Geology Reference
In-Depth Information
Figure 4.37 Impression packer. Paraf
n wax paper has been pushed against the walls of the
borehole by a rubber in
atable packer. A series of pale-grey traces can be seen, which represent a set
the base of the packer. Other options for orienting devices now include
ux gate magnetometers and
gyroscopes.
Processing System (BIPS), which gives a continual visual record of
the borehole wall (Kamewada et al., 1990). The tool is lowered
down the borehole and a video camera takes a 360 degree image
millimetre by millimetre down the hole through a conical mirror
(
Figure 4.38).
Despite modern instrumentation for this tool, whereby
azimuth can be measured by magnetic
flux gates or gyroscopes, studies
have revealed errors of up to 20 degrees in this measurement (Döse
et al., 2008). Care must also be taken in interpretation of discontinu-
ities logged in boreholes, especially if boreholes are all vertical. There
will be obvious bias to the measurements
steep joints will be under-
sampled in vertical boreholes. As an example, during the Ching
Cheung Road landslide investigation (Halcrow Asia Partnership
1998a), BIPS measurements were taken in vertical boreholes and
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