TRENCHLESS TECHNOLOGY
The need for trenchless technology standards
The provision of new water services has not kept pace with urban densification. Spatial constraints make the traditional approach of digging trenches extremely disruptive to the social and business environment. Using trenchless technology (TT) offers many advantages, but a unified approach must be adopted when it comes to local standards. By Alaster Goyns*
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lose to 70% of South Africa’s population is now concentrated in urban areas. The rate at which this urban population is increasing, especially in the metropoles, is probably more than double that of the national average. Many of these high-density areas are unserviced or poorly serviced and, for the health of these communities, there is a desperate need for water services. In addition to this, the densification of established urban areas, through subdividing stands and building townhouse complexes, means that the existing water services are frequently inadequate. What’s more, the condition of many first-generation water services has deteriorated, which now need replacement or rehabilitation. This situation is exacerbated by ageing infrastructure that results in the loss of clean water from the supply lines and soil pollution resulting from leakages from sewers. In many situations, the problem is keeping the clean water in the clean water pipes and the dirty water in the dirty water pipes.
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14
IMIESA April 2021
Many local authorities and consultants in South Africa are interested in using TT to provide services in the high-density urban areas mentioned above. However, they are reluctant for two main reasons: they need standards on which to base the planning, design and installation; and there are misconceptions about whether this approach will create employment opportunities. The Southern African Society for Trenchless Technology (SASTT) has addressed both issues. The focus of this article is on TT standards.
Function of pipelines Water pipelines fall into two broad categories,
ngoing condition assessment is 1 O essential to ensure the integrity of pipeline assets ipelines can fail functionally when 2 P unable to convey the required volume of water and structurally when unable to carry the imposed loads 3 Open cut trench 4 A deep trench excavation
Informal settlements in urban areas tend to be unserviced or poorly serviced in terms of water and sanitation infrastructure
namely freshwater supply pipelines that flow full and operate under pressure, and wastewater disposal pipelines that flow partly full and flow under gravity. Pipelines are considered as assets designed for a specific lifespan; in reality, it is the holes through the soil that are the real assets. Pipelines merely line these holes to ensure that they operate effectively and efficiently. They need to meet the primary requirement of hydraulic performance and the supporting requirements of strength, watertightness and durability. Pipelines can fail functionally when unable to convey the required volume of water and structurally when unable to carry the imposed loads. A functional failure is usually because the pipeline is not big enough, or there is a blockage. In the former situation, the problem can only be addressed by replacing
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