There are a number of reasons why Trenchless Technology is a sustainable and green alternative. In urban areas, trenchless reduces the carbon emissions generated from construction works, minimising both machinery use and traffic disruption.

No-Dig also protects natural environments – trees and root systems are usually unaffected, while it also avoids disturbing the habitat of local fauna. On pipeline projects, horizontal directional drilling (HDD) and microtunnelling can also be used to preserve fragile ecosystems such as coastal areas and wetlands, avoiding the disruption and damage caused by excavation.

Sustainable cities

Sewer rehabilitation and replacement is a growing industry throughout the world, as existing water and wastewater infrastructure deteriorates due to age, corrosion and the demands of a growing population.

Cutting carbon emissions

Traditional open cut methods and equipment for the installation and replacement of underground infrastructure can be highly polluting. According to trenchless specialist and ISTT Chairman Dr Sam Ariaratnam “The construction industry, which consumes a large quantity of fossil fuels, has been tasked with reducing airborne emissions.

“Recognition of the urgency to curb emissions worldwide has led to an increase in research efforts aimed at developing methods to quantify and reduce emissions.”

Recent research has demonstrated that trenchless projects produce substantially fewer carbon emissions. A study conducted for the North American Society for Trenchless Technology (NASTT) by the University of Waterloo, located in Ontario, Canada, identified two areas in which a trenchless approach is more environmentally friendly than conventional open cut techniques.

First, traffic fuel consumption is lowered by trenchless methods. By avoiding traffic disruptions, trenchless projects prevent the delays and detours associated with conventional underground infrastructure projects. This lowers the amount of petrol consumed, and subsequently reduces carbon emissions. Fewer traffic delays also create social benefits, increasing the liveability of cities and minimising disruption to residents.

Second, trenchless job sites produce fewer emissions. They require minimal construction machinery and equipment as there is no need for excavation, compaction, back-filling and re-paving, dramatically reducing fuel consumption.

“The use of multiple construction equipment during open-cut construction invariably results in considerably more emissions in the atmosphere compared to employing trenchless methods, which have minimal on-site requirements,” said Dr Ariaratnam.

Also, trenchless works are typically more time efficient than open cut alternatives, meaning that machinery is operated for shorter periods. Dr Ariaratnam compared the use of pipe bursting versus open cut for a typical urban sewer rehabilitation project, and found that the pipe bursting took three days while open cut took seven days. The No-Dig approach, therefore, was over 50 per cent more time efficient.

Through these combined environmental benefits, Dr Ariaratnam’s study found that trenchless construction methods resulted in 79 per cent lower greenhouse gas emissions than open cut pipeline installation.

No-Dig = no pollution

As well as reducing carbon emissions, Yeun J. Jung and Sunil K. Sinha have demonstrated that trenchless projects also avoid other forms of pollution typical of open-cut projects.

Contaminated soil is often discovered during open-cut pipeline construction, requiring specialised and costly disposal. In addition, rain and water created during open-cut construction can cause soil erosion and contaminated soils run-off, polluting streams, rivers and sewers. By only creating minimal surface disruption, trenchless projects avoid these environmental pitfalls.

Trenchless job sites also lack the dust caused by excavation, which can create air pollution and have a detrimental effect on the health of workers and residents.

Finally, the machinery required on open-cut job sites can create noise pollution in the surrounding environment, disturbing residents, schools, hospitals and businesses. With less machinery, No-Dig is a far quieter and less disruptive process.

Maintaining existing infrastructure

Finally, avoiding excavation also prevents damage to adjacent structures, and therefore reduces the environmental and economic costs of replacing this infrastructure. Isabel Tardiff from the Centre for Expertise and Research on Infrastructure in Urban Areas in Montreal, Canada, cites research which indicates that trenching near a paved surface will diminish its lifespan by at least 30 per cent.

Also, as Dr Mohammed Nafaji and Dr Sanjiv Gokhale note in their reference guide to Trenchless Technology, during construction, the use of detoured roads not designed to take heavy traffic results in damage to the pavement structure.

