In a tete-a-tete with Manasi Tahalani, Deputy Chief Engineer, Construction (Dadar) and the in-charge of the whole operation, Rajeev Mishra explained the technicalities behind the dismantling of the bridge and challenges faced by the Central Railway. It took 80 lakhs, 50 days and 650 railway officials to bring down the Hancock Bridge.
Central Railway brought down the 136-year-old Hancock Bridge on January 9 and 10. What were the reasons behind dismantling the bridge?
The bridge was constructed in 1879 and had therefore outlived its codal life, which essentially means, its maintainability had become poor (by maintainability we mean efforts and resources required to maintain it) and it had become difficult to guarantee its safety. Secondly, after conversion from DC to AC traction on Mumbai CST-Kalyan Main line section, a speed restriction of 15Kmph was imposed at this location due to inadequate clearance below the Road Over Bridge (ROB), which had to be increased. Third, an additional span was needed to be provided for accommodating the proposed CST-Kurla 5th and 6th lines and fourth, the track at this location was in a saucer and was getting frequently flooded during monsoon season leading to disruption of traffic, which had to be remedied.
What kind of planning and preparations were done by the CR in order to smoothly carry out the dismantling work on the D-day?
The bridge was closed for vehicular traffic on November 18 with the help of heavy police bandobast and thereafter, preparatory works were carried out. First, the 300mm thick bitumen layer was removed with the help of JCB and poclain machines. A total of 200cum of debris was removed and taken away from the premises on real time basis. Second, the 300mm thick concrete layer above the troughs was dismantled with the help of concrete breakers.
Third and the most tedious was the removal of concrete from the trough in fills. Breaking concrete in these narrow compartments, total 20 rows and at the same time ensuring safety of the bridge as well was a herculean task. Finally, the last step in the preparation work consisted of making cuts in the steel section, in such manner so as not to endanger the safety of the bridge and the railway traffic below it but also at the same time reduce the workload of cuts in the mega block.
Following this, how was the process of dismantling the bridge carried out?
Prior to the commencement of the mega block, two numbers of 300T capacity cranes were propped, one at each end, with each crane having a standby crane. Railway’s 140T capacity breakdown crane was also kept in readiness to cater to any emergencies. Two numbers of tower wagons and two wiring trains were also deployed for OHE works, one on each of the main lines. 50 numbers of gas cutters with 500 numbers of oxygen and 50 numbers of LPG cylinders were mobilized; steel cutting being the main activity during the block. As soon as the block commenced, first, the footpath portion was removed in convenient pieces. Due to heavy rust on these members it took quite some time to cut the same. Thereafter, the trough members were removed, again in convenient pieces starting from the centre towards either end by the respective end cranes. Finally, the columns were cut in convenient pieces and removed with the help of the cranes.
What were the challenges faced by the Central railway in carrying out this mammoth job?
The first major challenge was the presence of a large number of utilities crossing through the bridge, which were serving important sensitive establishments such as the JJ Hospital, traffic signals and police stations on either side or various others. The utilities consisted of 13 numbers of cables of BEST, 80 numbers of copper cables and 18 numbers of OFC cables of MTNL, two numbers of cables of BSNL, Reliance cables pertaining to traffic police CCTV cameras, Vodafone four numbers of cables, a 450mm diameter and a 150m diameter live and a 100mm diameter and a 150mm diameter dead water supply pipelines of MCGM and two numbers of cables pertaining to the railway traction department.
One of the major challenges lay in convincing all these departments about the urgent need of dismantling the bridge and also to get them on board to carry out the same within the quickest possible time. The second major challenge lay in the removal of encroachments, a number of which were there on the bridge footpath and a large number on the east end approach. The hutment dwellers on the footpath could be relocated only by January 8 and thereafter within 24hrs. The hutment dwellers within the working zone were served notices to vacate the premises during the block period and for them Railway coaches had been arranged so as to cause least inconvenience to them. The third major challenge lay in getting the pedestrians on board who were to lose their access.
What arrangements were done for the security of the railway officers and people involved in the process of dismantling?
The work was carried out professionally, with clockwork precision, ensuring safety of workmen as well as the OHE and other structures below the bridge. To avoid any public unrest, heavy RPSF and Civil police bandobast was made on either end as well as at the track level on either side. Doctors on shift duty, both of the Railways as well as of the MCGM, along with ambulances at either end were stationed at site throughout the duration of the block.
Who would you credit the work with?
First and foremost, the credit goes to the leadership of Central Railway, which includes the General Manager, the Chief Administrative Officer (Construction), the Chief Engineer (Construction) and the Chief Bridge Engineer.
There are a large number of such old bridges to be dismantled. How do you see the path ahead?
Our aim will always be to further improve the processes, wherever there is scope. If possible, we may take a completely different approach to the dismantling scheme itself. The homework has already started for the dismantling of the Carnac Bridge and we are looking at various technological solutions to come out with a better scheme.
