Cost Estimation and Cost Control Techniques for Underground Tunnels

Abstract

Underground railway tunnels constructed using the New Austrian Tunnelling Method (NATM) in India are highly susceptible to cost overruns due to adverse geological conditions, productivity loss, and uncertainties in resource planning. This study develops a comprehensive bottom-up cost estimation and cost control framework for an 820 m long NATM railway tunnel (Tunnel T1) excavated by the drill-and-blast method. The proposed methodology integrates detailed geotechnical investigations, rock mass classification (RMR and Q-System), excavation cycle analysis, muck haul lead calculations, equipment productivity, manpower deployment, and resource-based costing to generate realistic project estimates. Cost sensitivity analysis demonstrates that variations in rock class distribution, support requirements, and haul distance significantly influence the total construction cost. The results identify underground excavation and final reinforced concrete lining as the major cost contributors, together accounting for the largest proportion of project expenditure. An Earned Value Management (EVM)-based monitoring system, supported by dynamic risk registers and periodic cost reviews, is proposed to improve cost control during construction. The study also establishes a practical framework for quantifying the financial impact of adverse geology, additional temporary works, and productivity reduction in EPC tunnel projects. The developed model provides a replicable and field-oriented tool for cost engineers, project managers, and contractors involved in NATM railway tunnel construction in India.

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