TECHNICAL | DRILL & BLAST, CONVENTIONAL
NATM IN WEAK ROCK IN INDIA
The Harding Prize Competition is named after the founder of the British Tunnelling Society, Sir Harold Harding, and is for entrants under the age of 33. Shortlisted papers were presented to the BTS evening meeting on 19 March, at the Institution of Civil Engineers, in London. Ramnath Arumugam, Senior Engineer (Tunnelling) with Bedi Consulting, was a runner-up in the 2026 competition with a paper entitled ‘Design, construction and risk management of twin, large span NATM tunnels in weak rock masses with low overburden in India’.
1.0 INTRODUCTION The Delhi-Vadodara Greenfield Expressway forms part of the 1,350km-long, access-controlled eight-lane Delhi-Mumbai Expressway project connecting India’s capital, New Delhi, with its financial hub, Mumbai. The Delhi-Vadodara section is divided into 31 construction packages. This paper presents the design and construction challenges associated with Package 15, comprising twin four-lane tunnels and herein referred to as the Delhi- Vadodara Expressway Tunnel-15 (DVEXT-15). The DVEXT-15 tunnels (Tubes 01 & 02) each have an
Below: Figure 1. Typical cross section of tunnel showing different lining configurations.
excavation width of 20.9m at axis level and a height of 13.6m (see Figure 1) and pass through the Darah tiger sanctuary in Kota district. The twin tunnels were designed to carry four lanes each, with the large span dictated by highway geometry and operational requirements. During early design, the mined tunnel length of DVEXT-15 was originally approximately 3.5km; however, initial geotechnical assessment indicated that with such large span the portal sections could not be safely excavated and supported using a mined approach. The portals were therefore relocated, with the remaining sections constructed by cut-and-cover, reducing the mined length between portals of each tube to 3,300m. At the time of writing this paper, tunnel excavation has been
completed along the full length and secondary lining works are under way. The tunnel alignment of DVEXT-15 traverses
highly variable geological conditions including weak and weathered rock masses, low-cover sections and zones of deep overburden. These conditions, combined with the large tunnel spans of each tube and stringent environmental and time constraints, posed significant challenges to both design and construction. Notably, restrictions arising from forest clearances and limitations on working hours placed the project programme on the critical path and necessitated the adoption of an optimised excavation and support strategy to achieve faster construction cycles. Key features of the project included design optimisation
and selective adoption of international tunnelling practices tailored to Indian site conditions, as follows: ● The first-of-its-kind application of permanent- grade glass fibre reinforced polymer (GFRP) rock bolts in an Indian road tunnel, used in competent rock following detailed assessment of geological suitability and long-term performance requirements. The implementation was underpinned by bespoke material and workmanship specifications, a robust quality assurance and quality control (QA/QC) regime, comprehensive pre-construction trials and systematic production-stage testing to verify structural performance, durability and compliance with design intent.
● The use of corrosion-resistant permanent GFRPs in competent rock mass allowed rationalisation of the client’s originally proposed 300mm-thick, conventionally reinforced secondary lining to instead have a thinner 150mm-thick Steel Fibre Reinforced Concrete (SFRC) lining, significantly reducing construction time, material usage and embodied carbon.
● In Indian tunnelling practice, lattice girders are commonly used to maintain the desired tunnel opening profile. On this project, girders were deliberately eliminated through the adoption of real-time, survey-based profile control to ensure geometric compliance. While widely adopted internationally, this approach – which has seen
10 | August 2026
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