Numerical Evaluation of Empirically Suggested Support System for the Diversion Tunnels at Diamer Basha Dam Project, Pakistan
Keywords:
Characterization, classification, support, diversion tunnel, numerical modellingAbstract
During the design of the tunnel in rocks, inadequate geological and geotechnical data of the construction site is a way of life. Due to this insufficiency of data, the empirical systems for rock–mass are still required for the underground excavation design. The characterization of rock mass followed by classification is an essential part of the initial support design using RMR and Q systems. In this research, these systems are used for the classification of rock mass along the diversion tunnel of a hydropower project in Pakistan. The GSI system is used for the calculation of well-known failure criteria constants. Rock mass is characterized and classified into three geological units along the tunnel route, based on seven number of bore holes, drilled in this route. These rock mass quality values are used for the deformation modulus calculation. The in situ stresses are also calculated statistically, using the available empirical equations. The empirical support determined from the two systems is evaluated numerically, using FLAC2D. The results of numerical modelling indicate that the support suggested by empirical approaches are appropriate. The results are shown in term of critical strain, thrust–bending moment interaction diagram, and axial stresses in rock bolts. Although the highest critical strain value is 0.00058 for geotechnical unit 2, however, this deformation is within the control range.
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