Long HDD Bore for the Garzweiler Mines

Once again the bore team around Helmut Schürmann and Michael Foltin from the bore company REVOR from Roßbach-Wied, Germany, were confronted with what was not an everyday task.  

Foltin is a casual character, well known for his phlegmatic calmness, but also for his knowledge and experience.  He has been with REVOR since 2005 and is experienced with the GRUNDODRILL 15 N, manufacturered by TRACTO-TECHNIK, Lennestadt, Germany.  REVOR have been acquainted with the HDD bore technology since 1999.  

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“We have grown with every task and the challenges have become part of our everyday businesses. That is why the expertise of the colleagues and good team work are an important success factor, as well as the machine technology,” according to the responsible head engineer Helmut Schürmann.

In this case, the task took place at the large mining area Garzweiler II, to the East of the A61 motorway and South of the A46 motorway. The A44 motorway had already been extended at the junction at Jackerath up to junction Holz at the A44 over a 7-km length. The motorway section therefore went into the possession of RWE POWER for coal mining use.

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The new path and also the motorway junction Jackerath are to be moved approximately 1 km further to South-East to start running again from 2017 onward. Then the gigantic bucket-wheel excavators will work on making the A61 “disappear” further westward, which is planned to be rebuilt in 2035.  Today, these aspects have to be taken into consideration by RWE power for operation of the brown coal mining plant.

The Bore Task

From the Garzweiler mining area to the central base of the company’s own bore and water works a powerful fiber-optic connection was to be produced for the data transfer. To achieve this, the area of the future motorway junction Jackerath and the A 61 had to be crossed using horizontal directional drilling (HDD) to install a HDPE protection pipe, outer diameter 180 mm, over a length of 388 m. RWE Power held the responsibility for the planning and surveyance of the bore task.

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The special challenge was in the unusual steep entrance with a 30 percent inclination, to quickly get to a 12 m depth. The data cable then lies at a depth of approximately 5 to 6 m below the future motorway lanes, so that any construction work would not be influenced. The further process beneath the A 61 is carried out horizontally and rises at 17 percent again to the target point, which is at the same height as the starting pit.

The bore went through a 5-m strong covered layer of loess clay.  After that, at a maximal bore depth of 12 m, formations made of Rhine sand and coarse grained pebbles provided a further challenge to the borehole support required. This showed in the quantity of bentonite being added, which was almost double the usual amount applied in “bore friendly” loess clay.

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To accomplish the pilot bore they chose a bore head, Type Medium Drillhead.  The round framed chisel of this head tears the ground open and simultaneously equipped with hard metal to protect against wearing minerals.

The detection and steering was carried out with a Digitrak-Eclipse, which ran perfectly up to depths of approximately 6 m, but from then some passive disturbances occurred. These were probably caused by underground rubbish, which had been disposed during the motorway construction work in the early years. This meant a reverse of the pilot bore and installation of a special depth sonde Eclipse F2, which guaranteed a trouble-free detection and steering process. A TT backreamer with weld-on claws and flow grooves was applied for the two-step expanding process from 115 to 180 and then from 180 to 250 mm.

The cable protection pipe, HDPE 160×14.9, PN 11 from the company Rehau, was connected from partial lengths of 100 m with three butt-welds to produce a 400-m long pipe length and then laid out in the open terrain. Only 3 tonnes pulling force were measured during the pipe installation. The process itself took one day to accomplish and the same time was required for the pilot bore and each expanding process.
The bore and pipe installation work was carried out in difficult weather conditions, starting in the last week of February 2010 and completed on March 2 to the fullest satisfaction of the contractor.

This article was submitted by TRACTO-TECHNIK, headquartered in Lennestadt, Germany.