When replacing pipes using the pipe bursting method, the static Grundoburst system is a popular choice, especially with circular pipe profiles from 50 – 1,000 mm diameter. The manufacturer Tracto-Technik (TT Group) pioneered work in pipe bursting, earning worldwide acceptance and approval.

Five different bursting rig models with up to 2500 kN pulling force are now available. The Grundoburst system consists of a rig, a hydraulic power unit, the QuickLock bursting rods and the bursting tools. The Grundoburst is ready for action very quickly and is easy to operate, resulting in reduced set-up times.

The procedural principle is simple. First of all the rig is placed in a small, compact working pit and is connected to a hydraulic power unit standing outside the pit. The bore rig is telescopic and can be extended hydraulically from 1.2 - 1.9 metres as a support in the front of the pit wall. Then the bursting rods are pushed through the old main, which only takes a few minutes per 100 metres. A guiding cone is used to prevent the bursting rod string from jamming inside the old pipe, the available pulling force is sufficient to overcome any obstacles.

On arrival of the rod string in the target pit the guiding cone is exchanged for a bursting blade (roller blade) and expander with the new pipe connected to it. An elbow joint facilitates attaching the new pipe string and guides it. When pulling back the rod string through the old pipe, the roller blade destroys tough materials like steel, ductile iron or PE. The bursting head is used for brittle material like grey cast, stoneware or asbestos concrete. The upsizing head displaces the old pipe fragments, expands the bore hole, smooths the bore channel and the new pipe is pulled in simultaneously.

The roller blade for cutting steel, ductile iron or plastic pipes can even destroy sleeves and repair clamps. It consists of a basic body, an exchangeable guiding rail, guiding rolls, which can be exchanged, and the blade strip. The basic body is suitable for replacing old pipes from 400 – 1,000mm in diameter, this dimension range is only available from TT Group. Number and arrangement of the guiding rails, which maintain the old pipe’s circular profile during the bursting process, depend on the existing diameter.

Several guiding rails equipped with guiding rolls keep the roller blade in the correct position inside the old pipe, which is of major importance for a clean cut at the pipe bottom. During the cutting process the guiding rails maintain the old pipe’s circular profile. To ensure maintenance of the circular profile, the position of the guiding rolls can be adjusted exactly to the old pipe diameter. The actual cutting is done by a three-step roller blade rail. The first blade is an innovative TT development which comes into operation when the old pipe diameter is partially smaller than the diameter that is captured by the second blade. The main cutting work is done by the second blade. The third blade makes it possible to cut sleeves and repair clamps, which can stand out up to 150 mm from the old pipe’s outer coating.

The roller blade’s total length of 1,600 mm guarantees a stable longitudinal alignment, the integrated swivel ensures torque-free transmission of the pulling force.

The new pipe made of plastic; HDPE as long pipe, short pipe or coil, ductile cast iron or stoneware can be of smaller, equal or even larger diameter – up to two nominal widths – than the old pipe.

Wherever the installation of long pipe strings is economically unfeasible, when sewage pipes have to be replaced for example in case of short renewal sections or in great depths, short pipe segments can be installed. To guarantee safe pipe installation, these short pipe segments have to be pulled in at a certain tension. This can be done by means of the proven Burstfix tensioning device, another idea from TT.

Slight bends in the old pipe can easily be overcome by the flexible QuickLock bursting rods. The ladder-shaped QuickLock bursting rods are not screwed but simply clicked together, absolutely stable for pulling and pushing. This results in a time saving of 40 per cent compared to screwed rods because there is no interruption for rod insertion – making pipe bursting a single, continuous and fast operation. Time-consuming screwing and loosening, which is necessary with conventional threaded rods is also omitted. Furthermore, the click shut connection is resistant to wear and dirt. Due to the QuickLock rod design, 100 per cent of the available power is transferred from the rig to the bursting head.

Pipe bursting in action

The waterworks in Poland managed a difficult pipe replacement project quickly, using the Grundoburst. The task was to replace a 170 metre long section of grey cast iron drinking water pipe, ND 500. This pipeline is situated at a depth of approximately 2 metres and runs parallel to the busy main road between Görlitz and Warsaw. The pipe beneath this road section was cracked in several places, undermining the road and leading to severe damage. Repair collars had been inserted in four different places.

The heavy traffic would not allow the half-sided barrier required for the renewal of the section using the open trench method. A second reason for trenchless renewal was the road surface, which had recently been re-asphalted.

The new pipe was an SLM pipe 500 x 45.4 mm from manufacturer Egeplast. Because of the low temperatures, the 6 metre long pipe segments were laid out and butt-welded under the protection of a tent. Two days were needed to complete the welding. At the same time the towing head was welded together with the pipe string.

In the meantime the Grundoburst model 2,500 G with 250 tonnes pulling force was made ready for action and the crew could start pushing the rods through the old pipe. When working with a bursting rig of this size the rods cannot be inserted manually, as is the case with the Grundoburst 400 and 800 G. Here, a crane was used to insert the rods.

Then a roller blade for cutting the cast iron pipe and an expander, 550 mm OD, were attached to the rod string in the target pit; the expander reamed up the damaged pipe which had been cut open and makes room for the new pipe.

As part of the quality control the pulling forces affecting the new pipe during the pulling process were measured and logged. The Grundolog pulling force measuring device from TT was mounted between the bursting sleeve and the pipe string. Measuring the pulling force allows for the immediate detection of overstrain to the new pipe and corresponding counteraction during pipe pulling.

It was not necessary in this case as the pulling force measurement, shown in real- time, did not exceed 200 kN. This was far below the permissible pulling force of 648kN, a good result when considering the weight of the pipe string, which exceeded 12 tonnes.

The whole job was completed in three days. The final pressure test afforded no reason for complaint.

With so many pipe renewal projects being carried out worldwide the static pipe bursting method with Grundoburst proves its efficiency time and again. The system is well thought-out and technically sophisticated, guaranteeing safe, fast and reliable pipe replacement - which makes all the difference.