Parametric evaluation of drilling foothills’ effect on tunnel maintenance system

ABSTRACT: Stability analysis of underground spaces is one the important geo-technical issues. Understanding the position of induced and in-situ stress is one of the main necessities in designing tunnel and other underground structures, as in many cases stressesexceed the resistance limit of the rock and the maintenance system, causing the collapse of the structure. In this article induced stresses of static mode drillings on tunnel’s maintenance system has been discussed. Thus by the use of Phase2 software, a domain at 45 degree slope and 100 meters height has been modeled, where a tunnel with diameter of 10 meters has been drilled. Results indicate that due to foothill drillings, axial forces and tensions in the rock bolts have been increased. Examining reliability index of push values, it’s been determined that tensions resulting from drillings cause decrease in reliability indexes in different parts of the drilling site. Besides, values of axial forces, bending moments and Lining shear stresses, show a considerable increment. These cases indicate instability in tunnel’s complex maintenance system.