Environmental Engineering Reference
In-Depth Information
TABLE 5.18
Field Description of Rock Masses
Characteristic
Description of Grade or Class
Reference
Intact Rock
Hardness
Class I-V, extremely hard to very soft
Table 5.20
Weathering grade
F, WS, WM, WC, RS, fresh to residual soil
Table 5.21
Rock type
Identify type, minerals, and cementing agent
Sections 5.2.3 to 5.2.5
Coloring
Red, gray, variegated, etc.
Texture (gradation)
Coarse, medium, fine, very fine
Table 5.3
Fabric
Form
Equigranular, porphyritic, amorphous, platy,
Sections 5.2.3 to 5.2.5
(schistose or foliate), isotropic, anisotropic
Orientation
Horizontal, vertical, dipping (give degrees)
Discontinuities
Joint spacing
Very wide, wide, moderately close, close, very close. Give
Table 5.23
orientations of major joint sets. Solid, massive, blocky,
fractured, crushed mass
Joint Conditions
Form
Stepped, smooth, undulating, planar
Section 6.4
Surface
Rough, smooth, slickensided
Openings
Closed, open (give width)
Fillings
None, sand, clay, breccia, other minerals
Other discontinuities and
Faults, slickensides, foliation shear zones, cleavage, bedding,
mass characteristics
cavities, and groundwater conditions. Included in overall
mass descriptions
Note : Example as applied to a geologic unit: “Hard, moderately weathered GNEISS , light gray, medium grained
(quartz, feldspar, and mica); strongly foliated (anisotropic), joints moderately spaced (blocky), planar,
rough, open (to 1 cm), clay filled.”
Very, very hard
600
Sound rock
Very hard
500
400
Moderately sound,
somewhat weathered
Hard
200
Weak, decomposed rock
140
Soft
100
50
Completely decomposed
FIGURE 5.7
Rock classification based on uniaxial
compressive strength as given by various
investigators: consistency (Jennings, 1972),
degree of composition (Jaeger, 1972), and [E, D,
and strength (Deere, 1969); C from Table 5.19].
Ver y
soft
0
100
500
1000
7
Uniaxial compressive strength (tsf)
Jaeger (1972) relates strength to the degree of decomposition, also given in Figure 5.7.
”Completely decomposed” is given as below 100 tsf, but the boundary between very soft
rock and hard soil is usually accepted as 7 tsf (see Figure 3.39).
 
 
 
 
 
 
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