Expert Panel Identifies Critical Flaws in Bengaluru's Proposed Hebbal-Silk Board Underground Tunnel Project

Concerns regarding the Detailed Project Report encompass alignment issues, traffic design flaws, and potential flood risks.

Bengaluru:

A committee of expert engineers and specialists has raised critical objections to the Detailed Project Report (DPR) for the proposed Hebbal-Silk Board underground tunnel, describing it as incomplete, unrealistic, and significantly undercosted.

The expert panel submitted their findings to the Karnataka government in May, highlighting substantial design flaws, environmental concerns, and financial inadequacies in the project planning.

Rodic Consultants Pvt. Ltd. prepared the DPR following initial feasibility assessments conducted by Altinok Consulting Engineering Inc. and Lion Engineering Consultants Pvt. Ltd. Environmentalist Dattatreya Devar obtained the report through an RTI application.

The Greater Bengaluru Authority (GBA) proposed the 18.5-kilometer tunnel to alleviate north-south traffic congestion. The planned route would run parallel to the existing metro corridor, connecting major landmarks including Hebbal, Mekhri Circle, Race Course, Lalbagh, and Silk Board.

The expert panel identified several critical issues in their assessment. Environmental concerns arose as one proposed tunnel shaft would be situated within Lalbagh Botanical Garden, a protected green space. Additionally, the tunnel's alignment running parallel to the metro line raises questions about infrastructure duplication and economic viability.

Traffic design problems were also highlighted, with entry and exit ramps near key junctions potentially worsening congestion rather than alleviating it. The report noted incomplete stormwater drainage planning and described the proposed diversion of Hebbal nallah as "unrealistic."

Geological uncertainties present another significant concern. Only four of 27 planned boreholes underwent testing, prompting the panel to recommend Electrical Resistivity Tomography (ERT) to identify underground aquifers and ensure structural stability.

The panel determined the project was simultaneously overdesigned and undercosted. While traffic projections only justify 2+2 lanes, the DPR proposes a 3+3 lane configuration. Critical cost elements including grouting, muck disposal, and operations and maintenance were omitted, while a 306 crore TBM provision lacked proper justification. The experts suggested a 10-15% cost increase to address these omissions.

Safety considerations were also inadequately addressed, with insufficient detailing for fire safety systems, ventilation requirements, and cross-passage design – all critical elements for a long underground structure.

Although the GBA accepted most consultant explanations, the expert panel concluded that significant deficiencies remain in the DPR's technical, geological, and cost aspects. They recommended comprehensive revision, including updated surveys and financial estimates, before the project moves forward.