Trenchless techniques HAVE PROVEN ADVANTAGES THAT NEED EXPLORING

In recent years, there have been widespread media reports concerning the water problem facing South Africa and the amount of drinking water being lost before reaching the public. Possibly up to 40% of the extracted water is lost due to leaking supply pipelines.

By Alaster Goyns, Pr Eng*

For towns and cities, one of the key construction challenges in replacing pipelines is urban densification. This is where trenchless interventions excel, being generally more cost-effective and far less socially and environmentally disruptive.

There are a broad range of TT solutions to choose from, depending on the degree of degradation in scenarios where pipelines are partially or fully deteriorated and close to collapsing. Here, TT pipelining applications are highly efficient. They entail the insertion of tightfitting smooth liners within existing pipelines, often resulting in a slight improvement in the capacity of the buried conduits.

With wastewater, there is a similar situation, where sewers are leaking and polluting the natural water courses. During wet periods, these sewers are surcharged with groundwater flowing into them through the leaks and causing the overloading of wastewater treatment facilities. Urgent remediation interventions are therefore required.

One option is to replace the pipes; however, another far more beneficial approach is to rehabilitate them using trenchless technology (TT) – a technique that has proven beneficial worldwide, but with less prominence to date in South Africa.

These linings are continuous from manhole to manhole. Additionally, they are made from materials that are strong and impermeable, thereby eliminating problems with leaking joints.

For new infrastructure, or where existing pipes need to be replaced or upgraded in terms of capacity, common TT applications – each one being project-specific – include pipe bursting, horizontal directional drilling, pipejacking and microtunnelling. In most cases, these systems can be installed with minimum need for excavation, making them ideal for situations where services need to be installed under road and rail networks, as well as residential and commercial developments.

Geotechnical investigations

In dealing with buried conduits, whether they will be placed in open trenches or using TT techniques, it is essential to understand what the site conditions are before any design or construction takes place. Surface inspections do not provide information about what is underground and what buried problems there may be. So, an essential activity before any trenched or trenchless construction is commenced is to do an investigation of the conditions beneath the surface to a level below where the construction is to take place.

Sastt Webinar Series

2023 Programme and Dates

• General introduction to TT activities: 6 June 2023

• Performance and condition assessment of existing pipelines: 11 July 2023

• Pipe lining techniques, such as slip lining, cured-in-place-pipe and others: 12 September 2023

• On-line replacement techniques such as pipe bursting: 14 November 2023

2024 Programme

• New installations – short crossings such as moling, ramming and pipejacking

• New installations – long crossings such as directional drilling and microtunnelling

• Supporting services such as pipe cleaning and over-pumping

• International developments www.sastt.org.za

Performance and condition assessment

When it comes to the rehabilitation or upsizing of installed conduits, it is essential that their performance as well as their condition be assessed. By combining this with the site investigations, problems can be identified and their underlying causes usually determined.

Doing this means most of the problems that could arise during construction are identified and the necessary measures to avoid them can be taken. While this may be seen as incurring added cost at the beginning of a project, in the long run, it saves time, money and minimises claims due to unforeseen conditions.

Showcasing the benefits: the SASTT webinar series

Locally, TT practitioners – comprising consulting engineers, contractors, and OEMs – are represented as a body by the Southern African Society of Trenchless Technology (SASTT). The latter is recognised as a registered Voluntary Association by the Engineering Council of South Africa.

As part of its engagement, SASTT regularly runs industry events and workshops, which will now be expanded to include the phased introduction of a series of eight short webinars over the next two years. These webinars will cover the various techniques available for the installation, rehabilitation, repair, and replacement of buried conduits with minimal excavation.

The purpose of these events is to inform all role players involved in the planning, design, construction, operations and maintenance of buried pipelines about the role of TT in preserving and enhancing South Africa’s water and wastewater infrastructure. Local experience is benchmarked against global best practice via SASTT’s affiliate membership of the International Society of Trenchless Technology (ISTT).

SASTT’s webinar series will cover the full spectrum of trenchless techniques locally available. (See the SASTT Webinar Series box on the left for the 2023/24 programme.) As well as providing an overview of the topics, each webinar will cover the hydraulic, structural, watertightness and durability requirements for specific TT techniques, with reference to realworld case studies.

The webinars, which will be hosted via 3S Media’s webinar platform, earn Continuing Professional Development (CPD) points and will serve as invaluable building blocks towards a far greater appreciation of the proven value of TT to maximise asset management utilisation and sustain socio-economic development.

*Individual member of the Southern African Society for Trenchless Technology (SASTT) and owner of PIPES cc