Adoption of sustainable practices in infrastructure projects has been accorded the utmost importance in recent times. However, the construction industry has faced several challenges with respect to the adoption of new and innovative construction methods. There is thus a need to spread awareness and impart proper training to industry stakeholders on the latest, environment-friendly techniques and solutions for construction works.
A look at some of the key construction methods and materials being adopted across different sectors…
NATM and micro-tunnelling gaining prominence in tunnel construction
Tunnel development in the country has picked up pace in the past few years on account of increased uptake of projects involving longer tunnel lengths. The growth in tunnelling activity is driven by the robust pipeline of projects in the urban mass transit, railway, roads and highways, and water supply and sewerage sectors. With respect to the method of tunnelling, the drill-and-blast method has been the most prominent across all sectors. However, in recent years, the New Austrian Tunnelling Method (NATM) has gained importance, especially in the railway and metro sectors. It is a flexible and cost-efficient technique and is fast emerging as an alternative to traditional tunnelling methods in congested urban areas.
As of November 2019, the hydropower sector accounted for the largest share of 49 per cent (spanning a total length of 78.3 km) of the total tunnel length constructed (completed projects). However, the railway sector accounted for the largest share of 75 per cent (219.92 km) of the total tunnel length currently under construction. With the pipeline of metro projects planned for implementation, the use of NATM is expected to increase further in the times ahead.
Another advanced method which is seeing increasing acceptance is micro-tunnelling, also known as trenchless or pipe jacking technology. Emerging as a new trend in the country, it is being used to lay water supply pipelines and sewers in congested areas. Micro-tunnelling is being put to use for laying large diameter gravity sewers in cities where open-cut installation is difficult, for the installation of product pipelines in areas where the soil condition does not allow for horizontal directional drilling, and for long individual crossings across rivers. It is suitable for constructing tunnels with diameters ranging from 600 mm to 3,000 mm. A remote-controlled steerable boring machine is the main equipment deployed in micro-tunnelling. It is operated from a computer-operated station using drive motor controls.
In order to build underground subways without disrupting traffic movement, the Delhi Metro Rail Corporation adopted the “box pushing” technology at the ITO metro station on the Central Secretariat-Kashmere Gate corridor. Vertical excavation or large-scale digging is not required for this technology, which is much faster as compared to the conventional cut-and-cover technology.
Use of plastic waste and fly ash being promoted for road construction
India, like other countries, has started looking for alternative materials for road construction, and waste is one such option, especially when there are growing concerns regarding the generation of waste through construction, industrial and household activities. Road construction has emerged as one of the suitable options for putting waste to productive use. The use of fly ash is being increasingly promoted in the road sector, where it is mostly used for the construction of roads, embankments and flyovers. It is also used by the cement industry as a pozzolanic material for manufacturing cement.
The Ministry of Environment, Forest and Climate Change has issued several notifications for fly ash utilisation, the key among which was issued in September 1999. Subsequently, it was amended through notifications in August 2003, November 2009 and January 2016. As per the guidelines, it is mandatory to use fly ash in the construction of roads and flyover embankments within a radius of 300 km from a thermal power plant. Further, the cost of transportation of ash for road construction projects within a radius of 100 km will be borne by the power plant itself while that between 100 km and 300 km will be shared equally between the road developer and the power plant. For a radius of 300 km or more, the thermal power plant will bear the entire transportation cost, as committed under the Pradhan Mantri Gram Sadak Yojana. Meanwhile, in order to ensure optimal utilisation of fly ash as an environmentally sustainable and economically viable product, the government has reduced the goods and services tax on fly ash and its products to 5 per cent.
Besides fly ash, plastic waste has also garnered significant interest. Of the municipal waste generated, plastic waste accounts for a significant portion. Unrecycled plastic waste, which accounts for 40 per cent of total plastic waste, can be used for road construction. In 2015, the government made it mandatory for road developers to use waste plastic along with bituminous mixes for road construction within a 50 km radius of any city with a population of over 0.5 million. Cities such as Delhi, Mumbai, Chennai and Pune have actively started using shredded plastic waste in road construction. Of late, a number of stretches in the Delhi National Capital Region have been developed using plastic waste, including one near Dhaula Kuan, Delhi, and another near Sohna Road, Haryana.
Waste materials being used for construction activities
The Aligarh Municipal Corporation in collaboration with a waste management company is constructing eco-friendly bricks. Termed magic bricks, they are made using garbage, concrete and cement and can be used for construction.
Green building standards for airports
India’s aviation industry has been growing steadily. Airports can no longer afford to not go green and still be sustainable. Currently, the sustainable green buildings norms such as The Leadership in Energy and Environmental Design (LEED), Indian Green Building Council and Green Rating for Integrated Habitat Assessment are gaining popularity among airport developers and owners. Airport authorities are gradually adopting these global standards that include various innovative techniques such as high performance glazing systems, efficient and automated lighting systems, green materials and chemicals, water harvesting and recycling systems, waste management systems, etc. Terminal 3 of the Indira Gandhi International Airport was the first airport terminal to receive LEED gold rating for green buildings. The certification was awarded on the basis of T3’s features across six categories – sustainability, water efficiency, energy and atmosphere, material and resources, indoor environmental quality, and innovation in design. Another terminal to have received LEED certification is terminal T2 of the Chhatrapati Shivaji Maharaj International Airport in Mumbai. The terminal was awarded the certification for its green initiatives – energy savings of Rs 310 million lower than the ASHRAE baseline energy cost (a building should use less energy as compared to a baseline building built as per the ASHRAE 90.1 specifications), overall annual water savings of more than 34 per cent over the LEED India baseline, indoor air quality and thermal comfort parameters exceeding a conventional airport’s requirements, significant reduction in the use of natural resources, etc.
Future outlook
In light of the emphasis being given to sustainable construction methods, the prospects of green construction techniques seem bright. The construction industry is in the process of adopting new and sustainable technologies, with a group of progressive contractors leading the way. In the future, infrastructure projects are expected to adopt stringent sustainable guidelines ensuring the minimum usage of natural resources (energy and water), utilising recycled material, sourcing most of the construction material locally, managing the waste generated efficiently and, thus, ensuring a lower carbon footprint.
Undoubtedly, many new options have emerged as far as construction techniques are concerned. However, there is a need to ensure skill development at the grassroots level through imparting adequate training and guidance to contractors and operators to ease the process of adopting green technologies. Just the availability of the latest technologies will not help achieve the goal of sustainability unless all stakeholders join hands to make construction environment friendly.