Piling equipment and methods 111Various types of equipment are available for use with rotary augers. The standard and rock
augers (Figure 3.28a and b) have scoop-bladed openings fitted with projecting teeth. The
coring bucket is used to raise a solid core of rock (Figure 3.28c) and the bentonite bucket
(Figure 3.28d) is designed to avoid scouring the mud cake which forms on the wall of the
borehole. The buckets on some Calweld machines can be lifted through the ring drive gear
and swung clear to discharge the soil. Grabs can also be operated from the kelly bar.
Enlarged or under-reamed bases can be cut by rotating a belling-bucket within the
previously drilled straight-sided shaft. The bottom-hinged bucket (Figure 3.29a) cuts to a
hemispherical shape and because it is always cutting at the base it produces a clean and
stable bottom. However, the shape is not so stable as the conical form produced by the
top-hinged bucket (Figures 3.29b and 3.30), and the bottom-hinged arms have a tendency to
jam when raising the bucket. The arms of the top-hinged type are forced back when raising
the bucket, but this type requires a separate cleaning-up operation of the base of the hole
after completing the under-reaming. Belling buckets normally form enlargements up to 3.7 m
in diameter but can excavate to a diameter of 7.3 m with special attachments. Belling buckets
require a shaft diameter of at least 0.76 m to accommodate them.
The essential condition for the successful operation of a rotary auger rig is a fine-grained
soil which will stand without support until a temporary steel tubular liner is lowered down
the completed hole, or a granular soil supported by a bentonite slurry or other stabilizing
suspensions (also known as ‘drilling muds’see Section 3.3.8). In these conditions fast
drilling rates of up to 7 m per hour are possible for the smaller shaft sizes. Methods of
installing piles with these rigs are described in Section 3.4.6.
3.3.2 Boring with casing oscillators
For drilling through sands, gravels, and loose rock formations, the pile boreholes may require
continuous support by means of casing. For these conditions it is advantageous to use a
casing oscillator which imparts a semi-rotating motion to the casing through clamps. Vertical
Table 3.6Continued
Maker Type Standard Main Maximum Typical Maximum
stroke winch diameter maximum torque
(m) capacity (mm) depth (kNm)
(kN)a (m)
R 940 320 3000 92 469
CM 50 (CFA) 19.5 102 900 25 100
CM 70 (CFA) 22.3 170 1000 28 154
CM 700 (CFA) 22.5 80 1000 29 165
CM 120 (CFA) 24.5 290 1400 30.5 305
CM 1200 (CFA) 27.9 290 1400 33.5 305Wirth 13-SV 13.5 120 1500 45 130
(Germany) 18 6.8 190 2500 45 176
22-ZV 6.8b 180 1800 56 220
22-SV 13.8 180 1800 56 220
40 7.7 290 3000 36 400
Notes
a Pulling force.
b With pull-down winch.
c Various masts and rotary heads for these hydraulic crawlers.