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Abstract
During underground construction, the behavior of the ground is influenced by characteristics of the rock mass with situ stresses and ground water, cross section of the excavation area, excavation method, and the rate of excavation. These fundamental features are considered to ensure the support and stability of underground excavations and achieve long-term successful operation. However, the ground composition of the Himalayas hinders tunnel excavation, especially in case of mechanized tunneling; this causes time and cost overruns. This study has reviewed the recently completed Neelum–Jhelum Hydroelectric Project; the project complexities, geological environments involving significant overburden and tectonic stresses, and effects of the excavation method on tunnel stability were analyzed. The major challenges that were encountered during construction are discussed herein along with their countermeasures. An analysis of project-related data reveals that latest techniques and approaches considering rock mechanics were used to complete the project; the existing approaches and methods were accordingly verified and extended. Apart from ground composition, the excavation methods used play an important role in the occurrence of severe rock bursts. Thus, the findings of this study are expected to be helpful for future tunneling projects in the Himalayas.
Highlights
This study focuses on reviewing the effect of ground compositions and project-related features on tunnel stability that is based on previous research associated with this project
An overcoring stress measurement method, with hollow inclusion triaxial strain cells, was used for stress determination in the high overburden area along the tunnel boring machines (TBMs)-excavated tunnels of the project, which were susceptible to rock bursting
The successful completion of the complex Neelum–Jhelum Hydroelectric Project (NJHEP) in the challenging and unique insitu environment of the Himalayas is a great experience for the study of a significantly deep civil tunneling process
Summary
Underground excavation is a key aspect of almost every hydropower project in this area of the country, owing to the presence of valleys and mountains Constructing these hydroelectric power projects in the area is challenging, both technically and financially. Several locations in this area feature with subsurface water Geological factors, such as the properties of the rock mass, virgin stress settings, and inflow of groundwater through discontinuities, affect the stability of underground excavations and they are called ground composition parameters [1,2,3]. In situ stresses are comparatively unbalanced, as they are geologically age dependent, to a large extent As it is the youngest mountain chain worldwide, it is relatively more challenging to perform tunneling in this area using tunnel boring machines (TBMs) [5]
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