BENGALURU: While the state government is planning to dig tunnels 14-15 metres underground as part of the ambitious 195-Km-long tunnel road network for Bengaluru, experts are shocked at such a plan being considered without understanding the city’s subterranean features.
The experts, requesting anonymity, have questioned the state government’s decision to go ahead with the project, while questioning whether they are ready with a report with complete details of the underground features of the city. The state government is planning to call for tenders for the project in the next 38 days.
According to a scientist from Indian Institute of Science (IISc), who is familiar with how the state government is going about the project, the latter is impressed by the success of tunnel roads in Kuala Lumpur, Malaysia. However, geologists that The New Indian Express spoke to have pointed out that there is a marked difference between the subterranean features and crustal characteristics of that city and Bengaluru.
Geologists from IISc said the rocky terrain of South India, including Bengaluru, is very complex. In some places there are Dolerite rocks, some other places, granite. Some places have loose soil while elsewhere it’s clay. They cited the incident of the road caving in near Brigade Road where Bruhat Bengaluru Mahanagara Palike (BBMP) and Metro works were simultaneously progressing some days ago. “The road had caved in, leaving a motorist injured.
Digging tunnels for Metro takes a very long time, besides the blades of the tunnel boring machines (TBMs) have to be changed at regular intervals. Not many know that in some places the earth is filled with construction debris as was the case in Lakkasandra. There is a need for a proper recce before even considering such a project. The city is not ready for tunnel roads,” said a geologist from IISc.
Considering the hard subterranean features, the geologists have asked the state government to consider comparing how much time it had taken for the TBMs to bore the Metro tunnels, and calculate how much more time it would take for the same to drill 195 Km under Bengaluru. Besides, they also pointed to the damages that have occurred during the execution of the TenderSure footpath works while trying to shift utilities.
A senior official from the Mines and Geology Department said the state government has never undertaken an underground truth-finding study of the terrain, rock and soil. The only sample-based studies that are conducted are when projects like flyovers and underpasses are constructed. A thorough assessment of the overall carrying capacity and soil and rock strength of Bengaluru has never been undertaken.
Although Bengaluru is not in the seismic zone, the impact of deep excavations for foundations for high-rise buildings, Metro tunnels and pillars is already being felt in pockets of Bengaluru where roads are either caving in or sinking, besides water seepage being reported.
According to the urban development department, the BBMP will be executing the tunnel road project. But a senior BBMP official, privy to the project plans, admitted to TNIE that there are no underground maps of the water and sewage pipelines for immediate implementation. “The company which will be awarded with the tender for preparing the detailed project report and to implement the project will have to undertake underground studies, and then act accordingly,” the official said, adding that it would be a difficult proposition.