouldbetypicallyobtained in 15 secondsafter the A reading • (The rate ofpressureincreaseisvery slow in weaksoils and faster in stiffsoils) • NB: Forlongercables the flow rate mayhavetotobereducedtoallowpressureequalizationalong the cable!

  9. 8) When performing the DMT test, in approximately how much time should the A reading be taken: • As fast as possible • In about 1 minute • In exactly 15 seconds • In approximately 10-20 seconds after the blade has arrived to the test depth  On the membrane expansion rate… (Eurocode 7, 1997) • The timedelaybetween end ofpushing and start ofinflationis 1-2 seconds • A readingshouldbetypicallyobtained in 15 secondsfromreaching the desired test depth (evenwhenusing the automatic data acquisition) • B readingshouldbetypicallyobtained in 15 secondsafter the A reading (evenwhenusing the automatic data acquisition) • (Inflate the membrane relatively fast up toabout 70% of the expectedpressurereading, theninflateslowly in proximityof the expectedpressure) • NB: Forlongercables the flow rate mayhavetotobereducedtoallowpressureequalizationalong the cable!

  10. 9) When performing the DMT test, in approximately how much time should the B reading be taken: • As fast as possible • In about 1 minute • In about 10-20 seconds after the A-reading  On the membrane expansion rate… (Eurocode 7, 1997) • The timedelaybetween end ofpushing and start ofinflationis 1-2 seconds • A readingshouldbetypicallyobtained in 15 secondsfromreaching the desired test depth (evenwhenusing the automatic data acquisition) • B readingshouldbetypicallyobtained in 15 secondsafter the A reading (evenwhenusing the automatic data acquisition) • (Inflate the membrane relatively fast up toabout 70% of the expectedpressurereading, theninflateslowly in proximityof the expectedpressure) • NB: Forlongercables the flow rate mayhavetotobereducedtoallowpressureequalizationalong the cable!

  11. 10) What is the smartest rate of inflation for the A and B pressure readings: • Inflate at a constant rate • There is no smart rate of inflation • Inflate the membrane relatively fast up to about 70% of the expected pressure reading, then inflate slowly in proximity of the expected reading  On the membrane expansion rate… (Eurocode 7, 1997) • The timedelaybetween end ofpushing and start ofinflationis 1-2 seconds • A readingshouldbetypicallyobtained in 15 secondsfromreaching the desired test depth (evenwhenusing the automatic data acquisition) • B readingshouldbetypicallyobtained in 15 secondsafter the A reading (evenwhenusing the automatic data acquisition) • (Inflate the membrane relatively fast up toabout 70% of the expectedpressurereading, theninflateslowly in proximityof the expectedpressure) • NB: Forlongercables the flow rate mayhavetotobereducedtoallowpressureequalizationalong the cable!

  12. 11) When using the automatic data acquisition for the DMT readings, what should the operator do if digital pressure gauge on the screen does not show zero pressure when the vent valve is open: • Take the readings on the mechanical pressure gauges • Stop the test • Click on the Zero Gauge button, to reset the zero of the pressure transducer  AutomaticAcquisitionof DMT readings

  13. 11) When using the automatic data acquisition for the DMT readings, should the rate of inflation differ: • Yes, as fast as possible since the readings are taken automatically by the system • Follow the same recommendations as when no acquisition system is used • Any rate is acceptable  On the membrane expansion rate… (Eurocode 7, 1997) • The timedelaybetween end ofpushing and start ofinflationis 1-2 seconds • A readingshouldbetypicallyobtained in 15 secondsfromreaching the desired test depth(evenwhenusing the automatic data acquisition) • B readingshouldbetypicallyobtained in 15 secondsafter the A reading(evenwhenusing the automatic data acquisition) • (Inflate the membrane relatively fast up toabout 70% of the expectedpressurereading, theninflateslowly in proximityof the expectedpressure) • NB: Forlongercables the flow rate mayhavetotobereducedtoallowpressureequalizationalong the cable!

  14. 13) What is the main difference between performing only A and B readings rather than A, B and also the C reading: • Continue to inflate after B • After B, deflate with the slow vent valve instead of the fast vent valve • None of the above 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

  15. 14) When should the membrane calibration be done (multiple answers possible): • At each depth, before each DMT measurements • Just before inserting the blade in the ground and after extraction – in each sounding • At the end of the year • If a membrane is damaged, before continuing the test after membrane change   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 sounding • 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)

  16. 15) In which soils is the DMT calibration mostly critical, so that it should be taken with maximum accuracy: • In sands • In very stiff soils • In very soft soils, where the calibration readings are of the same order of magnitude of the DMT readings  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).

