|
 How
an Acoustic CPT System Works...
The cordless CPT does not require a cable for data transmission to the
surface. Inside the probe, the digital coded signal is converted to an
acoustic signal which is transmitted along the drill rods to the surface.
Sound signals are received by a microphone at the surface which transmits
the signal to a PC via a computer interface.
 |
|
|
| The 6625CPT machine was specifically designed for geotechnical CPT applications, but is also equipped with a GH62 hammer to drive casings and rods for environmental sampling and logging work. |
|
| A cordless Acoustic NOVA system is placed underneath the microphone in preparation for the next data transmission. The CPT tooling is being used in combination with the Geopobe® 6625CPT machine. |
|
| An adjustable hydraulic chuck on the 6625CPT machine clamps on to CPT tools during a static push. |
Cordless
Transmission Allows for Lubrication and Retraction Grouting
There are many reasons for the widespread use of the CPT method. Probably
the most important is the in situ measurement... it measures soil properties
in the right environment; in the soil as it is, where it is. Another advantage
of the cordless CPT design is the option of sealing off test holes to
eliminate the possible spread of pollutants. New possibilities for grouting
open up since the rod bore remains unused during sounding. Bentonite,
or other grout materials, can be injected downhole while pulling back
the sounding rods. At great depths, most of the pushing capacity of the
equipment can be taken up by friction along the sounding rods. Geoprobe®
Systems has developed tools for lubricating the rod with grout as the
probe is advanced. These same tools allow the hole to be filled with grout
as the CPT probe is retracted. Retraction grouting is the easiest and
most effective method for sealing small diameter probe holes.
(left)
Acoustic transmission of CPT data allows use of the annulus for rod lubrication.
(right)
Grout is pumped around the CPT probe to fill the holes as the tool is
retracted.
|
