Environmental Engineering Reference
In-Depth Information
FIGURE 6.2
Determination of strike and dip in the field: (a) dip and strike here being N 45
E and (b) measuring apparent
dip of bedding plane with Brunton compass. Finger points to cleavage. Care is required to establish if planar
surface being measured is bedding, a joint, or cleavage. (The rock being measured is a shale.)
°
Planar Orientation
A star diagram or joint rose is constructed to illustrate the planar orientation of concen-
trations of lineaments.
The strike of the lineations is determined on a large scale from the interpretation of
remote-sensing imagery (such as the SLAR image, Figure 6.4) , or on a small scale from sur-
face reconnaissance and patterns that are drawn of the major “sets” as shown in Figure 6.5 .
All joints with directions occurring in a given sector of a compass circle (usually 5 to 10 o )
are counted and a radial line representing their strike is drawn in the median direction on
a polar equal-area stereo-net ( Figure 6.6) . The length of the line represents the number of
joints and is drawn to a scale given by the concentric circles. The end of the line is identi-
fied by a dot. The star diagram or joint rose is constructed by closing the ends of the lines
represented by the dots as shown in Figure 6.7.
Spherical Orientations
Planes can be represented in normal, perspective, isometric, or orthographic projections.
Geologic structures are mapped on the spherical surface of the earth; therefore, it is fre-
quently desirable to study structures in their true spherical relationship, which can be rep-
resented on stereo-nets.
Stereo-nets are used to determine:
Strike and dip from apparent dips measured in the field
The attitude of two intersecting plane surfaces
 
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