Hafeezur Rehman; Ahmad Shah; Mohd Hazizan bin Mohd Hashim; Naseer Muhammad Khan; Wahid Ali; Kausar Sultan Shah; Muhammad Junaid; Rafi Ullah; Muhammad Bilal Adeel
Abstract
The major factors affecting tunnel stability include the ground conditions, in-situ stresses, and project-related features. In this research work, critical strain, stress reduction factor (SRF), and capacity diagrams are used for tunnel stability analysis. For this purpose, eighteen tunnel sections are ...
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The major factors affecting tunnel stability include the ground conditions, in-situ stresses, and project-related features. In this research work, critical strain, stress reduction factor (SRF), and capacity diagrams are used for tunnel stability analysis. For this purpose, eighteen tunnel sections are modelled using the FLAC2D software. The rock mass properties for the modelling are obtained using the RocLab software. The results obtained show that tunnel deformations in most cases are within the safety limit. Meanwhile, it is observed that the rock mass quality, tunnel size, and in-situ stresses contribute to the deformation. The resulting deformations also affect SRF. SRF depends on the in-situ stresses, rock mass quality, and excavation sequence. The capacity diagrams show that the liner experience stress-induced failures due to stress concentration at the tunnel corners. This study concludes that tunnel stability analysis must include an integrated approach that considers the rock quality, in-situ stress, excavation dimensions, and deformations.
Hafeezur Rehman; Wahid Ali; Kausar sultan Shah; Mohd Hazizan bin Mohd Hashim; Naseer Muhammad Khan; Muhammad Ali; Muhammad Kamran; Muhammad Junaid
Abstract
Support design is the main goal of the Q and rock mass rating (RMR) systems. An assessment of the Q and RMR system application in tunnelling involving high-stress ground conditions shows that the first system is more appropriate due to the stress reduction factor. Recently, these two systems have been ...
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Support design is the main goal of the Q and rock mass rating (RMR) systems. An assessment of the Q and RMR system application in tunnelling involving high-stress ground conditions shows that the first system is more appropriate due to the stress reduction factor. Recently, these two systems have been empirically modified for designing the excavation support pattern in jointed and highly stressed rock-mass conditions. This research work aims to highlight the significance of the numerical modelling, and numerically evaluate the empirically suggested support design for tunnelling in such an environment. A typical horse-shoe-shaped headrace tunnel at the Bunji hydropower project site is selected for this work. The borehole coring data reveal that amphibolite and Iskere Gneiss are the main rock mass units along the tunnel route. An evaluation of the proposed support based on the modified empirical systems indicate that the modified systems suggest heavy support compared to the original empirical systems. The intact and mass rock properties of the rock units are used as the input for numerical modelling. From numerical modelling, the axial stresses on rock bolts, thrust bending moment of shotcrete, and rock load from modified RMR and Q-systems are compared with the previous studies. The results obtained indicate that the support system designed based on modified version of the empirical systems produce better results in terms of tunnel stability in high-stress fractured rock mass conditions.
