ABSTRACT
If an elastically derived equation is used to calculate an LDP and the result is implemented in the CCM, the recommended timing of support installation will be erroneous and highly non-conservative (Figure 1). Also, if a generic empirical formula, (Chern et al., 1998) is utilized, the apparent factor of safety will be closer to reality but still non-conservative. On the other hand, if the recent plastic approaches are used, the factor of safety would be smaller than in the previous cases and closer to reality, which forces to install support further from the tunnel face than in the previous cases, and it may produce higher closure rates and the loss of rock strength. This has recently led to the development and use of sliding joints for support rings and high deformable concrete support elements in tunneling (Hoek et al, 2008; Barla, 2009).
