Engineering Rock Mechanics

(Jacob Rumans) #1
130 Rock masses: deformabiliQ strength and failure

140
g 120
5 100

v
C
ul^80
ul
60
x 40
= 20

E

(^0 0)
04 I
0 30 60 90
Inclination of discontinuity normal to major principal strength lOCUS Of
stress axis fracture set A
O).........
0 30 60 90
Inclination of discontinuity normal to major principal Strength locus of
stress axis fracture set B
minimal strengths. However, in the rock mass, the two fracture sets are
orthogonal, and so, when we superimpose the two curves to determine
the lowest strengths of the rock mass, we must apply an offset of + 90"
to the values of Bw for fracture set B, as indicated in the sketch below.
6 O3 + 63 O
set A
Fract
A
I
A
1
Superimposing the two strength loci in this manner, the strength
variation for the rock mass containing the two fracture sets over the full
range of /!Iw, 0" to 360", is shown below. The lower strength envelope is

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