Pile Design and Construction Practice, Fifth edition

medium transferring the uplift load from the pile on to the anchor. Where large uplift loads
are carried, the transfer of load is effected by welding a mild steel strip on to the interior sur-
face of the pile and the exterior of the anchor tube to act as a shear key, as described in the
following section. The drilling bit is left in place at the bottom of the tube where it acts as a
compression fitting, but the drilling rods are disconnected at a special coupling.

6.2.5 The uplift resistance of drilled-in rock anchors

The resistance to pull-out of anchors drilled and grouted into rock depends on five factors,
each of which must be separately evaluated. They are as follows:

(1) The safe working stress on the steel forming the anchor

316 Piles to resist uplift and lateral loading

Locking nut

Pocket filled

with concrete

Dock floor slab

M.S. plate welded to pile

to transfer compressive loading

Steel tubular pile

Flexible p.v.c. sheath

High-tensile steel tendon

wrapped by tape (bond breaker)

Top of weathered rock

Seal

Grout plug

Top of hard rock

Open drill hole

Cement grout

Anchor tendon unwrapped

Compression fitting

Bottom of grouting pipe

Bond

length

Weathered rock plug

removed by airlift

or baling

Soil overburden

Encapsulation

length

20 mm grout

injection pipe

Figure 6.10Stressed bar tendon in steel tubular pile supporting dock floor.