Abstract
Blasting‐induced vibration during the excavation of transition section in a branching‐out tunnel causes damage and hence affects the safety and stability of the supporting structure and surrounding rock. To examine the effects of excavation and blasting of the transition section in the posterior tunnel on the supporting structures of the anterior tunnel, the influences of the blasting‐induced vibration in the posterior tunnel on the anterior tunnel were analyzed under different surrounding rock levels, excavation techniques, distances from explosive source, and net spans. This method was performed by combining numerical simulation with blasting‐induced vibration monitoring according to the construction characteristics of the transition section in a branching‐out tunnel of a highway. A control technique was investigated to assure the safety and stability of the anterior tunnel during the excavation and blasting of the posterior tunnel. Results demonstrate that (1) the vibration velocity peak behind the blasting excavation surface of the tunnel is higher than that in front. These results suggest paying much attention in monitoring vibration velocity within 10 m behind the excavation surface. (2) The blasting‐induced vibration velocity peak on the spandrel at the side that faces the blasting in the anterior tunnel is 2.0–2.5 times than that at the side behind the blasting. Moreover, the blasting‐induced vibration velocity peak on the haunch at the side that faces the blasting in the anterior tunnel is 6‐7 times than that at the side behind the blasting. (3) Instead of the full‐face excavation method, the use of center cross diagram (CRD) technique or side wall pilot tunnel method is suggested for the excavation of surrounding rocks of IV‐level, V‐level, and III‐level with a net span smaller than 3 m. (4) Vibration control measures, such as double wedge‐shaped cut blasting and floor blast‐hole staged detonation, were adopted by designing and optimizing blasting parameters (e.g., total explosives, maximal segment explosive quantity, detonation order, and detonation interval) in posterior tunnel. According to the test, the blasting‐induced vibration velocity peak, which is monitored in the anterior tunnel, can be controlled within 10 cm/s to assure the safety and stability of the supporting structure and surrounding rocks of the tunnel.
Highlights
Branching-out tunnel, as a novel structural form, attracts increasing attention with the continuous development of high-level highway planning and construction in recent years and the limitations that are due to considerations of land resource utilization and low engineering cost caused by the terrain and construction site [1,2,3]. e branching-out tunnel is composed of three parts, namely, the large-span, multiarch, and small net span sections. e branching-out tunnel has promising application prospects in difficult highway construction and in transition project of bridges and tunnels because it exhibits the engineering characteristics of large-span multiarch tunnel and neighborhood tunnel [4,5,6]
The distance between the two holes changes continuously, and the stress structures in the transition section become complicated because the blasting excavation of the posterior tunnel in the transition section of the branching-out tunnel can influence the stability of the supporting structure of the anterior tunnel, thereby further
When the buried depth is smaller than the net span, the coverage layer on the tunnel roof is relatively thin, and strong blasting-induced vibrations are observed, thereby weakening the vibration velocity in the anterior tunnel at the side facing the blasting
Summary
Branching-out tunnel, as a novel structural form, attracts increasing attention with the continuous development of high-level highway planning and construction in recent years and the limitations that are due to considerations of land resource utilization and low engineering cost caused by the terrain and construction site [1,2,3]. e branching-out tunnel is composed of three parts, namely, the large-span, multiarch, and small net span sections. e branching-out tunnel has promising application prospects in difficult highway construction and in transition project of bridges and tunnels because it exhibits the engineering characteristics of large-span multiarch tunnel and neighborhood tunnel [4,5,6]. The distance between the two holes changes continuously, and the stress structures in the transition section become complicated because the blasting excavation of the posterior tunnel in the transition section of the branching-out tunnel can influence the stability of the supporting structure of the anterior tunnel, thereby further. Abundant field tests and numerical simulation studies on the propagation of blasting-induced vibration in tunnel and its influences on supporting structures and rock masses have been conducted to minimize blasting-related damage to the supporting structures and rock masses [17,18,19]. The blasting-induced vibration response features of the transition section of a branching-out tunnel under different buried depths, surrounding rock levels, excavation technique, shared rock thicknesses, and net spans were carried out by using a finite element numerical simulation analysis. Is study realized safety and stability during the controlled blasting construction of the transition section of a branching-out tunnel
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