Pile Design and Construction Practice, Fifth edition

322 Piles to resist uplift and lateral loading

(a) (b)

(c) (d)

Figure 6.13Pull-out failure in rock anchors (a) Horizontally bedded rock (thinly bedded) (b) Steeply
inclined bedding planes with anchor raked in direction of bedding joints (c) Horizontally
bedded rock (d) Alternating thinly and thickly bedded rocks.

Bar or cable anchor

in rock

Uplift cone

in rock

Position of cone

suggested by Wyllie

Rock head

L/2

30 °

B

H

Ground level

Anchor pile

B

H

30 ° L

(a) (b)

Figure 6.14Approximate method of calculating ultimate uplift resistance of rock anchors with soil
overburden (a) Clay overburden (b) Granular soil overburden.

overburden above the rock cone can be calculated as described in Section 6.2.3. The
dimensionsBand Hin equations 6.3 and 6.5 are as shown in Figure 6.14. Shaft friction on
the pile does not operate to resist uplift for this mode of failure. The mode of failure of a
group of anchors, assuming no failure occurs in the bond between grout and steel or grout
and rock, is shown in Figure 6.15. The anchors can be splayed out as shown in Figure 6.16
to increase the volume of rock bounded by the group.