Geostuff Wall-Lock Borehole Geophones
Geostuff offers a selection of wall-lock borehole geophones.
Model BHG-2 (pictured on the right in photograph) contains a 3-component
geophone in an X-Y-Z orientation. The outside diameter is 1.85 inches (47 mm),
small enough to fit inside a schedule-40, 2-inch plastic pipe. The clamping
mechanism is a robust, steel spring compressed
by a DC electric motor.
There
are no rubber bladders to break or tubes to leak, and operation is relatively
independent of depth. BHG-2 models have been used to depths of 500 meters
(consult factory for details). Geophone elements are 15 Hz natural frequency,
and are also available with 10, 14, 28 or 40 Hz natural frequencies.
The BHG-3 (pictured, center) includes both a fluxgate compass and a servo mechanism which automatically rotates the horizontal geophones to the azimuth of your choice. Simply point the compass (located in the lower cylinder) towards magnetic north, then orient the clamp spring toward the desired direction
The BHGC-1 Controller is available. This unit switches power to the clamp mechanism and compass, and also directs the geophones to selected seismograph channels.
The clamping mechanism is operated by a DC motor, actuated by power sent down two of the conductors. The polarity is reversed to release the clamp. A controller is relatively easy to construct and a schematic is provided in the instruction manual for those who wish to build their own.
The
cable is a 7-conductor copperweld with KevlarŪ braid and polyurethane
jacket, specially manufactured by Tescorp Seismic Products. A Reed Products
SU-8F waterproof connector is molded on the wet end and a Cannon NK-27-21C on
the dry end. The cable can be easily disconnected from the geophone for ease of
handling. Extension cables are also available with a pair of male and female
connectors, so that the cable can be temporarily lengthened for unusually deep
holes.
The standard clamp mechanism works for holes between 2 and 6 inches (48-150
mm), but for large holes the Big Hole Kit is available. This mechanism easily
installs in place of the standard spring on any of the BHG series and will
expand up to 19 inches (48 cm).
Geostuff has prepared a 14-page tutorial paper describing the field methods for conducting downhole shear wave surveys. To download a copy in Adobe Acrobat pdf format, click Borehole Shear-Wave Surveys for Engineering Site Investigations
Click data sheet to download a copy in Adobe Acrobat format.
For more information, contact info@geostuff.com
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