June 4, 2020 | 6 min read
With towns and cities expanding in size and population, existing potable water supply networks constantly need to be upgraded to accommodate growing needs. This means old malfunctioning lines need to be replaced and/or the network itself needs to be enlarged. In both cases, and especially in densely populated areas, space is limited above- as well as underground.
The increasing number of supply and discharge lines (water, power, telecommunication) but also building structures or water bodies make trenching difficult, very costly, or even impossible. For these or similar scenarios, trenchless installation methods are a perfect low-impact alternative that minimizes traffic interruptions and disturbances to dwellers while reducing the risks of damage to other underground structures and keeping costs at bay.
In the following, we present three common no-dig technologies, all of which have been conducted for a long time using specially developed Pipelife PE (Polyethylene) pressure pipe systems in gas, water, and wastewater applications.
Wherever water mains or supply lines need to be replaced because they are either old and at risk to fail or have become too small in capacity, it is often easiest to insert the new pipe directly into the existing line. Rather than opening up roads and dealing with lots of excavation material, trenchless technology requires only two excavated shafts per rehabilitated section, one where the pipe is inserted and one from which it is pulled through the host pipe (exit shaft).
The sections per se can be up to a couple of hundred meters long. Depending on the available space on site, specially designed PE 100-RC (resistant to crack) Pipes with an additional protective coat are pre-joined to the necessary length. Metal rods are inserted into the old host pipe and attached to a burst or cutter head and an expander, which in turn is attached to the new pipe. A rod puller in the recipient shaft slowly pulls the head, expander, and new pipe, destructing the host pipe and pushing the debris aside into the surrounding soil.
PE 100-RC pipes are generally very strong and resistant to point loads. However, to avoid any mechanical damage in addition to point loads, it is important to opt for coated pipes. "The debris from the host pipe can put high point loads on the new pipe and cause mechanical damage. Scores and deep scratches may not seem harmful at first glance but can shorten the pipes' service life considerably. I highly recommend exclusively use coated PE 100-RC pipes for this type of pipe rehabilitation", says Werner Sens, Product Manager Water, and Gas at Pipelife Austria.
"Take, for instance, Vienna's city department for water: For all trenchless installations using PE pipes, they accept only those with a protective coating. They know the risks and want their networks to last as long PE 100-RC pipes are supposed to last: at least one hundred years."
Sometimes, the installation of new water mains and service lines requires undercrossing roads, streams, or rivers. Or there are simply a lot of existing underground structures that are difficult, costly, or simply impossible to bypass. Also, where pipe bursting or splitting cannot be implemented safely due to soil or site restrictions, a new pressure pipe can be installed applying horizontal directional drilling (HDD) technology.
The principle of this method is to first create a pilot borehole that defines the pipe alignment. Provided, the location of all neighboring buried structures is known, the technician above ground can safely steer the drill head around these and through soil and rock. The hole is consequently enlarged to finally pull the new pipe through.
"The last step in horizontal directional drilling is preferably done in one go, before the drilling fluid supporting the boring procedure hardens. Depending on the required length, the coated PE 100-RC pipes are butt-welded to the desired length. Several hundred meters are impressive but very common for HDD", says Sens.
The probably oldest and simplest trenchless pipe repair is sliplining. As the name indicates, a new pipe is slipped inside the existing line and pulled through following the host pipe's alignment. The crux of this method is the reduction in diameter and the resulting reduced capacity of the pressure pipe.
The advantages of using coated PE 100-RC, in this case, is, for one, their flexibility and practically flush joints which allows for minimal radial clearance between the host and new pipe. For two, the smooth inner surface provides optimal flow and therefore partly compensates for the reduced capacity.
"Sliplining is a fast and extremely cost-efficient method. As an example, a more than 1-kilometer-long water supply pipe in Paternion in Austria could be completely renewed within only a couple of days even though the line was segmented due to bends and connections to housings. Excavation and backfilling were necessary for only 9 pits. Also, the heavily frequented road remained largely unobstructed", reports Werner Sens.
The advantages of trenchless pipe repair but also trenchless installation of new pipes are obvious. However, they require expertise, experience, and special equipment from the installer and they make high demands on the applied pipe.
Recognizing the growing trend towards trenchless pipe repair and rehabilitation somewhat 10 years ago, Pipelife Austria developed PE pipes that ensure a full-service life of at least 100 years despite the literally rough installation conditions.
The so-called Aqualine RC Robust Pipes are a PE 100-RC Pipe (RC standing for resistance to crack) and have a durable coat that can be peeled off for jointing. The PE 100-RC medium pipe itself is already highly resistant to point loads and slow crack development.
Under "normal" installation circumstances in an open trench, this pipe would be by far strong enough. Under no-dig conditions the pipes undergo mechanical forces from the host pipe or from debris and rock in addition to tensile loads when pulling the pipe through. This is where the coat provides extra protection during the trenchless pipe lining process.
All products are of course certified to national and international standards. "It is important to us, that our clients know right away that they are working with state-of-the-art, top quality products when they opt for Pipelife. Here in Austria, we have an industry acknowledged association for gas and water applications, the ÖVGW. To earn their quality approval, raw materials and products need to pass tests to defined specifications and procedures and we undergo annual external audits. In addition to EN 12201 and the certification for potable water supply, Aqualine also carries the ÖVGW mark for 'unconventional' no-dig technologies", affirms Sens.
"We are a sustainable company offering sustainable solutions", says Harald Schwarzmayr, CEO of Pipelife, "and with 'sustainable' I'm not only referring to environmental efforts. Yes, the products we are talking about are 100% recyclable, and yes, we make sure to re-use material wherever possible without compromising quality. But what I would like to underline here is, that we make sure our clients have piping solutions at hand that are built to last.
The idea is to develop products that have the smallest possible impact on the environment from production, through delivery to installation, and during the longest possible service life. We are proud when our products go unnoticed, this is how it should be – for the environment including the people. Ideally, nobody should even notice them being installed", Schwarzmayr adds, "this is why we 'dig' no-dig – but only with PE Pipes wearing a coat."