Bandra-Worli Sea Link

The Bandra–Worli Sea Link (BWSL) (Marathi: वांद्रे वरळी सेतू Wāndre Warḷi Setu), officially the Rajiv Gandhi Sea Link, (Marathi: राजीव गांधी सेतू), is a cable-stayed bridge with pre-stressed concrete viaduct approaches, which links Bandra and the western suburbs of Mumbai with Worli and central Mumbai, and is the first phase of the proposed West Island Freeway system.

The 1,600 crore (US$356.8 million) project of Maharashtra State Road Development Corporation (MSRDC) was executed by Hindustan Construction Company, with design and project management by DAR Consultants. The bridge was dedicated to the public on 30 June 2009 by Congress President and UPA Chairperson Sonia Gandhi, although only 4 of 8 lanes were opened to service. All the 8 lanes were opened to traffic on 24 March 2010.

The Sea Link reduces travel time between Bandra and Worli from 45–60 minutes to 7 minutes. The link has an average daily traffic of around 37,500 vehicles per day.

History

Mahim Causeway was the only link connecting the western suburbs to island city of Mumbai. This north-southwestern corridor would be highly congested resulting in a bottleneck at rush hours. The sea link was thus proposed to act as an alternate route between the western suburbs of Mumbai and central Mumbai, in addition to the existing Mahim Causeway, thus easing congestion. This link would also form a part of the larger West Island Freeway spanning the entire coastline.

The project was initiated more than 10 years ago in 1999 and was supposed to be completed within 5 years but it was delayed due to public interest litigations. The foundation stone was laid in 1999, by Shiv Sena supremo Balasaheb Thackeray.

It was to cost 300 crore and finished in 2004.

Purpose

The BWSL project is a part of the Western Freeway Sea Project, which, in turn, is a part of a larger proposal to upgrade the road transportation network of greater Mumbai. It is primarily meant to provide an alternative to the Mahim Causeway route that is presently the only connection between South Mumbai and the Western and Central suburbs. The project starts from the intersection of Western Express Highway and SV Road at the Bandra end, and connects it to Khan Abdul Gaffar Khan Road (Worli Seaface) at the Worli end which in turn connects to Mumbai's arterial Annie Besant Road at the Narayan Pujari Nagar corner.

The project has been commissioned by the Maharashtra State Road Development Corporation Ltd (MSRDC), designed by Dar Al-Handasah and is being built by Hindustan Construction Company (HCC)

Construction

The entire project was originally conceived as one large project comprising, different components, but in order to accelerate the overall construction schedule, the project has been divided into five construction packages. These packages helped, to an extent, to make the project meet its deadline.

  • Package I: Construction of flyover over Love Grove junction at Worli
  • Package II: Construction of cloverleaf interchange at Mahim intersection
  • Package III: Construction of solid approach road from the Mahim intersection up to the start of the Toll Plaza on the Bandra side and a public promenade
  • Package IV: Construction of Cable-Stayed Bridges together with viaduct approaches extending from Worli up to the Toll Plaza at Bandra end, Intelligent Bridge System (IBS).
  • Package V: Improvement to Khan Abdul Gaffar Khan Road

Package IV is the largest and main phase of Bandra-Worli Sea Link Project that has been awarded to HCC that includes cable-stayed bridge, viaduct approaches extending from Worli up to Toll Plaza at Bandra end and Modern Toll Plaza

Pre-Cast yard

The Pre-Cast yard was located on reclaimed land. The yard caters to casting, storing and handling of pre-cast segments for the project totalling 2342 in numbers. The storage capacity requirement of yard is to be about 470nos. As the area available is limited, the segments are to be stored in stacks of three layers.

