PLOTTING LINES AND PLANES ON A STEREONET CONTD.

1
PLOTTING LINES AND PLANES ON A STEREONET CONTD.
Pages 698-704
2
Plotting a plane by its dip and dip direction on
a stereonet

• Dip inclination of the line of greatest slope
  on an inclined plane
• Refers to TRUE DIP as opposed to APPARENT DIP of
  a plane
• 0 apparent dip lttrue dip
• Dip direction is ALWAYS perpendicular to strike
  direction
• The dip and dip direction of an inclined plane
  completely defines its attitude
• Plotted the same way as lines

3
Plotting dip lines of planes on stereonet (lab
3 contd.)
Plot the dip lines to the planes with the given
attitude
Dip/dip direction 38NE 57SW 43SE 65SW 23N 71NW

• Strike
• 342
• N35W
• S27W
• 132
• 278
• N25E

4
Plotting dip lines of planes on stereonet
Dip amount 67 58 59 26 90 58 23

• Dip direction
• 357.5
• 17.5
• 282.5
• 112.5
• 77.5
• 330.5
• 55.5

Data from Rock-fall Hazard Assessment of the
Aspen Forest Trail, Navajo National Monument,
Arizona U. S. Geological Survey Open-file Report
00-305, 2000 http//pubs.usgs.gov/of/2000/ofr-00-0
305/
5
Constructing Markland test plots using stereonets

• On the tracing paper where you plotted the dip
  lines, draw a circle representing a cone making
  60 angle around a vertical axis. This circle
  represents all planes dipping 30
• Similarly draw a circle representing all planes
  dipping 35 and 60. The 35 circle represents
  all planes at the critical friction angle
  (anything dipping more than that has the
  potential for failure)

6
Whats the point?
Data from Rock-fall Hazard Assessment of the
Aspen Forest Trail, Navajo National Monument,
Arizona U. S. Geological Survey Open-file Report
00-305, 2000 http//pubs.usgs.gov/of/2000/ofr-00-0
305/
7
Markland test plots using stereonets

• On the same tracing paper plot
• Slope face 1 as a great circle (dip direction
  003, dip angle 65
• If a plane has dip value greater than the
  friction angle and less than the slope angle,
  then sliding along the plane is possible. Such
  planes will fall within the critical zone bound
  by the intersection of the friction circle and
  the slope face great circle.
• Determine the potential for rockfall hazard based
  on your plot

8
Interpretation Rockfall or no rockfall?
Data from Rock-fall Hazard Assessment of the
Aspen Forest Trail, Navajo National Monument,
Arizona U. S. Geological Survey Open-file Report
00-305, 2000 http//pubs.usgs.gov/of/2000/ofr-00-0
305/
9
Interpretation Rockfall or no rockfall?
Data from Rock-fall Hazard Assessment of the
Aspen Forest Trail, Navajo National Monument,
Arizona U. S. Geological Survey Open-file Report
00-305, 2000 http//pubs.usgs.gov/of/2000/ofr-00-0
305/
10
Interpretation Rockfall or no rockfall?
Data from Rock-fall Hazard Assessment of the
Aspen Forest Trail, Navajo National Monument,
Arizona U. S. Geological Survey Open-file Report
00-305, 2000 http//pubs.usgs.gov/of/2000/ofr-00-0
305/
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Steps for determining the orientation of the line
of intersection of two planes (page 703)

• We will use the example given in the text and
  determine the trend and plunge of the line of
  intersection of the planes N49E/42SE and
  N10W/65NE.
• Plot both planes as great circles and label them.
• The line of intersection of those two planes is
  the point where the great circles meet. Label
  this point.

12

• Rotate the tracing paper in such a way that this
  point lies on the NS straight line. Draw a
  straight line from this point along the NS
  straight line all the way to the outside circle.
  This line represents the vertical plane passing
  through the line of intersection and will give
  you the TREND for that line.
• Count off the small circle intercepts between
  this point and the equatorial plane (the outside
  circle) along the NS straight line. This will
  give you the PLUNGE AMOUNT for the line of
  intersection.

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• Now rotate the tracing paper back to the original
  position (the point marked NORTH on the tracing
  paper coinciding with the top of the stereonet).
  Determine where the straight line segment you
  drew for step 3 intersects the equatorial plane.
  This is the TREND for the line of intersection.

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Identify the line of intersection of the
following planes
Dip/dip direction 38NE 43SE 57SW 23N 65SW 71NW

• Strike
• 342
• S27W
• N35W
• 278
• 132
• N25E

Pair 1
Pair 2
Pair 3
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Identify the line of intersection of the
following planes
Dip amount 58 26 23 59 67 58

• Dip direction
• 17.5
• 112.5
• 55.5
• 282.5
• 357.5
• 330.5

Pair 1
Pair 2
Pair 3