Bengaluru: The contentious tunnel road project is facing fresh scrutiny over its proposed passage near Lalbagh, with a Geological Survey of India (GSI) expert committee recommending an independent review of the location of a key tunnel-boring machine (TBM) shaft to ensure maximum distance from the botanical garden’s National Geological Monument.The recommendation comes amid mounting opposition to the ambitious underground road project, with environmentalists and citizen groups questioning the implications of tunnelling beneath and around Bengaluru’s sensitive ecological and heritage zones.Lalbagh is home to a National Geological Monument showcasing an exposure of the Peninsular Gneissic Complex, one of the oldest exposed rock formations in the Indian Peninsula.In its April 2026 geological and geotechnical appraisal of the proposed underground road, the GSI committee specifically flagged TBM shaft 4 and its associated ramps, which are proposed close to the geological monument. The experts have called for an independent technical review of the shaft location before pre-construction work begins, with the setback from the protected monument to be maximised.The proposed shaft would require excavation to a depth of around 40 metres. The expert panel has recommended additional boreholes and geophysical investigations, including seismic refraction surveys and other suitable subsurface studies, to establish the nature and depth of weathered and fresh bedrock and to identify potential geological weak zones. The committee has also suggested bringing in specialised institutions, including the National Institute of Rock Mechanics and other competent agencies wherever necessary, to strengthen the technical assessment.Groundwater monitoringThe GSI committee has also recommended establishing a hydrogeological monitoring network covering Lalbagh and its adjoining areas. The monitoring is intended to establish baseline groundwater conditions and track any changes during and after construction.The report notes that excavation for TBM shafts and ramps could influence groundwater movement and potentially result in groundwater drawdown, making continuous monitoring necessary.
