Engineering Rock Mechanics

328 Design of surfoce excavations

These overlays are used in conjunction with a hemispherical projection
plot of both the great circles (for wedge sliding) and normals (for plane
sliding) of the fracture data, which is shown below.
I

The result of this kinematic assessment is as shown in the table below.

Slope dip Plane sliding Wedge sliding

direction

000

030

060

090

normal to cleavage, entire face

normal to cleavage, entire face

normal to Joints B, entire face

normal to Joints B, entire face

Joints A and B, individual benches

Joints A and B, entire face

Joints A and B, entire face

Joints A and B, individual benches

120

150

180

210

240

270

300

330

Instability due to toppling has not been included in this table as the

conditions for its development (i.e. normal to one fracture set and the

intersection of two other fracture sets both sub-vertical) are absent from

the rock mass.

The sketch below summarizes the instability conditions, with the

overlay being used to determine more exactly the angular boundaries

between the various instability conditions. It is clear from this sketch

that almost the entire southwest quadrant of the quarry will suffer from

sliding instability that will effect the entire face. There are regions to the