Water & Wastewater Treatment

26 | JUly 2014 | WWT | www.wwtonline.co.uk In the know Getting to grips with pipe bursting Why no dig is no problem Sometimes a project doesn't need to break new ground to be groundbreaking… Pipe bursting explained. O nline pipe replacement comprises a family of techniques that are used to replace existing pipelines in the ground using the same routing followed by that of the existing pipe. This can be a size-for-size or upsized replacement. In the right circumstances pipe replacement is oen a very viable and cost-effective option given the congested nature of most modern urban subsurface locations as it uses the existing utility route and does not break new ground. What must be borne in mind at the design stage, however, are the various limitations of the different techniques. It is vital that the right investigations are made prior to selecting pipe bursting to ensure that right option is ultimately selected Ian Clarke Freelance Technical JoUrnaliST The process 1. a rod pulling machine that is set up in a launch pit feeds high strength rods through the old pipe to a reception pit a suitable distance away usually using a guide rod with a narrow tip that is commonly rounded to ensure that it will pass through or around any obstruction in the old pipe. 2. once through the pipe the guide rod is removed and the relevant bursting head, cutting blade or splitter is attached to the rod string along with any required expansion head to push aside the old shards or pipe remains. The new pipe fol- lows behind. 3. as the rods are drawn back towards the pulling machine, the old pipe is broken down or cut open and the shards/remains are pushed out into the surrounding ground. Simultaneously the new pipe enters the void created directly behind the bursting head to ensure that the pipe passes into the ground before any potential ground movement can close down the access for the new pipe. once fully installed, the new pipe is connected to any exiting or other replaced pipe sections at either end to establish the new pipe network for service once again. from those that are available. The distance potential and replacement diameters for all these systems depends on the ground conditions, the size of the old pipe, the material from which it is made and the degree of any upsize required when installing the new replacement pipe. The size of the pipe bursting machine used will also be very dependent on these factors In all circumstances, other than pipe extraction and pipe eating which either have no ground effect or remove spoil during the replacement process, the ground surrounding the old pipe must be compressible to allow broken pipe shards and old pipe remains to be pushed away from the pipe route, otherwise potential for damage to the new pipe as it is installed may be high. The systems available currently include pipe extraction, pneumatic pipe bursting, static/rod-based pipe bursting, dynamic or expansion shell pipe bursting, and pipe eating. Probably the most widely used of these techniques currently is the static/rod-based pipe bursting option (see right). This option is usually the most direct and easily exploited pipe bursting technique in most circumstances, although as with all pipe replacement techniques there are limitations that need to be addressed. For further reading please go to wwwtonline.co.uk "in the right circumstances pipe replacement is o en a very viable and cost effective option given the congested nature of most modern urban subsurface locations" www.wwtonline.co.uk | WWT | july 2014 | 27 • PREPARATION KEY TO SUCCESS ● Any potential 'upsize' needs to allow for the limiting factor of ground compressibility. Different ground types will compress to different degrees and will ultimately place a finite upsize limit on most replacement options. ● Pipes originally placed in the ground in a concrete surround or a concrete trough may have limited, if any, potential for pipe replacement by bursting as none of the systems tend to be able to fracture such sur- rounds. It is also important to be sure that the original pipe is made of a material that can be 'burst'. Various bursting heads have been developed that allow not only friable materi- als like clay and unreinforced concrete to be replaced but also now steel, ductile iron and even plastic pipe can be cut open to allow replacement options to be used. Pipe eating may be applicable but only if all of the concrete surround can be fully removed. ● In the case of water mains, the presence of steel or ductile iron repair collars may require adaptation of the bursting head system. Collars may cause bursting runs to stall if not handled correctly. ● Different techniques have different effects on the local area, e.g. Pneumatic burst- ing may cause significant vibration through the ground and nearby buildings. It is important to ensure all parties likely to be affected are warned in advance. ● Proximity of other utilities is also important. If nearby utili- ties are too close they may be damaged directly by any of the pipe bursting processes used or localised ground compres- sion may cause damage to other services, potentially incurring high repair costs for the bursting contractor or its client. • OTHER OPTIONS Pipe Extraction – usually utilises a winch and cable pro- cess whereby the winch cable is passed through and grouted into the existing pipe. The winch pulls the old pipe out of the ground whilst simultane- ously pulling the new pipe into the void created as the old pipe is removed. Pneumatic Pipe Bursting – utilises impact hammer tech- nology. Either with a special bursting head or not, an im- pact hammer that is of larger diameter than the old pipe is attached to a winch cable running through it to provide directional stability. With the cable in tension to align the hammer, the impact forces break the old pipe and the bursting head/hammer body or additional expander pushes the broken shards into the surrounding ground. The new pipe is usually pulled in behind the advancing hammer. Dynamic/Expansion shell Pipe Bursting– again using a winch cable for directional stability, bursting uses a spe- cial, usually hydraulic, bursting head that is designed to open out/expand within the old pipe breaking it and pushing the broken shards aside. The shell expansion is reversed so that the bursting head can be moved forward the next posi- tion in the pipe to progressively burst successive pipe sections. The new pipe is pulled in be- hind the advancing head. Pipe Eating – usually achieved using Microtunnellers, spe- cially designed HDD reamers or pulled rod systems. This still allows the existing pipe to be broken down insitu, but ensures that the broken shards are removed from the ground completely either in the equip- ment's spoil removal system, if using tunnelling or drilling machines, or as the spoil is extracted from within a casing pipe that would normally be used with the pulled rod option.

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