Effect of rock mass intactness on tunnel safety and stability in blasting excavation

Effect of rock mass intactness on tunnel safety and stability in blasting excavation

Pingyuan Yang  Xiaoen Wu  Junhua Chen 

Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China

China Energy Engineering Group Equipment Co. Ltd., Beijing 100044, China

School of Civil Engineering, Central South University, Changsha 410075, China

Corresponding Author Email: 
xewu@ceec.net.cn
Page: 
75-101
|
DOI: 
https://doi.org/10.3166/ACSM.42.75-101
Received: 
|
Accepted: 
|
Published: 
31 March 2018
| Citation

OPEN ACCESS

Abstract: 

This paper attempts to make an accurate assessment of the safety and stability of tunnels in blasting excavation, considering the effect of rock mass intactness. For this purpose, numerical simulations and field tests of tunnel blasting excavations were carried out in rocks with different intactness indexes. For simplicity, the multi-hole blasting load was replaced with the equivalent blasting load according to the Chapman-Jouguet (C-J) detonation mechanism and the theory of stress wave propagation in elastic medium. Then, the existing blasting damage model of rock mass was improved into a continuum damage model of rock blasting considering the intactness of rock mass, and imported to FLAC3D for numerical simulations of tunnel blasting excavation. The simulation results were then verified through field tests on blasting vibration velocity and acoustic wave velocity. The attenuation law of blasting vibration was obtained from the tests on blasting vibration velocity, while the blasting-induced fracture zone was determined through the tests on acoustic wave velocity in the borehole before and after blasting. The blasting-induced fracture zone near the explosion sources and the attenuation law of blasting vibration velocity far from the sources were both identified in the numerical simulations and the field tests. After that, the results of the numerical simulations were compared with those of the field tests. The comparison shows that: after the blasting excavation of pressure diversion tunnels, the maximum and the minimum depths of blasting-induced fracture in the surrounding rock respectively appeared at the haunch and the vault of tunnels; when the drilling and blasting parameters remained constant, the maximum depth of blasting-induced fracture and several other factors decreased significantly with the growth of the intactness index; meanwhile, the vibration-influenced distance of blasting increased first and then decreased. The results of numerical simulations agree well with those of the field tests. The research findings provide valuable guidance to blasting excavation of pressure diversion tunnels

Keywords: 

 hydropower plant; pressure diversion tunnel, numerical simulation, the intactness index, blasting vibration velocity, acoustic wave velocity

1. Introduction
2. The blasting excavation of tunnels
3. Simulation of multi-holes blasting for tunnel excavation
4. Constitutive model of blasting damage considering the intactness of rock mass
5. Numerical simulation and field test
6. Conclusions
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