ABSTRACT
The present research aims to investigate the effect of the rock mass disturbance due to the tunnel excavation method, as incorporated through the disturbance factor (D) in the Generalized Hoek & Brown (2002) rock mass failure criterion, on the tunnel lining loading. Particular emphasis is given on the drill and blast method, which is the most common tunnel excavation method in intact or massive and blocky rock masses, both in civil and in mining engineering. The tunnel perimeter blasting charge determines the tunnel overbreak and the disturbance zone around the tunnel perimeter. Thus, the tunnel lining may be overloaded due to the development of the disturbance zone with higher than the anticipated and designed load values. In order to investigate the disturbance zone’s effect on the tunnel support measures, two dimensional numerical analyses are used, based on the RS2 – Rocscience software. Different quality rock masses are examined, with GSI values ranging between 60 and 80 while the disturbance factor D takes values between 0 and 1, incorporating in the analysis all possible blast conditions. From the parametric numerical analysis, it is shown that the increment of the rockmass disturbance due to the tunnel excavation has a significant effect in the tunnel lining’s overload, where for low rockmass disturbance the lining load increases higher than 30%, especially on the tunnel perimeter rockbolts. Moreover, the effect of the rockmass disturbance increases the tunnel deformation higher than 10%, in a comparison with non – rockmass disturbance.