  17. 16) When performing a deep DMT test, which requires to combine two pneumatic‑electric cables, how should the operator start the DMT test: • Using the full length of the two combined cables • Start with one cable then, when its length is not sufficient, add the second cable and continue the test • No difference Pneumatic-electric cables 3/4  2_ Extendable cable (terminale male isolated to blade and a terminale female not directly connectable to control unit)  by using an extendable cable the operator may connect additional cable(s) as needed during the test  Cable leader (short adaptor removed when a new cable is added) start with extendable cable with cable leader (when using both)

  18. 17) When performing a deep DMT test and combining an extendable pneumatic-electric cable with a non-extendable cable, which cable should the operator connect to the DMT blade: • The extendable cable • The non-extendable cable • No difference Pneumatic-electric cables 3/4  2_ Extendable cable (terminale male isolated to blade and a terminale female not directly connectable to control unit)  by using an extendable cable the operator may connect additional cable(s) as needed during the test  Cable leader (short adaptor removed when a new cable is added) start with extendable cable with cable leader (when using both)

  19. 18) How many times should the operator clean the inner part of the blade: • Every day • Once a week • Every 10 tests • After the membrane is cut or when dirt is inside the blade  Cleaning inside the blade Using the syringe apply 10 or more cycles of vacuum – pressure to verify sharpness of the electrical signal at the off and on inversions. If the signals inversions are not sharp, the likely reason is dirt between the contacts and the blade must be disassembled and cleaned. The parts of the instrument inside the membrane (disc, spring, metal cylinder…) must be kept perfectly clean to ensure proper electrical contacts. NO NEED to clean periodically (day, week ...) but only after damage (or dirt inside).

  20. 19) How is it possible to obtain the equilibrium pore water pressure with the DMT: • Performing a dissipation test • Performing C-readings in all soils • Performing C-readings in sands • It is not possible  • Sand, silt • Clay C readings • It is possible the determination of the pre-insertion equilibrium pore pressure • Only in sandy, silty layers the closing pressure approximates u0

  21. 20) When should the DMT membrane be replaced (multiple answers possible): • When there is a large difference between before/after A & B values • After 10-15 DMT Tests • When initial values of A, B (before inserting the blade) are not in the ranges: A = 5-30 kPaB = 5-80 kPa • When the membrane is not clean • When the membrane is not free of wrinkles or deep scratches • When the membrane does not expand smoothly, without popping or snapping sounds     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 kPaIf 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 kPaIf not, test results must be discarded. • TYPICAL values of A, B • A= 15 kPa • B = 40 kPa

  22. total contact horizontal stress σh (kPa) Time (min) • 21) What is the aim of the DMT dissipation test: • To obtain the equilibrium pore water pressure • To estimate the vertical effective stress • To estimate in situ the Consolidation and Permeability Coefficients  Dissipation test: estimation of in situ consolidation and permeability coefficient (not feasible in sandy silt, sand or gravel) (Totani, Calabrese & Monaco,1998) Clay and Silt in which the excess pore water pressure induced by the blade penetraton dissipates over a period of time greater than required one for the DMT test

  23. total contact horizontal stress σh (kPa) Time (min) • 22) In which kind of soil is the DMT dissipation test possible: • Only silt • Silt and Sand • Only clay and silts with a low permeability • In all soils  Dissipation test: estimation of in situ consolidation and permeability coefficient (not feasible in sandy silt, sand or gravel) (Totani, Calabrese & Monaco,1998) Clay and Silt in which the excess pore water pressure induced by the blade penetraton dissipates over a period of time greater than required one for the DMT test

  24. 23) For settlements calculation using “DMT Settlement” Program, which input file is needed? • .doc • .xls • .UNI • Graphs • Tabular Output • Report .UNI file = Input for allsubsequent software  SDMTElab • DMT Settlements • Laterallyloadedpiles (.dos) • CPTe-IT (Robertson) • 3rd party Software “DMT Settlements” program downloadable: www.marchetti-dmt.it/software/indexUpdate.htm

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