Seismic Receiver Rods
The receiver rods are screwable glass-fibre reinforced polymer resin rock anchor equipped either with three orthogonal mounted geophones building a 3 component (3 x GS-14 L3, 28 Hz) geophone or with a 3C-piezoelectrical receiver (PCB 356A17) to measure the signal frequency range up to a few kilohertz. The receiver rods can be installed in drill holes in two ways. For permanent installation the receivers are glued into the boreholes with a two-component epoxy resin. Alternatively they are screwed into a closed tube equipped with an internal screw thread which is cemented in the drill hole. After finishing the measurements these receivers can be removed. Only the tube remains in the rock and is lost. The receiver rods are applied along and around tunnels and drifts in 1 or 2 m deep boreholes to minimize the influence of the excavation damage zone (EDZ) and noise on the registration of the incoming 3D wave field.
Receiver systems available:
- 74 x 2m long geophone receiver rods
- 14 x 1 m long geophone receiver rods
- 10 x 2 m long piezoelectrical rods
For the operation of the 3C piezos in the measuring armature, corresponding signal conditioners consisting of a constant current source with a downstream low-noise amplifier are required. Four times three signal conditioners were installed in pelicases, so that four piezo measurement anchors can be operated with one pelicase.
Borehole Receiver Chain
The receiver module is clamped to a GRP (glass fiber reinforced plastic) rod, such as is used when pulling cables into protective tubes. Up to 8 modules can be used with variable spacing between receivers in one borehole. By modifying the undercarriages, the receiver units can be adapted to different borehole diameters, with a minimum diameter of 76 mm and a maximum of 96 mm. The receiver modules are pushed into the borehole with the GRP rod to the desired position. Compressed air is then applied to the assembly via the hose provided. The lifting bag inflates and presses the geophone head against the borehole wall, while the unit is supported on the opposite borehole wall via the undercarriage. The lifting bag also decouples the geophone head from the rest of the installation, so that vibrations are largely prevented from being coupled in via the GRP rod and the undercarriage. When the compressed air is released from the system after the measurement has been completed, the geophone head is retracted via the return springs integrated in the guides. The entire installation can then be repositioned or removed.
Technical parameters:
- Receiver chain with up to 8 levels
- 25 cm length / module
- 3-Component-Geophon (3x GS 14 L9)
- Pneumatically coupled
- Applicaple up to 200 m length in horizontal wells with 76 - 96 mm diameter
Available modules: 9