Joint Spacing

The Joint Spacing option allows you to calculate the true joint spacing of joints in a joint Set, calculated from distance measurements recorded along a linear or borehole Traverse.

To use the Joint Spacing option:

• You must have at least one (or more) joint Sets defined. See the Sets topic for more information.
• You must have at least one (or more) Linear or Borehole Traverses defined (e.g., Linear Scanline, Linear Borehole Oriented Core, Linear Borehole Televiewer, Curved Borehole Oriented Core, Curved Borehole Televiewer).

If the above 3 criteria are met, then the Spacing option will be enabled.

To create a Joint Spacing chart:

1. Select Joint Analysis > Spacing from the Analysis ribbon.
2. In the Joint Spacing dialog:
1. Select the Spacing Type from the drop down, either True or Apparent spacing
3. Select a joint Set from the drop down.
4. Select all or any combination of individual traverse(s) using the Traverses checkboxes. You can quickly select all or none using the Select All and Deselect All buttons.
At least one Traverse must be selected.
5. Enter the Number of Intervals.
6. Optionally select the Best Fit Distribution checkbox to show the best-fitting statistical distribution for the joint spacing data. See the Statistical Distributions topic for more information.
7. Click OK, and a histogram of joint spacing (true or apparent) and statistics will be generated for the selected joint Set and Traverse(s).

See below for more details.

True Spacing and Apparent Spacing

The Apparent Spacing is equal to the difference in Distance values (entered in the Distance column) between adjacent joints which belong to the SAME joint set. This is the raw, unprocessed spacing as measured directly from a linear scanline or borehole.

The True Spacing is the actual perpendicular spacing between adjacent joints in a joint set. The True Spacing is always less than or equal to the Apparent Spacing, and is calculated as follows:

True Spacing = Apparent Spacing * cos ( a) = Apparent Spacing / Terzaghi Weighting

where:

• a is the angle between the pole of the mean joint set plane and the linear Traverse direction; alternatively, Terzaghi Weighting (= 1 / cos ( a)) = the bias correction factor for the mean joint set plane and the linear Traverse direction. If joints are exactly perpendicular to a linear Traverse, then true spacing = apparent spacing.

Joint Set

You can only choose one joint Set for plotting at a time. To analyze spacing for a different joint Set, repeat the above steps for each desired Set.

Traverses

You can choose to plot spacing data based on all traverses together, or select any combination of individual traverses.