Construction Optimization of Shallow Railway Tunnels under Unsymmetrical Pressure for Reducing Blasting Over-excavation

Abstract

Objective Over-excavation in tunnel construction, mainly caused by inappropriate blasting,will affect the smooth progress and safety of tunnel excavation, increase construction cost and reduce economic benefits. In order to radically solve this problem, blasting design and blasting construction technology should be studied and optimized. Method Based on the shallow buried unsymmetrical pressured layered railway tunnel project for Chongqing Railway Hub East Ring Line(Chongqing East Ring Railway),the causes of vault, arch haunch and arch foot over-excavation are analyzed with theoretical method and modern computer technology. The drilling positions are designed with dynamic optimization, and control measures and solutions for over-excavation are put forward. Result & Conclusion Over-excavation at the tunnel vault is mainly caused by the secondary disturbance of the surrounding rock in smashed area by mechanical excavation after blasting, and over-excavation at the arch waist and arch foot is mainly caused by the improper amount of blasting explosive and improper drilling. In addition, the existence of rock cracks will also lead to significant decrease of the surrounding rock strength. Therefore, proper blasting and under-excavation should be done at the vault to reduce the disturbance of the surrounding rock, and then manual + mechanical excavation and trimming should be combined to reduce the amount of over-excavation. Secondly, according to the attributes of surrounding rock, and based on GA-SVR model and genetic algorithm, the blasthole spacing is properly optimized. On-site monitoring results show that in the initial stage without optimized blasthole spacing, the over-excavation in cracked stratum is about 40cm, which is reduced to about 9cm after the blasthole spacing optimization. The results indicate that optimizing the blasthole spacing can effectively control tunnel over-excavation. The above results can provide reference for similar projects.

Keywords

• shallow railway tunnel under unsymmetrical pressure
• blasting over-excavation
• machine learning
• control measures