Engineering Rock Mechanics

370 Underground excavation instability mechanisms

..

Plan view of

shaft and

instable block

I' '

4

N

W

-3

E

-2

-1

1 indicates that there is one adverse fracture

2 indicates that there are no adverse fractures

3 indicates that there are two fractures which intersect adversely

4 indicates that a block can form from three fractures and slide into the shaft

Figure 19.7 Example composite diagram showing the type of presentation that can be
prepared to assist a rock engineer in deciding on the necessity and type of rock support.

blocks and the nature of stress distributions, but computer programs are
commercially available now which can support the analysis with graph-
ics and do most, if not all, of the tedious computation. For example, the
rock mass visualization shown in Fig. 19.6 was obtained using 3DEC '.

3DEC and other programs are available from Itasca at http://www.itascacg.com