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Downhole
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Seismic downhole(DH) measures the time necessary for
P and S waves to go from a surface seimic source, to
tthe receivers place in a sounding well.
With project data and the measured transmission
times the following may be derived:
Distance from source to receiver
Corrected transit times
Speed of P & S waves
Some important geotecnical parameters
The dromochrone graphic with seismic strata from
which the average velocity in each strata,some
average geotechnical parameters and VS30.
The graphic of P & S interval velocity, definition
of seismic strata and VS30
Graphics relating to geotechnic parameters can be
derived for each interval
The stratigraphy of the sounding well
The final report.
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Interpretation with direct method
In the interval method, transit times for the seismic waves,
are between two consecutive receivers, which are placed at different
depths before being measured, thus achieving an improvement in
measurements. (Interval velocity)
When only one receiver is available, i.e. reading pairs which are
not derived from a single impulse, the velocity values are treated
as pseudo intervals, which allows only an apparently improved
velocity profile.
When readings have been collected, it is possible to calculate
corrected times, the interval velocity of P & S waves, and the
relevant graphic.
Once interval velocities are available, the following are derived
for each interval: Density; Poisson's coefficient; Shear deformation
modulus; Edometric compressibility modulus; Young's modulus;
Volumetric compressibility modulus and VS30
Interpretation with Interval method
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