Blind zone

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 i.e. the discontinuities line up or are approximately parallel with 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 pass through (or intersect). Hence, there could be the possibility of many discontinuities around the drillhole but no samples in the drillhole.

Note: This tool defines a Stereonet region of an unknown quantity of discontinuities. There may be none, some or many...

1. Open the Stereonet intended to show the Blind zone.

2. On the Geotechnical ribbon tab navigate to the Stereonet group and select Blind Zone.

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

   • Drillhole trend - angle from North (see Glossary).
   • Drillhole plunge - angle down from horizontal (see Glossary).
   • Intersection angle limit is the extra angle around the Drillhole trend and plunge to create a band of similar values.
   • 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.

EG. The region / band of trend and plunge representing a blind zone for a drillhole.
(drillhole trend = 40° , drillhole plunge = 60° , Intersection angle limit = 10° )