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Impressing pipe renewal in Australia

Yarraville is one of the many fringe areas in the west of the Australian metropolis Melbourne. Like all suburbs of Melbourne within a circumference of 5 to 10 km, it belongs to the administration district of the city of Maribyrnong. Typical for Yarraville is the chequered streetscape with its detached houses bedded in gardens and rows of trees. The overall picture encompasses parks and recreation areas like the McIvor Reserve, with large and small sports grounds and recreation centres, playing fields, dog runs and adventure playgrounds, which are used intensely by the residents.




PROBLEMS WITH AN AGEING SEWER
Of all places, the Benbow Street, coursing from east to west on the outskirts of Yarraville, hits the McIvor Reserve. This is exactly where the problems with a sewer reaching the end of its service life had started, in the street close to the nature reserve. Along a stretch of 99 m, the old ferroconcrete pipes ND 750, which had been rehabilitated with a GFRP-liner some time before, now had to be replaced. The specific challenges accompanying this installation measure:

•  its proximity to a highly sensitive nature reserve in the middle of a residential area
•   the open rainwater draining system running parallel to the sewer
•   the position of the ferroconcrete pipes in a depth of 4 to 5 m
•   the diameters of the old and new pipes, ferroconcrete pipe 750 mm and PE pipe 800 mm
•   the interest / residents groups formed in the course of the announced installation measure
 
CIRCUMSPECT AND FARSIGHTED PLANNING
These special features demanded circumspect and farsighted planning and preparation. Soon it became clear that the trenchless dynamic pipe bursting methodology was the only solution for an economical and for all parties agreeable renewal measure within this section of the sewer. So the task was to replace the old reinforced concrete pipe ND 750 by a new PE pipe ND 800 in the already existing path without tearing open the ground for trenching within an almost 100 m long sector.
 
The building contractors Harris Civil Pty Ltd., tagging themselves as "The Trenchless Experts", were assigned with the renewal of this sewer section in the Benbow Street by the City West Water, Melbourne. Preparatory jobs comprised, among others, the provision of the new PE pipes to be pulled in. The pipes were delivered in lengths of 12 m each and welded together to form a string for the pipe bursting installation by the plastic pipe specialist GEM Industrial Services, applying a butt welding technique. On finishing the welding works, the launch and exit shafts were excavated and the flow control system for the existing sewer during installation was set up. To do so, a bypass was established and operated by two fully silenced 150 mm pumps. The inspected building ground showed that the old pipe was bedded on sand and rubble and promised an undisturbed course of action.
 
PIPE RENEWAL TOOK THREE HOURS
Owing to the large pipe diameters ND 750 / 800, the people responsible for the job chose the ramming machine GRUNDORAMGOLIATH, which was equipped as a cracker (bursting head on the rear cone), and a Bagela winch for this application. With dynamic pipe bursting, the pure thrust performance and cracking up of the defective pipe is carried out by the dynamic power of the cracker exclusively, in this case by the ramming machine. The ramming machine was pre-stressed by a winch with a maximum pulling force of 200 kN to guarantee safe guidance in the old bore path and optimal leading-in of dynamic impact for bursting and expanding the old line. For once, the prevailing temperatures of 38 °C contributed pleasantly to the work progress: they increased the flexibility of the prepared PE pipe string, therefore pulling into the existing bore path was much easier. The GRUNDORAMGOLIATH system, used as a cracker, worked completely without trouble; after a little more than three hours, the renewal of the pipe was achieved, with the additional feature of a raised line capacity from ND 750 to ND 800.
 
One tiny mishap occurred, however, in connection with the GFRP hose liner in the old pipe: due to the fact that the liner was not lying close to the pipe wall, it was displaced in the process of cracking and "slipped" out of the pipe. Several stops in between were required to remove the liner pieces from the exit shaft. The ramming machine easily started again every time, working reliably and problem-free.
 
RECORD DIMENSIONS
But the renewal of the 100 m long sewer section was not all: of course, the connections to the manholes lying in front of and behind the new line had to be established again, too. This was done with two 800 mm PE couplings installed by heating coil welding technique. It was also necessary to drive through the renewed pipe line with a camera to make sure that the build-up and correct location were in perfect condition. The result: impeccable - and these pipe dimensions were a premiere in Australia!
 
CONVINCING QUALITY
The City West Water, in its capacity as the building owner, was won over to the quality of the result and the process technology: they immediately invited tenders for the renewal of the 79 m long sewer section lying in front of the renewed sewer pipe. The building contractor Harris Civil Pty Ltd., known as "The Trenchless Experts", and the "dynamic pipe bursting specialists" GRUNDORAMGOLIATH and Bagela winch, met the challenge of this segment in top-shelf quality and even shorter time.
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