Piling equipment and methods 113Figure 3.30Top-hinged under-reaming bucket.rams attached to the clamps enable the casing to be forced down, as the hole is deepened or
raised as necessary. The semi-rotating motion is continuous, which prevents the casing from
becoming ‘frozen’to the soil, and it is continued while extracting the casing after placing the
concrete. The essential feature of pile boring with a casing oscillator is that the special double-
wall casing is always kept tight against the bottom of the hole. For this purpose the casing is
jointed. The typical casings (e.g. the Bauer and Casagrande types) have male/female joints
which are locked by inserting and tightening bolts manually (which can have safety implications)
or by an automatic adapter lock to resist the high rotating or oscillating forces.
Hydraulic casing oscillators are available from most of the large rig manufacturers to attach
to crane-mounted rigs or to rotary drills with diameters from 1000 to 3000 mm and torque
capability up to, for example, 8350 kNm from the Soilmec VRM 3000, which has a clamping
force of 4780 kN and lifting force of 7250 kN (Figure 3.31). Typically the rotation angle is 25 ,
but Soilmec and Leffer also manufacture 360 full rotation units with torque up to 7400 kN,
designed to reduce friction losses and capable of depths to 70 m using carbide casing shoes. The
material is broken up and excavated from the pile by hammer grabs hanging from a crane or
attached to the drill rig, or removed by augers, grabs and down-the-hole hammers using crawler
or crane attachment rigs. The German Hochstrasser-Weise oscillator system which operates on
compressed air has been used to install casing up to 3000 mm vertically, and 2400 mm casing