Abstract
To accommodate traffic volume on roads due to ever-increasing population growth, the widening of highways and motorways is in high demand. Nevertheless, the widening of tunnels on these road networks is quite complex due to the presence of numerous rock types, in situ stress, and different widening modes. To overcome these complexities, eight different tunnel shapes were simulated under varying support conditions for asymmetric and symmetric widening. It was found that the tunnels with a round shape, such as horseshoe and semicircular with flatbed, are more effective for asymmetric widening, whereas the provision of a rounded invert in these shapes can reverse the widening option to symmetric. Furthermore, an insignificant effect of the difference in asymmetric and symmetric widening of regular tunnel shapes, such as box, rectangular, and semi-elliptical, was found. A full factorial design statistical analysis confirmed the decrease in tunnel deformation by using various tunnel support systems and showed a significant deformation difference according to monitoring locations at the tunnel periphery. The deformation difference in the case of both tunnel widening modes was also analyzed according to different design parameters. This study provides a comprehensive understanding of rock mass behavior when the widening of any underground opening is carried out.
Highlights
The population of the world is increasing with every passing year [1]
As granite gneiss rock was encountered at the selected section of Lowari tunnel, the bulk and shear moduli were calculated from the deformation modulus, which was derived from geological strength index (GSI) [32]
The tunnel deformation at the monitoring section of eight different tunnel shapes (Table 4) was observed during asymmetric and symmetric widening under three different support modes (Table 3)
Summary
The population of the world is increasing with every passing year [1]. In addition to that, the phenomenon of urbanization is increasing tremendously [2], thereby causing huge congestion on existing roads, highways, motorways, and railway systems. After validation of the model, a detailed study was carried out using numerical simulation to evaluate the rock mass behavior in asymmetric and symmetric tunnel widening utilizing eight different shapes: horseshoe shape with flatbed, horseshoe shape with invert, circular shape, semicircular shape with flatbed, semicircular shape with invert, box shape, rectangular shape, and semi-elliptical shape. These shapes were evaluated for three support system modes which were related to (a) a tunnel without any support,. The risk, cost, and uncertainties will be mitigated, thereby increasing the comfort in the planning and safety of future widening of any tunnel or cavern
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