The town of Wiehl, located a short drive to the East of Cologne, has a number of attractions to offer: a public accessible stalactite cave with a 868 m long tunnel system, a 13,4 km length panorama trail, the so-called “Beer Trail”, the “Axle, Wheel and Carriage” museum and a wildlife park with nature trail.
The town had another temporary attraction to offer at the end of May 2020 with the renewal of a 275 m length combined sewer pipeline under rather difficult conditions:
The municipal works Wiehl commissioned the Schumacher Planning Agency with the planning and tendering for the renewal of the problematic pipe section, which due to the complicated framework conditions, would only be possible, using static pipe-bursting equipment with the closed, trenchless construction method. The course of the pipeline on the steep slope and the extremely poor accessibility alone definitely did not allow the open trench method without causing a cost explosion. Not to mention the need to re-locate the country road by 150 m, which would have been unavoidable using the open trench method. The contract was awarded to Alfes & Sons GmbH from Wenden, who have mastered many a difficult project over the years with the pipe-bursting method, even in the Oberbergisch district in Wiehl.
The result of two prior dynamic probes hardly provided much room for optimism. The entire pipe route, with a length of 275 m, was completely embedded in the existing rock and it was a complete mystery how much modifiable soil was available next to the pipe path. Therefore, room for soil displacement probably as good as zero. This also meant that the application of pipe bursting was on thin ice, as – despite all the advantages – there was quite a big risk involved! In the absence of an affordable alternative and with the confidence of the responsible employees at the specialists Alfes & Sons, the Stadtwerke Wiehl decided to use pipe bursting after all.
There is a solution for everything! In Wiehl one part of the solution meant, a powerful, resilient and reliable machine had to be applied – in this case the GRUNDOBURST 2500G. The second part of the solution was an adapted dimensioning of the installation lengths. It made sense to carry out the first installation length over 45 m and the second over 100 m. The third length, over 130 m, was planned to be the last, as it also seemed to be the most critical. The 300 m length PP-HM installation pipes 730 x 35 mm (long pipes), ordered for this task, were welded together on site to form three separate sections.
The excavation pits on the slope, which were up to 5,5 m deep, were clad with SBH Mega-sheeting panels, which even had to be secured with rock anchors at the deepest point. Likewise, the 25-ton chain excavator was secured during the excavation with the aid of rock anchors to prevent it from falling into the approx. 20 m deep and 60° steep abyss.
And off they went: The GRUNDOBURST 2500G with its maximum pulling force of 2.550 KN, the strongest among the strong, was brought into position, together with the magazine with the Quicklock-burst rods. Not exactly smooth, but nonetheless pretty even, the bore rig pushed the burst rods into the old pipeline. Here the old reinforced concrete pipes had a diameter of ND 700. Breaking open and displacing the old pipes worked quite well, as did the expansion to 800 mm with four welded-on blade strips and the pulling in of the new pipe length. The renewal of the first two installation lengths had already proved to be a success.
Then, in the last 130 m installation length, which ran at a depth of 7 m, things started to get tougher and sweat started to flow – for man and machine: the old pipe narrows down to ND 600 in a manhole and the bore path no longer runs in a straight line. It bends in the flow path 10° to the right and then runs in the final third in a slight curve to the left. Now all power reserves of the GRUNDOBURST 2500G were required. Shortly after the 10° bend the pulling force increased considerably until, after only a few burst rods, pipe pulling came to a standstill. About 30 m before the end of the pulling-in process a weld seam tore and split the pipe length into two sections of equal length. Work was brought to a halt immediately in order to locate the exact point of the tear. In doing so, they discovered that an approximately 6 m long section was missing at the first manhole passed through, but the bore canal was still distinctive in the entire cross-section
Problem identified, problem eliminated: The next day the team closed this “gap” from the manhole, by installing short pipe sections. Parallel to this they dug an additional excavation pit at the current location of the bursting head, which now no longer had to be created in the steep slope and was therefore sufficiently dimensioned with a depth of 3,5 m. Now the remaining 30 m of the old pipe could be completed with the pipe bursting method, by pulling in short pipes.
