Evaluating tunnel stability in challenging terrains: a comprehensive study of geological factors and support system in the Lowari Tunnel, Northern Pakistan

Abstract

This study investigated the stability and sustainability of the Lowari tunnel constructed in the geologically challenging Himalayan terrain by analyzing geological parameters, deformation monitoring, and support system performance. Detailed face mapping across the 8.509 km tunnel revealed highly variable rock types, weathering conditions, and discontinuities-ranging from stable, compact granite to fractured and sheared zones requiring enhanced stabilization. Groundwater ingress in critical sections further exacerbated stability challenges. A network of 269 monitoring stations provided comprehensive deformation data, with 93% of stations recording inward displacements (0.000 m to -0.0364 m), confirming the effectiveness of the new Austrian tunneling method (NATM) in managing excavation-induced stresses. Support systems, including shotcrete (28-day compressive strength: 28.6-30.8 MPa), rock bolts (pull-out load >165 kN), wire mesh, and lattice girders, demonstrated reliable performance, ensuring structural integrity under varying geological conditions. Over-breakspredominantly in jointed and sheared zones-emphasized the need for refined excavation techniques and real-time monitoring to mitigate avoidable instabilities. The findings underscore the adaptability of NATM, the importance of accurate geological mapping, and the effectiveness of robust support systems in ensuring tunnel stability.