KOCHI: Even as the National Highways Authority of India (NHAI) faces backlash over the collapse of an under-construction stretch of NH 66 at Kooriyad in Malappuram, it has successfully completed construction of the only balanced cantilever bridge — in Varapuzha — that is part of the road-widening project.
Considered a complex construction activity, the 1.03-km-long balanced cantilever bridge was completed in a record 604 days at a cost of Rs 100 crore.
The old Varapuzha bridge over the Periyar River, inaugurated on January 16, 2001, was the first balanced cantilever bridge constructed in Kerala. It went on to bag structural awards.
“We opted for the balanced cantilever technology to cater to navigational requirements, as the bridge falls under the purview of the Inland Waterways Authority of India, which mandates minimum vertical and horizontal clearance for the safe passage of vessels and ships,” a senior NHAI official said.
While normal bridges have a shorter span--the distance between two consecutive supports of a bridge—the balanced cantilever is best suited for spans exceeding 50 metres and generally limited to 150 metres.
“The bridge has a total of 26 spans. The river portion has 83-metre spans on both sides with the central span measuring 120 metres, adequate for smooth navigational traffic below. Oriental Structural Engineers Pvt Ltd completed the work in a timely manner,” the official added.
The stretch of the Periyar sees regular boat services operated by Kochi Water Metro and State Water Transport Department (SWTD). This is besides local ferry services. The District Tourism Promotion Council (DTPC), in collaboration with Eloor municipality, is planning to launch adventure water sports in the water body.
Balanced cantilever method
The relatively speedy, cost-effective construction method is specifically suited to areas with difficult terrain or over perennial waterbodies. The technology involves constructing the bridge using ‘segments’ which are concreted into formwork fixed to a special movable steel structure called form traveller. An optimal design and weight of the form traveller is fundamental for the design and cost-effectiveness of the structure.
The bridge construction proceeds from the pier towards the centre of the span in segments. The number of segments on the right- and left-hand side of the pier shall be same for stable cantilever configuration. Once each balanced cantilever reaches the mid-span of the respective span, it is met with the balanced cantilever from the next span. Thus the enter span gets bridged. A typical feature of this type of bridge is that there is no cap over the piers.
Edappally-Moothakunnam widening
NHAI said it has completed nearly 65% of the Rs 1,618-crore project to widen the Edappally-Moothakunnam NH 66 stretch. Construction activities have been delayed due to dearth of red soil.
“Now a committee headed by the district collector has been formed to address the issue,” the official said.
The 26.03-km stretch, from Edappally to Moothakunnam, in Kodungallur, is the first of the five reaches of the 164-km Edappally-Ramanattukara (Kozhikode) NH 66 section, where the road widening exercise has been taken up. The works involve the construction of a railway overbridge (ROB) at Edappally, four flyovers, seven major bridges, eight minor bridges, eight vehicle underpasses, five small vehicular underpasses, four light vehicular underpasses, and one pedestrian underpass.