Deformation Study of Gharkhola Hydroelectric Project Tunnel Emphasis on Squeezing, West Central Nepal

This research investigates the deformation and squeezing phenomena in the headrace tunnel of the Gharkhola Hydroelectric Project in Nepal, emphasizing the challenges posed by weak rock masses in the Himalayan region. The study employs a multifaceted methodology, integrating empirical, semi-analytical, and numerical approaches to evaluate the deformation modulus (Em) and predict tunnel stability. Utilizing regression analysis, the sensitivity of (Em) and predict tunnel stability. Utilizing regression analysis, the sensitivity of Em to rock mass classification Q, GSI, and RMR is scrutinized, revealing that euations proposed by Barton (2002), Hoek and Diederichs (2006), and Gokceoglu et al. (2003) exhibit the least sensitivity to rock mass variability, rendering them particularly efficacious for deformability estimation. The analysis identifies severe squeezing conditions in specific tunnel sections, with maximum wall closure reaching 0.432803 meters at an overburden height of 134 meters. Empirical and semi-analytical methods, including Singh et al. (1992) and Hoek and Marinos (2000), corroborate the prevalance of squeezing, while finite element modelling quantifies deformation, validating field observations. The study underscores the imperative of employing diverse methodologies to corroborate rock mass parameters, thereby enhancing the accuracy of squeezing predictions. The findings advocate for meticulous parameter selection and interdisciplinary validation to mitigate instability in tunneling projects within geologically complex terrains.