Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgements
- Stereographic Projection Techniques for Geologists and Civil Engineers
- 1 Geological structures of planar type
- 2 Measuring and recording the orientation of planar structures
- 3 Geological structures of linear type
- 4 Measuring and recording the orientation of lines
- 5 Why do we need projections?
- 6 Idea of stereographic projection
- 7 Approximate method of plotting lines and planes
- 8 Exercises 1
- 9 The stereographic net
- 10 Precise method for plotting planes. Great circles and poles
- 11 Precise methods for plotting lines 1. Where the plunge of the line is known
- 12 Precise methods for plotting lines 2. Where the line is known from its pitch
- 13 The intersection of two planes
- 14 Plane containing two lines
- 15 Apparent dip
- 16 The angle between two lines
- 17 The angle between two planes
- 18 The plane that bisects the angle between two planes
- 19 Projecting a line onto a plane
- 20 Stereographic and equal-area projections
- 21 The polar net
- 22 Analysing folds 1. Cylindricity and plunge of axis
- 23 Analysing folds 2. Inter-limb angle and axial surface
- 24 Analysing folds 3. Style of folding
- 25 Analysing folds 4. The orientation of folds
- 26 Folds and cleavage
- 27 Analysing folds with cleavage
- 28 Faults 1. Calculating net slip
- 29 Faults 2. Estimating stress directions
- 30 Cones/small circles
- 31 Plotting a cone
- 32 Rotations about a horizontal axis
- 33 Example of rotation about a horizontal axis. Restoration of tilt of beds
- 34 Example of rotation. Restoring palaeocurrents
- 35 Rotation about an inclined axis
- 36 Example of rotation about an inclined axis. Borehole data
- 37 Density contouring on stereograms
- 38 Superposed folding 1
- 39 Superposed folding 2. Sub-area concept
- 40 Example of analysis of folds. Bristol area
- 41 Geometrical analysis of folds. Examples from SW England
- 42 Example of analysis of jointing. Glamorgan coast
- 43 Geotechnical applications. Rock slope stability
- 44 Assessing plane failure. Frictional resistance
- 45 Assessing plane failure. Daylighting
- 46 Assessing wedge failure
- 47 Exercises 2
- 48 Solutions to exercises
- Appendix 1 Stereographic (Wulff) equatorial net
- Appendix 2 Equal-area (Lambert/Schmidt) equatorial net
- Appendix 3 Equal-area polar net
- Appendix 4 Kalsbeek counting net
- Appendix 5 Classification chart for fold orientations
- Appendix 6 Some useful formulae
- Appendix 7 Alternative method of plotting planes and lines
- Availability of computer programs for plotting stereograms
- Further reading
- Index
2 - Measuring and recording the orientation of planar structures
from Stereographic Projection Techniques for Geologists and Civil Engineers
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface
- Acknowledgements
- Stereographic Projection Techniques for Geologists and Civil Engineers
- 1 Geological structures of planar type
- 2 Measuring and recording the orientation of planar structures
- 3 Geological structures of linear type
- 4 Measuring and recording the orientation of lines
- 5 Why do we need projections?
- 6 Idea of stereographic projection
- 7 Approximate method of plotting lines and planes
- 8 Exercises 1
- 9 The stereographic net
- 10 Precise method for plotting planes. Great circles and poles
- 11 Precise methods for plotting lines 1. Where the plunge of the line is known
- 12 Precise methods for plotting lines 2. Where the line is known from its pitch
- 13 The intersection of two planes
- 14 Plane containing two lines
- 15 Apparent dip
- 16 The angle between two lines
- 17 The angle between two planes
- 18 The plane that bisects the angle between two planes
- 19 Projecting a line onto a plane
- 20 Stereographic and equal-area projections
- 21 The polar net
- 22 Analysing folds 1. Cylindricity and plunge of axis
- 23 Analysing folds 2. Inter-limb angle and axial surface
- 24 Analysing folds 3. Style of folding
- 25 Analysing folds 4. The orientation of folds
- 26 Folds and cleavage
- 27 Analysing folds with cleavage
- 28 Faults 1. Calculating net slip
- 29 Faults 2. Estimating stress directions
- 30 Cones/small circles
- 31 Plotting a cone
- 32 Rotations about a horizontal axis
- 33 Example of rotation about a horizontal axis. Restoration of tilt of beds
- 34 Example of rotation. Restoring palaeocurrents
- 35 Rotation about an inclined axis
- 36 Example of rotation about an inclined axis. Borehole data
- 37 Density contouring on stereograms
- 38 Superposed folding 1
- 39 Superposed folding 2. Sub-area concept
- 40 Example of analysis of folds. Bristol area
- 41 Geometrical analysis of folds. Examples from SW England
- 42 Example of analysis of jointing. Glamorgan coast
- 43 Geotechnical applications. Rock slope stability
- 44 Assessing plane failure. Frictional resistance
- 45 Assessing plane failure. Daylighting
- 46 Assessing wedge failure
- 47 Exercises 2
- 48 Solutions to exercises
- Appendix 1 Stereographic (Wulff) equatorial net
- Appendix 2 Equal-area (Lambert/Schmidt) equatorial net
- Appendix 3 Equal-area polar net
- Appendix 4 Kalsbeek counting net
- Appendix 5 Classification chart for fold orientations
- Appendix 6 Some useful formulae
- Appendix 7 Alternative method of plotting planes and lines
- Availability of computer programs for plotting stereograms
- Further reading
- Index
Summary
A frequently used way of describing the attitude of a planar structure is to measure and record:
1 The strike of the planar structure (Fig. 2a). The strike is the compass direction (or bearing) of the special line in the plane which is horizontal, i.e. is not tilted at all. This horizontal line on the plane is found by means of a spirit-level or device for measuring angles of tilt called a clinometer and its bearing is measured with a compass (Fig. 2c).
2 The dip of the planar structure (Fig. 2a). The dip is the angle of slope of the plane. A horizontal plane has a dip of 0°; a vertical plane dips at 90°. The dip is also measured with the clinometer but in a direction on the plane at right angles to the line of strike (Fig. 2d).
3 The approximate direction of dip expressed as one of the eight compass points (N, NE, E, SE, S, SW, W, NW). The direction of dip is the direction of maximum downward slope and is at right angles to the strike.
When recording the orientation in written form the three items above are combined into a single expression:
strike/dip direction of dip
Here are four planes as examples: 183/54W, 126/33NE, 140/10SW, 072/80N. It is important not to forget the last item, the dip direction; it is not optional. For example, the first of the above planes has a southerly strike and a dip of 54°.
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- Publisher: Cambridge University PressPrint publication year: 2004