Geology Reference
In-Depth Information
Figure 6.6
Relative effect of a thin, horizontal high-resistance bed in other-
wise homogeneous ground. The areas under the curves have been made
equal, concealing the fact that the voltage observed using the Schlumberger
array will be somewhat less, and using the dipole-dipole array very much
less, than with the Wenner array.
sufficiently, a pit can be dug, lined with aluminium foil, wetted with salt
water and backfilled with soil. In arid conditions, detergent can be added
to the water to break down surface tension and improve contact with the
ground. A useful method of improving contact in coarse-grained materials
such as gravel is to fill holes with a clay slurry before inserting the metal
stake. In extreme cases, holes may have to be blasted through highly resistive
caliche or laterite surface layers.
Metal stake electrodes come in many forms. Lengths of drill steel are
excellent if the ground is stony and heavy hammering necessary. Pointed
lengths of angle-iron are only slightly less robust and have larger contact
