DRILL & BLAST, CONVENTIONAL | TECHNICAL


Left: Figure 2. Geotechnical risk zoning of the tunnel alignment based on the geological and


hydrogeological condition.


very limited application in India – resulted in approximately 20% faster construction cycles, eliminated steel usage and delivered significant programme, cost and carbon-reduction benefits.


● The introduction of a Daily Review Meeting (DRM) process, implemented for the first time on an Indian tunnelling project, which played a pivotal role in enabling the above optimisations. The DRM provided continuous real-time verification of construction against design intent through systematic review of observed ground behaviour, support performance, monitoring data and QA/QC outcomes. This structured decision-making framework acted as a critical control mechanism, allowing design refinements and construction efficiencies to be implemented safely under changing ground conditions.


This paper presents a comprehensive account of


the geological conditions encountered and the risk- based ground zoning scheme developed, along with the rationale behind the selected design solutions and construction methodologies tailored to highly variable ground conditions. Emphasis is placed on the challenges faced during tunnelling; the engineering decisions adopted in response to evolving ground behaviour; how safety and quality is ensured through DRM control process; and the key lessons learned, offering valuable insights for future tunnelling projects.


Geology


Rock mass quality


1.1 Author’s contribution As the tunnel design engineer, the author was involved from early conceptual development through detailed design and construction, supporting the works through to completion. The author was based on-site, assisting the contractor in implementing innovative practices rarely applied in India, and developed project-specific QA/QC protocols for permanent GFRP rock bolts, validated through pre-construction trials, and ensured its consistent performance during production. As chair of the DRM, the author ensured compliance with design intent and enabled informed, data-driven decision-making throughout the project.


2.0 GROUND CONDITIONS:


RISKS, CHALLENGES, OPPORTUNITIES 2.1 Overview The Kota region is predominantly underlain by sedimentary rocks of the Vindhyan Supergroup, forming part of the Vindhyan Basin. The regional stratigraphy comprises sedimentary successions dominated by sandstone and shale. The alignment of DVEXT-15 lies within the Upper Rewa Group characterised by alternating sandstone and shale with subordinate limestone, siltstone and mudstone units. Sandstones are typically fine-to- medium-grained with competent local grading into quarzitic varieties, while the shale units are generally weak, laminated and fissile, exhibiting low strength


Table 1 - Summary of geotechnical risk zoning, ground behaviour and key challenges Zone


Predicted instability mechanism


Zone I


sandstone with local quarzitic bands


Zone II


Interbedded sandstone and grey shale with local sheared clay bands


Zone III


sandstone and siltstone, and extremely weak Mudstone and soft shale


Zone IV


Green Shale with clay-filled discontinuities


Highly weathered


Low-cover zone comprising disintegrated rock, fractured


Competent


RQD: 70–100% GSI: 55–80


RQD: 10–40% GSI: 25–60


(locally < 10)


RQD: 20–30% GSI: 10–25


RQD: 0–65% GSI: < 30


Kinematic block instability along joints and bedding; limited stress-induced failure in high overburden


cavitation along bedding


ravelling ground; crown collapse to surface


Crown slabbing; stress-driven shear failure; progressive collapse to surface at the portal location


Face instability;


Localised stress-induced shear failure in shale; slabbing and crown


construction challenges


Control of blocky wedge failures; overbreak control


Variable ground response; groundwater perched in shale layers; overbreak


groundwater inflow; face stability under monsoon conditions


exacerbated by groundwater ingress


Very weak rock mass; shallow cover near portal; swelling behaviour of clay-filled joints


Shallow cover beneath seasonal Nala (<10m); high


Key design and


August 2026 | 11


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