The upgrade to a three lane motorway is almost complete with general renewal work underway, numerous motorway exits and merging points are also required. The road works are in various stages of construction.

Sound barriers are being built over a distance of two kilometres from the merging section of Cologne-West towards Dortmund. Pipe installations were planned in conjunction with the road works as they would be difficult to achieve at a later date.

HDD ingenuity

Utility company Rhein Energie AG in Cologne opened tenders to establish two parallel bores running over a 138 metre length below the A1 at the motorway exit Cologne, Lövenich. The first bore was for a protection pipe OD 450 mm to accommodate a 255 mm potable water pipe. Two bundled 160 mm cable protection pipes were to be pulled into the second bore.

The company Steinbrecher from Rheine, Germany was awarded with the contract. Steinbrecher assigned the company HDD bore specialists ME Meischen from Nerstedt, Germany to complete the project.

The motorway section, where the bore was planned, cuts almost nine metre deep into the landscape. Foundation remains from an old pedestrian bridge are buried about five metre below the road surface. The exact depth of the foundations was not known before the boring commenced. Furthermore, about 40 metre away from the starting point for the bores, 6 metre long I-beams were already rammed in place approximately every two metres for planking.

In the difficult pebbled soil, ME Meischen set out to use an MDH-bore head and a drilling fluid adapted to the soil conditions. A machine type Grundodrill 15N, manufactured by Tracto-Technik in Lennestadt, with an almost 20 tonne pulling force, was utilised for the bore.

ME Meischen had owned the Grundodrill 15 N for only four weeks. Bore team leader Mr Hildebrandt said “There is loads of performance potential inside this machine, which can clearly be seen on this jobsite.”

The very busy motorway was not accessible and so a Digitrac detection system with a remote transmission monitor was used to plan the bore path. Direction measurements and control of the bore path could only be carried out to the edge of the roadway. The receiver was set up on the opposite side of the road and used practically as an electronic target disc. Controlling the data was carried out directly via the operator on the bore rig, who was able to keep to the bore path despite the limited range of the receiver.

The first bore reached the expected target point, despite all the obstacles. However, later the contractors discovered that the distance to the I-beams was insufficient with an expander diameter of 640 mm. After a discussion onsite it was decided to drive further below the I-beams and the foundations of the old pedestrian footpath.

ME Meischen was relieved that it was not necessary to pull back the complete set of drill rods. Mr Hildebrandt was able to leave the existing bore path at the halfway point and make the required alteration. At approximately eight metres depth, the bore path between the foundation and the target pit on the other side of the motorway was inevitably a steeper exit angle over the last 30 metres than previously expected. Due to the confined conditions it was not possible to move the target pit to another area.

The pilot bore was expanded to 350, 480, 560 and 640 mm in succession. The pipe installation was carried out with a 570 mm backreamer. The weight of the welded 12 metre pipe length was approximately 12 tonnes. The pipe was installed in four hours, including another welding process, which was required as the tight space prevented the pipe from being laid out.

The 300 cubic metres of drilling fluid was later extracted by a local farmer and spread over his fields.

With the experiences gained from the first bore, the second pilot bore could be started after an almost six week break. The bore unit Grundodrill 15 N was now placed in the exact opposite position than initially planned. The reason for this was the proximity of a 700 mm oil pipeline, which required a safety distance of at least five metres.

The obstacles in the bore path were now well known, so the pilot bore was almost a routine job. Due to the tight conditions on the target side it was not possible to pull in the 160 mm pipes bundled together, they had to be pulled in individually, one pipe directly with the expander and the other one immediately following.

After successful completion of the bore and the pipe installation Mr Hildebrandt commented “They were really not easy bores to accomplish and we learnt a lot from these!”