Pile Design and Construction Practice, Fifth edition

Piling equipment and methods 117

drilling 4000 mm diameter holes with a drill string weighing 130 tonne. The largest Teredo rig,
equipped with a 460 kNm power swivel, is capable of rock drilling up to 7000 mm diameter. The
Bauer power auger in Figure 3.27 can be classified as a pile top rig, but has to be handled off
the pile to discharge the bucket, requiring continuous service by a suitable crane.
Reverse-circulation rigs can drill at a fast rate in a wide range of ground conditions
including weak rocks. They are most effective in granular soils and the large diameter of the
airlift pipes enables them to lift large gravel, cobbles, and small boulders when drilling in
glacial soils, or in jointed rocks which are broken up by the rock roller bits. Under-reamed
bases can be provided in stiff clays or weak rocks by means of a hydraulically operated
rotary enlarging tool mounted above the cutter head.

3.3.6 Large grab rigs

The use of diaphragm wall grabs to form barrettes in preference to large-diameter bored
pile groups is well established. The grabs may be suspended from cranes or mounted on

Rotary table

Air hose

Hydraulic motor

Hydraulic

power pack

Hydraulic

hoses

Airlift

drill pipe

Water level Pile casing

Stabilizer

Drill collar

Rock roller bit

assembly

Figure 3.34Wirth rotary table and rotating cutter.