The Vidhana Soudha underground metro station is an engineering feat
In a matter of about nine months or so, people travelling on the Dr. B.R. Ambedkar Road between the Vidhana Soudha and the High Court would see no sign of the huge trench, 275 m long, 27 m wide and 18 m deep, between these two landmark structures.
This 1.33 lakh sq m trench, excavated for construction of the Vidhana Soudha underground metro station on Namma Metro’s east-west corridor, will exist no more as the Bangalore Metro Rail Corporation Ltd. (BMRCL) is almost done with the construction of the station box and has commenced filling the gaps.
As one descends the excavated slopes to enter the station box under final stages of construction, what is immediately obvious is the engineering feat. When The Hindu team visited the construction site earlier in the week, very few workers were at the site and one could get an unhindered view of the station from end-to-end thanks to absence of pillars.
BMRCL Deputy Chief Engineer (Underground) Subrahmanya G. Gudge, who was accompanying the team, explained that the 1.4 m-thick roof slab is designed to take not only the station box load but also that of the soil to be filled above it to bring the station site to the original level. According to N.P. Sharma, Chief Engineer (Underground), concrete columns would obstruct free movement of commuters. Besides, a column-less construction enhances the aesthetics.
The station box is being built with strong concrete reinforcement. While the station walls are 1 m thick, the roof slab is 1.4 m thick and the concourse slab 0.75 m thick. The contractor is using specially fabricated steel gantry — 10 m wide and 6 m high — to enable speedy and uniform construction of the walls. The entire station box is being wrapped with a waterproofing agent, a bituminous membrane 3 mm thick, said D.N. Devendra, Section Engineer of the general consultant (RITES is the lead consultant) of the project.
Construction of the station box (13 m long and 24 m wide) near the Gopala Gowda Circle and towards the General Post Office (GPO) respectively is to be completed. While the space near Gopala Gowda Circle had to be kept free for the entry of tunnel boring machines (TBMs), the one towards the General Post Office is free to launch TBMs towards Cubbon Park underground station. By July-August, the entire box would be complete.
Restoration of site
Even as BMRCL has already commenced the restoration process of the Vidhana Soudha underground metro station site, the contractor, CEC-Soma-CICI Joint Venture, is busy filling the gap.
Asked if the excavated soil is used for refilling, Mr. Gudge said not all could be used. “The excavated material is already dumped far away. Rocky material cannot be used for refilling.”
The fine quality soil of the neighbouring Cubbon Park underground station was stored on BRV Parade Grounds and some of it is being used. So are sand and smooth rock extracted during tunnel boring.
The contractor is also sourcing fine soil from elsewhere, he said. Mr. Gudge said the top 4 m above the station has to be good red soil. The refilling involves restoration of the site to its original — the two-lane Dr. B.R. Ambedkar Road and lawns in front of the Vidhana Soudha and High Court. The entire process is expected to be completed in about nine months.