Questions 19.1 -1 9.1 0:
underground
excavation instability
mechanisms
419.1 The diagram to the right shows the !jorn^5 Om
cross-section of an underground machine
hall. The hall is to be excavated in a se-
quence of metamorphosed argillaceous rocks,
of unit weight 22 kN/m3, which contains
five fracture sets with the following orienta-
tions:
Set Dip direction Dip angle
1 058" 54"
2 195" 70"
3 127" 81"
4 160" 32"
5 335" 64"
Each set has a friction angle of approx-
imately 30" and zero cohesion. It is proposed
that the axis of the machine hall will be oriented on a heading 030" and
will be horizontal.
Determine the kinematic feasibility of all the tetrahedral blocks formed
by the intersection of the fracture sets and the roof.419.2 For the unstable roof blocks established in the answer to Q19.1,
determine the direction of movement, and plane(s) of sliding where
relevant.419.3 For the unstable roof blocks established in the answer to Q19.1,
determine the volume of the largest block that could fall from the roof
and hence calculate the necessary support pressure to ensure stability.419.4 Repeat Qs 19.1 and 19.2 for the haunch A (as illustrated in Q19.1).419.5 Repeat Qs 19.1 and 19.2 for side wall B (as illustrated in Q19.1).