Stability of Rock Wedges and Excavation Surfaces - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 296

are the components normal and parallel to the sliding surface of the required anchor
force per meter and is the angle between the direction of the anchor force and the

sliding surface (Fig. 11.8). Thus, the required anchor force is obtained by setting

α

μ = 1

and solving (11.12) for A d :

(11.15)

As a result, A d depends on . A d serves as a basis for the selection of anchor type and

spacing. Also the required cross-section of the anchor steel and the fi xed anchor length
can be calculated from A d considering the corresponding partial safety factors.

α

Figure 11.8 Stabilization of a two-dimensional rock wedge supported by one discontinuity by an
anchor force

For economic reasons, A d should be minimized by selecting a corresponding direction
for the anchor force. An analytic solution of this problem for a more general three-di-
mensional case (Section 11.3.2) was presented by Wittke (1967). Applying this method
to Equation (11.15) yields:

(11.16)