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The Bandra Worli Sea Link

The Rajiv Gandhi Sea Link , popularly known as Bandra Worli Sea Link is the first sea bridge of India . The cable stayed sections of this bridge , the tall towers along which the cables take support and E-Toll service are the striking features of the Bridge . The Sea Link reduces travel time between Bandra and Worli to 6 - 8 minutes , which would otherwise be more than 20 minutues . However , due to huge toll bills , very few vehicles ply through the bridge . As of October 2009 , BWSL had an average daily traffic of about 37,500 vehicles . The construction began in 2000 . 4 lanes were opened to the public in 2009 . All the 8 lanes became operational in 2010 .

Route

The Bandra Worli Sea Link connects Bandra & Worli . It is an extension of the Western Express Highway and also the end point of the W.E.H . It connects S.V. Road and W.E.H in Bandra to Khan Abdul Gaffar Khan Marg (Worli Sea Face) in Worli . The Sea Link Crosses the Mahim Bay , where Mithi River meets the Arabian Sea . It takes a sharp left turn to reach Worli , which is very dangerous . The route of the bridge forms a "L" Formation . The bridge has 2 major spans and 4 minor spans . This route is also important as a route that connects the suburbs to the island city (South Mumbai) .

Planning

Along with the sealink , there were five parts supportive to the bridge .

  1. Construction of a flyover over Love Grove junction in Worli .
  2. Construction of a cloverleaf interchange at the intersection of the Western Express Highway and S.V. Road in Bandra .
  3. Construction of solidapproach road from the interchange to the Toll Plaza on the Bandra side along with a public promenade
  4. Construction of the central cable-stayed spans with northern and southern viaducts from Worli to the Toll Plaza at the Bandra end .
  5. Improvements to Khan Abdul Gaffar Khan Road .

Geology

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Surveys of the seabed under the planned route were conducted before the bridge design commenced. The marine geology underneath the bridge 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 clay silt with some fine sand overlying weathered, dark brown basaltic boulders embedded in the silt.

Design

BWSL was designed as the first cable-stayed bridge to be constructed in open seas in India. Due to the underlying geology, the pylons have a complex geometry and the main span over the Bandra channel is one of the longest spans of concrete deck attempted. Balancing these engineering complexities with the aesthetics of the bridge presented significant challenges for the project.

The superstructure of the viaducts were the heaviest precast segments to be built in India. They were built using a span-by-span method using overhead gantry through a series of vertical and horizontal curves.' The 20,000 tonne Bandra-end span of the bridge deck is supported by stay cables within a very close tolerance of deviations in plan and elevation.
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Foundation & Substructure

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The construction of the bridge's structure presented major engineering challenges. These included the highly variable geotechnical conditions due to the underlying marine geology of the seabed. At times, even for plan area of a single pile had a highly uneven foundation bed. Further compilcations included the presence of a variable intertidal zone, with parts of the foundation bed exposed in low tide and submerged in high tide.

The foundations for the BWSL's cable-stayed bridges consist of 120 reinforced concrete piles of 2,000 millimetres (6.6 ft) diameter. Those for the viaducts consist of 484 piles of 1,500 millimetres (4.9 ft). These 604 piles were driven between 6m and 34m into the substrate in geotechnical conditions that varied from highly weathered volcanic material to massive high strength rocks.

Pylon Tower

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The largest pylons for the bridge consist of diamond shaped 128 metres (420 ft) high concrete tower featuring flaring lower legs, converging upper legs, a unified tower head housing the stays and a continuously varying cross section along the height of tower.

The bridge's pylon towers gradually decrease in cross-section with height. They have horizontal grooves every 3m in height, which permitted inserts. Vertical grooves in the circular sections require special form liners, as well as require attention for de-shuttering. The tower legs are inclined in two directions, which presented challenges in alignment and climbing of soldiers. Construction joints were permitted at 3m intervals only.

To build the pylons, Doka of Austria was commissioned to build a custom automatic climbing shutter formwork system, based on their SKE-100 automatic climbing shutter system. This was fabricated on site and employed to execute all tower leg lifts below deck level.

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Pre-cast Yard

The pre-cast yard was located on reclaimed land. The yard catered to casting, storing and handling of 2342 concrete-steel pre-cast segments for the project. The storage capacity requirement of yard was about 470 precast segments. As the area available was limited, the segments were stored in stacks of up to three layers .  

 

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BWSL 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 50 metres (160 ft) apart. Each section is designed to support four lanes of traffic with break-down lanes and concrete barriers. Sections also provide for service side-walks on one side. The bridge alignment is defined with vertical and horizontal curves.

The bridge consists of three distinct parts: the north end viaduct, the central cable-stayed spans and the south end viaduct. Both the viaducts used precast segmental construction. The cable-stayed bridge on the Bandra channel has a 50m-250m-250m-50m span arrangement and on the Worli channel it has a 50m-50m-150m-50m-50m span arrangement.

Bridge Management

Toll Collection

The Bandra end of the toll plaza has 16 approach lanes. The toll plaza is equipped with anelectronic toll collection system.
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Vehicle Toll
Single Journey Return Journey Day Pass
Car 55 (US$1) 82.50 (US$1.49) 137.50 (US$2.49)
Tempo/LCV 80 (US$1.45) 120 (US$2.17) 200 (US$3.62)
Truck/Bus 110 (US$1.99) 165 (US$2.99) 275 (US$4.98)

Monitoring

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An intelligent bridge management system (IBS) provides traffic information, surveillance, monitoring and control systems. It comprises CCTVs, automatic traffic counters and vehicle classification system, variable message signs, remote weather information system and emergency telephones. The control centre is located near the toll plaza along with the electronic tolling controls. The control system uses fibre-optic cables running the entire span of the BWSL. The toll management system and advanced traffic management system was installed by Efkon India.

For traffic enforcement, the bridge includes facilities for vehicles to pull over when stopped by enforcement officers or in the event of a breakdown.

Security

The bridge uses mobile explosive scanners for vehicles traveling on the sea link. Scans take less than 20 seconds for each vehicle with sensors above and below the vehicles. Over 180 cars can be scanned per hour by each scanner.

The pillars and the towers supporting the bridge are protected by buoys designed to withstand explosions and collisions. These inflated buoys surround each pillar of the sea link to avoid any damage.

The bridge tower and the control centers feature lightning protection, designed to protect the bridge monitoring, communication and power equipment from possible surges.

Power Supply and Lighting

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The bridge has a reliable and redundant power supply, backed up by diesel generators and auto mains failure panels for critical loads, such as monitoring, surveillance, emergency equipment and communication services including aviation and obstruction indicators. BWSL exclusively uses energy saving illlumination systems.

Criticisms

The Economic Times was critical of the Bandra-Worli Sea Link in every particular. First, the cost was not the projected 300 crore but actually cost 1,600 crore or about 430% cost overrun. Second, the project was 5 year behind schedule. Third, the supposedly reduction in commute time did not occur. Traffic bunched up at both ends of the Link causing nightmarish grid lock. The blame rest, as usual, on the notorious Indian corruption and political in-efficiencies. Compared to China, who in a span of 6 years, completed 7 sea links, under budgets and within the time schedules.

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