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 President 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.”
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 ways in which a trenchless approach is more environmentally friendly.
First, traffic fuel consumption is lowered through the use of No-Dig. 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 our cities and minimising disruption to residents.
Second, trenchless jobsites produce fewer emissions. They require minimal construction machinery and equipment as there is no need for excavation, compaction, back-filling and re-paving, which dramatically reduces 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 onsite 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. 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 Õ 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 or water created during open-cut construction can cause soil erosion and contaminated soils run-off, polluting streams, rivers and sewers. Because of minimal surface disruption, trenchless projects avoid these environmental pitfalls.
Trenchless jobsites are also free of 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 jobsites 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
Avoiding excavation 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, located 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.
Green energy with No-Dig
Australian energy companies are increasingly concerned with reducing the environmental impact of large infrastructure projects. As a result, a large number of pipeline projects and LNG projects are currently avoiding surface disruption in environmentally sensitive areas through the use of trenchless installation techniques, such as HDD and microtunnelling.
Gorgon LNG
Contractors working on the Gorgon LNG project will protect the pristine West Australian coast by drilling landfalls with HDD. The project includes the drilling of shore crossings to connect the upstream facilities for the Gorgon project to the onshore infrastructure on Barrow Island, located off the coast of northern Western Australia. AJ Lucas has been contracted to construct nine HDD landfalls: eight for gas flow lines and umbilical connections and one “÷water-wining’ hole to bring ashore the water needed for drilling fluid.
It is imperative that the project has minimal environmental impact as the landfalls come ashore under North Whites Beach, one of the principal rookeries for the green turtle (Chelonia mydas), which has a conservation status of vulnerable. Consequently, AJ Lucas ordered two new Herrenknecht HDD rigs, along with two new custom-built Brandt mud systems and five new Gardner-Denver PZ8 mudpumps. The equipment will be made soundproof and the site carefully designed to reduce the impact on local fauna and marine life.
Australia Pacific LNG
HDD will also be used on the Australia Pacific LNG (APLNG) project in Queensland. The project includes the construction of a 42 inch diameter gas transmission pipeline from the Surat and Bowen basins to a proposed LNG processing site located at Laird Point on Curtis Island, Gladstone. Beginning east of Wandoan, the main pipeline extends 362 km north, veering east during the latter stages, with a marine crossing at The Narrows to arrive at the LNG facility.
In the project’s recently released Environmental Impact Statement, HDD was outlined as the preferred method for crossing the marine section of The Narrows, as it will limit potential impacts to the shoreline construction area, where workspace is required to set up the drilling rig and pipe-string.
The pipe will be pulled into place through the hole drilled under the sea bed, and tied into the rest of the pipeline, or capped, awaiting the tie-in.
Desal goes green
A number of desalination projects have been constructed or are in planning to secure water supplies across Australia. As the projects tend to be located in environmentally sensitive coastal areas, Trenchless Technology has been used when installing come components of the projects.
The $A1.2 billion Gold Coast Desalination Project is the first large scale water desalination plant on Australia’s eastern seaboard, having the capacity to provide up to 133 ML/d of water to southeast Queensland.
Trenchless Technology was used in two of the project areas. Tunnel boring machines were used for the construction of the marine intake and outfall tunnels, while microtunnel machines were used for the construction of road and creek crossings on the network pipeline.
In the case of marine tunnels, Trenchless Technology was chosen after a risk assessment process ascertained that microtunnelling would minimise the environment impact on the beach zone and remove potential damage from severe storms.
The marine tunnel works consisted of two tunnels, both with an outside diameter of 3.2 m lined with concrete segments providing an internal diameter of 2.8 m. The intake tunnel is 2.2 km long while the outlet tunnel is 2 km long. John Holland completed the marine tunnels using Herrenknecht machines and some Herrenknecht personnel.
Similarly, microtunnelling was used on the installation of pipelines associated with Sydney’s desalination plant. The southern shore of Botany Bay contains extensive seagrass beds, which are a valued and protected part of the estuarine environment.
Trenching through these seagrass beds would have required a seagrass management plan to be implemented during and after construction, and a compensatory seagrass package involving transplantation. Instead, Sydney Water selected microtunnelling for the Silver Beach construction area under Botany Bay for a distance of about 800 m in order to protect the seagrass.
Water and wastewater silver lining
Trenchless Technology is also being used in the management and construction of traditional water and wastewater pipelines and projects.
Mardi-Mangrove Link Project
Work commenced in February on the HDD installation of a 260 m section of pipe under Wyong River as part of the Mardi-Mangrove Link Project, located in New South Wales.
Mardi-Mangrove Link Project Director Greg McDonald said “HDD allows us to cross the river with less need to disrupt the local environment. This site has a significant stand of trees, animal burrows in the river banks and a billabong on one side.”
Keeping Sydney green
Sydney Water has also highlighted the benefits of using Trenchless Technology in its efforts to reduce waste and minimise the environmental impact of its operations.
In its 2010 Annual Report, Sydney Water said it continues to reduce the amount of waste it produces by using innovative measures to cut down the need for excavation.
“Relining old sewers, rather than excavating and replacing pipes, has prevented about 6,000 tonnes of potential waste generation.
“Trenchless excavation methods are significantly reducing waste generation in water delivery network renewal projects,” Sydney Water said.
Sydney Water also enlisted some HDD assistance as part of its Sewerfix Wet Weather Alliance (SWWA) Wet Weather Overflow Abatement Program.
UEA completed a 1,403 m horizontal directional drill of 500 mm HDPE from Brightmore Reserve in Cremorne for the SWWA as part of the Eaton Street Wet Weather Storage Facility (WWSF) in Neutral Bay, on the north shore of Sydney Harbour.
Primarily targeted at swimming sites, the program will provide benefits to the environment and human health, and is part of Sydney Water’s long-term SewerFix program of sewage system improvements.
Prior to this project, (diluted) sewage was discharged to Sydney Harbour via two overflows on the Mosman Submain approximately 185 times in ten years. The Eaton Street WWSF reduces this frequency to the catchment target frequency of 20 spills in ten years.
Conclusions
Trenchless techniques reduce traffic congestion and minimise the excavation required, reducing energy consumption.
Meanwhile, marine environments, bushland and other waterways can all benefit from the ongoing promotion of the various innovative trenchless solutions.
In Australia, the trenchless industry needs to take advantage of the move towards sustainable construction practises and promote these greener credentials to governments and the community at large.