Challenging fresh water pipe rehabilitation

The site is part of an industrial development in the mined out area of what is still elsewhere a working quarry site and investigations showed that the pipes which carried away fresh water between two lakes was in need of rehabilitation. However, the fact that the site was industrialised with other operations as well as the cement mixing works, meant that operating conditions for any rehabilitation works would be far from easy.

The client expressly demanded that the rehabilitation be completed in a set timeframe with all traffic management being undertaken by the contractor and, most of all, that not only during the rehabilitation works but subsequently there should be no pollution created by the products used to complete the works.

With the cement works and other industrial units remaining operational during the course of the works, traffic was obviously going to be a significant factor in how the work could be completed. Before DALROD was brought to site a number of other contractors had attempted to survey the pipeline in question but failed due to the level of pipeline deterioration. One company did however complete the survey very successfully but at the time they were unable to complete the rehabilitation work within the timeframe stipulated due to other commitments elsewhere. However, not wanting to let the client down and knowing of DALROD’s reputation for this type of work, the contractor that successfully completed the pipeline survey passed the project details over to DALROD to see if they could offer a solution. Having examined the survey results and discussed options with the client, DALROD was awarded the contract to complete the works.

Difficult access and circumstances

The pipeline in need of rehabilitation runs between two freshwater lakes, both of which hold expensive fishery stocks such as carp and other species which had to be protected during the rehabilitation operation. The water supply available from the lakes also provided process water for a nearby cement mixing factory that needed to remain operational throughout the works.

Initially, it was thought that the pipeline to be repaired was a 300 mm diameter concrete pipe. However, it turned out that the pipeline was in fact a mix of materials both from the original construction and the changing of the pipe material as subsequent repairs were necessary. Furthermore, the survey also revealed that various repair jobs had changed the nominal diameter at several points along the route as non-standard pipe had been used to complete the repairs. So, now the pipeline varied in diameter generally to less than 300mm in places.

The survey results also showed that the state of the original pipe was worse than originally expected in that there was significant ground water infiltration due to the very high ground water experienced in the vicinity of the freshwater lakes. On top of this several of the pipe joints were also experiencing running sand infiltration from the surrounding soils. This meant that the pipe foundations were in danger of being washed out, potentially leading to the pipe collapsing. To alleviate this problem before lining works could be undertaken in full DALROD completed some 10 liner patch installations over the sand infiltration joints to eliminate the sand wash-in.

Once this problem had been solved it was decided that the full pipe lining works could be completed to the project specification using mainly the standard hot water cured resin impregnated felt liner material in three separate installations of 46, 110 and 125 m in length. In just a few short runs, totalling about 10 m length, DALROD also utilised the standard Brawoliner product where tight pipeline bends and other challenging circumstances occurred and the Brawoliner was the easier liner to install for the best results.

New highly environmentally resin tested by DALROD

Where the difficulty came with this was that the standard resin used with the felt liner did not fully meet the very stringent non-pollution requirement of the contract. However, DALROD employed a new resin which is highly environmentally friendly and trials undertaken by DALROD showed that neither during nor post installation does the new resin produce any form of pollution, nor does any leaching of by-products occur out of liner subsequent to lining completion and cure.

DALROD’s Mike Pollard commented: This was the only products that we could find that offered this non-polluting capability and we understand that this is one of the few projects yet undertaken using the new resin. It proved to be just the right product for these circumstances.

The blue pigmented resin enables control of the impregnation process whilst the liner resin combination is flexible enough to negotiate pipe bends. The thermosetting resin has a high chemical and thermal resistance and is easy to use at a construction site due to variable application and hardening times. There are also no annulus gaps between the host pipe and liner as the installed lining material sits flush to the old pipe wall. More importantly for the project in hand the resin is certified to be environmentally compatible with groundwater.

During the course of the lining works, it was not only the level of traffic and the need to keep the industrial sites working that caused DALROD’s crew problems. Initially some water was over-pumped from the upper lake to the lower lake in order to maintain the necessary water supplies to the cement mixing factory. However, very inclement weather added to problems of over pumping during the course of the works as very significant rain fall caused the upper lake to fill to the point of flooding, so increasing the need to monitor the lake level and over pump more to ensure that excessive flooding did occur in the surrounding area.

No adverse effects on fish population

The lining work was carried out between November and December 2014. DALROD’s Mike Pollard went on to say: The successful completion of the work now means that the fresh water supply pipeline is now able to operate very effectively with no sand infiltration or potential for adverse effects on the lakes or their highly prized fish populations. All in all despite the challenging circumstances a job well done.

 

 

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