Nuvoco Providing Expertise For Underground Tunnelling By Pranav Desai
Metro Rail or Mass Rapid Transit systems have been cited as the smartest solution to tackle both traffic as well as environmental pollution. These projects are currently undertaken in a big way across major cities, including Jaipur, Mumbai, Noida, and Delhi. What these projects share in common has been the role that Nuvoco Vistas Corp. Ltd. (formerly Lafarge India Ltd) has played in providing them with the required smart solutions and expertise. As one of the leading and most trusted building materials manufacturers in the country, Nuvoco has had the privilege of being the primary supplier for four major Metro projects in India, namely the Delhi, Mumbai, Noida, and Jaipur Metro.
Large scale projects like these require precision and planning as they are always accompanied by their fare share of challenges, the most major one being supplying the required quantity and quality of concrete for the projects. In addition to that, the project deadlines are another factor to keep in mind, besides the site locations, which are often in the heart of the city. Addressing all these challenges, Nuvoco presented the best solution upholding the quality and quantity of concrete. For all the above mentioned metro projects, Nuvoco has handled the full scope of the work, from setting up batching plants to operations, maintenance and procuring of raw materials. Metro projects have the highest concrete requirements of all, for which, good quality aggregates are an absolute necessity, but so is ensuring its consistent supply.
Mumbai Metro, where Nuvoco is suppliying concrete for Package 4, is fully underground, and comprises three underground stations at Siddhivinayak, Dadar and Shitladevi temple, and associated tunnels. The project consists of 6082-meter twin bored tunnels with internal finished diameters of 5.80 meters. It will be a fully underground section, 33 kms long, with 27 stations, and the most difficult metro line so far undertaken in the country. Once completed, it is expected to transform the travel style and pattern of Mumbaikars. The project faces many technical challenges due to adverse rock conditions, along with proximity to many heritage buildings and very old residential buildings.
Per practice, Nuvoco carried out a need-gap identification for the Metro projects, and provided customised solutions basis the issues identified. For instance, while working on the underground tunnel section, Nuvoco had to make sure that the precast liner was suitable enough not just to bear the heavy load; but also malleable enough to set properly. Tunnel Boring Machines (TBM) were used for tunneling, in which, precast tunnel segments are assembled and erected by a robotic ring assembler that snaps the segment into place, and then grouted. Thus, the project required manufacturing of superior quality and high strength precast segments while ensuring production cycle management, and keeping the rate of production synchronised with the elements required for uninterrupted feeding to the TBM. Nuvoco addressed all these issues with Agile™ (its free flowing concrete) and Robuste™ (high strength concete), which eliminated the extra setting time requirement, and eased the placement of concrete in the thin structural moulds; thereby ensuring a faster production cycle. Robuste being more compact and denser than conventional concrete products; allowed de-shuttering to be done in a matter of hours, while requiring lesser precast yard area and reducing the size and thickness of the section of elements.
The Mumbai Metro project has diaphragm walls, which are structural concrete retaining walls constructed before a deep trench excavation; either cast in-situ or using precast concrete components. They are often used at congested sites, or close to existing structures, or where there is restricted headroom, or where the excavation is at a depth that would otherwise require the removal of much greater volumes of soil to provide stable battered slopes. Nuvoco, being the primary concrete solutions supplier, was posed with attaining proper compaction under these challenging circumstances. The space – around 600 to 500 mm in width – had to be filled with compacted concrete with a strong reinforcement cage in place. The solution was using Agile with Lente (delay set concrete) for casting the D-wall as it offered better compaction and the possible elimination of bentonite slurry. Instamix Mortare™ a fibre reinforced water resistance cement plaster available in 30 kg packaging ready to apply wet plaster was used for plastering and finishing the wall, and Robuste™ was used to reduce the amount of reinforcement. As a result, Nuvoco ended up completing the casting of the entire diaphragm wall without any gliches and with utmost customer satisfaction.
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