Dynamic Soil properties using Downhole Tests

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  • 8/16/2019 Dynamic Soil properties using Downhole Tests

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    Am Tonnenberg 18

    56567 Neuwied

    Tel.: 02631 / 778135

    Fax.: 02631 / 778136

    email: [email protected]

    Internet: http://www.geotomographie.de

    Geotomographie GmbH

    The aim of the downhole testing is to derive elastic rockproperties such as Poissons ratio or YOUNGs modulus. Shearwaves have to be generated at surface. A shear wave source(sledge hammer hit sidewise) is used at surface and a coupledreceiver system is moved in the borehole.

    Traveltimes of the seismic waves are analysed and seismicvelocity is calculated. Shear wave velocity can be transformed tosoil stiffness.

    Principle

    Test Result

    Shot point

       B  o  r  e   h  o   l  e

       G  e  o  p   h  o  n  e

    0 10 20 30 40 50

    Traveltime [ms]

    -35

    -30

    -25

    -20

    -15

    -10

    -5

    0

       D  e  p   t   h   [  m   ]

    P-Wave

    S-Wave

    Layer 1

    Layer 2

    Layer 3

    0 1000 2000 3000 4000

    Velocity [m/s]

    -35

    -30

    -25

    -20

    -15

    -10

    -5

    0

       D  e  p  t   h   [  m   ]

    S-Wave   P-Wave

    334  786

    572  1276

    1359  3608

     

    Seismic tests can be divided in two groups, surface tests andborehole tests. Surface tests are used to determine subsurfaceproperties using geophones on surface and a surface seismicsource. Borehole tests are bound to one or two boreholes whichhave to be drilled. Therefore, borehole tests are more expensivecompared to surface tests but provide more accurate data withdepth.

    The Downhole Test is a method which determines soilstiffness properties by analyzing direct compressional andshear waves along a borehole down to about 30 m.

    Dynamic Soil properties using Downhole Tests

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