Expert committee flags major flaws in Bengaluru tunnel project report
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An expert committee of senior engineers and specialists has raised serious concerns over the Detailed Project Report (DPR) for the proposed 18.5-kilometre Hebbal–Silk Board underground tunnel in Bengaluru.
The panel described the DPR as incomplete, unrealistic, and undercosted.
The report, prepared by Rodic Consultants Pvt. Ltd. after feasibility studies by Altinok Consulting Engineering Inc. and Lion Engineering Consultants Pvt. Ltd., was submitted to the Karnataka government in May.
It was accessed by environmentalist Dattatreya Devar through an RTI.
The tunnel, planned by the Greater Bengaluru Authority (GBA) to ease north-south traffic congestion, will run parallel to the metro corridor, linking Hebbal, Mekhri Circle, Race Course, Lalbagh, and Silk Board.
The panel’s assessment pointed out major environmental, design, and financial shortcomings. One of the most serious concerns is environmental — a tunnel shaft is proposed inside the Lalbagh Botanical Garden, which is a protected green zone.
The tunnel alignment also runs almost parallel to the metro line, raising duplication and viability concerns.
The committee highlighted several traffic design flaws, noting that entry and exit ramps near key junctions might worsen congestion instead of easing it. The stormwater drainage plan was found incomplete, and the proposed diversion of the Hebbal drain was called “unrealistic.”
Geological assessments were also deemed insufficient. Out of the planned 27 boreholes, only four were tested. The panel advised conducting Electrical Resistivity Tomography (ERT) to detect underground aquifers and ensure the tunnel’s structural stability.
The DPR was also criticised for being both overdesigned and undercosted.
While the plan proposes 3+3 lanes, projections only justify a 2+2 lane design. The report omits key expenses such as grouting, muck disposal, and operations and maintenance costs. A ₹306 crore provision for a Tunnel Boring Machine (TBM) was included without clear justification. The panel recommended increasing the total estimated cost by 10–15% to account for these missing components.
Safety measures were another area of concern. The report lacks adequate detailing for fire safety, ventilation, and cross-passage design — all critical features for a long underground tunnel.
While the GBA accepted most of the consultant’s explanations, the expert committee concluded that the DPR remains deficient in crucial geological, technical, and financial aspects. It recommended a complete revision, including updated surveys and cost estimates, before moving forward with the project.