Guralp Systems Limited
Radian - Technical Manual

Chapter 6. Recommended Field Procedures

Note: The Radian connector is fitted with two O-rings to guarantee the waterproofing. To connect the cable, maintain the Radian in vertical position and roughly align the grooves in the plug with the tongues in the socket before inserting the cable connector. Kindly push and rotate the connector until it lines up perfectly. Push it to down until it reaches the end stop. Screw the fixing ring down to the end of the thread.

Caution: The air compressed inside the connector can push in the opposite direction because of the O-rings. Do not use the fixing ring to help you pushing the connector inside the Radian to prevent any damage on the thread.

6.1 Post-hole installation

Compared to traditional vault-style installations, the post-hole method has the potential to save significant time and resources (material, labour), without loss of performance. The technique minimises thermal effects and improves noise performance, especially for horizontal sensor components at low frequencies.

To minimise surface noise effects, you should ensure that the hole is at least one metre deeper than the full length of the Radian Post-hole.

6.1.1 Procedure

6.2 Single-instrument bore-hole installation

6.2.1 Installation using hole-locks

For a bore-hole installation, you should have been provided with a winch and tripod from Güralp.

The key benefit of the Radian instrument is that it can operate at any angle so excellent seismic data can be obtained even if the the bore-hole is not completely vertical.

Before installing any instrument in a bore-hole, you should prepare the installation site.

6.2.1.1 Procedure

6.2.2 Installation using sand back-fill

Dry sand back-fill is a convenient and effective way of installing a single Radian bore-hole instrument in a time-stable environment. The presence of sand not only fixes the sensor in place at the bottom of the hole, but also reduces noise due to air convection.

The ideal type of sand to use is the fine, kiln-dried sand supplied for use in children's play sandpits. This is readily available in airtight bags, is thoroughly washed and clean, and will contain little sediment (when dried out after wetting, sand containing foreign matter may solidify and form a concrete-like substance, permanently trapping the sensor in position.) This sand is suitable for use in both dry and damp bore-holes.

In the procedure outlined below, the sensor will rest on a pad of sand around 300 mm thick. This pad will absorb any residual moisture at the bottom of the bore-hole, and ensure that the surroundings of the instrument are kept dry.

After positioning the sensor, more sand is added to fill the space between it and the bore-hole casing, holding it firmly in place. The sand should reach within 30 mm of the top of the instrument, but should not cover it. This way, the instrument can be more easily recovered when it requires maintenance or replacement. This is particularly important if the bore-hole is not completely dry, since moist sand does not flow well.

6.2.2.1 Procedure

6.3 Multi-instrument bore-hole installation (i.e. VSP tool)

The maximum number of instruments that can be strung together is six; this is due to limitations in the voltage that can be carried through to the vertical array and the safe loading strength of the power/signal cables.

6.3.1 Procedure

Caution: To prevent ingress of moisture, make sure that an end cap is securely fitted to the bottom of the lowermost instrument