Disturbance Action of First Excavation on Reinforcement Effect of Later Excavation in layered Tunnels

Abstract

Objective In the ultra-close layered tunnel construction, the preceding excavated tunnel can cause unpredictable damage to the surrounding rock, which will affect the smooth construction of the following tunnel and increase the difficulties of engineering construction. Therefore, it is necessary to study the effect of the preceding tunnel on the following ones in the layered tunnel construction. Method Based on a tunnel project in Chongqing, a numerical simulation method is used to compare and analyze the stress distribution patterns and deformation characteristics of the surrounding rock caused by the preceding excavation of the lower layer tunnel. According to the stress characteristics and the deformation law of the upper layer tunnel under different working conditions, the relationship between the deformation control effect of the anchor rod reinforcement measures and the weakening effect of the surrounding rock caused by the lower layer tunnel excavation is analyzed. Result & Conclusion The preceding excavation of the lower layer tunnel causes the vault area settlement with a maximum of 4.1mm and the arch bottom area bulging with a maximum of 6.9 mm. According to the variation intensity of the stress distribution and the equivalent plastic strain range of the surrounding rock, the loosening area of the lower layer tunnel surrounding rock is equivalent to a circular range, and the average thickness of the loosening circle is 2.5m. The excavation unloading of the upper layer tunnel will cause the lower layer tunnel upfloating. After the anchor rod reinforcement measures are taken for the surrounding rock in the lower layer tunnel loosening circle,the strength coefficient of the corresponding surrounding rock is reduced to 0.70~0.75.

Keywords

• tunnel engineering
• surrounding rock disturbance
• deformation reinforcement
• numerical simulation