Introduction
The Robertson Geo PS suspension logger
measures compression and shear velocities of surrounding rock and soil from
within deep uncased boreholes.
Operation
The system uses a seven metre probe,
containing a source and two receivers placed one metre apart and suspended on a
cable, which also acts as the data umbilical to the receiver/control device on
the vessel. The probe is lowered in to the borehole to the specified depth,
where the source generates a pressure wave in the borehole. The pressure wave
is converted into seismic waves at the borehole wall. At the wall at each
receiver location the seismic waves are converted back into pressure waves and
received by the geophones that send the data to the recorder on the vessel.
Application
The probe is a high energy shear-wave
source that has around 20x the output energy of a conventional borehole sonic.
This makes it highly effective in soft soils and other attenuating formations
where conventional full-wave form sonics often perform poorly.
Measurements
Able to measure compression wave velocities
and formation shear wave velocity. Utilised to measure the physical properties
of soil and rock to determine the shear modulus, bulk modulus, compressibility
and Poission’s ratio.