Engineering Rock Mechanics

Questions 8.1-8. 1 0: rock masses 42 7

from which we find

5 = 1 - E& cos2 a (cos' a + k sin2 a).

Using E = 2.75 GPa, h = 2 m-' and s = 0.05 m/GPa, the plots as shown
in Diagram Q8.l result.
For two sets with hl = h2 = A, s:l = stl = s and si2 = s;2 = ks, the
basic equation reduces to

• = 1 - E,hs (cos4 a + 2k cos' a sin2 a + sin4 a).
  Em
  E

Using E = 2.75 GPa, h = 2 m-' and s = 0.05 m/GPa, the plots as shown
in Diagram Q8.2 result.
Explain why terms such as c0s4a appear in the formula and comment
on any general principles that are apparent from these illustrative plots.

E

Diagram 48.2

48.4 A rock mass has the following characteristics: the compressive
strength of the intact rock is 80 MPa, the RMR (Rock Mass Rating) is
62%, and the GSI (Geological Strength Index) is 50. Estimate the in situ
deformation modulus, E,.