SDMT MULTIPLE CHOICE QUESTIONNAIRE (ANSWERS)

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

2. 1) 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!

3. 2) When generating the shear wave with a hammer and beam, at what approximate distance from the rods should the shear beam be placed: • About 5 m • As close as possible, in contact with the rods • As close as possible, but not in contact with the rods (say between 0.5-1.0 m) Shear Wave Source Issues  • Distance from SWS to rods (closest without touching rods) • SWS Placement and Orientation • SDMT Sensor Orientation

4. 3) Where should the shear beam be placed if the test site has a pavement: • On the pavement • On natural soil, after pavement removal (adding soil if necessary)  Shear Wave Source (hammer) • Geometry & weight: influence only on max test depth (not results) • SWS transmitsvibrationonlyifgoodadherencewithsoil • Applyload on SWS (i.e. truck jacks) • Removepavement under SWS (ifpresent) • Userubberfordecouplingwithloadenergytosoilnottoload

5. 4) Why should the operator load the shear beam (ex. with a lift jack of the pushing machine): • In order to minimize the beam’s vibration when the hammer hits it • So that there is a good coupling between the beam and the soil and also so that the shear beam does not advance when the hammer hits it • None of the above  Shear Wave Source (hammer) • Geometry & weight: influence only on max test depth (not results) • SWS transmitsvibrationonlyifgoodadherencewithsoil • Applyload on SWS (i.e. truck jacks) • Removepavement under SWS (ifpresent) • Userubberfordecouplingwithloadenergytosoilnottoload

6. 5) Why is it recommended to place a rubber sheet between the load and the shear beam: • To avoid scratches on the beam • To avoid scratches on the load • To minimize the energy transmitted to the load on the beam  Shear Wave Source (hammer) • Geometry & weight: influence only on max test depth (not results) • SWS transmitsvibrationonlyifgoodadherencewithsoil • Applyload on SWS (i.e. truck jacks) • Removepavement under SWS (ifpresent) • Userubberfordecouplingwithloadenergytosoilnottoload

7. 6) What is the correct placement of the shear beam with respect to the rods: • The hitting direction of the hammer should be approximately perpendicular to the line between the center of the beam and the rods • The hitting direction of the hammer must be approximately parallel to the line between the center of the beam and the rods • A preferential orientation does not exist 

8. 7) What is the correct orientation of the sensors with respect to the hitting direction of the hammer ? • The hitting direction of the hammer must be perpendicular to the axis of the sensors • The hitting direction of the hammer must be parallel to the axis of the sensors • A preferential direction does not exist 

9. 8) When performing SDMT test in marine sites, where should the shear beam be installed: • Floating on the water • Anywhere on the seafloor • On the seafloor, as close as possible to the rods without contact (say between 0.5-1.5 m) 

10. 9) Is it possible to perform seismic measurements in non-penetrable soils: • Yes, as a standard SDMT test in a borehole filled with water • Yes, as a standard SDMT test in a borehole with casing • Yes, as a standard SDMT test in a uncased borehole backfilled with clay or silt • Yes, as a standard SDMT test in a uncased borehole backfilled with gravel (diameter grain size between 5-15mm) • It is not possible 

11. 10) Why are SDMT shear wave velocity measurements performed every 0.50 m: • Because 0.50 m is a standard recommended by the norms • Because the sensors are spaced 0.50 m, to cover all the soil profile • Because the sensors are spaced 1.0 m  Seismic dilatometer – SDMT 0.5 m 0.5 m

12. 11) In penetrable soils, why are Vs measurements faster with the SDMT compared to the traditional innhole seismic measurements (multiple answers possible): • It is not faster • The downhole method requires to wait for the cementation of the pipe in the borehole • The downhole method requires at each depth to guarantee a good contact between the sensors and the pipe   SDMT features SDMT • Vs interpretation • automatic • operator indipendant • real time • Accuracy of delay (Δt) calculation • True-interval (2 receivers instead of 1) • Same wave to both receivers • No Trigger influence on Δt calculation • Signals are amplified and digitized in depth  clean waves  delay Δt very clear • Test execution is rapid • no hole • no cementation (e.g. crosshole)

13. 12) To perform SDMT tests, in what position must the DMT membrane be: • In the open position (sound off) • In the closed position (sound on) • In any position  Seismic Test Configuration • DMT membrane mustbe in A position (checkacousticsignal ON whenswitchis on DMT) • After DMT readings in sand, generally membrane isnotpushed back to A position  no contact no sound (advance a few cm untilsignal ON) • Switchto ‘Seismic’