“The heavy traffic decreases the life span of detoured road, which is an additional cost to municipalities and local governments,” Dr Nafaji and Dr Gokhale said.

Calculating the benefits

Trenchless industry representatives are working to identify and quantify the ecological advantages of selecting trenchless techniques, which can assist suppliers and contractors in arguing for a certain technology.

For example, Dr Ariaratnam has introduced a commercially-available emissions calculator, known as eCalc, which has been developed to enable the comparison of the environmental impact of different utility installation methods.

“Now we actually have a way of calculating the sustainable solution,” said Dr Ariaratnam.

Developed by Arizona State University and Vermeer Corporation to aid stakeholders in calculating anticipated emissions from competing technology options, as of early 2009 eCalc had been successfully used on twelve projects and four different utility construction methods.

A similar Greenhouse Gas (GHG) calculator was also developed in 2007 by the British Columbia Chapter of the NASTT (NASTT-BC). In 2010, the NASTT-BC, with the assistance of Vancouver-based PW Trenchless Construction, released an upgraded Carbon Calculator designed by Habitat Enterprises of Vancouver, which is freely available for use on the branch website.

This device has indicated that, on average, Trenchless Technology produces 90 per cent fewer GHG emissions than open cut excavations, and can provide overall cost savings of 25–50 per cent.

Protecting heritage trees

Trenchless can also play an important role in protecting historically and environmentally significant trees located in urban parks and gardens.

A major sewer replacement project at the Royal Botanic Gardens in London, UK, avoided tree root damage through the careful use of Trenchless Technology by Perco Engineering Services Ltd.

The project involved the installation of 160 m of 9 inch diameter pipe to expand the public facilities at these internationally renowned gardens.

“It was essential to avoid damage to the root systems of trees with scientific and historic value. An open cut method would have carried the risk of damage that Kew Gardens could not accept,” Dr Nafaji and Dr Gokhale said.

Perco worked according to the guidelines issued by the National Joint Utilities Group (NJUG) regarding the installation and maintenance of services close to trees, and only trenchless techniques were found to fulfil the high standards required by the NJUG.

The pipe bursting technique used by Perco avoided the need for excavation and only used existing manholes for access, thus guaranteeing tree safety. The pipebursting technique was employed to expand the existing 6 inch sewer, jacking a powerful expanding mole through the existing pipe, while 790 mm sections of segmental pipes were jacked into the existing annulus. These sections were then joined with an ethylene-propylene-diene-monomer (EPDM) rubber O-ring seals.

At ground level, it was impossible to detect that the pipe bursting was occurring beneath the surface. The royal opening of a new conservatory even took place in the midst of the project.

Trenchless – the international choice

The use of trenchless techniques to reduce the environmental impact of pipeline projects is also a noticeable international trend.

Trinidad and Tobago

For instance, the National Gas Company of Trinidad and Tobago is using HDD in the construction of a new offshore gas pipeline. The North – Eastern Offshore (NEO) pipeline will transport natural gas from the Angostura Field, located off the northeastern coast of Trinidad, to the New Abyssinia Accumulator Station, then on to the existing domestic gas distribution network.

The 93.5 km, 36 inch diameter pipeline will be composed of an 83 km offshore section, running from the Angostura Field to landfall at Mayaro Bay, as well as a 10.5 km onshore section which will traverse the remaining distance to the Accumulator Station. HDD will be used to install the landfall section of the pipe, to prevent cutting through the coastline and thereby minimise disruption to this sensitive environment. In addition, only water-based environmentally friendly bentonite will be used.

Russia

Similarly, HDD has been used by Gazprom to install sections of the Dzhubga – Lazarevskove – Sochi gas pipeline in Russia. The 177 km pipeline is intended to secure energy supplies to the mountain resort of Sochi and Olympic facilities under construction, and runs along the Black Sea to the Kudepsta gas distribution station near Sochi, with landfalls near Dzhubga, Tuapse, Kudepsta and Novomikhailovskove.

