Trenchless Technologies Earns ISTT Project Award

Subsurface pipeline constructionand rehabilitation company Trenchless Technologies cc has been awarded theInternational Society for Trenchless Technology (ISTT) 2012 Annual ProjectAward for a contract that the company undertook for the Mandela Bay DevelopmentAgency involving the rehabilitation of two parallel sewers located in the heartof the Port Elizabeth Central Business District (CBD).

TrenchlessTechnologies managing member Sam Efrat saysthat the ISTT Annual Project Award is the highest accolade available worldwidein the trenchless technology industry and is chosen from nominations receivedfrom companies who are members of the 30 ISTT-affiliated trenchless societiesacross the globe.

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Thecontract was undertaken by Trenchless Technologies in conjunction withAfricoast Consulting Engineers, Sekisui Ribloc Australia (part of SPR Asia),sub-contractor Tuboseal, as well as consultants Pipes cc and Engineering Adviceand Services cc. Efrat explains thatthis was the second phase of a two phase project – phase one was completed in2009 and involved the rehabilitation of 570 m of 450DN sewer using SPR EXtechnology, as well as 560 m of 840DN sewer using SPR PE spiral woundtechnology. The pipeline rehabilitation took place concurrent with an urbanenvironmental upgrading project involving decorative paving and resurfacingworks on the surface above the existing pipes

Further downstream,the 450DN and 840DN sewers increased in capacity to 525 mm and 1,000 mm indiameter. Phase two involved the rehabilitation of these two sewers. Efratexplains that what made this project unique was its location – the 525DN sewerwas located beneath one of Port Elizabeth’s busiest and most heavily congestedstreets, Govan Mbeki Avenue. Additionally, the 1050DN sewer was locatedunderneath a newly-constructed Bus Rapid Transport (BRT) lane. Considering thatthe BRT and road lanes are utilised every day, only non-destructive trenchlesstechniques could be employed for the rehabilitation of these pipelines.

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Efrat explains thatcondition assessments were carried out on both sewers using CCTV inspection andcutting of windows from the sewers for physical inspection. It was ascertainedthat the 525DN sewer was severely corroded around its entire circumference dueto acidic effluent with pH values measuring as low as 3.3. The sewer’s mortarhad corroded out of the construction joints and was no longer water tight.

Additionally, the 1,050DNsewer was severely corroded above the water line and the reinforcement wasexposed and corroded away at places. Particularly severe deterioration occurredat the sides and invert of the sewer due to a combination of corrosion anderosion along the sections of the sewer where the fluid velocity was high.Efrat explains that this corrosion is typical of what occurs in a sewerdownstream of a rising main where there is an accumulation of gas due to longretention times. Efrat points out that it was estimated that sections of thesewer would collapse within 10 years.

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Speaking on thetechnology used by Trenchless Technologies on the project, Efrat explains:“Altogether the project used five different trenchless techniques – spiralwound expanded to a close fit, spiral wound in-place, ambient cured-in-placepipe (CIPP), UV CIPP and pipe bursting. The contract was awarded based onutilising spiral wound technology, namely SPR EX for the 525 sewer and SPR ROfor the 1050 sewer. However, during the project unforeseen site conditions,such as a 15-m 90 degree radius bend on the 525 pipe and a 43-m length of 800-mmdiameter pipe was discovered where the 1,000 sewer reduces in size, whichrequired the introduction of additional ambient cure and UV CIPP methods.Additionally, pipe bursting of a 225DN clay lateral pipe became necessary as acracked and leaking lateral 225DN clay pipe was preventing plugging and over-pumpingat a critical manhole.”

Efrat adds that thewide range of technologies used on this project allowed for a complete ‘no-dig’solution that enabled rehabilitation to take place entirely through accesschambers. What’s more, the solution was design-compliant and the risk was loweras the entire process could be reversed in the event of unforeseen problems. With CIPP, once the liner cures, it is extremely difficult to removein the event of a failure, whereas with Spiral Wound it is far easier to removeyour liner if you have a failure thus your risk is lower.

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Despite the challenges encountered, the combined team managed topull off the successful rehabilitation of the two sewer pipelines without anydisruptions to traffic or the public. “This project is an excellent example ofusing trenchless technology options to address unanticipated site conditionsallowing the project to be completed successfully without excavation and sitedisruption,” concludes Efrat.

Thisarticle was submitted by Trenchless Technologies cc, based in South Africa.

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