In the Austrian town of Linz the importance of trenchless pipe installations showed it’s worth once more.
Generally, the application of bore rigs is seen as environmentally friendly, especially in inner-city areas the underground new installations and renewals of pressure and sewage pipes involves shorter construction times, as there is no need to dispose of any excavated soil and re-instatement work is also not required.

This is all leads to an immense reduction of the costs, which means the following: Almost no disturbance to the surface, minimal excavations for jobsite pits – no transportation and intermediate storing, less construction machinery (excavator, compacting units, trucks etc.) and the prevention of traffic jams, diversions and repair work, as well as a low emission for noise, CO² and fine dust. The CO² loads can be calculated exactly, according to Prof. Hölterhoff from the German Society for Trenchless Technology (GSTT) Institute and are 30 to 50 times higher in open trenching, than in the trenchless field.

In connection with the complete re-structure of the Haidfeld Street in Linz a grey cast iron pipe ND 400, used as a drinking water transportation line and which had seen better days, was to be renewed in two sections over a total length of 200 m. The Haidfeld Street is one of the busiest shopping streets in Austria. To prevent any traffic chaos, it was necessary to apply the trenchless method with minimal traffic influence being a
main priority. It was also an aim to avoid as much trouble as possible for the numerous shop owners.

Therefore, the work had to be carried out in only three days over the weekend. The open-trench method, being the only other alternative would have provided these disadvantages with a pipeline depth of 1.40 m, especially leading to longer construction times.

As the pipe cross-section ND 400 and the hydraulic pipe were to remain intact, only the static pipe bursting method came into consideration. Using this method, pipes with the same size or larger pipes can be renewed in the same bore path. It is rather unusual to replace an old cast iron pipe with a new cast iron pipe of the same nominal size with the trenchless method, but it is possible and common with the pipe bursting method without any restrictions.
            
In order to burst the old cast iron pipe, to expand the bore channel and at the same time pull in the ductile iron pipe ND 400 (Manufacturer: Duktus), a machine technology with tensile strengths in these proportion is necessary. A further requirement was the task of measuring and documenting the tensile strengths, as the pipes were only allowed to be strained up to maximally 650 kN. The choice for this work fell on a GRUNDOBURST Type 1900 G with 1900 kN tensile strength and the tensile strength measuring device GRUNDOLOG, manufactured by TRACTO-TECHNIK.
            
The working sequence for a pipe bursting task is already well-known. First, the rig is installed inside the machine pit and connected to the hydraulic power unit. Then the burst rods, together with the guiding cone are pushed through the old pipe and at the end replaced by a bursting and expander head and at the end replaced by the attached new pipe.  During the reverse mode the head, equipped with a cutting blade, bursts through the old pipe, the adjacent expander widens the bore channel, in this case due to the sockets up to 610 mm and immediately pulls in the ductile iron pipe. The ductile iron pipe in single lengths of 6 m is connected successively with the previously pulled in pipe.

The measured and documented tensile forces were 500 kN and well below the permitted strains for the connection of the new pipe.

The exemplary co-operation of all the companies participating was the reason for the completion of the dimensionally largest pipe bursting jobsite in Austria within the planned construction time of three days and to the fullest satisfaction.

This article was submitted by Tracto-Technik, headquartered in Lennestadt, Germany.

Project data:

Material old pipe: Grey cast iron
Nominal width old pipe: 400 mm
Material new pipe: Ductile iron
Nominal width new pipe: 400 mm
Method Static Pipe bursting
Machine technology: GRUNDOBURST, Type 1900 G with a pulling force of 1900 kN
Tensile strength measuring device: GRUNDOLOG  
Total length 200 m
Quantity construction sections: 1 section over 62 m and 1 section over 133 m
Contractor: LINZ AG, Water Department
Sub-contractor: SWIETELSKY-FABER
Duration of the renewal: 3 days