Marine works

The foundations for the BWSL project consist of 2000-mm diameter piles numbering 120 for the cable-stayed bridges and 1500-mm diameter piles numbering 484 for the approach bridges. The project’s site geology consists of basalts, volcanic tuffs and breccias with some intertrappean deposits. These are overlain by completely weathered rocks and residual soil. The strength of these rocks range from extremely weak to extremely strong and their conditions range from highly weathered and fractured, to fresh, massive and intact. The weathered rock beds are further overlain by transported soil, calcareous sandstone and thin bed of coarse grained conglomerate. The top of these strata are overlain by marine soil layer up to 9m thick consisting of dark brown clayey silt with some fine sand overlying weathered, dark brown basaltic boulders embedded in the silt. The major engineering problems that needed suitable solutions before proceeding with the work were as follows:

It is for the first time that cable stay bridges have been attempted on open seas in India. Coupled with the fact that the aesthetically designed pylons have an extremely complex geometry and one of the longest spans for concrete deck, the challenges encountered were formidable.

The salient characteristics of the pylon tower that make it complex and challenging from the point of view of constructability are as follows: (a) The section decreases gradually with height; (b) There are horizontal grooves at every 3m height and vertical grooves for circular portion that requires special form liners as well as it requires attention for de-shuttering; (c) The tower legs are inclined in two directions, which creates complexities in alignment and climbing of soldiers; (d) Construction joints permitted only at 3m level. Inserts were permitted only in horizontal grooves provided at 3m height. On not being able to get immediate solution from reputed worldwide formwork manufacturers, the project design team designed an automatic climbing shutter formwork system, which was fabricated on site and employed to execute all tower leg lifts below deck level. To affect further reduction in time cycles, HCC approached Doka, Austria. Doka then devised a customized solution based on their SKE-100 automatic climbing shutter system.

Engineering challenges

Before undertaking the construction, there were several major challenges to be addressed namely

Main bridge structure

The bridge consists of twin continuous concrete box girder bridge sections for traffic in each direction. Each bridge section, except at the cable-stayed portion, is supported on piers typically spaced at 50 metres. Each section is meant for four lanes of traffic, complete with concrete barriers and service side-walks on one side. The bridge alignment is defined with vertical and horizontal curves. The bridge layout is categorized into three different parts:

  • Part 1 - The north-end approach structure with Pre-Cast (PC) segmental construction.
  • Part 2 - The Cable-Stayed Bridge at Bandra channel is with 50m -250m-250m-50m span arrangement and the Cable-Stayed Bridge at Worli channel is with 50m-50m-150m-50m-50m span arrangement.
  • Part 3 - The south end approach structure with Pre-Cast segmental construction.
North End approach dx

The bridge is arranged in units of typically six continuous spans of 50 metres each. Expansion joints are provided at each end of the units. The superstructure and substructure are designed in accordance with IRC codes. Specifications conform to the IRC standard with supplementary specifications covering special items. The foundation consists of 1.5 metres diameter drilled piles (4 nos. for each pier) with pile caps. Bridge bearings are of Disc Type.

The bridge has been built utilising the concept of Pre-Cast, post-tensioned, segmental concrete box girder sections. An overhead gantry crane with self-launching capability is custom built by the company to lay the superstructure of the precast segments. The Pre-Cast segments are joined together using high strength epoxy glue with nominal pre-stressing initially. The end segments adjacent to the pier are short segments "cast-in-situ joints". Geometrical adjustments of the span are made before primary continuous tendons are stressed.

Segment types are further defined by the changes in the web thickness and type of diaphragms cast in cell. The segment weights vary from 110 tonnes to 140 tonnes per segment. The segment length varies from 3000 mm to 3200 mm. Deck post tensioning is performed at the completion of the erection of each 50m bridge span.

Cable-stayed bridge

The cable-stayed portion of the Bandra channel is 600 metres in overall length between expansion joints and consists of two 250-metre cable supported main spans flanked by 50 metres conventional approach spans. A centre tower, with an overall height of 128 metres above pile cap level, supports the superstructure by means of four planes of cable stay in a semi-harp arrangement. Cable spacing is 6.0 metres along the bridge deck.

