Liebherr LRB 125 XL - Manual (Page 2)

2
Double rotary drilling
Description
With pile production using double rotary drilling, an
outer casing and an inner auger (hollow auger) are
driven in counter-rotation by two independant rotary
drives which are mounted on a common carriage. The
outer casing provides support for the ground, while the
auger removes drilling cuttings up through the casing.
Once the final depth is reached, a concrete pump is
used to pump pumpable concrete via the hollow stem
of the auger inside the outer casing to the bottom
of the borehole. More concrete is pumped in under
simultaneous extraction of the casing and the auger
filled with drilling cuttings. The extraction speed is
selected as a function of the quantity of concrete and
the concrete pressure. In a further step a reinforcement
cage can then be inserted into the liquid concrete.
Soil types
Double rotary drilling is suitable for noncohesive soils
up to maximum density as well as cohesive soils up to
stiff consistency.
Advantages
• Suitable for nearly all soil types
• High productivity
• Very precise drilling
• Low noise level
• Low vibration
• Adjustment of casing and auger possible
• Drilling does not have to be carried out with water
injection