Making of Bandra-Worli Sea Link

Construction of Pylon Tower Legs
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 deshuttering;
PIER TABLE
CABLE ANCHOR ZONE 10
LIFTS
UPPER TOWER LEGS 24
LIFTS
LOWER TOWER LEGS 8
LIFTS
SIDE VIEW OF TOWER P19 FOR BANDRA CABLE-STAYED
BRIDGE
(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. Construction of tower legs below deck level DOKA SKE-100 Automatic Climbing Scaffolding System erected on tower legs
a. Survey of Tower Legs
The complex pylon geometry was another challenge for surveyors. Coupled with geometry, the construction stage analysis indicated leaning and progressively increasing inward inclination of pylon legs during construction. HCC’s Principal Surveyor devised a sophisticated technology to measure coordinates through a combination of total station and prisms mounted on pylon legs. The temperature and construction stage analysis factors were applied to derive the corrected coordinates. The pylon legs were constructed within an accuracy of ±5mm, which speaks volumes about the technique employed.]
b. Anchorage Box
Anchorage Box for Bandra Cable Stay Bridge placed on Tower Head Junction Anchorage Box for Worli Cable Stay Bridge Anchorage Box is used as inner shuttering for tower head. Bearing plates with guide pipes are fixed to the anchorage box. Guide Pipe and Bearing Plates actually transfer the deck loads to tower concrete which are generated due to stressing of stay cables. The anchorage box is fabricated with 12mm thick high grade steel plates. It is fabricated in pieces and then bolted at tower head portion. The bearing plates and guide pipes of anchorage box are galvanized and the remaining portion was painted with anticorrosive polyurethane based paint.
Anchorage boxes are fixed with the help of co-ordinate system for accurately fixing the anchorage point and angle of stay cable. c. Compression struts
Compression struts are provided at various levels of tower legs. These were basically provided to keep the alignment of all tower legs in their required position. During construction, due to geometry it was possible that the tower legs might lean inwards due to weight and stresses involved in the base. In order to avoid that, compression struts were
provided and jacking done to desired load to maintain the alignment.
d. Erection of Pier Table segments The pier table segments numbering 42 for both the carriageways were another hurdle encountered. The reasons being –
(a) Launching Truss could not be deployed;
(b) Being generally over the pylon pile cap, lifting segments from the sea was not possible. To overcome this hurdle, HCC’s Expat devised a brilliant and ingenious solution in the form of –
-Pier Table Trusses (PTT): One each was erected for each carriageway. It had rails on top to move segments with the help of hydraulic jacks from one end to another.
-Lifting Frame: This was an ingenious little devise mounted at either end of PTT.
SLU (Strand Lifting Units) were mounted on top to lift the segment from barges anchored in the sea. After lifting the segment, the front frame closed down, where the segment was lowered on the rails. The rear frame lifted up to enable the segment to slide across the PTT hydraulically.
STAGE: 1
Open the Support Bracket and Lift the Segment. Close the Support Bracket, Slide in the Trolley and Lower the Segment on Sliding Trolley
STAGE: 2
Opening of the Lifting Boom & Strut, Slide out the Segment and Close the Lifting Boom and & Strut. Repeat operations for the other segment lifting.
e. Erection of segments of Cable Stay Bridge by Derrick The method used for erection of segments at Cable-Stayed bridge was balance cantilever construction method. During construction, the length of free cantilever for Bandra Cable-
Stayed bridge was 215m and for Worli Cable-Stayed bridge it was 73m. The segments were lifted by the instrument named Derrick which was fixed on both ends of the pier table segment and then forwarded. Lifting operation was done simultaneously on both ends. At a time, Derrick can lift one segment. Deck is constructed of alternate stay and
non stay segments joined to pier table segments.
Lifting of Segment with Derrick
f. Dry Matching, Epoxy and temporary stressing for gluing When the segment is positioned, it is to be joined with the existing segment. Therefore, the segment was first dry-matched with the already erected segment. On completion of drymatching, the segment was moved back by sliding the lifting beam for a distance of 400mm of the derrick and epoxy was applied on the face of both segments. After application of the glue, the segments were joined together and were stressed by Temporary PT bars. Post this step, the segment lifting beam on derrick is moved forward to lift the next segment i.e. stay segment.
g. Erection of Stay segment
These segments were also erected similarly as the non-stay segment and were also joined in the similar way. After this, guide pipes were installed over the ducts left behind during segment casting.