The cable-stayed portion of the Worli channel is 350 metres in overall length between expansion joints and consists of one 150 metres cable supported main span flanked by two 50 metres conventional approach spans. A centre tower, with an overall height of 55 metres, supports the superstructure above the pile cap level by means of four planes of cable stay in a semi-harp arrangement. Cable spacing here is also 6.0 metres along the bridge deck.

The superstructure comprises twin precast concrete box girders with a fish belly cross sectional shape, identical to the approaches. A typical Pre-Cast segment length is 3.0 metres with the heaviest superstructure segment approaching 140 tonnes. Balanced cantilever construction is used for erecting the cable supported superstructure as compared to span-by-span construction for the approaches. For every second segment, cable anchorages are provided.

A total of 264 cable stays are used at Bandra channel with cable lengths varying from approximately 85 metres minimum to nearly 250 metres maximum. The tower is cast in-situ reinforced concrete using the climbing form method of construction. The overall tower configuration is an inverted "Y" shape with the inclined legs oriented along the axis of the bridge. Tower cable anchorage recesses are achieved by use of formed pockets and transverse and longitudinal bar post-tensioning is provided in the tower head to resist local cable forces.

A total of 160 cable stays are used at Worli channel with cable lengths varying from approximately 30 metres minimum to nearly 80 metres maximum. Like the Bandra channel, the tower here is also cast in-situ reinforced concrete using the climbing form method of construction but the overall tower configuration is "I" shape with the inclined legs. Similarly, tower cable anchorage recesses are achieved by use of formed pockets.

The foundations for the main tower comprise 2 metre-drilled shafts of 25 metres length each. Cofferdam and tremie seal construction have been used to construct the six metre deep foundation in the dry.

South End approach structure

This portion of the bridge is similar to the North end approach structure in construction methodology with span by span match cast concrete box girder sections.dhanu advise the sea link is good cantruction of civil engg. thats b the

Toll plaza

A modern toll plaza with 16 lanes is provided at the Bandra end. The toll plaza is equipped with a state-of-the-art toll collection system. A structure is provided at this location to house the control system for the ITS.

Intelligent Bridge System

The toll station (TP) and collection system will provide for three different types of toll collection, as follows: - Fully automatic system: Electronic payment through On board Units mounted on the vehicles which allow passage without stopping. - Semi-automatic system: Electronic payment through a smart card, which allows payment without having to pay cash. - Manual toll collection: Payment of toll by cash, requiring vehicle drivers to make cash payment to a toll attendant, and stopping for cash exchange.

The intelligent bridge system will provide additional traffic information, surveillance, monitoring and control systems. It comprises CCTVs, traffic counting and vehicle classification system, variable message signs, remote weather information system and emergency telephones. The control centre located near the toll plaza is housed with the electronic tolling controls. The transmission system comprises fibre-optic cable housed in PVC conduits running parallel to the Bandra-Worli corridor. In addition, facilities to assist enforcement are provided in the form of pullout locations, which will allow drivers and enforcement officers to safely pullout of traffic.

The toll management system and advanced traffic management system has been installed and commissioned by Efkon India.

Security System

The State Government has planned to add mobile based explosive scanners on the sea link at a cost of 50 crore (US$11.15 million). There will four scanner that will be installed about 50-100 metres ahead of the toll plaza. It would take 20 seconds to scan a vehicle that drives under the device and nearly 180 cars can be scanned per hour. Also the waterfront would be fortified using rubber buoys. These inflated buoys will be garlanded around the pillars of the sea link to avoid any damage due to collision. The buoys are supposed to be tough enough to sustain an impact.

Power supply and road lighting system

A reliable and dependable power supply has been arranged for the entire project. It will also house diesel generator sets and auto mains failure panels to cater to critical load, e.g., monitoring, surveillance and communication equipment emergency services like aviation obstruction lights. Adequate levels of lighting levels have been maintained and energy saving luminaries have been installed. Special emphasis has been given to incorporate lighting protection at bridge tower and control room building to protect those building/ structures and the sophisticated monitoring and communication equipment installed therein.

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