Environmental Engineering Reference
In-Depth Information
Plunge of
intersection = 6
°
N
80
°
30
°
70
°
40
°
60
°
50
°
1
50
°
60
°
40
°
10
20
70
°
30
°
1
2
20
°
2
80
°
Strike N31
°
W
dip 50
°
SW
10
W
2
E
20
30
2
Strike N44W
dip 35
10
°
NE
2
1
1
S
FIGURE 6.13
Contoured equal-area plot of a joint system containing two sets. The concentration of poles in the figure
indicates that the intersection of the sets plunges at a small angle from the horizontal. Plot is on the lower
hemisphere. (From Wahistrom, E. C.,
Tunneling in Rock,
Elsevier, New York, 1973.)
6.2.3
Sedimentary Rocks
Sandstones and Shales
Formations
Sandstones and shales are commonly found interbedded in horizontal beds covering large
areas, often forming the remnants of peneplains, which are dissected by valleys from
stream erosion. The drainage patterns are dendritic unless structure controlled.
Humid Climate
Chemical weathering results in rounded landforms and gentle slopes as shown on the
topographic map
(Figure 6.20).
The more resistant sandstone strata form the steeper slopes
and the shales the flatter slopes. Thick formations of marine shales develop very gentle
slopes and are subjected to slumping and landsliding (see
Section 6.7.3)
.
Arid Climate
Weathering is primarily mechanical in arid climates, and erosion proceeds along the stream
valleys, leaving very steep slopes with irregular shapes as shown on the topographic map
