*3.1. Q-System Method*

To estimate the support system it is necessary to establish an equivalent diameter for the tunnel, De, which is the width/height of excavation divided by the ESR (excavation support ratio), which for transversal tunnels can be established at 1.3, so *D<sup>e</sup>* = 5.0. For the central tunnel, a value of ESR of 1.0 has been estimated, obtaining an equivalent diameter for the tunnel, *D<sup>e</sup>* = 6.5. The evaluations of rock masses in sandstone and shale rock masses by using the Q-system and the GSI are summarized in Table 4. By applying Equation (1), in sandstone formation a value of Q of 1.27 is obtained, while in the shale rock mass the value of Q is 0.23.

**Table 4.** Evaluating results using the Q-system.


The suggested support systems based on the Q-system for the central tunnel and the transversal tunnels are given in Table 5 following the recommendations proposed by Grimstad and Barton [31] using an equivalent diameter of 5.0 and 6.5 for transversal tunnel and central tunnel, respectively.


