Blind Zone

Source file: blind-zone.htm

A blind zone on a stereonet represents the region of trend and plunge of discontinuity poles that are perpendicular to those of drillholes used to take samples. That is, the discontinuities line up with, or are approximately parallel to, the drillhole. This region is of interest because any potential discontinuities that line up with the drillhole are likely to be missed as they don't intersect. Hence there may be many discontinuities around the drillhole but no samples in the drillhole.

To create a blind zone, proceed as follows:

1. View and select the stereonet intended to show the blind zone.

2. On the Geotechnical tab, in the Stereonet group, click Blind Zone.

3. Enter the following values into the fields on the Blind Zone panel:

   • Drillhole trend: angle from North (see Glossary > Plunge)
   • Drillhole plunge: angle down from horizontal (see Glossary > Trend)
   • Intersection angle limit: the angle around the drillhole trend and plunge within which discontinuities are included in the blind zone
   • Other information such as a Name, Colour (for the lines surrounding the zone) and Destination stereonet

4. Select OK or Apply to create lines defining the blind zone limits on the stereonet, and stored in the Destination stereonet container.