# 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.

In order to use the **Joint Spacing** option:

- You must have at least one (or more) joint Sets defined, using the options available for creating Sets (e.g. Add Set Window, Add Set Freehand).
- You must have at least one (or more) Linear or Borehole Traverses defined (e.g., Linear, Linear BH Oriented Core, Linear BH Televiewer, Curved BH Oriented Core, Curved BH Televiewer).
- The Distance Column must be enabled (checkbox in
**Project Settings**) and**Distance**values entered in Grid Data view. - Select
**Joint Spacing**from the**Analysis**menu. - In the
**Joint Spacing**dialog: - Select the
**Spacing**from either**True Spacing**or**Apparent Spacing** - Select a joint
**Set.** - Select all or any combination of individual
**Traverse**(s). You can quickly select all or no Traverses using the**Select All**/**Deselect All**options.**NOTE**: At least one Traverse must be selected.

- Select the
- Select
**OK**and a distribution graph of joint spacing (true or apparent) and statistics will be generated for the selected joint set and Traverse(s). See below for more details.

If the above 3 criteria are met:

## 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 Traverse, borehole or oriented core.

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 = 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.

**NOTE**: The Spacing calculation is valid for all Traverse types except Planar, since the calculation assumes data collection along a line rather than a planar surface.

## Summary of Spacing Results

The Info Viewer automatically provides a summary of joint spacing results for *all* Sets and *all* Traverses, as long as the 3 criteria are met (Linear Traverses / Sets / Distance column). Even if you do not actually select the **Joint Spacing** option to plot results, the Joint Spacing summary will be available in the Info Viewer.