h. Stay cable
Stay Cables used are ‘Parallel Wire Stay Cables’. They were manufactured by “Shanghai Pujiang Cable Co. Ltd” China. Each cable consists of a group of different number of steel wires. Each wire is made up of high tensile steel. Diameter of single wire was 7mm with a
breaking limit of 6.28 Tones. Six different sizes of cables were used in the cable-stayed portion. The difference between them was only on the basis of number of steel wires in each cable. Six different types used were of 61, 73, 85, 91, 109 and 121 steel wires. Group of these wires was packed in two layers of HDPE (High Density Poly Ethylene) material to protect them from atmospheric effects. Typical Cross Section of Stay Cable i. Closure pour
In Bandra Cable-Stayed Bridge, closure pour is provided between main cable-stayed cantilevers and back span. In Worli Cable-Stayed bridge, closure pour is provided between two cable-stayed cantilever decks
j. Longitudinal stressing and grouting
When all the segments and cables were erected, the segments were post tensioned longitudinally. This post tensioning was done by stressing the steel tendons placed in the ducts provided inside the body of segments. This helps the members to stay together and to increase their load carrying capacity as a large number of segments were joined together to make single unit. Once the stressing was done as per requirement, these holes or ducts were filled with cement grout and were plugged at both ends.
k. Fine tuning
After completion of closure pour and post-tensioning of the deck, fine tuning of stay cables is done. Fine tuning is fine force adjustments of the stay cables to achieve the required stresses in the deck and profile of the deck.
During fine tuning, forces in the stay cables are adjusted to suit further addition of superimposed dead loads such as wearing coat, crash barriers, handrails and also vehicle loads.
During fine tuning operation, longitudinal and transverse deck profiles are also monitored to provide smooth curve.
l. Wearing Coat over south bound bridge deck Bridge deck surface of south bound carriageway is provided with 40mm thick Polymer Modified Bituminous pavement in conjunction with water-proofing system to seal the bridge deck. Working during monsoon The Maritime Board does not allow marine traffic in monsoon season. Thus, work was halted mid-May only to re-commence in October, effectively reducing the work schedule to only seven months in a year. To overcome this hurdle and to use this time to speed up the construction activities at Bandra Pylon, HCC put forth the solution in the form of an innovatively designed temporary bridge. This bridge had a total length of 325 metres. It had the facility of a walkway, a concrete pipe line, an electrically-operated trolley mounted on rail, water line and a pipe line. It paved the way for successful continuation of work during the monsoon season when the sea was rough and the winds were strong. Logistics Another challenge was ensuring effective supply chain at all working locations spread across the alignment in the sea and formulating measures to ensure the same. A diligently worked out logistic plan was put into action to ensure that commodities were handled at dedicated
location and dispatches monitored meticulously. State-of-the-art electronic devices were placed on the barges to cut down on idle timings.
During peak construction activities, innovative procedures and specialized equipments were required to enable high accuracy. Expert crews had to also exercise good judgement in assessing sea behavior and priorities during foundation/ substructure constructions and final
placement of concrete in situ. Navigation and transporting 19 precast segments in 24 hours at different open sea locations was a challenge. Secondly, concrete consumption at the peak had been at the rate of 50cum/hr. Under marine conditions, the consumption rate has been in the order of 700cum per day. To add to this, maintaining adequate food supply for around 2500 people (in a shift) working in the sea at over 30 locations was a big challenge. These complete requirements were met with an effective utilization of a fleet of 30 marine vessels
including 13 barges for concrete, segments and material transport, eight steel boats for material and workers transport, three tug boats and six smaller passenger boats.
Around four passenger boats were used for carrying food to approximately 30 locations in the sea. Each employee, while starting his day, entered the log indicating the location at which they would be working. Thereafter began the clockwork of gathering tiffin boxes, washing and cleaning, allocation and dispatch as per the log entries along with the drinking water supply including tea supply at two time intervals per shift. During rough sea conditions in the normal working season, extra tiffins were carried to take care of possible spillage while
transferring the tiffins from boats to working locations. Thus workers were also suitably cared for, while meeting the engineering challenges posed during construction of the Bandra- Worli Sea Link. Psychological conditioning With a long track record and experienced in building large infrastructure projects, HCC follows strict guidelines for occupational health and safety and environment protection.
Safety is extremely important to HCC and the company officials worked towards sensitising labour and creating greater awareness of safety standards with gentle persuasion, consistent motivation and tool box meetings. The kind of structured processes that were implemented by HCC for ensuring safety is nothing short of phenomenal.
Lack of awareness is the biggest hazard for safety. Since the primary safety hazard are related to engineering control, equipment, job methodology, material handling, structural fabrication and emergency preparedness, HCC made sure that every worker is taken through the HSE program. The orientation program made them aware of the various safety hazards associated with a project and necessary precautions to be taken to prevent them. They are also taught how to evacuate during any emergency. For its meticulous planning and implementation of safety practices for the BWSL project, HCC has won the prestigious “Golden Peacock Award” for safety, health and environment in June 2007. Key people Over 3000 workers were employed to work on the project. Several teams of HCC engineers and foreign engineers and technicians have been involved in specialised tasks on the structure of the Sea Link. These include professionals from China, Egypt, Canada, Switzerland,
Britain, Serbia, Australia, Singapore, Thailand, Hong Kong, Indonesia and the Philippines. In terms of language, cultural differences and methods of work these key people were different, yet the engineering challenges kept the group creatively involved, and they worked enthusiastically as a team.