Laying of fiber-optics at record speed - TERRA-JET DJ 23

Laying of fiber-optic cables in Germany

Not only since the Corona crisis the enormous importance of an up-to-date infrastructure was recognized to ensure fast and secure internet connections for the increased demand of working from home. Nevertheless, by international comparison, Germany had already before fallen far behind other leading industrialized countries in terms of broadband availability. It is an enormous task to build this infrastructure networks until the year 2025 and meet the legal entitlement to fast internet for all citizens, which has been announced by the German government. Therefore, the implementation of a nationwide fiber to the home (FTTH) network, will entail a dramatic increase in the construction activities required for this purpose in the years ahead along with intensified political and organizational efforts. The time- and cost-saving civil engineering sector "trenchless pipeline construction" will play a key role in many places to an increasing extent in achieving the ambitious goals of the German government by 2025.

Fiber to the home (FTTH)

As part of this nationwide fibre optics network expansion a 85 m (250 ft) long HDD bore was required in an inner-city area along a pavement at a maximum depth of 2.5 m (8 ft). The special technical challenges consisted of several electrical lines having to be crossed under as well as a gas pipeline and several water pipes. In addition, a 25 m (75 ft) long section of a water main pipe with various connecting pipes branching off to a group of houses ran parallel to the planned drilling route. After thorough preliminary clarification of the respective pipeline positions, special attention had to be paid to precise control along the target route and to exact drill head positioning during the drilling carried out with the HDD drilling rig TERRA-JET DJ 23.

Pilot drilling, subsoil

Due to the difficult subsoil conditions in the entry and exit pit, characterised by loose sediment of clay interspersed with gravel and stones, the experienced driller selected the 3-finger drilling head for the pilot bore. Equipped with several replaceable hard metal teeth made out of carbide-tungsten teeth (WC-Co), this drilling head was particularly suitable for the partly harder subsoil conditions. The pilot bore was carried out at an entry angle of 15 ° (slope = 27 %). Thanks to the patented oscillating drill ramp, which allows to adjust the drill ramp up and down but also vertically forwards and backwards, the entry point of the drill head could be placed directly in front of the TERRA-JET DJ 23.
After only 75 min the exit pit was reached accurately corresponding to an average drilling progress of around 70 m/h or more than 1 m/min. Particularly for reasons of preservation of evidence the customer had digitally recorded both all the machine data of the TERRA-JET DJ 23 as well as the locating data of the DigiTrak Falcon F5, i.e. the depth, slope and roll data.

Pipe bundle laid within record time

Immediately after having finished the pilot bore with a diameter of ø 106 mm (4”), the bore was expanded with a reamer KODIAK ø 254 mm (10”). A pipe bundle, consisting of a larger diameter pipe ø 180 mm (7.5”) and five fiberglass protective pipes, was pulled in within record time.
Due to the fact that the bore channel was expanded only once, the reaming and pipe pulling process took around 2.5 h, i.e. just twice the time needed for the pilot bore.
The maximum permissible pipe pull-in forces could be undercut by far as a result of the optimally adjusted water-bentonite mixture with a viscosity η of 36 mPa∙s.

Multitalent and powerpack DJ 23

The TERRA-JET DJ 23 HDD drilling rig performed its strength in this trenchless pipe construction project due to its unique technical innovations such as the oscillating drill ramp or the AutoTork, many of which have been patented. 11 tons (23,000 lbs) of thrust and pullback force with a torque of 3’100 Nm (2,290 ft. lbs) and a maximum drillrod rotational speed of 284 rpm are generated by a DEUTZ diesel engine with 101 hp (74.4 kW) of power. That, combined with the comparatively low machine dimensions, guaranteed the efficient and precise execution of this more than 80 m long bore in record time with little space requirement.
During the pilote bore, backreaming and pipe pulling procedure, the driller was supported by these manifold performance parameters of the TERRA-JET DJ 23, in particular the variable use of the electronic drilling assistance systems such as the AutoTork, ADBSe and the thrust control. The AutoTork adjusts automatically the drill rod rotation speed and the torque, the machine performes always at its highest optimum.
As a compact, extremely productive and powerful machine the TERRA-JET DJ 23, representative for all products of the TERRA AG, successfully demonstrated its Swiss quality at the highest level and met all the requirements placed on a HDD drilling rig to the complete satisfaction of the customer.

Pic 1: TERRA-JET DJ 23 in action.

Pic 2: Drill head location during the pilot bore with the Falcon F5 location system from DCI.

Pic 3: Screen from Falcon F5.

Pic 4: Pipe bundle pulled in directly behind the reamer KODIAK ø 254 mm (10”)

Pic 5: Reaming and pipe pulling completed.

Pic 6: The pipe bundle at its destination.