TRENCHLESS TECHNOLOGY
TRENCHLESS PIPELINE REHABILITATION: TECHNICAL AND PRACTICAL CONSIDERATIONS South Africa’s urban population is growing at about 150% of the national rate and has doubled over the past 26 years. This has put an enormous strain on the existing urban water services and increased the need for installing new ones. By Alaster Goyns*
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outh Africa’s pipelines are the arteries and veins of our communities, delivering clean and removing dirty water. If they are not healthy, then the population’s health will suffer the consequences. There are two components to this: first, the densification of the established urban areas where these pipelines have deteriorated with age and in many cases have inadequate capacity; and second, the mushrooming of informal and semiformal settlements, which are only partly serviced or not serviced at all.
and operate. If the environmental resources are damaged, the people and the economy on which they depend will suffer the consequences. There needs to be a change in the way these services are provided, which takes a holistic view of the long-term health of society and the environment in which we live.
The challenge
Benefits of trenchless rehabilitation
In both situations, the problem of installing new or rehabilitating existing buried pipelines is compounded by the fact that there is generally insufficient space for effectively doing this using the traditional way of digging trenches, which causes social and business disruption and environmental damage, plus the associated costs and inconvenience. What is usually not appreciated is the interdependence of these factors. Our communities are not just people and their businesses; they include the environment within which we live
Many of the existing water services that are malfunctioning can be rehabilitated at a direct cost that is significantly less than their replacement cost, without even considering the social, commercial and environmental inconveniences, disruption and associated costs. Once rehabilitated, these services can provide a virtually trouble-free useful life of between 50 and 100 years, or longer, provided the correct design parameters are used. The basic reason for this is that the route for these services has already
been established and little or no excavation is needed for their rehabilitation. This means the footprint during rehabilitation is only a fraction of that needed for open trench replacement, where there is space needed for the trench, excavated material and the movement of construction equipment. Before making any decisions about how to rehabilitate an existing pipeline, it is essential that practical constraints on the particular site are ascertained and understood, along with how these are going to be technically addressed using the technology available.
Technical and practical considerations
Once the social needs and environmental constraints for a particular pipeline are established (whether a new or existing pipeline in
S E P T/ O CT 2020
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