The town had another temporary attraction to offer at the end of May 2020 with the renewal of a 275 m length combined sewer pipeline under rather difficult conditions:
- Course of the pipeline to be renewed on a steep slope
- Situated 7 m beneath a country road
- Embedded in solid and fragmented rock
- Oppressive slope
- Extremely difficult access in impassable terrain and
- 4 to 5 m excess cover
The municipal works Wiehl commissioned the Schumacher Planning Agency with the planning and tendering for the renewal of the problematic pipe section, which due to the complicated framework conditions, would only be possible, using static pipe-bursting equipment with the closed, trenchless construction method. The course of the pipeline on the steep slope and the extremely poor accessibility alone definitely did not allow the open trench method without causing a cost explosion. Not to mention the need to re-locate the country road by 150 m, which would have been unavoidable using the open trench method. The contract was awarded to Alfes & Sons GmbH from Wenden, who have mastered many a difficult project over the years with the pipe-bursting method, even in the Oberbergisch district in Wiehl.
The result of two prior dynamic probes hardly provided much room for optimism. The entire pipe route, with a length of 275 m, was completely embedded in the existing rock and it was a complete mystery how much modifiable soil was available next to the pipe path. Therefore, room for soil displacement probably as good as zero. This also meant that the application of pipe bursting was on thin ice, as – despite all the advantages – there was quite a big risk involved! In the absence of an affordable alternative and with the confidence of the responsible employees at the specialists Alfes & Sons, the Stadtwerke Wiehl decided to use pipe bursting after all.
There is a solution for everything! In Wiehl one part of the solution meant, a powerful, resilient and reliable machine had to be applied – in this case the GRUNDOBURST 2500G. The second part of the solution was an adapted dimensioning of the installation lengths. It made sense to carry out the first installation length over 45 m and the second over 100 m. The third length, over 130 m, was planned to be the last, as it also seemed to be the most critical. The 300 m length PP-HM installation pipes 730 x 35 mm (long pipes), ordered for this task, were welded together on site to form three separate sections.
The excavation pits on the slope, which were up to 5,5 m deep, were clad with SBH Mega-sheeting panels, which even had to be secured with rock anchors at the deepest point. Likewise, the 25-ton chain excavator was secured during the excavation with the aid of rock anchors to prevent it from falling into the approx. 20 m deep and 60° steep abyss.
And off they went: The GRUNDOBURST 2500G with its maximum pulling force of 2.550 KN, the strongest among the strong, was brought into position, together with the magazine with the Quicklock-burst rods. Not exactly smooth, but nonetheless pretty even, the bore rig pushed the burst rods into the old pipeline. Here the old reinforced concrete pipes had a diameter of ND 700. Breaking open and displacing the old pipes worked quite well, as did the expansion to 800 mm with four welded-on blade strips and the pulling in of the new pipe length. The renewal of the first two installation lengths had already proved to be a success.
Then, in the last 130 m installation length, which ran at a depth of 7 m, things started to get tougher and sweat started to flow – for man and machine: the old pipe narrows down to ND 600 in a manhole and the bore path no longer runs in a straight line. It bends in the flow path 10° to the right and then runs in the final third in a slight curve to the left. Now all power reserves of the GRUNDOBURST 2500G were required. Shortly after the 10° bend the pulling force increased considerably until, after only a few burst rods, pipe pulling came to a standstill. About 30 m before the end of the pulling-in process a weld seam tore and split the pipe length into two sections of equal length. Work was brought to a halt immediately in order to locate the exact point of the tear. In doing so, they discovered that an approximately 6 m long section was missing at the first manhole passed through, but the bore canal was still distinctive in the entire cross-section
Problem identified, problem eliminated: The next day the team closed this “gap” from the manhole, by installing short pipe sections. Parallel to this they dug an additional excavation pit at the current location of the bursting head, which now no longer had to be created in the steep slope and was therefore sufficiently dimensioned with a depth of 3,5 m. Now the remaining 30 m of the old pipe could be completed with the pipe bursting method, by pulling in short pipes.
