An expert committee, appointed by the Karnataka government, has raised serious concerns over the Detailed Project Report (DPR) for the proposed underground tunnel between Hebbal and Silk Board.
In April 2025, Karnataka set up an expert committee headed by S Hegga Reddy, executive director and chief engineer (Bangalore Metro Rail Corporation Limited) to review the Hebbal-Silk Board tunnel DPR.
The report, obtained through an RTI filed by environmental activist Dattatraya T Devare and made public on October 12, flags major concerns about the project, which is backed by deputy CM and Bengaluru Development Minister DK Shivakumar.
Also read: Skeletons tumble out of Bengaluru tunnel road project reports, BBMP left red-faced
Cost estimates under scrutiny
The expert panel flagged that the DPR’s cost estimates for the Bengaluru tunnel appear lower than similar projects in Mumbai, citing the city's complex geology as a key challenge. The committee report stated that only minimal geological investigations were conducted and recommended extensive surveys to mitigate execution risks, suggesting that tunnelling costs should be increased by 10-15 percent to account for unforeseen conditions.
In January 2025, Bruhat Bengaluru Mahanagara Palike (now Greater Bengaluru Authority), fined Rodic Consultants Rs 5 lakh over a Rs 9.5-crore tunnel DPR ‘copy-paste’ error, citing Maharashtra instead of Karnataka. After a Moneycontrol report on January 6, the firm apologised and promised action.
Also, read: Copy-paste fiasco: Bengaluru civic body slaps Rs 5-lakh penalty on Rodic Consultants for tunnel road DPR
Alignment and environmental risks
The panel stated that the proposed alignment runs almost parallel to the upcoming Metro corridor, raising the risk of redundancy and overlap in public investment. It flagged environmental concerns, particularly a proposed shaft inside Lalbagh, which requires a detailed reassessment of ecological impact.
The report also warned that entry and exit ramps at key junctions, such as Mehkri Circle and Silk Board, could worsen congestion unless roads are widened and junctions redesigned.
Design and safety shortcomings
Several design and safety lapses were identified. The committee pointed out violations of Indian Roads Congress (IRC) norms at Mehkri Circle, where ramps are narrower than the minimum two-lane requirement, and termed the diversion of the Hebbal nallah ‘unrealistic,’ recommending a fresh hydraulic study.
Also read: 'Brand Bengaluru' caught between DK Shivakumar’s vanity projects and city's crumbling infra
The major technical components, including drainage, ventilation, and fire safety systems, were found inadequate. The DPR lacked proper drainage calculations, relied on limited borehole data, and did not include Electrical Resistivity Testing (ERT). The panel called for a complete geotechnical study and a redesign of mechanical systems to ensure safety and cost efficiency.
Traffic analysis was inconsistent with Bengaluru’s Comprehensive Mobility Plan (CMP) 2020. The report stated that the DPR failed to provide 25-year traffic projections, mode-wise data, or estimates of modal shifts due to the Metro, questioning the project’s long-term viability.
Also read: Bengaluru's infra body invites global bids for Rs 17,700 crore tunnel road project
Cost and missing details
On costs, the committee warned that estimates appeared ‘on the lower side’ and were based on a single vendor quotation. The major expenses, including muck disposal, TBM yard setup, grouting, and 25-year operations and maintenance (O&M) costs, were missing.
The DPR also omitted critical details on land acquisition, utility shifting, tree relocation, environmental and disaster management plans, and pavement design.
Panel recommendations
The committee recommended that BBMP undertake detailed geotechnical investigations, revise the construction schedule to account for land and utility constraints, and optimise the tunnel cross-section. It also suggested using abandoned quarries for muck disposal and forming a single-window technical committee for DPR oversight.
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