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.
Rock Mechanics
M. Zoorabadi
Abstract
Numerical modelling techniques are not new for mining industry and civil engineering projects anymore. These techniques have been widely used for rock engineering problems such as stability analysis and support design of roadways and tunnels, caving and subsidence prediction, and stability analysis of ...
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Numerical modelling techniques are not new for mining industry and civil engineering projects anymore. These techniques have been widely used for rock engineering problems such as stability analysis and support design of roadways and tunnels, caving and subsidence prediction, and stability analysis of rock slopes. Despite the significant advancement in the computational mechanics and availability of high speed computing hardware, the input data and constitutive models remain the main source of errors affecting the reliability of numerical simulations. The problem with the input data has been deepened more by introducing empirical-based methods such as GSI classification to downgrade the rock properties from laboratory scale to field scale. The deformability modulus and strength parameters are the main outputs of these downgrading techniques. Numerical modelling users simply apply these downgrading methods and run the model without considering the real mechanics behind the stress induced failure and deformation around the underground excavations. While to the contrary to the commonly used downgrading methods that produce a constant modulus for rock at all depths, the rock modulus is stress dependent and varies with depth. In addition to this, the mechanism of stress induced displacement is not similar to the deformation of a continuum model simulated with equivalent rock properties. Apart from the mechanical characteristics of rocks, the magnitude and orientation of in-situ stresses are two other important parameters that have significant impacts on stress induced rock fracturing. The impacts of these two parameters have also been neglected in many practical cases. This paper discuss this old fashioned topic in more details with presenting the known facts and mechanics which numerical modelling users ignore them due to the unquestioning acceptance of downgrading methods. It also covers the influence of the stress magnitude and orientation on stress induced rock fracturing.
