In a series of interviews with prominent civil engineers, Basil Manoj, Manager (Civil), L&T Metro Rail (Hyderabad) Ltd shares his experience of constructing flyovers through innovative technologies.
It is said that destiny is not a matter of chance, but choice. Well, Basil Manoj really had no choice when it came to his mTtier! While he originally wished to pursue a diploma in electronics engineering, civil engineering went on to become his calling. Today, with 19 years of experience in the construction and supervision of major bridges, flyovers and urban viaducts constructed with innovative design and advanced technology, Manoj is Manager (Civil) with L&T Metro Rail (Hyderabad) Ltd. "My family was against my decision to opt for civil engineering as it was not considered a profession of repute back then," he recalls. "But I came to realise that it was one subject to explore." Finding the right job also took time. He started his career with Dar Consultants as an AutoCAD Operator for two years. He was further transferred to an on-site job to monitor the pre-casting of concrete when the company bagged the JJ Flyover project in Mumbai. While Manoj was in charge of the erection and foundation works, he came to realise where he should be heading to. "Dar Consultants was among the first to introduce the precast segmental construction technology in India, and as a budding engineer, understanding the details was a big challenge," he confesses. Another challenging project was the Bandra-Worli Sea Link. "Understanding the technology in detail and ensuring it was implemented was no cakewalk," he reveals. In conversation with CW, he shares more about his projects, technology and the construction industry.
Project: Flyover from JJ Hospital to Palton Road, Mumbai
Cost: Rs 60 crore
Client: Maharashtra State Road Development Corporation
Features: The flyover starts adjacent to JJ Hospital and proceeds along Mohammed Ali Road to Palton Road. It is 2.4 km long with a dual carriageway of 16.2 m width with a span of 34.5 m. The bridge deck consists of a central spine and cantilever segments on either side to form the carriageway. The precast spine segments were cast by long line method and erected by using an under slung launching girder. The precast cantilever segments were erected using an overhead hanger system and stitched to the spine segment.
Background: This stretch forms an important arterial road in Mumbai and is one of the busiest traffic corridors of South Mumbai. Hence, to ease traffic congestion and reduce commuting time, this flyover was proposed. It also aimed to eliminate traffic signals and save fuel and vehicle operating costs.
Challenges: The first challenge was to construct the flyover with minimum hindrance to traffic. As the foundations were to be constructed only at the median, the types of underground utilities that would be encountered were not known.
Solution: Most of the bridge structures were precast and brought to site and erected in place at night. Before starting the construction work, utility probing was done by excavating trial pits at the location of piers. The costs for shifting utilities were paid in advance to the concerned departments, which helped in speedy action at affected locations.
Project: Bandra-Worli Sea Link Project (Package-IV), Mumbai
Cost: Rs 850 crore
Client: Maharashtra State Road Development Corporation
Features: The 5.6-km long sea link consists of a twin, four-lane deck linking Worli and Bandra across Mahim Bay. It consists of approach bridges, cable stay bridges, toll plaza, control building, link bridge and approach road. The bridge consists of precast deck segments cast by short line method and has been erected using overhead launching truss or derrick.
The cable-stayed bridges provide for a 500-m main span with a single support tower of 125 m high at Bandra, and a 150-m span conventional, twin-tower, cable-stayed bridge at Worli.
Background: To commute from Bandra to Worli during peak hours through the existing road, one encounters 23 signals; it takes about 40 minute with an average journey speed of 13 km per hour. To reduce commuting time, save fuel and reduce air, noise and sound pollution, an alternative corridor was proposed. The sea link was one of the most highly recommended links by transport studies conducted for the metropolitan region as it saves time and reduces the traffic on existing roads, thereby reducing the level of pollution.
Challenges: The bridge alignment was in the shallow waters of Mahim Bay and the movement of marine equipment to do the foundations was a challenging job. Also, transporting men and materials to different locations in the open, rough sea was difficult. The pylons of the cable-stayed bridge have a unique shape with varying geometry throughout its height of 128 m; the construction of this within tolerance was a great challenge. At one point of time, after completion of the erection at one end of the approach bridge, the 1,200-mt launching truss had to be shifted to the other location to proceed with the erection work.
Solution: Tidal variation was used to move the marine equipment to carry out foundation works at different locations.
Barge-mounted millers were used to transport concrete to the designated locations. Specially designed self-climbing formwork was imported from Austria and used to construct the pylons. Also, a high-capacity floating crane of 1,600 mt capacity was hired from Singapore to shift the entire launching truss from one end to the other without dismantling. The normal method of dismantling the launching truss, transporting it to a new location and erecting it again would have consumed a minimum of three months.