MISSION IMPOSSIBLE - PHASE THREE OF SEWER REHABILITATION
Every problem has a solution, but sometimes environmental and technical constraints, demand exceptional efforts. This was certainly the case with a major 750,000 sewer rehabilitation project undertaken by Insituform Technologies for Scottish Water at Edinburgh's Water of Leith.
Every problem has a solution, but sometimes environmental and technical constraints, demand exceptional efforts. This was certainly the case with a major 750,000 sewer rehabilitation project undertaken by Insituform Technologies for Scottish Water at Edinburgh's Water of Leith.
The programme required 2.1 kilometre of brick and clayware sewer in a local beauty spot to be CIPP lined while causing minimal disruption to the riverbank and mature woodland. Problems were compounded by a lack of access roads, requiring substantial scaffolding over the river at one point so that Insituform could get material into the site. Conventional rebuild of the badly congested sewer would have been almost impossible, requiring new access roads and upheaval for many months. This would have caused habitat damage that would have taken decades to recover.
Working in close collaboration with main the contractor, John Kennedy Civil Engineering, who were responsible for cleaning and enabling works, Insituform undertook the no-dig lining in ten stages. The largest of these sections was some 300 metres so the environmental impact at points of entry and exit were reduced. Kennedy undertook civils at access and egress points and subsequently made good.
The original sewer survey identified massive ingress of tree roots, compounded by gross sedimentation, as the main causes of poor flow. This was giving rise to storm overflow into the river, threatening river quality and wild life. Minor collapses were found and the sewer had deformed from its original profile in places.
A specialist cleaning contractor undertook jetting to remove roots and debris before lining started. Insituform maintained a huge over pumping operation during each phase of the lining. Resin impregnated liners were shipped to site in refrigerated vehicles and transferred at one point over the scaffold to the working area. The temporary bridge was also used to pipe displacement water and heated water for curing to the working area.
The sewers, dating from 1864 in places, included round and egg profile sections varying in diameter from 450mm to 750mm. Liner thickness varied from 12mm to 22mm depending on structural needs. Loss of cross sectional area will therefore be minimal, while the smooth surface of the liners and elimination of brickwork joints will greatly improve flow. The Insituform CIPP system, first used 30 years ago in Hackney, is the only process to have been independently tested by a university in the USA and proven to give a projected minimum life of 50 years.
Insituform's site manager, Colin Kay paid tribute to his project partners, particularly Bill Barclay of Scottish Water and David Fraser of Kennedy Civil Engineering for their positive approach. "In 26 years in the lining business I have never encountered a more technically challenging project. Despite months of preliminary survey and planning there were several unforeseen difficulties that were overcome by good teamwork."
At one stage a 90 degree bend was discovered that was not shown on any drawing or survey report. "These are normally impossible to line through, but, by agreement with the client, the problem was solved by lining into the bend from either side. This involved a difficult 250 metre uphill liner insertion in a large bore 760mm by 600mm egg profile sewer," added Colin.
This is the third phase of work that Insituform have undertaken on the Water of Leith sewer. In an earlier phase, where access was less of a problem, four kilometres of sewer were lined in just seven weeks. By late summer regeneration of surface vegetation will have hidden most traces of the civil engineering works. The mature trees that were the cause of the problem will remain intact. The integrity of the class one waterway, rich in wildlife, is once again assured.
High and low resolution images for this text are on the web at www.ainsmag.co.uk/in198/3205in1a.htm
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