For wedges sliding on one plane, can I use Dips to determine which joint is the sliding joint?

This information is not directly available in Dips.  For wedges sliding on one plane, Dips does not identify which is the sliding plane and which is the release plane. 

However, follow the instructions below for a way to determine this information:

  1. Select File>Export>Export Data to Excel, and all available analysis data will be exported to an Excel file.
  2. Select the Plane Intersections tab.  This lists analysis data for the Direct Toppling and Wedge Sliding modes.
  3. In the Wedge Sliding column, you will see a flag which identifies critical intersections (P2=sliding on two planes, P1=sliding on one plane)
  4. The associated planes from the original Dips file are identified in the columns Plane ID#1 and Plane ID#2.  This gives the row ID number of the planes from the original Dips file.
  5. You can go back to the original file and get the dip/dip direction of the two planes forming the wedge.

If you have Swedge you can simply input these two planes into Swedge, along with the slope orientation.  The Swedge InfoViewer will give you the details about sliding plane / release plane.  For more information about Swedge see the Swedge product page.

You can also determine the wedge sliding mode graphically on a stereonet.  See the attached document on wedge failure for more details.  The following article is also useful:

Yoon, W.S., Jeong, U.J., and Kim, J.H. (2002) Kinematic analysis for sliding failure of multi-faced rock slopes. Engineering Geology. 67:51-61