Buderus Manual on Trenchless Installation of Ductile Cast ... - Duktus

the outlet nozzles. In rocky soils, drilling heads fitted with roller chisels can be used.
The pilot bore is steered by controlled rotation of the bevelled steering surface of the
drilling head. This surface moves off-line and it can be forced to move off-line in the
desired direction by rotating it (Fig. . ).
The actual position of the drilling head is detected above the path of the bore by means
of radio signals from a transmitter housed in the drilling head. Any deviations from the
desired line are corrected by appropriate steered movements. Today, the accuracy of
steering is so high that, after being driven for a length of more than 1000 metres, pilot
bores can be made to arrive within a target area measuring only a square metre in size.
Fig. 5.7
The tool for the first stage of upsizing
5.2.2 The upsized bore or bores
A description of the technique
Fig. 5. 8
The tool for the second stage of upsizing
If the pilot bore needs to be upsized, suitable tools are used to upsize it, in a number
of stages, to a diameter suitable for the pulling-in of the medium-carrying pipe. For this
purpose, an upsizing head is fitted to the pilot drilling linkage, the size and configuration
of this head being governed by the particular soil conditions and the size of the
pipe which is subsequently going to be pulled in (Figs. .7 and .8). The upsizing head
is pulled through the bore while rotating continuously and in this way it enlarges the
size of the pilot bore. The soil which is cut away is carried out with the drilling mud and
this latter supports the bore at the same time. The upsizing process is repeated with
increasingly large heads until the bore is of the desired inside diameter.
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