The Hidden Costs of Geological Overbreak (GOB) in EPC Tunnel Projects: Assessing the Economic Impact

Abstract

Overbreak, defined as the excavation of excess material beyond the required tunnel profile, is a common issue in tunnel construction, particularly in tunnels constructed using New Austrian Tunnelling Method (NATM). In the context of Jammu and Kashmir, India, five tunnels are currently being constructed along National Highway-44 (NH-44) under the National Highways Authority of India (NHAI). Given the region's complex and varied geology, NATM has been adopted for these tunnel projects. This study focuses on one such under-construction twin-tube tunnel, measuring 4.3 km in length. Notably, the contract agreements for these tunnels do not account for geological overbreak (GOB), with no provisions for compensating contractors for additional excavation costs. The study involved a detailed analysis comparing the theoretical and actual quantities of shotcrete applied, along with the calculation of rebound quantities. Using Amberg Software, tunnel sections were modelled to better understand the extent of overbreak. The research quantified the additional costs incurred by the contractor due to GOB and proposed recommendations for addressing such issues in future projects.