The pride of SoBo, the Chhatrapati Shivaji Maharaj Terminus (CSMT), built in 1878, is all set to have restored domes. The repair work on the station’s near-best architectural element will start after Diwali. Central Railway officials said the prestigious heritage restoration project, with an estimated cost of Rs 50 crore, is almost complete and only the domes remain.
The conical domes, experts said, have developed cracks due to ageing of stones. They started leaking a few years ago and the problem has only aggravated over the last few monsoons. An attempt was made to seal the joints of the external surfaces of stone masonry a couple of years ago by the Central Railway (CR) but it didn’t offer much relief. The current restoration work will be undertaken under the guidance of noted conservation architect and structural engineer Chetan Raikar.
Raikar on Wednesday said these well-dressed stone elements started showing material cracking a few years ago. This, he said, permitted entry of rainwater into the structure. “It would be interesting to note that these cracks are in individual stones and do not extend beyond a single piece of stone at a single location,” said Raikar, adding that these are hence classified as geological failure of the stone, which is age related and is due to inclusions at the time of formation of the stones.
Raikar said the restoration work needs for the stone to be stitched using non-corroding stainless-steel pins. He said the gaps would be grouted using lime mixture to prevent entry of rainwater into the structure. “These two engineering conservation techniques, when adopted, will collectively offer a long-term solution for strengthening this heritage structure,” he said.
A CR official said more than 140 years ago stones were the only material used for construction. While the CSMT’s central dome supports the Statue of Progress which is about 7.74 mt high and weighs approximately five tonne, the diameter of the central main dome is 12 mt.
In 2019, a drone survey by CR revealed that the cracks existed despite the repair work. Hence it was decided to carry out radar tests from inside of the dome. This is a modern non-destructive testing technique used by engineers for assessing heritage structures. It works on the principle of sending electromagnetic waves through the material to be tested.
A CR official said the radar test indicated that the stones have developed structural cracking, which is one of the major causes of leakage. Radar testing also confirmed that the thickness of the central dome varies from around 250 mm to around 500 mm.