*2.8. Numerical Modelling. Support System Design*

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Table 3 shows the design of the support system in the transversal tunnels and the central tunnel for the existing rock masses in the study area. The bolt lengths were calculated by Equation (4), as 2.75 m; therefore, the rock bolt length design was 3 m. In the shale formation grouted rock bolts were selected

with the following specifications: 25 mm diameter, 245 KN (25 t) of load capacity, 3 m long, and spacing between bolts of 1.2 m. Furthermore, there was a layer of 150 mm thick reinforced shotcrete in the central tunnel and a layer that was 120 mm thick in transversal tunnels. In the sandstone formation, grouted rock bolts were selected with the following specifications: 25 mm in diameter, 245 kN of load capacity, 3 m long, and spacing between bolts of 1.5 m. A layer of 80 mm thick reinforced shotcrete in the central tunnel and 60 mm thick in transversal tunnels is also simulated.


**Table 3.** Support system design.