The Black Sea coast is part of the Sochi National Park and one of the most carefully conserved ecosystems in Russia. To avoid harming local wildlife, pipeline installation was scheduled to take into account the life cycle of native fauna. HDD was used to install the shore approaches near Tuapse and Kudepsta, further minimising disruption to this fragile coastal environment. According to a Gazprom spokesperson, this is the first time that HDD has been used in a shore approach in Russia.

The use of HDD not only helped preserve the coastal ecosystem, but also allowed the pipe to negotiate the steep coastal cliffs. Microtunnelling was also used to install the pipeline at all river crossings, which offered further environmental protection.

While making the project more expensive, these various environmental protection measures were considered by Gazprom to be more than worthwhile, and a company spokesperson reported that all works were conducted without impacting the surrounding landscape.

Green award winner

The environmental benefits of trenchless are also being recognised by leading industry bodies.

At the 2008 ISTT International No-Dig awards, the Trenchless Project of the Year was selected for its innovative use of HDD to preserve an internationally renowned coastal ecosystem. The Strangford Lough Marine Turbine Cable in Northern Ireland is the world’s first commercial scale tidal energy system. Developed by Marine Current Turbine, the system was designed to generate 1.2 MW of energy – enough to supply electricity to 1,000 homes.

In addition to the engineering challenges inherent in such a ground-breaking project, the developers were faced with the daunting task of installing a high voltage power export cable in the protected wetland and intertidal environment of Strangford Lough. The Lough supports 75,000 migrating waders and wildfowl, colonies of breeding terns, Common and Grey seals, otters, porpoises, basking sharks, conger eels, octopodes, oysters, mussels and a giant leather backed turtle. It is a designated Special Area of Conservation, an Area of Outstanding Natural Beauty, a Ramsar Site, a National Nature Reserve, a Special Protection Area, a Marine Nature Reserve and a Site of Special Scientific Interest.

HDD was decided to be the best installation method for this fragile ecosystem, and Marine Current Turbines contracted Longbore TT to drill a bore deep into the bedrock. Longbore TT’s DD-140 rig and closed-loop fluids recycling system was rigged up on a purpose-built pad laid with pond liner to protect the ground from fluid spills. The top soil stripped from the site was used to form an acoustic barrier between the drilling operation and the foreshore, to minimise the disturbance to the seals.

In recognition of this outstanding example of environmental protection, Longbore TT was awarded the prize for New Installation (Small Project) at the UKSTT 2008 Awards Dinner. It then went on to win Trenchless Project of the Year at the 2008 ISTT Awards.

The ISTT said that the project “clearly demonstrates the environmental benefits of using directional drilling to cross one of the most sensitive marine environments in the world.

“Marine Renewable Energy Systems are helping to save the world’s resources and solve the planet’s energy supply problems. HDD makes a significant contribution to their objectives.”

Conclusions

Trenchless techniques reduce traffic congestion and minimise the excavation required, reducing energy consumption.

Meanwhile, marine environments, bushland and other waterways, not to mention landscaped gardens and yards, can all benefit from the ongoing promotion of the various innovative trenchless solutions.

References

1. Samuel T. Ariaratnam, “Methodology for calculating the carbon footprint of underground utility projects.” Paper presented at the NASTT and ISTT No-Dig Show 2009, pp. 1-8. 2. Yeun J. Jung and Sunil K. Sinha, “Trenchless Technology: An efficient and environmentally sound approach for underground municipal pipeline infrastructure systems.” Paper presented at the NASTT No-Dig Show 2004, p. 3. 3. Isabel Tardiff, “How to take advantage of ‘green’ thinking to get more funding for infrastructure.” Paper presented at the NASTT and ISTT No-Dig Show 2009, p. 6. 4. Dr Mohammad Najafi and Dr Sanjiv Gokhale, Trenchless Technology: Pipeline and Utility Design, Construction and Renewal (New York: McGraw-Hill, 2005), p. 37. 5. Najafi and Gokhale, Trenchless Technology, pp. 39-40.